Seed Production Procedures in Sorghum and Pearl Millet

Seed Production Procedures in Sorghum and Pearl Millet

Information Bulletin no. 58 International Crops Research Institute for the Semi-Arid Tropics

Citation: G u p t a , S.C. 1 9 9 9 . S e e d p r o d u c t i o n p r o c e d u r e s i n s o r g h u m a n d p e a r l m i l l e t . I n f o r m a t i o n Bulletin n o . 5 8 . (In En. S u m m a r i e s i n En, Fr.) P a t a n c h e r u 5 0 2 3 2 4 , A n d h r a Pradesh, India: I n t e r n a t i o n a l C r o p s R e s e a r c h I n s t i t u t e for t h e S e m i - A r i d Tropics. 1 6 p p . I S B N 9 2 - 9 0 6 6 - 4 1 5 - 0 . O r d e r c o d e IBE 0 5 8 .

Abstract Functional and healthy seed is one of t h e i m p o r t a n t factors in improving agricultural p r o d u c t i o n . F a r m e r - b a s e d s e e d p r o d u c t i o n p r o g r a m s for pearl millet a n d s o r g h u m h a v e been introduced in s o m e of t h e developing countries (Senegal and Namibia) a n d are proving to be successful. T h e areas of responsibility in t e r m s of producing i m p r o v e d cultivars (pure-line varieties, c o m p o s i t e s , a n d hybrids) are breeding, c o m m e r c i a l seed production, a n d certification. W h i l e breeding is carried out by a research station, commercial production and distribution require an well-organized operation. Certification is carried out by i n d e p e n d e n t agencies that monitor t h e quality and purity of t h e cultivar during production. T h e p r o c e d u r e s for s e e d p r o d u c t i o n of t h e o p e n - p o l l i n a t e d varieties differ f r o m t h o s e of hybrids. T h e r e are also differences in t h e s e e d p r o d u c t i o n of b o t h s o r g h u m a n d pearl millet. Maintaining varietal purity of b o t h t h e crops requires a d e q u a t e precautions t h a t n e e d to be t a k e n against physical a d m i x t u r e s during sowing, harvesting, threshing, a n d storage. B o t h pearl millet a n d s o r g h u m h a v e specific r e q u i r e m e n t s for p r o t e c t i o n against contamination so that good quality seed can be produced.

Seed Production Procedures in Sorghum and Pearl Millet S C Gupta

Information Bulletin no. 58

ICRISAT International Crops Research Institute for the Semi-Arid Tropics Patancheru 502 324, Andhra Pradesh, India 1999

Contents Introduction

1

Seed Production of Open-Pollinated Varieties

2

Pearl Millet

2

Sorghum

4

Hybrid Seed Production (Sorghum and Pearl Millet)

6

Identification of Potential Hybrid Parents (A-,B- and R-lines)

6

Seed Multiplication of Parental Lines (R-line, B-line, and A-linesl: Nucleus, Breeder, and Foundation Seed

7

Hybrid (A X R) Seed Production (Certified Seed)

8

Planning Commercial Hybrid Seed Production

11

Purification of Varieties/Hybrid Parents

12

Introduction Lack of functional s e e d p r o d u c t i o n and distribution p r o g r a m s have b e e n limiting progress a n d i m p a c t o f c r o p i m p r o v e m e n t research p r o g r a m s i n m a n y developing c o u n t r i e s . G o o d seeds, along w i t h fertilizer, water, and pesticides are i m p o r t a n t c o m p o n e n t s of improving agricultural p r o d u c t i o n . I m p r o v e d cultivars (pure-line varieties, c o m p o s i t e s , and hybrids) are p r o d u c t s of r e s e a r c h c o n d u c t e d at e x p e r i m e n t stations. M a n y c o u n t r i e s have d e v e l o p e d p r o c e d u r e s for an orderly increase, distribution, and m a i n t e n a n c e of i m p r o v e d cultivars. T h e s e p r o c e d u r e s involve t h r e e b r o a d areas of responsibility: breeding, c o m m e r c i a l s e e d p r o d u c t i o n , a n d certification. Usually, an e x p e r i m e n t station develops a n d releases (upon approval from a variety release c o m m i t t e e ) a cultivar to t h e farmers, after comparing t h e n e w cultivar p r o p o s e d by t h e b r e e d e r w i t h t h e cultivars already u n d e r u s e in a specific agroecological z o n e . E x p e r i m e n t stations have t h e a d d e d responsibility t o provide and maintain p u r e seed o f t h e variety or p a r e n t s of t h e hybrid in small q u a n t i t i e s . Multiplication and d i s t r i b u t i o n of t h e seed is carried o u t by c o m p e t e n t private or public agencies including e x p e r i e n c e d g r o w e r s . Recently, farmer-based seed p r o d u c t i o n p r o g r a m s have b e e n s t a r t e d in s o m e developing c o u n t r i e s like Senegal and N a m i b i a . C o m m e r c i a l p r o d u c t i o n a n d distribution of h y b r i d seed requires a high level of c o m p e t e n c e and a c o o r d i n a t e d , well-organized o p e r a t i o n . Seed certification is carried o u t b y a n i n d e p e n d e n t agency t h a t m o n i t o r s a n d certifies t h e genetic purity and quality o f t h e cultivar during p r o d u c t i o n and distribution t o t h e farmer, according t o well-established s t a n d a r d s . Certification s t a n d a r d s vary according to t h e stage or class of seed u n d e r p r o d u c t i o n , w h i c h include, nucleus seed, b r e e d e r seed, foundation seed, a n d certified seed. P r o c e d u r e s for t h e seed p r o d u c t i o n of o p e n - p o l l i n a t e d varieties differ from t h o s e of hybrids. T h e r e are also s o m e differences i n t h e seed p r o d u c t i o n m e t h o d s b e t w e e n s o r g h u m and pearl millet b e c a u s e of t h e difference in floral biology. H o w e v e r , t h e p r o c e d u r e s for hybrid seed p r o d u c t i o n in b o t h t h e crops are m o r e or less t h e s a m e . This information bulletin c o n c e n t r a t e s on certain aspects of varietal p u r i t y of s o r g h u m a n d pearl millet w h e n t h e v a r i e t y / h y b r i d s e e d i s being p r o d u c e d . I t a s s u m e s t h a t a d e q u a t e p r e c a u t i o n s are t a k e n against physical a d m i x t u r e s e i t h e r during sowing (e.g., s e e d carryover in m a c h i n e r y or v o l u n t e e r seed in t h e soil) or during harvest, threshing, a n d storage (in m a c h i n e r y or c o n t a i n e r s ) .

