Theoretical and Applied Genetics 44, 77--81 (1974) | b y Springer-Verlag 1974
Differential Response of Maize (Zea mays L.) to Mass Selection in Diverse Selection Environments 1 FERNANDO ARBOLEDA-RIVERA~ and WILLIAM A. COMPTON Department
of A g r o n o m y , U n i v e r s i t y of N e b r a s k a , Lincoln, N e b r a s k a (USA) a n d I n s t i t u t o C o l o m b i a n o A g r o p e c u a r i o , Medellln (Colombia)
Summary. The present study was designed to find what seasonal effect mass selection would render when practiced within a maize (Zea mays L.) population. Three subpopulations of "Mezcla Varietales Amarillos" population (MVA) were selected for prolificacy and grain yield in three different seasonal conditions: (i) MVA-A selected in rainy seasons (A); (ii) MVA-B selected in d r y seasons (B); (iii) MVA-AB selected under both seasonal conditions each year. Three cycles in MVA-A and,MVA-B , and six in MVA-AB were tested during three A and three B growing seasons for evaluation of progress. Mass selection in MVA-A resulted in an increase in grain yield of 10.5% per cycle when tested in the A seasons (direct response) and only 0.8% when tested in the B seasons (indirect response). For ears per p l a n t the corresponding responses were 8.8 and t.0%. The direct response in grain yield in MVA-B was only 2.5% per cycle whereas it was 7.6% when tested in the A seasons. The gain in ears per p l a n t was 11.4% in the tests in the A seasons, b u t the direct response was 4.4% per cycle. In MVA-AB, there was a gain in grain yield of 5.3 and l.t~o per cycle in the tests in A and B seasons. F o r prolificacy, the respective gains were 7.0 and 3.3% per cycle. Introduction Mass selection has been p r a c t i c e d successfully in m a i z e (Zea mays L.) b y s e v e r a l b r e e d e r s ( G a r d n e r 1961, t969, H a r p s t e a d et al. 1967, L o n n q u i s t 1964, 1967, L o n n q u i s t e t a l . t966, T o r r e g r o z a a n d H a r p s t e a d t967). All t h e r e p o r t s d e a l w i t h selection in o n l y one selection e n v i r o n m e n t . T h e a u t h o r s are n o t a w a r e of r e p o r t s in t h e l i t e r a t u r e on m a s s select i o n for p r o l i f i c a c y a n d g r a i n y i e l d in m a i z e in differe n t selection e n v i r o n m e n t s b e g i n n i n g w i t h t h e s a m e o r i g i n a l p o p u l a t i o n . S u c h s t u d i e s h a v e been done in some a n i m a l species (Cockrem 1963, F a l c o n e r a n d L a t y s z e w s k i t952, F r a h m a n d K o j i m a 1966, H a m m o n d 1947), u n d e r g o o d a n d p o o r d i e t s a n d h i g h a n d low t e m p e r a t u r e c o n d i t i o n s . T h e q u e s t i o n is w h e t h e r environmental conditions that enhance the expression of a d e s i r e d c h a r a c t e r will r e s u l t in m o r e g a i n from selection t h a n will u n f a v o r a b l e conditions. A large g e n o t y p e X e n v i r o n m e n t i n t e r a c t i o n necessit a t e s t h e d e v e l o p m e n t of v a r i e t i e s h i g h l y a d a p t e d to specific e n v i r o n m e n t s , a n d a s m a l l i n t e r a c t i o n p e r m i t s t h e d e v e l o p m e n t of v a r i e t i e s t h a t will p e r f o r m well in a b r o a d s p e c t r u m of e n v i r o n m e n t s ( A l l a r d a n d B r a d s h a w t968, C o c k r e m 1963). 1 Published as Paper No. 3452 Journal Series Nebraska Agricultural Experiment Station. 2 Rockefeller F o u n d a t i o n Fellow The authors acknowledge the cooperation of J. Antonio Rivera and L. Miguel Estrada, Agronomists, of the Corn Program of the I n s t i t u t o Colombiano Agropecuario at .Turipana Experimental Center for their invaluable help m collecting some of the data. This work was supported in p a r t b y grants from the Rockefeller Foundation to the corn program of ICA in Colombia and to the corn program at the University of Nebraska.
