(1977) Factors Affecting Selection for Seed Coat Thickness in ...

Published January, 1977

Factors Affecting Selection for Seed Coat Thickness in Fababeans (Vicia faba L.)1 G. G. Rowland and D. B. Fowler2 ABSTRACT Smaller seed size in fababeans (Vicia faba L.) would make seeding easier and more economical. However, the seed coat contains 89% of the seed crude fiber and it is imperative that any reduction in seed size be accompanied by at least a corresponding reduction in the seed coat contribution. Therefore, this study was initiated to evaluate the factors affecting variation in seed coat thickness in fababeans. Analysis of seven varieties of fababeans grown at three locations in Saskatchewan in 1973 revealed significant differences in seed coat thickness due to cultivars, locations, replicates within locations, and seeds within cultivars times replicates within locations. Variance components from this analysis were utilized to estimate the numbers of locations, field replicates, seeds, and measurements per seed coat required for detection of specified differences in seed coat thickness. These estimates indicated that the largest number of measurements were required within seed coats and among seeds within cultivars. The position of the seed on the plant had no effect on seed coat thickness. Seed weight and seed coat thickness were not correlated within varieties but were highly correlated among varieties (r = 0.70). Additional index words: Seed size, Seed weight, Horsebeans.

ABABEANS (Vicia faba L.) are an ancient crop F1974). species which originated in the Near East (Cubero, They are presently grown mainly in Europe, North Africa, the Middle East, and China and are utilized as both a livestock feed and a human food in these countries. Fababeans were introduced commercially into Western Canada in 1972. In this area, the seed has been considered to have potential in livestock feeds because of a high protein content (25 to 30%). Fababeans have been criticized by industry and potential importers for having a tough seed coat which causes difficulty in grinding and is responsible for the seeds' high fiber content. The seed coat accounts for 13 to 17% of the seed dry weight, most of the seed crude fiber (89%), but little of the seed protein (2 to 4%) (Cerning et al., 1975; Evans et al., 1972). This compares to soybeans (Glycine max L.) and peas (Pisum sativum L.) in which the seed coat comprises 8.8 and 8.2% of the seed dry weight, respectively (Wolf and Cowan, 1971; Youngs, personal communication, 1975). Chaudhary and Buth (1970) examined the seed 1

Crop Development Centre, Univ. of Saskatchewan, Saskatoon, Saskatchewan, S7N OWO, Canada. Received 9 Mar. 1976. -' Professional research associates.

coats of 14 Indian pulses and found that V. faba had the largest palisade and hourglass cells. These cells are primarily responsible for the thickness of the seed coat. A wide range in variation in thickness of hourgass cells of fababeans has been observed by McEwen et al. (1974). This variation in cell size and the known differences in seed coat thickness of various pulses indicate the possible presence of variation in seed coat thickness in fababeans. The large seed size of commercial fababean cultivars and the resulting high seeding rates required to obtain an optimum stand result in a high seed cost to the producer. It would therefore be desirable to have a smaller-seeded fababean. However, because of the large influence of the seed coat on seed composition, it is imperative that any reduction in seed size be accompanied by at least a corresponding reduction in seed coat contribution. Consequently, this study was initiated to investigate several factors which could influence the success of selection for thinner seed coats in fababeans. The primary objectives were to develop sampling techniques and to determine the optimum number of measurements required to detect small differences in seed coat thickness. A secondary objective was to determine the relationship between seed coat thickness and seed weight. MATERIALS AND METHODS Determination of Seed Coat Thickness. Seeds were dried at 80 C for 14 hours after which the seed coat was removed. Seed coat thickness was then measured with a micrometer. Ten measurements were made on each seed coat and recorded to the nearest 0.001 mm. Care was taken not to make these measurements near the hilum or lens area of the seed where the seed coat has additional layers of cells. Number of Measurements. Twenty seeds were taken at random from each plot of three fababean yield trials grown at Saskatoon, Bellevue, and Nipawin, Saskatchewan in 1973. Each triarwas seeded as a randomized complete block with four replications. The seven fababean varieties in these yield trials were selected because of their wide range of yield, seed size, and protein content. The varieties 'Klien Thuringer', 'Maris Bead', 'Maxime', 'Ostlers', 'Ringot', and 'Wieselburger', are from the smaller seeded V. faba minor subspecies while 'Wierboon' is from the large seeded V. faba major subspecies. Analysis of variance was computed on seed coat thickness data from these trials (Table 1). The following variance components were then estimated. (r'tc.Hcrxi) component arising due to variability in measurements of single seed coats. "•a.(cDd> component arising due to differences among seeds within cultivars times replicates within locations.

