Amer J of Potato Res (1999) 76:137-141
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Identification of Stem Soft Rot (Erwinia Carotovora Subspecies Atroseptica) Resistance in Potato Piara S. Bains ~*, Vikram S. Bisht ~, Dermot R. Lynch ~, Lawrence M. Kawchuk 2, and J o h n P. Helgeson 3 ~CropDiversificationCentre North, AlbertaAgriculture Food & Rural Development,R.R.#6, Edmonton,AlbertaTSB 4K3 Canada. (Present address for V.S.B.,Ag-QuestInc., Box 144,Minto, ManitobaR0K 1M0Canada). 2Research Centre, Agriculture&Agri-FoodCanada, Lethbridge, AlbertaT1J 4B1 Canada. :'USDA/ARS,Department of Plant Pathology,Universityof Wisconsin, Madison, W153706. *CorrespondingAuthor: Phone:403415-2302, Fax: 403-422-6096,e-mail:
[email protected]
ABSTRACT
INTRODUCTION
Development of potato cultivars resistant to Erwinia species (Erwinia carotovora subspecies atroseptica, E. carotovora subspecies carotovora, and E r w i n i a c h r y s a n t h e m i ) causing soft rot o f stems and tubers involves identification and transfer o f the resistance to breeding lines possessing desirable agronomic traits. In total, 363 a c c e s s i o n s o f six wild S o l a n u m species, three somatic hybrids and nine sexual progeny o f s o m a t i c hybrids w e r e s c r e e n e d for s t e m s o f t rot resistance. Thirty-one, 50, and 67 percent o f accessions o f S o l a n u m b o l i v i e n s e , S o l a n u m c h a c o e n s e , and Solanum sancta-rosae, respectively, were resistant or highly resistant, whereas, 100, 97, and 95 percent o f accessions of Solanum canasense, Solanum tarUense, and Solanum s p e g a z z i n i i were susceptible or highly susceptible, respectively. T w o tuber soft-rot resistant somatic hybrids, A937 and T355-11 produced earlier by t h e f u s i o n o f S o l a n u m b r e v i d e n s (PI 2 1 8 2 2 8 ) and Solanum t u b e r o s u m ( P I 2 0 3 9 0 0 ) or S. tuberosum cv. Russet Burbank, respectively, and the sexual progeny o f A 9 3 7 and S. t u b e r o s u m cv. K a t a h d i n w e r e a l s o highly resistant. Transfer o f resistance from S. brevidens to somatic hybrid ( A 9 3 7 ) and subsequently to the progeny suggests that the resistance is simply inherited. In addition to the identification o f 65 resistant or highly resistant clones o f wild Solanum species, this s t u d y has i d e n t i f i e d t h r e e t u b e r s o f t r o t - r e s i s t a n t clones that are also resistant to stem soft rot. Potato cultivars showed a range o f responses to the pathogen.