Seed Production of Open-pollinated Varieties Pearl Millet T h e t e r m variety, for a cross p o l l i n a t e d c r o p (such as p e a r l m i l l e t ) , indicates a selfr e p r o d u c i n g p o p u l a t i o n of p l a n t s t h a t , although n o t genetically identical, e x h i b i t u n i q u e , recognizable, a n d stable association of characteristics. T h e pearl millet varieties include: landrace varieties, s y n t h e t i c varieties m a d e from i n b r e d p a r e n t s , and varieties resulting from r e c u r r e n t selection, including m a s s selection. A variety is a n a r r o w - b a s e d b r e e d i n g p o p u l a t i o n exhibiting a range of variability t h a t n e e d s to be p r o t e c t e d against c o n t a m i n a t i o n by pollen of e x t e r n a l origin during s e e d m u l t i p l i c a t i o n . A field of pearl millet, as c o m p a r e d to maize, is far m o r e easily c o n t a m i n a t e d by o u t s i d e pollen b e c a u s e o f t h e species' p r o t o g y n y (that is, t h e e m e r g i n g h e a d s b e c o m e femaler e c e p t i v e b e f o r e t h e y b e c o m e m a l e - f e r t i l e ) . T h e r e f o r e , d u r i n g t h e first o r second day o f flowering, a field of pearl millet is vulnerable to any e x t e r n a l w i n d - b o r n e pollen. In maize, however, tassels n o r m a l l y s h e d pollen before t h e silks e m e r g e . W h i l e t h e n e e d for isolation d u r i n g s e e d multiplication is recognized, permissible levels of off-types in varieties of cross-pollinated crops such as pearl millet can be higher t h a n in varieties of self-pollinated c r o p s or in h y b r i d p a r e n t lines. T h i s is b e c a u s e : a.

Cross-pollinated c r o p varieties have a higher "buffering" capacity for off-type effects (a natural c o n s e q u e n c e of t h e i r variety p o p u l a t i o n s t r u c t u r e ) .

b.

If g o o d isolation has b e e n m a i n t a i n e d , m o s t of t h e o b s e r v e d "off-types" will have arisen t h r o u g h r e c o m b i n a t i o n of genes already p r e s e n t a n d n o t from t h e i n t r o d u c t i o n of alien genes or m u t a t i o n s .

Multiplication r a t e s in pearl millet are high, particularly w i t h varieties. Five kg of seed is m o r e t h a n sufficient to s o w o n e ha. This should p r o d u c e at least 1 5 0 0 kg of clean seed even at a m o d e r a t e level of soil fertility. Pearl millet varieties vary slightly w i t h each stage of multiplication, indicating t h a t e x t r a care is n e e d e d to m a i n t a i n genetic p u r i t y at t h e early stages, a n d also, t h e r e should always b e a n o n w a r d flow from o n e stage t o t h e n e x t . S e e d p r o d u c t i o n p r o c e d u r e s o f various classes are d e s c r i b e d below. N u c l e u s s e e d . N u c l e u s seed, m a i n t a i n e d b y t h e b r e e d e r i s t h e f u n d a m e n t a l s t o c k from w h i c h all else is d e r i v e d a n d should be t h e only stock t h a t r e g e n e r a t e s itself. 5 0 - 1 0 0 kg of s e e d should be p r o d u c e d only o n c e in 4 years. T h e n u c l e u s seed p r o d u c e s h o u l d be t h o r o u g h l y d r i e d a n d t r e a t e d against insects a n d p e s t s . It is d i v i d e d into six lots of 5-10 kg e a c h t h a t are s t o r e d in sealed c o n t a i n e r s in a cool place. L o t s 1, 2, 3, and 4 are u s e d to p l a n t t h e b r e e d e r s e e d p l o t s for t h e n e x t 4 years. Lot 5 is u s e d to p l a n t t h e n e x t n u c l e u s

2

s e e d p l o t 4 years h e n c e , a n d lot 6 is a b a c k u p or insurance lot t h a t s h o u l d be s t o r e d in a different building from t h e o t h e r lots. N u c l e u s seed plots should be g r o w n in e x t r e m e l y isolated conditions; at least 1 km from any o t h e r plot of pearl millet, w i l d pearl millets, and e l e p h a n t / n a p i e r grass. T h e plot should be t h i n n e d at an early stage to evenly space a single p l a n t p e r hill. Several inspections are r e c o m m e n d e d prior t o f l o w e r i n g t o r e m o v e (by u p r o o t i n g o r roguing) any off-type plants. Daily i n s p e c t i o n s d u r i n g flowering are n e e d e d to identify a n d r e m o v e all plants t h a t are n o t t r u e to t y p e b e f o r e t h e y s h e d pollen. H o w e v e r , a final rouging should b e c o n d u c t e d i n t h e standing c r o p b e f o r e harvest t o e l i m i n a t e any r e m a i n i n g off-types. T h e r e c o m m e n d e d size for n u c l e u s s e e d p l o t s is from 0 . 1 - 0 . 2 ha containing a b o u t 3 0 0 0 plants. T h i s e n s u r e s t h a t variety n o r m s d o n o t change b e c a u s e t o o few p l a n t s have b e e n grown. In plots of larger size, it is difficult to scrutinize all plants w h e n daily inspections are r e q u i r e d . Early flowering p l a n t s ( a r o u n d 50) s h o u l d be tagged, a n d h a r v e s t e d separately (as grain) b e c a u s e t h e y are m o r e susceptible to foreign pollen. Breeder seed. B r e e d e r s e e d i s p r o d u c e d from t h e nucleus s e e d a n d t h e s e e d p r o d u c t i o n t e c h n i q u e is similar to n u c l e u s s e e d p r o d u c t i o n . T h e isolation d i s t a n c e s h o u l d be at least 1 km a n d a good roguing at t h e flowering stage will r e d u c e t h e n e e d for f u r t h e r roguing. Normally, no m o r e t h a n 1% of g e n e t i c off-types a r e p e r m i t t e d at final inspection. H o w e v e r , this d e p e n d s o n t h e s e e d certification s t a n d a r d s o f t h e country. T h e plot size can b e 0 . 5 - 1 . 0 h a according t o h o w m u c h s e e d i s r e q u i r e d a t t h e certified s e e d p r o d u c t i o n stage. A s s u m i n g a multiplication factor of x 3 0 0 , for e x a m p l e :