KOWLAND g:

FOWLER.:

SEED COAT THICKNESS

Table 1. Analysis of variance and mean squares (mixed model -- cultivars fixed). Sourceof variation df

Mean square

Expectedmeansquare

IN FABABEANS

89

38 36 34

Cultivars (C)

6

o{~(s)(cr)(l)+~TO~(cr)(I) + TSO~r(I) TSRLo~ 12 O~(s)(cr)(l + T~Oc~r(l) + ) + T~s2(cr)(1) 9 o’~(s)(cr)(l) + TOs2(cr)(I) + TSC~I 54 O~(s)(cr)(I) + Tos~(cr)(l) + 1,596 o~(s)(cr)(l)+ Tas~(cr)(I)

LXc Replicates(R)/L C XR/L Seeds(S)/C XR/L Measurements (T)/ S/C X R/L 15,120O~(s)(cr)(l) Total 16,799

1.6269 0.0086 0.0839 0.0093 0.0022 0.0002

32 30 28 26

Table 2. Average seed coat thickness of seven fababean varieties grown at Saskatoon, Bellevue, and Nipawin, Saskatchewan in 1973. Cultivar Maxime MarlsBead KleinThuringer Wieselburger Ringot Ostlers Wierboon Standard errorof mean

Thickness 0.141 0.147 0.151 0.152 0.155 0.159 0.218 0.006

12 t0

o~o,(~) component arising due to the interaction between cultivats by replicates within locations. o~le component arising due to the interaction between locations and cultivars. These components were then utilized to estimate the number of measurements per seed coat (a~t(,)(~r)(~) and number of (a~,(cr),)), field replicates (a~r(~)), and locations (o~) to have an 80% probability of detecting differences between cultivars for a test of significance at the 5% level (Cochran and Cox, 1957). For these estimates it was assumed there would be four cultivars in the stud~, Seed Position. Seed coat thickness was determined from three positions on the plant: l) the lowest podded node, 2) the podded nodes between the lowest and highest podded nodes, and 3) the highest podded node. Twenty seeds were taken from each position of plants selected at random from each plot of a six replicate, six cultivar yield trial grown at Saskatoon in 1973. The cultivars were ’Ackerperle’, ’Diana’, ’Erfordia’, ’Fioletowy’, Klein Thuringer, and ’Pavane’ (all subspecies minor). Seed Weight. Seed coat thickness and seed weight were determined for 25 seeds taken at random from each of 33 fababean varieties (subspecies minor) grown in the field at Saskatoon in 197~. Seed weight was recorded to the nearest 0.01 g. Simple correlation coefficients for seed coat thickness and seed weight were then deter~nined, using the mean values for seeds within cultivars. This gave a correlation coefficient for seed size and seed coat thickness for each cultivar. These correlation coefficients for cultivars were tested for homogeneity before pooling. To gaiu a further understanding of the factors influencing seed coat thickness, multiple correlation analyses were performed utilizing cultivar means for yield, 1,000-seed weight, seed protein content, and seed coat thickness from the 1973 Saskatoon, Beliewin, and Nipawin yield trials described earlier.

RESULTS Number of Measurements. Differences in seed coat thickness due to cultivars (Table 2), locations, replicates within locations, cultivars times replicates within locations, and seeds within cultivars times replicates within locations were highly significant (P

T R

.01

.02

.03

.04

.OS

.06

Seed Coat Thickness- Difference in ram. Fig. 1. The number of field replicates (R), seeds (S), measurements per seed coat (T) required to give an 80% probability of detecting differences in seed coat thickness between cultivaxs when utilizing a test of significance at the 5%probability level.