Soft rot of stems and tubers of potato caused by any of the three soft rot Erwinias, E r w i n i a carotovora subspecies atroseptica (van Hall) Dye (Eca), E. carotovora subspecies carotovora (Jones) Bergey et al., and E r w i n i a chrysanthemi Burkholder, McFadden and Dimock, is an economically important disease worldwide (Perombelon & Kelman, 1980). Commercially effective bactericides do not exist for this disease. Development of potato cultivars resistant to Erwinias is considered to be the most effective method to reduce losses (French & de Lindo, 1985; Lapwood et al., 1985; Wastie & Mackay, 1985). Wild S o l a n u m species are known to possess resistance to many economically important diseases of potato. Resistance to tuber soft rot has been identified in wild S o l a n u m species, hybrids of wild S o l a n u m species, and hybrids of wild S o l a n u m species and S o l a n u m tuberosum L. and their sexual progeny (Allefs et al., 1995; Austin eta/., 1988; Carputo et al., 1997; Corsini & Pavek, 1986; French & de Lindo, 1985; Helgeson et al., 1986; 1993; Rousselle-Bourgeois & Priou, 1995; Wolters & Collins, 1994; Zimnoch-Guzowska & Lojkowska, 1993). Some species, however are sexually incompatible with cultivated potato. Interspecific somatic hybrids developed by fusion of protoplasts of S o l a n u m brevidens, a non tuber-bearing wild species, and S. t u b e r o s u m have expressed P h y t o p h t h o r a i n f e s t a n s (race 0) resistance (derived from S. tuberosum PI 203900) or potato leaf roll virus resistance (derived from S. b r e v i d e n s PI 218228) (Helgeson et al., 1986; 1993; Gibson et al., 1988). Furthermore, P. infestans resistance was transmitted to sexual progeny from crosses between somatic hybrids and Katahdin (Helgeson et al., 1993). No correlation, however, has been observed between tuber soft rot and stem soft rot resistance in a particular clone (Allefs et al., 1995; Carputo et al., 1997; Hidalgo & Echandi, 1982) suggesting that entirely different mechanisms might be involved in the two resistances (Tzeng et al., 1990). Breeding for increased tuber soft rot resistance, therefore
Acceptedfor publication October 13, 1998. ADDITIONALKEY WORDS:WildSolanum species, somatic hybrids, potato blackleg.
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would not necessarily improve resistance to blackleg (Wastie and Mackay, 1985). Development of parental lines with both types of resistances would facilitate breeding for resistance to both tuber and stem soft rots. It has been suggested that stem soft rot resistance could identify blackleg resistance (Lojkowska and Kelman, 1989; Wastie and Mackay, 1985). The objectives of this study were to identify stem soft rot resistance in accessions of wild S o l a n u m species and tuber soft rot-resistant hexaploid somatic hybrids and their sexual progeny (Helgeson et al., 1993), and determine the comparative resistance/susceptibility of potato cultivars to Eca.
MATERIALS AND METHODS P l a n t M a t e r i a l - - T u b e r soft rot-resistant, hexaploid somatic hybrids and crosses with S. tuberosum cv. Katahdin tested in this study were produced previously (Helgeson et al., 1993). Hybrids A206 and A937 were produced by the fusion of protoplasts of S. brevidens (PI 218228, 2n=2x=24) and S. tuberosum (PI203900, 2n=4x=48), and hybrid T355-11 by the fusion of protoplasts ofS. brevidens (P1218228, 2n= 2x=24) and S. t:uberosum cv. Russet Burbank (2n=4x=48). Somatic hybrids and their progeny were nficropropagated by single-node cuttings on MS (Murashige and Skoog, 1962) medium containing 0.8 g/L agar and 30.0 g/L sucrose, pH 5.7. The cuttings were grown for 3 weeks in a growth chanlber at 24/17 C day/night temperature and 18 hours of 140 pmol/m2/ sec light provided by cool white fluorescent tubes. The resultant plantlets were grown in soil-less medium (Metro-Mix, Terra-Lite 2000, W.R. Grace & Co., Ajax, Ontario) in 4 inch pots in growth chambers at 22/18 C (day/night) and 18-hours photoperiod. True seed (Potato Introduction Station, NRSP6, Sturgeon Bay, WI) of S. boliviense (PI 310928), S. canasense (P1283080), S. chacoense (PIs 275139, 275141, 472810, 471819, WRF 267), S. sanctae-rosae (P1230464), S. spegazzi n i i (P1310985) and S. tarijense (PIs 195206, 208881, 473223, 473236) were soaked for 24 hours in 1,000 ppm GA3 and germinated in soilless medium. The seedlings were transplanted into soil-less medium in 18 hole-propagation trays and were grown at 18 - 24 C with 18-hours of photoperiod. Potato cultivars (Table 3) were grown from micropropagated plants in a greenhouse at 18 - 24 C. I n o c u l u m and I n o c u l a t i o n s - - E c a used in this study was isolated previously from potato grown in Alberta, Canada. Bacterial cells were grown for 20 to 24 hours at 20 + 2 C on tryptic soy agar (Difco Labs, Detroit, Michigan). Bacterial colonies were washed with sterile distilled water and the concentration of bacterial cells in the suspension was