T h e r e are t w o p l a n t i n g seasons in t h e i n t e r m e d i a t e a l t i t u d e s a n d in t h e l o w l a n d s of Colombia. A t t h e T u r i p a n a E x p e r i m e n t a l Center, t h e s e t w o p l a n t i n g seasons h a v e v e r y d i f f e r e n t w e a t h e r c o n d i t i o n s . T h e Maize B r e e d i n g P r o g r a m of t h e I n s t i t u t o C o l o m b i a n o A g r o p e c u a r i o has f o u n d l i m i t e d p r o g r e s s from m a s s selection in m a n y p o p u l a t i o n s w h e n cycles are o b t a i n ed c o n t i n u o u s l y in e v e r y season, H o w e v e r , in t h e h i g h l a n d s , where corn can be g r o w n o n l y in one season, m a s s selection has r e s u l t e d in r a p i d p r o g r e s s in i n c r e a s i n g n u m b e r of ears p e r p l a n t a n d g r a i n yield. N o i n f o r m a t i o n is a v a i l a b l e on g e n o t y p e • season i n t e r a c t i o n in this t w o - s e a s o n selection s y s t e m . T h e p u r p o s e of this p a p e r is to r e p o r t t h e r e s u l t s of s e v e r a l cycles o b t a i n e d b y m a s s selection for prolif i c a c y a n d g r a i n y i e l d in a t r o p i c a l v a r i e t y of m a i z e in d i f f e r e n t selection e n v i r o n m e n t s .
Materials and Methods This s t u d y was carried out at Turipana Agriculture Experimental Center,of the tnstituto Colombiano Agropecuario (ICA). I t is located at t2 meters above sea level, 12 kilometers northeast of Monteria, about 80 kilometers from the Atlantic coast of Colombia. For this paper, the two planting seasons each year a t t h a t location are called A and B seasons. The A season extends from April to September and has an average rainfall of about 600 ram. I t is considered to be the more favorable cropping season. The B season extends from October to March and has an average rainfall of about 300 mm. Little or no rain usually occurs in the latter p a r t of this season and there is less cloudiness than in the A season. There also is a larger difference between d a y and night temperatures in the B season, b u t the average temperature is about the same as for the A season (29 ~ The population "Mezcla Varietales Amarillos" (MVA) was chosen for the present study due to its great diversity in genetic and geographic origin. In t96t A (season A in
78
F. A r b o l e d a - R i v e r a and W. A. C o m p t o n : Differential Response of Maize to Mass Selection
the y e a r 1961) a diallel cross was m a d e a m o n g t0 yellow flint varieties a d a p t e d to Turipana. Those varieties were :
Venezuela I,
Ven. 400 and Ven. 47t. Varieties rep r e s e n t a t i v e of t h e race Coste~o g r o w n in t h e Caribbean coast of Venezuela and Colombia. Cuba 2 and Cuba 345. Collections f r o m t h e Cuba flint t y p e f r o m the Caribbean zone. ETO. A Colombia composite a d a p t e d to a l m o s t all t h e tropical areas around t h e world. Amarillo Theobromina. A collection f r o m the Colombian race Coste~o. Nari~o 330. R e p r e s e n t a t i v e of t h e corn p l a n t e d in t h e middle lands in s o u t h e r n Colombia. Ecuador 542. F r o m t h e l o w l a n d s of the coast of E c u a dor. Per(, 3309 F r o m t h e lowlands of t h e coast of Peril. Fifteen to t w e n t y disease free ears from 50-- 60 h e a l t h y cross-pollinated plants were selected f r o m each of the 45 F~'s. All ears f r o m each cross were shelled and bulked. T w o h u n d r e d seeds from each F~ were m i x e d and t h e composite was p l a n t e d in a 1/4 h e c t a r e isolation in 1962A on t h r e e dates to assure crossing of different m a t u r i t y groups. Seeds f r o m all ear-bearing plants were bulked 9 T h e p o p u l a t i o n was t h e n r a n d o m m a t e d for four generations. T h e seed of each generation was r a n d o m l y picked f r o m square isolated plots, 60X 60 hills; the hills had two plants and each hill was s e p a r a t e d 92 cm in either direction. I n t 9 6 6 A t h r e e samples of t h r e e kilos each were s e p a r a t e d f r o m t h e bulked sample of t h e fifth r a n d o m m a t e d generation 9 T h e y were called subpopulations M V A - A to be mass selected o n l y in season A, M V A - B t o be selected o n l y in season 13, and M V A - A B to be selected c o n t i n u o u s l y in b o t h seasons 9 T h e selection criteria were prolificacy (two or m o r e ears per plant) and grain yield for all three subpopulations. E a c h isolation had 42 • 52 hills s e p a r a t e d 92 cm in either direction w i t h 2 p l a n t s per hill at harvest 9 T h e selection i n t e n s i t y was 5%. E a c h grid consisted of 4 rows of 5 hills each (40 plants). A t h a r v e s t t h e ears of 6 - - t 0 prolific p l a n t s per grid were dried to c o n s t a n t m o i s t u r e and t h e t w o highest yielding plants were selected to be included in the composite for p l a n t i n g the n e x t cycle. F o r t y - t h r e e seeds f r o m each of t h e 200 selected p l a n t s were bulked together. T h r e e composites were m a d e in each cycle; one of these was for p l a n t i n g t h e n e x t cycle, one for testing purposes and one for reserve which was stored in a cold room. Yield trials were p l a n t e d in seasons t968B, 1969A, 1970A, 1970B, 1971A, and 197113. T h e first three consisted of M V A - I A and I I A , M V A - I B and l i B , MVAI A B to M V A - I V A B , MVA original, ICA V.105 and D H . 