0.01) for these trials. The cultivar by location interaction was nonsignificant (P ~ 0.05). Estimates of the number of measurements per seed coat (T), number of seeds (S), and number of field replicates (R) required to detect specific differences, based on components of variance estimated in this study (Table 1), are given in Fig. Seed Position. Analyses of variance indicated that seed coat thickness was not significantly different for seeds from the top, middle, or bottom nodes of the plant. However,the cultivar by replicate and cultivar by replicate by seed position ~nteractions were significant (P < 0.05 and P < 0.01, respectively). Seed Weight. Analysis of variance indicated significant (P < 0.01) differences in seed coat thickness and seed weight among seeds within cultivars and amongcultivars (Table 3). Correlations between seed coat thickness and seed weight were not significant (P > 0.05) when based on differences among seed within cultivars. Similar comparisons based on differ-

90

CROP SCIENCE, VOL. 17, JANUARY-FEBRUARY 1977

Table 3. Seed coat thickness and seed weight of 33 fababcan varieties grown at Saskatoon in 1973. Cultivar P1 270056 P1 221517 Diana P1 331422 Columba B P1 268477 P1 343831 P1 223303 P1 223304 P1 251331 Columba A Ascott Picard 280(5) Klein Thuringer P1 251232 Strubbe Picard 279(2) P1 254003 Ackerperle India 10-83-4 Picard 278(2) P1 254002 P1 306699 Picard KL Picard G 79(7) India 79F Vesuvio India B.C. 6122 P1 244345 Manfredini India B.C. 24960 Cubero 16 India 30A Standard error of mean

Thickness

Weight

— mm — 0.132 0.135 0.135 0.137 0.137 0.137 0.138 0.138 0.138 0.139 0.140 0.140 0.141 0.141 0.141 0.143 0.143 0.143 0.144 0.145 0.145 0.145 0.146 0.147 0.148 0.148 0.148 0.149 0.150 0.150 0.152 0.152 0.166

—g— 0.20 0.20 0.35 0.29 0.31 0.21 0.35 0.33 0.34 0.32 0.33 0.38 0.33 0.41 0.54 0.52 0.30 0.41 0.31 0.32 0.33 0.39 0.40 0.42 0.40 0.45 0.32 0.45 0.46 0.51 0.53 0.56 0.52

0.008

0.02

be utilized as an index of seed coat thickness among seeds within cultivars. In addition, position of the seed on the plant did not influence seed coat thickness. Therefore, it was concluded that, when comparing the seed coat thickness of cultivars, measurements can be made on seeds selected at random from each cultivar. When comparisons were based on differences among cultivars, a significant positive correlation was found between seed weight and seed coat thickness. The fact that the seed coat apparently gets thinner as seed weight is genetically reduced is of importance to breeding programs as it should mean that small seeded cultivars need not produce a meal with a higher fiber content than large seeded cultivars. Cultivar by field replicate interactions were significant for seed coat thickness in all trials considered in this stuly. However, this interaction is of minor importance in determining the number of measurements required to detect differences among cultivars (Fig. 1). Variability within the seed coat and among seeds both severely limit the ability to detect differences in seed coat thickness before the number of field replicates becomes a restrictive factor. Trial locations had a significant influence on seed coat thickness. However, the location by cultivar interaction was not significant and therefore for purposes of preliminary cultivar selection for seed coat thickness, a replicated trial at one location is adequate. ACKNOWLEDGMENTS

ences among cultivars gave a highly significant positive correlation (r = 0.70, P < 0.01). Analyses based on cultivar means from the three location yield trials indicated that seed coat thickness was positively correlated with seed weight (r = 0.79, P < 0.01) and negatively correlated with seed protein content (r — — 0.60, P < 0.01). Seed yield was not associated with seed coat thickness (r — 0.11, P > 0.05). DISCUSSION Variation in thickness within the fababean seed coat provided an important restriction to selection for thinner seed coats, especially where cultivar differences were less than 0.02 mm (Fig. 1). Differences in cell size within the fababean seed coat have been reported (McEwen et al., 1974) and it is possible that this variability could be reflected in seed coat thickness. Variation in seed coat thickness among seeds within cultivars was large. Significant differences in seed weight were found among seeds within cultivars, however, these differences were not related to seed coat thickness. For this reason seed weight could not

The authors are indebted to Bev Howell and Cheryl Hedlin for their patience and perseverance in making the thousands of measurements needed for this study. We are also grateful to J. Picard, J. I. Cubero, the USDA Plant Introduction Service, and the Indian Agric. Res. Inst. for seed of many of the varieties used in this investigation. The assistance of Dr. S. Jana in the preparation of this manuscript is greatly appreciated.. The financial support of Agriculture Canada is sincerely acknowledged.