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determined by percent absorbance at 640 nm. The inoculum (105 bacterial cfu/ml) was prepared by diluting the concentrated bacterial suspension with sterile distilled water. Inoculations of leaf petioles were done as described by Bisht et al. 1993. Five freshly cut leaf petioles (-2-3 mm dia. and 85 mm length) were inserted to about 5 mm in 50 grams of sterile autoclaved sand drenched with 17 ml of the inoculum in a Magenta jar (GA-7 vessel, Magenta Corp., Chicago, IL). The Magenta jar with lid closed was kept on a laboratory bench (20 + 2 C, 16.hours photoperiod). The length of the rot developed in the petioles was recorded 72 hours after inoculation. and mean rot lengths of 0-5, 6-10, 11-50, >50 mm were scored as highly resistant, resistant, susceptible, and highly susceptible, respectively. All potato cultivars and somatic hybrids were tested using four replicated Magenta jars and the experiment was repeated twice. Due to a limited number of petioles, plants of wild S o l a n u m species were tested using 5 petioles and the experiment was repeated once. Data were analyzed by SAS (SAS Institute, Cary, NC).
RESULTS Stem Soft Rot Resistance Screening o f Wild S o l a n u m Species. Wild Solanum species showed a wide range of reactions to inoculation with Eca (Table 1, Fig. 1). Not only the species but also the accession lines within the species differed in their reaction to the pathogen. Resistant and/or highly resistant clones were found in all the species except S. canasense. A large number (50 of 162) of S. chacoense, and a high percentage ofS. boliviense (6 of 9, 67%) and S. sancta-rosae (3 of 6, 50%) were resistant or highly resistant. One hundred, 97 and 95 percent S. canasense, S. tarijense, and S. spegazzi n i i clones were either susceptible or highly susceptible, respectively.
Stem Soft Rot Reaction o f Somatic H y b r i d s a n d Their Crosses with S. t u b e r o s u m cv. Katahdin. In this study, only tuber soft rot-resistant clones (somatic hybrids and their sexual progeny) previously identified by Helgeson et al. (1993) were tested for their stem soft rot reaction to Eca. Reaction of the clones ranged from highly resistant to highly susceptible (Table 2). Somatic hybrids A937 and T355-11 were highly resistant whereas somatic hybrid A206 was susceptible. Of the nine sexual progeny clones tested, one (4682) showed high resistance to Eca. The clone is the progeny of a cross between A937 and S. tuberosum cv.
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TABLE 1.---Soft rot reaction o f leaf petioles o f wild Solanum species to inoculation w i t h Erwinia carotovora subspecies atroseptica. Solanum species
Length of rot lesion (mm)1 0-5 6-10 (HR) 2 (R)
Total
11-50 >50 (S) (HS)
S. boliviense P1310928 S. canasense P1283080 S. chacoense P1275139 S. chazoense P1275141 S. ehacoense P1472810 S. chacoense P1472819 S. chacoer~e WRF 267 S. sanctae-~vsaeP1230464 S. spegazzinii P1310985 S. ta~gjensePI 195206 S. tarijense P1208881 S. tarijense P1473223 S. tarijense P1473236
3 0 5 6 2 4 13 3 1 0 1 1 2
3 0 2 5 1 5 7 0 0 0 0 1 0
2 9 19 20 10 20 34 2 10 1 27 43 9
1 7 2 0 0 6 1 1 9 19 2 22 22
9 16 28 31 13 35 55 6 20 20 30 67 33
Total
41
24
206
92
363
1Freshlycut leaf petioles were inoculated with Erwinia carotovora subspecies atroseptica by insertin~them into sterile sand drenched with 17 ml of bacterial suspension (10° bacterial cfu/ml) in Magentajars. The jars with lids closed were kept on a laboratory bench (20 + 2 C, 16 hours light). Rot lesions on petioles were measured 3 days after inoculation. 2Soft rot reaction of petioles: HR = highly resistant, R = resistant, S = susceptible, HS = highlysusceptible.