Breeder

Foundation

Certified

Area (ha)

0.5 ha =

1 5 0 ha =

4 5 0 0 0 ha =

Q u a n t i t y (t)

0.75 t

225 t

67500 t

Grain production 13.5 m ha

B r e e d e r seed can be p r o d u c e d o n c e a n d u s e d for foundation seed p r o d u c t i o n for 2-4 years.

Foundation s e e d . O n l y b r e e d e r s e e d is u s e d to plant t h e s e plots a n d is s o w n early in uniform land, at least 4 0 0 m away from t h e nearest pearl millet, napier grass, a n d wild pearl millet fields. T h e plot should preferably be further away from any pearl millet, according to t h e direction of t h e prevailing w i n d . As a p r e c a u t i o n a r y m e a s u r e , first p l a n t a b e l t o f 5 - 1 0 m w i d e a r o u n d t h e p e r i m e t e r o f t h e plot w i t h t h e s a m e seed, a t least 7-10 days b e f o r e planting i n t h e center. T h e p e r i m e t e r can b e p l a n t e d d r y while t h e c e n t e r can b e p l a n t e d , just after t h e rains. T h e p u r p o s e o f t h e p e r i m e t e r planting (from w h i c h t h e s e e d will b e h a r v e s t e d separately a n d sold a s grain) i s t o p r o v i d e pollen b y t h e t i m e t h e

3

plants i n t h e c e n t e r begin t o f l o w e r . T h i s p r o v i d e s p r o t e c t i o n , b a s e d o n dilution, against incoming w i n d - b o r n e alien pollen. Before flowering, search for and d e s t r o y any v o l u n t e e r pearl millet plants on t h e field b o r d e r s a n d d i t c h e s , a n d in nearby cropland. Rogue obvious off-types before flowering, to m e e t f o u n d a t i o n s e e d s t a n d a r d s . N o r m a l l y varietal offt y p e s should b e less t h a n 2 % a t t h e final i n s p e c t i o n . Certified seed. U s e only a p p r o v e d f o u n d a t i o n s e e d a n d sow large c o n t i g u o u s blocks, if possible in areas w h e r e o t h e r pearl millet p l o t s will n o t be p l a n t e d ; b u t t h e r e s h o u l d be a gap of at least 3 0 0 m from o t h e r pearl millet p l a n t s . Ensure t h a t pearl millet farmers near t h e certified s e e d p r o d u c t i o n plots are all p r o v i d e d w i t h a n d agree t o g r o w t h e s a m e variety as t h a t being p r o d u c e d . Rogue if possible, a n d m a k e sure t h a t varietal off-types do n o t e x c e e d 5 % a t t h e final inspection.

Sorghum S o r g h u m varieties are generally p u r e or highly i n b r e d lines, and are rarely c o m p o s i t e s . T h e y are u n i f o r m , a n d it is easy to identify off-types unlike in pearl millet varieties. S o r g h u m is classified p r e d o m i n a n t l y as a self-pollinated c r o p . T h e a m o u n t of crosspollination is usually 2-10%, a n d is normally higher in t h e t o p q u a r t e r of t h e panicle. This is possibly b e c a u s e , according to t h e o r d e r of flowering, t h e stigmas e m e r g i n g in this region have relatively less access to p o l l e n from t h e s a m e panicle. Florets o p e n i n g t i m e varies a m o n g regions a n d c l i m a t e s . U n d e r tropical conditions, it is usually b e t w e e n 0 2 0 0 - 0 8 0 0 hrs. A s g l u m e s o p e n , t h e stigmas a n d a n t h e r s e m e r g e o u t w a r d s a n d usually t h e stigmas a n d a n t h e r s p r o t r u d e just before t h e g l u m e s o p e n and frequently a n t h e r s p r o t r u d e first. Flowering of a panicle m a y be s p r e a d over a p e r i o d of 4-9 days d e p e n d i n g u p o n t h e cultivar, t h e panicle size, t e m p e r a t u r e , a n d humidity. In cooler climates, t h e panicle b l o o m i n g p e r i o d m a y b e e x t e n d e d . T h e t i m e o f d e h i s c e n c e i s very m u c h d e p e n d e n t u p o n w e a t h e r conditions. In t h e tropics, on clear days, d e h i s c e n c e occurs a r o u n d sunrise. If d a m p o r cool w e a t h e r prevails early i n t h e m o r n i n g , d e h i s c e n c e could b e d e l a y e d u p t o 1 0 0 0 hrs. A n t h e r s d e h i s c e w h e n t h e y are d r y a n d t h e pollen i s liberated. S o r g h u m is a w i n d - p o l l i n a t e d c r o p . Pollen is normally viable for 3-6 hrs, so long as it is c o n t a i n e d in t h e anther, even after d e h i s c e n c e a n d it is s h e d rapidly w h e n t h e w e a t h e r is w a r m a n d a m i l d b r e e z e is prevailing. Pollen is usually available for a p e r i o d of 4 - 1 0 days, since n o t all t h e panicles in t h e field flower simultaneously. T h e stigmas r e m a i n r e c e p t i v e u p t o a w e e k o r m o r e after b l o o m i n g d e p e n d i n g u p o n t h e w e a t h e r . H o w e v e r , t h e y are m o s t r e c e p t i v e d u r i n g t h e first 3 days after t h e i r e m e r g e n c e . Multiplication rates in s o r g h u m are high, particularly w i t h varieties. Ten kg of s e e d is m o r e t h a n sufficient to sow 1 ha. T h i s s h o u l d p r o d u c e at least 2 0 0 0 kg of clean s e e d even at a m o d e r a t e level of soil fertility.

