Individual Plant Selection in
376 JOURNAL OF THE A. S. S. B. T.
variances w e r e e s t i m a t e d b y s u b t r a c t i n g t h e e s t i m a t e d e n v i r o n m e n t a l variance from t h e total variance of each s e g r e g a t i n g line.
B r o a d sense heritabilities w e r e calculated from t h e s e variances for r o o t yield, s u g a r p e r c e n t a g e , a n d gross s u g a r o f each s e g r e g a t i n g line ( T a b l e 1). F r o m t h e s e estimates, lines Acc 107, D2, B 8 8 9 , a n d RW 4 6 7 w e r e picked as h a v i n g t h e g r e a t e s t selection p o t e n t i a l for i n c r e a s e d yield a n d gross s u g a r . Lines 590-1 a n d 590-9 c a r r i e d curly t o p resis- t a n c e a n d w e r e also i n c l u d e d for selection.
F o r each of t h e above lines, g e n e t i c deviate probabilities w e r e placed o n each r o o t for r o o t yield, s u g a r p e r c e n t a g e , a n d gross s u g a r . T h e s e probabilities w e r e o b t a i n e d f r o m a s t a n d a r d t table a n d a r e t h e probabilities o f each individual beet differing f r o m t h e m e a n o f t h e p a r e n t line. A p a r t of these probabilities for line D2 is s h o w n in T a b l e 2. Roots with h i g h probabilities for r o o t yield a n d gross s u g a r a n d n o t d i f f e r i n g from t h e p a r e n t i n s u g a r p e r c e n t a g e w e r e selected from each line.
Seed from each selected r o o t was p r o d u c e d in 1969. B e c a u s e all plants w e r e self-sterile, roots from each line w e r e p l a n t e d in a s e p a r a t e crossing block a n d allowed to i n t e r p o l l i n a t e within lines. Seed was h a r v e s t e d separately f r o m e a c h plant.
Field tests w e r e c o n d u c t e d for selections of lines Acc 107 a n d RW 4 6 7 at Salinas, California, in 1970 a n d for selections of lines 590-1 a n d 590-9 at F a r m i n g t o n , U t a h , in 1970 a n d 1 9 7 1 . Selections of lines D2 a n d B 8 8 9 p r o d u c e d insufficient seed for field testing. T h e test at Salinas, California, was in n e m a t o d e - i n f e s t e d soil, w h e r e a s t h e tests at F a r m i n g t o n , U t a h , w e r e in soil free of n e m a t o d e s . P a r e n t a l lines w e r e i n c l u d e d in all field tests. All tests w e r e in a r a n d o m i z e d block design.
Probabilities w e r e c o m p u t e d for e a c h selection relative to its p a r e n t a l line. T h e probabilities o f t h e original r o o t selections (predic- ted probabilities) w e r e calculated from an a d j u s t e d m e a n of each selection tested relative to its p a r e n t a l m e a n .
Table 1.—Broad sense heritability estimates for root yield, sugar percentage, and gross sugar for each segregating line.
V O L . 17, N o . 4 , O C T O B E R 1973 3 7 7 Table 2.—A portion of the D2 population showing the probabilities for individual
beets for root yield, sugar percentage, and gross sugar.
*This table can be read (using beet number 10 as an example) as follows: The probability of another beet having a sugar percentage as low or lower than that of beet No. 10 by chance alone is .2 (2 out of 10); of it having a root yield as large or larger than that of beet No. 10 by chance alone is .005 (5 out of 1,000); and of its having as much or more gross sugar than beet No. 10 by chance alone is .01 (1 out of 100).
The adjusted mean for each selection was calculated as follows:
where n = the number of selections within the crossing block, X
jj= yield of the ith selection in the crossing block of which the jth
selection was present X
j= yield of the jth selection
The assumption was made that each of the pollinators within the cross- ing block contributed pollen equally.
Results
All selections yielded more than their respective parents in root yield and gross sugar (Tables 3, 4, and 5). However, yields of some of the individual selections were not significantly larger than their parents (Table 6). There was little difference in sugar percentage between the parents and selections. This confirms the fact that selec- tion was not for increased sugar percentage, but to maintain the parental sugar percentage. Selections outyielded their parents in both soil types. Thus, selection increased vigor and yield potential, whether the soil was nematode infested or nematode free.
T h e probabilities of the original root selections (predicted
probabilities) and the resultant progenies (actual probabilities) are
3 7 8 J O U R N A L O F T H E A . S . S . B . T .
Table 3.—Root yields, sugar percentage, and gross sugar of selections and parents. Trial was conducted in 1970 at Salinas, California, in nematode-infested soil.
Note RW 467 was a nematode resistant selection obtained from Henk Rietberg, the Netherlands.
Acc 107 was a mixture of nematode selections obtained from G. J. Curtis, Cambridge, England.
Table 4.—Root yields, sugar percentage, and gross sugar of selections and parents. Trial was conducted in 1970 at Farmington, Utah, in nematode-free soil.
Note Lines 590-1 and 590-9 are nematode resistant selections made by Charles Price, USDA.
Table 5.—Root yield, sugar percentage, and gross sugar of selections and parents.
Trial was conducted in 1971 at Farmington, Utah, in nematode-free soil.
VOL. 17, No. 4, OCTOBER 1973 379
given in Table 6. These probabilities are for the superiority of the selections over their respective parent mean.
The actual probabilities are not as high as the original probabilities (Table 6). This could be the result of an overestimation of the genetic variance or an underestimation of environmental variation in the original selections. There was, however, a close agreement between the two probabilities; i.e., a high predicted probability resulted in a high actual probability and vice versa (Table 6). A highly significant correlation of .73 was obtained between the two probabilities for individual selections.
Predicted genetic advance (1) was not calculated for several reasons; first, selection was based on probabilities and not on a pre- determined percentage; second, not. all selections were tested; and third, the predicted advance for 1 year at one location could not be compared with actual gains measured another year at another location because of differences in means and variances. Probabilities are based on the variances and means relative to the parental line and are there- fore comparable.
This use of probabilities can be extended to other types of selec- tion pressure. Under most types of selection schemes, the plant breeder is faced with the problem of selecting genetically superior plants (genetic deviates). When environmental variances are large relative to genetic variances, they can mask genetic deviates. In such situations, selection by individual plant weights will produce mostly environmental deviates. The use of probabilities can overcome this problem by giving the breeder assurance of selecting genetically superior genotypes.
Space planting in the field in uniformly mixed nematode-infested soil reduced the environmental variation such that genetically superior
Table 6.—Means of parents and selections, and actual and predicted probabilities for root yield, sugar percentage, and gross sugar.