FIGURE 1.
Solanum tar~]ense l e a f petioles (Left to right) showing highly susceptible, susceptible and highly resistant stem soft rot reactions 3 days after inoculation w i t h Erwinia carotovora subs p e c i e s atroseptica (Eca). The p e t i o l e s w e r e i n o c u l a t e d by inserting them into sterile sand drenched with 17 ml of Eca suspension (105 bacterial cfu/ml) in Magenta jars. The jars with lids closed were kept on a laboratory bench (20 + 2 C, 16 hours light).
o t h e r v a l u a b l e a g r o n o m i c traits. This s t u d y i d e n t i f i e d a large n u m b e r (65) of c l o n e s of s e v e r a l w i l d S o l a n u m species that are either resistant or highly resistant to stem r o t b y Eca. Of the six s p e c i e s t e s t e d , c l o n e s f r o m five species were either resistant or highly resistant. Although the n u m b e r of clones tested was relatively small, a high percentage (31-67%)ofS. boliviense, S. chacoense and S. sanc-
Katahdin. All other clones were susceptible or highly susceptible to the pathogen.
tae-rosae c l o n e s w e r e r e s i s t a n t or h i g h l y r e s i s t a n t . Screening of these three species might, therefore be more productive for identification of additional resistant clones
The cultivars showed a wide range of susceptibility/resistance reactions to the pathogen (Table 3). Comparatively,
rather than screening S. canasense, S. s p e g a z z i n i i , and S. tarijense which had fewer (0-5%) resistant or highly resistant clones. Lines of S. chacoense have also b e e n s h o w n to have resistance to t u b e r soft rot (Rousselle-Bourgeois and Priou, 1995; Z i m n o c h - G u z o w s k a a n d Lojkowska, 1993).
Carlton and Banana were the most susceptible and the most resistant cultivar, respectively. There was n o correlation
Lojkowska and Kelman (1989) screened a large n u m b e r of accession lines ofS. chacoense and S. tarijense and, similar
b e t w e e n s u s c e p t i b i l i t y / r e s i s t a n c e a n d t e x t u r e of skin or colour of skin or flesh. In general, the overall reaction of the cultivars remained the same b e t w e e n the experiments.
to the p r e s e n t study, found high resistance in most S. cha-
S t e m S o f t R o t R e a c t i o n o f P o t a t o C u l t i v a r s to Eca.
coense lines. In contrast to the p r e s e n t study however, the majority S. tarijense accessions were highly resistant. With
Blackleg resistant potato cultivars would be an effective method to reduce the economic losses caused by this disease. The development of resistant cultivars involves the
one exception, the two studies s c r e e n e d different accessions ofS. tarijense. Carputa et al. (1997) also reported distinct susceptibility/resistance difference b e t w e e n two S. t a ~ j e n s e clones. The stem soft rot reactions of tuber soft rot-resistant somatic hybrids and their sexual progeny ranged from highly
identification of sources of resistance and transfer of the resistance to potato breeding lines and cultivars containing
susceptible to highly resistant. Somatic hybrids, A937 a n d T355-11 were resistant whereas A206 was susceptible. Both
DISCUSSION
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TABLE 2.--Soft rot reaction o f leaf petioles o f tuber soft rotresistant s o m a t i c hybrids ( S o l a n u m b r e v i d e n s x S. t u b e r o s u m and the progeny o f crosses between the hybrids a n d S. t u b e r o s u m cv. Katahdin. Length of rot lesion (mm) Mean (Range) l
Soft rot reaction 2
S. tuberosum cv. Katahdin
43 (10 - 81) 5 (9 - 27) 0 (0 - 0) 72 (40 - 85)
susceptible highly resistant highly resistant highly susceptible
A206 x S. tuberosum cv. Katahdin 4704 4709 4711
41(15 - 81) 52 (34 - 76) 11 (6-21)
susceptible highly susceptible susceptible
A937 x S. tuberosum cv. Katahdin 4680 4682 4683
36 (5 - 87) 0 (0 - 0) 49 (29 - 79)
susceptible higlfly resistant susceptible
Clone
A206 A937 T355-11
T355-11 x S. tubetvsum cv. Katahdin 1487 32 (10 - 74) 1732 15 (0 - 32) 1745 51 (5 - 81)
susceptible susceptible highly susceptible
1Freshly cut leaf petioles were inoculated with Erwinia carotovo~u subspecies atroseptica by inserting them into sterile sand drenched with 17 ml of bacterial suspension (105 bacterial cfu/ml) in Magenta jars. The jars with lids closed were kept on a laboratory bench (20 + 2 C, 16 hours light). Rot lesions on petioles were measured 3 days after inoculation. 2Soft rot reaction of petioles: 0-5 mm = highly resistant, 6-10 mm = resistant, 11-50 m m = susceptible, >50 m m = highly susceptible.