4

N u c l e u s seed. T h e n u c l e u s s e e d m a i n t a i n e d b y t h e b r e e d e r i s t h e f u n d a m e n t a l stock from w h i c h all else is derived and should be t h e only stock t h a t r e g e n e r a t e s itself. O n c e in 4 years, 3 0 - 5 0 kg of seed should be p r o d u c e d . T h e n u c l e u s seed p r o d u c e should be t h o r o u g h l y d r i e d and t r e a t e d against insects a n d p e s t s , a n d divided i n t o six lots of 5-10 kg each, a n d k e p t in sealed c o n t a i n e r s in a cool s t o r e . Lots 1, 2, 3, and 4 are u s e d to p l a n t t h e b r e e d e r seed plots for t h e n e x t 4 years; lot 5 is u s e d to plant t h e n e x t nucleus seed plot 4 years h e n c e . Lot 6 is a b a c k u p or insurance lot t h a t should be k e p t in a different building from t h e o t h e r lots. N u c l e u s seed can be p r o d u c e d by selfing 1 0 0 0 to 2 0 0 0 good panicles in b r e e d e r seed p r o d u c t i o n plots by an e x p e r i e n c e d b r e e d e r . O t h e r w i s e , a h e a d - t o - r o w p r o c e d u r e is usually followed to confirm t h e u n i f o r m i t y of plants. Individual self-pollinated t r u e to t y p e panicles ( 1 0 0 - 2 0 0 ) of t h e cultivar are selected, h a r v e s t e d , and t h r e s h e d individually. T h e seed of e a c h panicle is used to establish a single r o w in t h e s u b s e q u e n t season, all t h e plants are selfed by bagging. T h e plants in r o w s are scrutinized t h o r o u g h l y to d e t e r m i n e t h e i r a u t h e n t i c i t y t o t y p e . Any rows, w h i c h s h o w variation a n d deviation from t h e description, are discarded. T h e r o w s in w h i c h all t h e plants are uniform and t r u e to t y p e are h a r v e s t e d a n d b u l k e d to form t h e basis for n u c l e u s / b r e e d e r seed multiplication. Breeder seed. T h e nucleus seed i s p l a n t e d t o p r o d u c e t h e b r e e d e r seed. T h e s e plots should be e x t r e m e l y isolated a n d at least 4 0 0 m away from any o t h e r plot of s o r g h u m , J o h n s o n grass, and o t h e r forage or grassy s o r g h u m t y p e s . T h e s e plots should be g r o w n preferably in t h e off-season, w h e n c r o p g r o w t h and s e e d quality is good. T h e plot should be t h i n n e d at an early stage to an evenly s p a c e d single p l a n t p e r hill. Several inspections prior to flowering are r e c o m m e n d e d , to r e m o v e any off-type plants. D u r i n g flowering daily inspections are n e e d e d to identify a n d r e m o v e all plants t h a t are not t r u e to t y p e before t h e y s h e d pollen. H o w e v e r , a final roguing should be c o n d u c t e d in t h e standing c r o p before harvest to eliminate any remaining off-types. Roguing at t h e flowering stage will r e d u c e t h e n e e d for any further roguing. G e n e t i c off-types p e r m i t t e d at t h e final inspection d e p e n d s on t h e seed certification s t a n d a r d s of t h e country; normally it should n o t e x c e e d 0 . 0 1 % . T h e plot size can be 0 . 5 - 1 . 0 ha according to h o w m u c h seed is r e q u i r e d at t h e certified seed p r o d u c t i o n stage, assuming a multiplication factor of x 2 0 0 . For example: Breeder

Foundation

Certified

Grain

Area (ha)

0.5 ha =

100 ha =

20,000 ha =

4 m ha

Quantity (t)

1t

200 t

40,000 t

Foundation seed. U s e only b r e e d e r s e e d t o plant t h e foundation seed plots and should b e sown on good uniform land at least 3 0 0 m away from t h e nearest grain and forage s o r g h u m plots. Before flowering, search for and d e s t r o y any v o l u n t e e r sorghum plants on field

5

b o r d e r s a n d d i t c h e s , a n d in n e a r b y cropland. Rogue obvious off-types b e f o r e flowering, to m e e t f o u n d a t i o n s e e d s t a n d a r d s . T h e g e n e t i c off-types p e r m i t t e d a t t h e final inspection d e p e n d s o n t h e seed certification s t a n d a r d s o f t h e country; n o r m a l l y i t s h o u l d n o t e x c e e d 0.05%. Certified s e e d . U s e only a p p r o v e d foundation s e e d and s o w large c o n t i g u o u s blocks, if possible in areas w h e r e o t h e r s o r g h u m plots will n o t be p l a n t e d ; b u t t h e r e should be a gap of at least 2 0 0 m from o t h e r s o r g h u m p l a n t s . E n s u r e t h a t t h e s o r g h u m farmers near t h e certified s e e d p r o d u c t i o n plots are all p r o v i d e d w i t h a n d agree to g r o w t h e s a m e variety as t h e o n e being m u l t i p l i e d . Rogue, i f possible t o r e d u c e t h e varietal off-types. G e n e t i c off-types p e r m i t t e d a t t h e final inspection d e p e n d s o n t h e s e e d certification s t a n d a r d s o f t h e country; normally i t s h o u l d n o t e x c e e d 0 . 1 % .

Hybrid Seed Production (Sorghum and Pearl Millet) T h e p r o c e d u r e s for h y b r i d s e e d p r o d u c t i o n in b o t h s o r g h u m a n d pearl millet are similar. Both c r o p s u s e cytoplasmic-genetic m a l e sterility s y s t e m in h y b r i d s e e d p r o d u c t i o n t h a t is c a u s e d b y a n interactio n o f t h e sterility-inducing factors i n t h e c y t o p l a s m w i t h t h e genetic factors in t h e n u c l e u s . T h e p r o c e d u r e s d e s c r i b e d earlier for t h e p r o d u c t i o n of different varieties of s e e d ( p u r e line, a n d c o m p o s i t e s ) is largely applicable to t h e s e e d p r o d u c t i o n of h y b r i d s t o o . Additional information is given below:

Identification of Potential Hybrid Parents (A-, B-, and R-lines) Potential m a l e a n d female p a r e n t s for h y b r i d s e e d p r o d u c t i o n a r e identified b y crossing male-fertile plants (inbreeds, varieties, g e r m p l a s m , b r e e d i n g stocks in a d v a n c e d generations, etc.) to a male-sterile line (A-line) and observing t h e i r c o r r e s p o n d i n g hybrids in small plots of an observation nursery. A few plants of e a c h cross are subjected to a bagging t e s t , i.e., covering a few panicles w i t h p a p e r bags b e f o r e anthesis, and observing s e e d - s e t u n d e r t h e bag after a few w e e k s . A n o r m a l bisexual fertile panicle w o u l d exhibit nearly 1 0 0 % s e e d set w h e r e a s in crosses w i t h A-lines, t h e following t h r e e t y p e s of hybrids are e n c o u n t e r e d . 1.