A206 a n d A937 h a v e t h e s a m e p a r e n t s , t h e d i f f e r e n c e is t h a t c h l o r o p l a s t s o f A206 a r e f r o m S. brevidens p a r e n t w h e r e a s t h a t o f A937 a r e f r o m S. t u b e r o s u m p a r e n t ( K i t z i n g e r a n d Helgeson, u n p u b l i s h e d d a t a as c i t e d b y H e l g e s o n et al., 1993). A n a l y s e s o f t h e i n t r o g r e s s i o n o f S. b r e v i d e n s D N A i n t o p o t a t o b r e e d i n g l i n e s i n d i c a t e t h a t s o m e o f t h e D N A is o f t e n
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TABLE 3.---Soft rot reaction o f leaf petioles o f various potato cultivars to E r w i n i a c a r o t o v o r a subspecies atroseptica~ Cultivar Carlton Caribe Conestoga Warba F72004 Eramosa Rode Eel~teling Norchip Yukon Gold Bintje Sangre Jemseg Niska Norland Monona Atlantic Desiree Saginaw Gold Frontier Russet Purple Vildng Norgold Russet AC Ptarmigan Viking Shepody A74117-9 Amisk Kennebec Russet Burbank Russet Norkotah Batoche Red Pontiac Superior Nooksack Banana
Length of rot lesion (mm) 1 66 a 2 62 ab 56 bc 56 bc 56 bc 53 bcd 52 cde 51 cdef 51 cdef 51 cdefg 50 cdefg 50 cdefgh 48 cdefgid 43 defghij 43 defghij 43 defghij 42 efghij 42 efgtfijk 41 fghijk 40 ghijkl 39 hijkl 38 ijkl 38 tjka 37jkl 35 jklm 34 jklmn 34 jklmn 31 klmno 30 lmno 28 lmno 26 mno 25 no 23 o 14 p
1Freshly cut leaf petioles were inoculated with Erwinia carotovora subspecies at~vseptica by inserting them into sterile sand drenched with 17 ml of bacterial suspension (105 bacterial cfu/ml) in Magenta jars. The jars with lids closed were kept on a laboratory bench (20 + 2 C, 16 hours light). Rot lesions on petioles were measured 3 days after inoculation. 2Means within the column followed by the same letter are not significantly different (P=0.05) as calculated by the Duncan's multiple range test.