H y b r i d s have no seed-set, i.e., male-sterility is m a i n t a i n e d in t h e s e h y b r i d s . T h e c o r r e s p o n d i n g pollen p a r e n t is classified as a n o n - r e s t o r e r / m a i n t a i n e r or B-line a n d as a p o t e n t i a l n e w A-line.

2.

H y b r i d s exhibiting c o m p l e t e seed-set u n d e r t h e bag, i.e., m a l e fertility has b e e n c o m p l e t e l y r e s t o r e d in t h e s e h y b r i d s . T h e c o r r e s p o n d i n g pollen p a r e n t is classified as a p o t e n t i a l m a l e - p a r e n t / r e s t o r e r line or R-line a n d c o u l d be useful in p r o d u c i n g hybrids.

3.

H y b r i d s exhibiting partial seed set u n d e r t h e bag.

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Such hybrids and their male

p a r e n t s are r e j e c t e d for f u r t h e r s t u d i e s b e c a u s e e x p e r i e n c e s h o w s t h a t it is difficult to e x t r a c t stable R-lines or B-lines from such p a r e n t s . Type 2 hybrids, in w h i c h fertility was f o u n d to be n o r m a l , are e v a l u a t e d visually in c o m p a r i s o n to local control g e n o t y p e s . Various agronomic traits such as days to maturity, plant height, fodder yield quality, grain color quality, panicle size, hybrid vigor, grain yield, threshability, a n d resistance t o diseases a n d insects are c o n s i d e r e d . S e l e c t e d h y b r i d s are a d v a n c e d for further studies and t h e i r c o r r e s p o n d i n g m a l e p a r e n t s i n c l u d e d in t h e R-line collection.

Seed Multiplication of Parental Lines (R-line, B-line, and A-lines): Nucleus, Breeder, and Foundation Seed N u c l e u s seed is p r o d u c e d in small q u a n t i t i e s on e x p e r i m e n t stations by t h e sponsoring b r e e d e r u n d e r his d i r e c t supervision a n d is t h e basis for f u r t h e r s e e d multiplication. T h e organization sponsoring cultivar release has t h e responsibility for t h e supply a n d safe storage of n u c l e u s and b r e e d e r seed. T h e b r e e d e r provides a c o m p l e t e d e s c r i p t i o n of all distinguishing morphological traits of t h e cultivars. In t h e case of hybrids, t h e A-line, Bline, R-line and t h e hybrid all r e q u i r e individual and a c c u r a t e d e s c r i p t i o n s b e c a u s e t h e certification process d e p e n d s u p o n it. T h e b r e e d e r provides small q u a n t i t i e s of seed of t h e A-line, B-line, a n d R-line t o t h e foundation s e e d p r o d u c e r s . W h i l e t h e e x p e r i m e n t station sponsoring t h e release of t h e hybrid, trains t h e technical staff involved in t h e p r o d u c t i o n and certification of hybrid seed and familiarizes t h e m in t h e identification of distinguishing characters of t h e p a r e n t s a n d t h e hybrid. B r e e d e r seed is t h e source of basic or foundation s e e d a n d is subject to s e e d certification. In case of hybrids, foundation seed is p r o d u c e d to increase t h e seed q u a n t i t y (certified seed) of p a r e n t a l lines from b r e e d e r seed. T h i s is d o n e u n d e r close supervision of t h e b r e e d e r a n d certified seed p r o d u c t i o n agencies, as it re quires specific a n d high s t a n d a r d s during p r o d u c t i o n a n d processing. T h e s e A-line and R-line seeds r e q u i r e g r o w - o u t t e s t s in small p l o t s b e f o r e being supplied to certified s e e d g r o w e r s . T h e details of p r o d u c t i o n of R-line, B-line, a n d A-lines are given below: R-line. T h e s o r g h u m r e s t o r e r (R) line has self-fertile bisexual florets a n d is a p u r e line. T h e r e f o r e , it can be m u l t i p l i e d w i t h ease in a m a n n e r similar to t h a t of p u r e line varieties (described earlier). T h e pearl millet R-line could be e i t h e r an i n b r e d line or o p e n pollinated variety; can be m u l t i p l i e d as variety (describe earlier). H o w e v e r , in t h e s e e d multiplication of an i n b r e d line, at t h e final inspection, genetic off-type s h o u l d n o t be p e r m i t t e d m o r e t h a n 0 . 0 5 % . A n y plant i n t h e R-line plot appearing different from t h e t r u e R-type (as d e s c r i b e d by t h e b r e e d e r ) in any w a y (major or m i n o r ) should be u p r o o t e d , o r rogued, before anthesis. A l t h o u g h t h e process of roguing starts soon after t h e seedling stage, t h e b o o t leaf a n d panicle e m e r g e n c e stages are critical, as d e t e c t i o n of off-types is

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easier d u r i n g t h e s e stages. Off-types t h a t e s c a p e d e t e c t i o n during t h e flowering stage should b e r e m o v e d b e f o r e harvest t o m i n i m i z e c o n t a m i n a t i o n . I t i s r e c o m m e n d e d t h a t p l a n t s of d o u b t f u l status s h o u l d also be r e m o v e d . Purity of t h e p a r e n t a l s e e d is very i m p o r t a n t b e c a u s e it affects t h e quality of h y b r i d s e e d t h a t is g e n e r a t e d . B-line. T h e m a i n t a i n e r or B-line is self-fertile a n d can be m u l t i p l i e d in an isolated p l o t in t h e s a m e m a n n e r d e s c r i b e d for t h e R-line. H o w e v e r , i t can also b e h a r v e s t e d from t h e A line/B-line s e e d p r o d u c t i o n p l o t s t h a t are e x p l a i n e d below. A-lines. Large scale p r o d u c t i o n of m a l e sterile (A) lines is carried o u t by growing t h e A-line a n d its c o r r e s p o n d i n g maintainer, B-line t o g e t h e r in an isolated plot. T h e isolation d i s t a n c e r e q u i r e d for A x B p r o d u c t i o n fields is at least 1 k m . A ratio of 4 A : 2B or 6 A : 2B r o w s is m a i n t a i n e d and t h e b o r d e r s of t h e field are s o w n w i t h B-line, T h e male-sterile line (A) a n d its m a i n t a i n e r (B) flower at a b o u t t h e s a m e t i m e and t h u s t h e r e are no p r o b l e m s o f a s y n c h r o n o u s flowering. Pollen p r o d u c e d b y t h e B-line fertilizes t h e male-sterile p l a n t s (A) a n d t h e s e e d p r o d u c e d t h u s , gives rise to t h e A-line again. Roguing in A-line s e e d p r o d u c t i o n p l o t s should be m o r e stringent b e c a u s e A a n d B plants c a n n o t be easily distinguished after flowering. T h e pollen s h e d d e r s i n t h e A-line r o w s m u s t b e identified a n d u p r o o t e d e a c h m o r n i n g during t h e flowering p e r i o d . U t m o s t caution m u s t b e exercised in labeling a n d harvesting A-line a n d B-line rows a n d t h e B-line r o w s are h a r v e s t e d first, followed by t h e A-line r o w s . Purity of t h e A-line is very i m p o r t a n t a n d any lapses can lead t o h u g e losses o f b o t h t i m e a n d m o n e y s p e n t i n roguing t h e h y b r i d s e e d (A x R) p r o d u c t i o n plots in t h e n e x t generation. Normally, no m o r e t h a n 0 . 0 5 % genetic oft y p e are p e r m i t t e d at final inspection in foundation s e e d . Since b o t h A-lines and B-lines exhibit s y n c h r o n o u s flowering, seed yields on t h e A-line in A / B seed p r o d u c t i o n p l o t s are relatively b e t t e r t h a n in t h e A and R (hybrid) p r o d u c t i o n plots. S e e d of t h e B-line h a r v e s t e d from t h e A / B p r o d u c t i o n p l o t s m i g h t b e r e u s e d for t h e n e x t generation, d e p e n d i n g o n t h e s e e d laws o f t h e country.

Hybrid (A x R) Seed Production (Certified Seed) T h e h y b r i d s e e d is p r o d u c e d only as a certified s e e d u n d e r t h e vigilance of s e e d certification agencies on a very large scale by private agencies, seed farms, e x p e r i e n c e d growers, a n d o t h e r e x t e n s i o n organizations using foundation seed. Millet and s o r g h u m h y b r i d s involve A x R seed p r o d u c t i o n a n d are carried o u t according to t h e p r e s c r i b e d s t a n d a r d s of p r o d u c t i o n and processing in t e r m s of isolation distance, genetic purity, a n d s e e d quality. S e e d certification and seed law e n f o r c e m e n t agencies have an i m p o r t a n t role t o play i n certified h y b r i d s e e d p r o d u c t i o n a n d distribution, b e c a u s e t h e f a r m e r s ' c r o p p e r f o r m a n c e i s directly d e p e n d e n t u p o n t h e quality o f t h e certified s e e d u s e d . A l t h o u g h p r o d u c t i o n of h y b r i d s e e d can be carried o u t by small individual growers, it is c o n v e n i e n t to g r o w it in large areas of 1 0 0 - 1 5 0 ha. T h e q u a n t i t i e s of certified seed p r o d u c e d d e p e n d s u p o n t h e p r o j e c t e d d e m a n d for t h e s e e d o f t h e r e s p e c t i v e cultivar; normally a n excess o f 2 0 % over t h e d e m a n d i s p r o d u c e d . T h e r e q u i r e m e n t s o f isolation distance m u s t b e