n o t c a r r i e d o v e r i n t o s o m a t i c h y b r i d s (Willimns et al., 1993). T h u s it is n o t s u r p r i s i n g t h a t s o m e t r a i t s o f t h e w i l d s p e c i e s
was transferred to somatic hybrids and subsequently to the
d o n o t o c c u r in t h e p r o g e n y . E x c e p t f o r 4682, all t h e s e x u a l
progeny of a sexual cross between the somatic hybrid and
p r o g e n y o f c r o s s e s b e t w e e n t h e s o m a t i c h y b r i d s a n d Katah-
K a t a h d i n . Similar r e s u l t s f o r t r a n s f e r o f t u b e r s o f t r o t resis-
din w e r e s u s c e p t i b l e o r h i g h l y s u s c e p t i b l e . T h e p r e s e n c e o f
t a n c e w e r e o b t a i n e d b y A u s t i n et al. (1988). T h e h i g h level o f
r e s i s t a n c e in 4682 s u g g e s t s t h a t t h e r e s i s t a n c e is c o n t r i b u t e d
t u b e r s o f t r o t r e s i s t a n c e p r e s e n t in S. brevidens w a s t r a n s -
b y t h e h y b r i d p a r e n t A937. T h i s level o f r e s i s t a n c e is s i m i l a r
ferred to the somatic hybrids produced by protoplast fusion
t o t h a t p r e s e n t in t h e s o m a t i c h y b r i d w h i c h s u g g e s t s t h a t t h e
b e t w e e n S. brevidens and S. tuberosum a n d t h e n t o s o m e o f
r e s i s t a n c e is h e r i t a b l e . T h e r e s u l t s o f t h e p r e s e n t s t u d y sug-
the sexual progeny via a cross between the somatic hybrids
g e s t t h a t t h e h i g h level o f s t e m s o f t r o t r e s i s t a n c e p r e s e n t in
a n d K a t a h d i n . O u r s t u d y h a s i d e n t i f i e d t h r e e t u b e r s o f t rot-
S. brevidens ( u n p u b l i s h e d d a t a a s c i t e d in A u s t i n eta/., 1988)
r e s i s t a n t c l o n e s w h i c h a r e also r e s i s t a n t t o s t e m s o f t r o t a n d
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c o n f i r m s t h e s e x u a l t r a n s m i s s i o n to p r o g e n y . T h e c l o n e s could be very useful for development of potato cultivars resistant to b o t h s t e m and t u b e r soft rots. P o t a t o cultivars s h o w e d a range o f r e a c t i o n s to the pathogen. Although there w a s s o m e variation in the reaction rankings o f p o t a t o cultivars a m o n g e x p e r i m e n t s , in general, the overall reaction remained the same. Since information on c o m p a r a t i v e s u s c e p t i b i l i t y / r e s i s t a n c e o f p o t a t o cultivars to blackleg is lacking, the results o f this study could be v e r y useful to the g r o w e r s in selecting cultivars. Of 34 cultivars tested, only t h r e e had their reactions to b l a c k l e g listed in a publication of description of p o t a t o varieties in C a n a d a (Barclay and Schrage, 1993). U n f o m m a t e l y , according to the criterion used to study r e s i s t a n c e in t h e w i l d s p e c i e s and s o m a t i c hybrids n o n e of the cultivars s h o w e d a resistant or a highly resistant reaction. Banana, the cultivar that s h o w e d the l o w e s t length o f lesion f o r m a t i o n w o u l d still be classified as susceptible. Results o f t h e p r e s e n t study, h a v e identified high levels o f s t e m soft-rot r e s i s t a n c e w h i c h is s e x u a l l y transferable. It has also s h o w n that p o t a t o cultivars, tested in this study, possess a m u c h l o w e r level of s t e m soft-rot r e s i s t a n c e t h a n that identified in this study. D e v e l o p m e n t o f r e s i s t a n t cultivars has been previously suggested to be the most effective m e t h o d of r e d u c i n g losses c a u s e d by this disease, the resist a n c e p r e s e n t in wild S o l a n u m
s p e c i e s and s o m a t i c hybrids
s h o u l d t h e r e f o r e b e u s e f u l in d e v e l o p i n g p o t a t o c u l t i v a r s w i t h high levels of r e s i s t a n c e to Erwinias.
ACKNOWLEDGMENTS We are grateful to the Alberta Agricultural Research Institute for funding this project, F a r m i n g for the F u t u r e p r o j e c t #920117. We t h a n k May Yu for e x c e l l e n t technical assistance. The wild Solanum
species u s e d in this study w e r e p r o v i d e d
by the Potato Introduction Station, NRSP-6, Sturgeon Bay, WI.
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