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satisfied by a n e g o t i a t e d c o n t r a c t b e t w e e n a g r o u p of farmers living in a c o m m u n i t y ( t h e seed village) a n d t h e seed firm. T h e seed c o m p a n i e s train supervisory staff w h o will in t u r n advise and assist t h e seed growers in h y b r i d seed p r o d u c t i o n during various stages o f t h e c r o p . Foundation s e e d i s supplied t o t h e seed g r o w e r s b y t h e c o m p a n y o r firm. T h e c o m p a n y staff should train t h e growers in identification of t h e c o r r e c t plant t y p e s , m a l e steriles, a n d roguing of s h e d d e r s and o t h e r off-types. C l o s e c o m m u n i c a t i o n b e t w e e n seed growers and t h e c o m p a n y supervisory staff during t h e e n t i r e h y b r i d seed p r o d u c t i o n season is necessary. Male-sterile (A) a n d r e s t o r e r (R) lines are sown in a l t e r n a t e strips of rows, normally in a ratio of 4 A : 2 R or 6 A: 2 R, d e p e n d i n g on t h e local e x p e r i e n c e of success a n d t h e ability of t h e R-line to disperse pollen. T h e b o r d e r s on all four sides of t h e hybrid seed p r o d u c t i o n field are s o w n w i t h t h e r e s t o r e r (R) lines to e n s u r e an a d e q u a t e supply of pollen and guard against incoming stray pollen. An isolation distance of at least 3 0 0 m is generally r e c o m m e n d e d for hybrid seed p r o d u c t i o n . In case of s o r g h u m , a distance of at least 4 0 0 m is necessary if J o h n s o n grass and o t h e r forage or grassy sorghum t y p e s are growing in t h e vicinity. Similarly, isolation distance should be increased for pearl millet hybrids if napier grass and wild millet are in t h e vicinity. T i m e isolation seed p r o d u c t i o n (i.e., sowing a seed p r o d u c t i o n plot so t h a t t h e r e is no overlap in t h e flowering p e r i o d of t h e p r o d u c t i o n plot a n d t h e adjacent crop) is possible only on e x p e r i m e n t stations u n d e r t h e supervision of b r e e d e r s . Row spacing can vary from 4 5 - 9 0 c m . It is essential t h a t t h e p a r e n t a l lines chosen for hybrid seed p r o d u c t i o n , flower at t h e s a m e t i m e i.e., t h e viable pollen is available w h e n stigmas are r e c e p t i v e . T h e r e f o r e , a prior k n o w l e d g e of t h e flowering p a t t e r n s of b o t h t h e p a r e n t s in h y b r i d seed p r o d u c t i o n is i m p o r t a n t . Sowing d a t e s o f t h e respective p a r e n t s should b e synchronized w i t h t h e flowering of t h e m a l e and female p a r e n t s . H y b r i d s w h o s e p a r e n t s 'nick' in t h e i r flowering w h e n s o w n simultaneously are ideal, b e c a u s e a difference of 4-5 days in flowering b e t w e e n t h e t w o p a r e n t s could seriously affect seed set on t h e male-sterile line. If p a r e n t s differ in t h e i r days to 5 0 % flowering by m o r e t h a n 3 days, staggering of sowing d a t e s is r e c o m m e n d e d . For e x a m p l e , if t h e male p a r e n t is k n o w n to t a k e 65 days to 5 0 % flowing and t h e female p a r e n t (A-line), 7 5 days t o 5 0 % flowering, t h e n t h e m a l e p a r e n t has t o b e sown 10 days after sowing t h e female p a r e n t . U n d e r rain-fed p r o d u c t i o n conditions, this m i g h t be difficult. W h e n t h e difference in days to 5 0 % flowering is narrow, i.e., less t h a n 5 days, t h e n t h e m a l e p a r e n t can b e sown simultaneously w i t h t h e female rows, while t h e b o r d e r rows m a y b e sown 4-5 days later. T h e flowering behavior o f t h e t w o p a r e n t s m a y change w i t h different day lengths a n d t e m p e r a t u r e s at various locations or seasons. T h e r e f o r e , s o m e preliminary data on flowering behavior of t h e m a l e and female parents, and pollen p r o d u c i n g capability o f t h e m a l e p a r e n t from t h e s e e d p r o d u c t i o n locations during t h e a p p r o p r i a t e season, is necessary b e f o r e u n d e r t a k i n g c o m m e r c i a l hybrid seed production.

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T h e relative g r o w t h stages o f t h e m a l e a n d female p a r e n t s should b e critically e x a m i n e d w h e n t h e c r o p i s 3-4 w e e k s old, o r e v e n later d e p e n d i n g u p o n t h e length o f t h e i r vegetative g r o w t h p e r i o d . Plants from t h e m a l e a n d female r o w s c o u l d b e r a n d o m l y s a m p l e d , t h e s t e m s s t r i p p e d o f leaves a n d t h e floral p r i m o r d i a a n d t h e a p e x carefully e x a m i n e d . Differences in t h e t i m e of initiation a n d size of t h e panicle b u d w o u l d indicate t h e differences in t h e i r t i m e to 5 0 % flowering. T h e late flowering of a p a r e n t can be h a s t e n e d by selective application of n i t r o g e n o u s fertilizers like urea a n d a m m o n i u m sulfate. Alternatively, selective irrigation of o n e p a r e n t a n d d e l a y e d irrigation of t h e o t h e r will also h e l p in synchronizing t h e flowering d a t e of t h e p a r e n t s . Careful m a n i p u l a t i o n of n i t r o g e n o u s fertilizers a n d irrigation can synchronize flowering of p a r e n t s t h a t differ by up to a w e e k . U n i f o r m a n d good c r o p m a n a g e m e n t practices t h r o u g h o u t t h e field h e l p in s y n c h r o n o u s flowering and good s e e d yields. G o o d nick (flowering a t t h e s a m e t i m e ) o f t h e m a l e a n d female p a r e n t s s h o u l d b e c o n s i d e r e d w h i l e selecting t h e hybrids. Differential susceptibility o f t h e p a r e n t s t o insect attack, nutritional factors, a n d diseases f r e q u e n t l y result in asynchronous flowering, t h e r e f o r e , t i m e l y plant p r o t e c t i o n m e a s u r e s have an i m p o r t a n t role in seed p r o d u c t i o n . Roguing should be carried o u t in t h e h y b r i d s e e d p r o d u c t i o n fields regularly as soon as t h e c r o p c o m m e n c e s flowering. A p a r t from off-types, pollen ' s h e d d e r s ' can also be a p r o b l e m in A-lines. S h e d d e r s are plants t h a t look similar to t h e B-type and exhibit fertile a n t h e r s a n d s h e d pollen. S u c h plants can only be identified at anthesis and should be u p r o o t e d i m m e d i a t e l y . S h e d d e r s can also arise from partial b r e a k d o w n of sterility in t h e A-lines d u e to high t e m p e r a t u r e s ( > 3 8 ° C ) . D e l a y in identifying s h e d d e r s will result in o u t crossing to male-sterile plants a n d s u b s e q u e n t c o n t a m i n a t i o n o f t h e h y b r i d w i t h female p a r e n t t y p e p l a n t s . T h e r e f o r e , it is r e c o m m e n d e d t h a t roguing be carried o u t in t h e early m o r n i n g h o u r s b e f o r e pollen shedding t a k e s place. T h e R-line should also be r o g u e d periodically. P r o d u c e r s are i n t e r e s t e d in h y b r i d s e e d h a r v e s t e d from t h e male-sterile p a r e n t (A-line) a n d t h u s t h e objective i s t o achieve m a x i m u m p e r c e n t a g e seed-set o n t h e male-sterile line. To achieve good seed-set, pollen should be b a t t e d o u t of h e a d s in t h e m o r n i n g w i t h sticks a n d a m o t o r i z e d back pack d u s t e r ( w i t h o u t d u s t ) . It is beneficial for s e e d setting if t h e Rline is taller t h a n t h e A-line as pollen p r e d o m i n a n t l y disperses d o w n w a r d s , and this should b e b o r n e i n m i n d w h e n making e x p e r i m e n t a l h y b r i d c o m b i n a t i o n s . I f t h e c o m m o n t r e n d in w i n d direction during t h e p r o d u c t i o n season is k n o w n , seed p r o d u c t i o n plot rows should b e sown p e r p e n d i c u l a r t o t h e w i n d d i r e c t i o n . O n e x p e r i m e n t stations, w h e n s y n c h r o n y of flowering is poor, b u l k pollination by h a n d (using p a p e r bags) m i g h t be adopted. All possible p r e c a u t i o n s against seed c o n t a m i n a t i o n should be t a k e n during harvesting of h y b r i d s e e d p r o d u c t i o n plots a n d t h r e s h i n g of panicles from t h e A-line rows. Usually, t h e R-line is h a r v e s t e d first a n d t h e harvest r e m o v e d from t h e field. L a t e r t h e A-line r o w s are carefully i n s p e c t e d for off-types a n d o t h e r c h a n c e a d m i x t u r e s and t h e n h a r v e s t e d . H y b r i d s e e d yield (on t h e A-line) d e p e n d s u p o n t h e yield p o t e n t i a l o f t h e A-line, p e r c e n t seed set,

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a n d e n v i r o n m e n t a l c o n d i t i o n s . U n d e r good conditions, s e e d yields c o u l d range from 1-2 t ha - 1 . Harvest of R-line s e e d from A x R plots. S e e d p e r m i t t e d to be r e u s e d as ' s e e d ' for hybrid (A x season b u t instead sold as grain. H o w e v e r , if t h e r e of seed c o n t a m i n a t i o n , R-line s e e d from selected A production.

of t h e R-line harvest is generally n o t R) seed p r o d u c t i o n again in t h e n e x t are no pollen s h e d d e r s , a n d no c h a n c e x R plots can be r e u s e d for h y b r i d seed

Planning Commercial Hybrid Seed Production C o m m e r c i a l seed p r o d u c t i o n m u s t b e carried o u t i n a n well-organized m a n n e r . H y b r i d s e e d p r o d u c t i o n agencies have to identify suitable areas for efficient s e e d p r o d u c t i o n t h r o u g h preliminary e x p e r i m e n t a t i o n . Areas e n d e m i c t o serious diseases, p e s t s , a n d obnoxious w e e d s like S. halepense (in case of s o r g h u m ) , P. purpureum, and P. glaucum sp monodii (in case of pearl millet) and Striga are n o t suitable. A r e a s t h a t are p r o n e to such natural disasters as floods, excessive b i r d d a m a g e , or h a i l s t o r m s should be avoided. Excessive rains or high h u m i d i t y during t h e grain-filling stages of s o r g h u m could cause grain m o l d s , discoloration, w e a t h e r i n g , and p r e h a r v e s t sprouting, all of w h i c h affect germinability. D a y s to 5 0 % flowering of t h e hybrid p a r e n t s , p r o d u c t i v i t y vs. cost, a n d climatic conditions, particularly during grain-filling stages, should be i m p o r t a n t considerations w h e n selecting areas for seed p r o d u c t i o n . If s e e d p r o d u c t i o n is p l a n n e d for t h e off-season, access to irrigation facilities is i m p o r t a n t . T h e quantities of each class of seed r e q u i r e d should be roughly e s t i m a t e d on an annual basis i n advance, d e p e n d i n g u p o n t h e p r o j e c t e d d e m a n d for t h e c o m m e r c i a l hybrid u n d e r cultivation. It is desirable to maintain significant q u a n t i t i e s of carry-over s e e d as an insurance against u n f o r e s e e n seed c r o p losses. T h e progress of seed p r o d u c t i o n and status of seed stocks should be r e v i e w e d annually in joint m e e t i n g s a m o n g r e p r e s e n t a t i v e s of seed growers, foundation s e e d agencies, a n d national seed agencies. T h e various activities of t h e multiplication chain of b r e e d e r seed, foundation seed, and certified s e e d s h o u l d be coordinated. Q u a l i t y control, e i t h e r voluntary or compulsory, has an i m p o r t a n t role in hybrid seed p r o d u c t i o n . Suitable laws t h a t provide for m i n i m u m s t a n d a r d s of seed certification should be e n a c t e d and rigorously enforced. A d e q u a t e laboratory facilities for seed testing a n d certification should be p r o v i d e d . T h e m a i n objective of hybrid seed p r o d u c t i o n is to k e e p t h e farmer a d e q u a t e l y s u p p l i e d w i t h large q u a n t i t i e s o f good quality ( t r u e t o t y p e ) s e e d o f p r e s c r i b e d germinability a n d o t h e r s t a n d a r d s . In this c o n t e x t , t i m e l y roguing p r a c t i c e by t h e seed growers, supervisors, a n d certification agents is of critical i m p o r t a n c e . Proper training of all technical staff involved in t h e h y b r i d seed p r o d u c t i o n a n d certification processes is essential. T h e y m u s t be supplied w i t h a list of all morphological distinguishing characters of t h e A-, B-, a n d R-lines involved in t h e h y b r i d seed p r o d u c t i o n a n d b e c o m e

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familiar with them through field demonstrations and orientation courses. Seed processing, treatment, and certification facilities should be made accessible in seed production areas.

Purification of Varieties/Hybrid Parents Sorghum varieties. About 1000 plants of true type should be selfed, harvested, and threshed separately to be evaluated in the next season for uniformity. The seed of true types should be mixed to produce pure seed. Millet varieties. About 2000 plants of true type should be selfed. Harvest only 400-500 self plants based on visual performance, and thresh them together. The selected selfed bulk should be grown in isolation for random mating. This procedure should be repeated for 2-3 cycles to obtain purified seed. Hybrids. The seed parent (A-line) can be improved by making several hundred A x B plant to plant crosses and evaluating them for pollen shedding, and other traits. The remnant seed of selected A-lines can be mixed to produce pure A-line. Similarly, the seed of corresponding B-line can be mixed to produce pure B-line. R-lines can be purified as described in the nucleus seed production.

RA

- 0346

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ICRISAT International Crops Research Institute for the Semi-Arid Tropics Patancheru 502 324, Andhra Pradesh, India ISBN 92-9066-415-0

Order code: IBE 058

94-99