104. ICA V.105 is a c o m m e r c i a l v a r i e t y released after t w o r a n d o m m a t i n g generations of M V A - I I B . This cycle showed v e r y good a d a p t a b i l i t y and yield p e r f o r m a n c e t h r o u g h o u t t h e A t l a n t i c Coast in Colombia, based on 90 replications in t e n e n v i r o n m e n t s . T h e last three seasonal tests consisted of M V A - I A to M V A - I I I A (obtained in 1967A, 1968A, a n d 1969A, respectively), M V A - I B , to M V A - I I I B (obtained in 1966B, t967B, and 1968B, respectively), a n d M V A - I A B to M V A - V I A B (obtained in 1966B, 1967A, 1967B, 1968A, 1968B, and 1969A, respectively). T h e design used in each t e s t was a r a n d o m ized c o m p l e t e b i o c k w i t h t e n replications. Plots were t w o rows w i t h 10 hills each, w i t h hills and rows separated 92 cms in either direction 9 F i v e seeds were p l a n t e d per hill a n d later t h i n n e d to t h r e e p l a n t s per hill. A t h a r v e s t ear yields were recorded to the nearest t e n t h of a kilogram. T h e ear yields were corrected for missing hills b y t h e m e t h o d given b y J u g e n h e i m e r a n d W i l l i a m s (1957). Grain yields, a d j u s t e d to 15.5% moisture, were o b t a i n e d b y t h e m e t h o d of Gorsline and T h o m a s (t 963).
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The gains per cycle based on both seasons (a total of six) were 4.9% for MVA-A, 4.7% for MVA-B, and 2.9% for MVA-AB. Total gains as estimated from the above rates were 3 (4.9%) = t4.7% for MVA-A, 3(4.7%) = 14.1% for MVA-B, and 6(2.9%) = 17.4% for MVA-AB. From a combined analysis of variance, the MVA-A cycles by A season interaction showed significance (P = .01) whereas the MVA-A cycles by B season interaction showed no significance. Also the MVA-B by A season interaction was significant (P = .05) while no significance was shown by the MVA-B b y B
80
F. Arboleda-Rivera and W. A. Compton : Differential Response of Maize to Mass Selection
season interaction. The interaction of MVA-AB subpopulation was non-significant in either season.
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The results of seasonal mass selection on prolificacy are summarized in Table 2. The MVA-A subpopulation showed an increase of 8.8% per cycle when tested in the A seasons but only ~.0% in the B season tests. The MVA-B subpopulation showed a substantial increase per cycle of ~ t.4% when tested in the A and 4.4% when tested in the 13 seasons. In the MVA-AB selections a gain of 7.0% and 3.3% per cycle were obtained when tested in A and 13 seasons, respectively. Based on the overall means, the gain per cycle in ears per plant was larger in the MVA-13 selections (7.4%) than in the other two selected sub-populations (4.3% for MVA-A and 4.9% for MVA-AB). Total gains after three cycles in MVA-A and MVA-B, and six cycles in MVA-AB were 12.9%, 22.2%, and 29.4% over the original MVA population, respectively. The lVlVA-B selection cycles by A season interaction was significant (P = .01) for prolificacy whereas no other interactions were significant for the other subpopulations when tested in either season.
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Discussion The results reported in this paper are in agreement with other studies in different populations of maize when mass selection either for prolificacy or for yield was made within each subpopulation in only one selection environment (Gardner ~96~, ~969, Harpstead et al. ~967, Lonnquist 1964, ~967, Lonnquist et al. ~966, Torregroza and Harpstead a967). Although genetic variance studies have not been performed in the MVA population and its subpopulations, the data suggest that, because of the upward linear trend in both traits, the seasonal mass selection practiced had successfully increased the frequency of favorable genes. In a two-season per year breeding program, such as the one in Colombia, the results obtained in this study are of importance. It appears that more gain per cycle is achieved by selecting for grain yield in either the A or in the B seasons under similar environmental conditions, than when selecting in both seasons continuously. It is not clear w h y the indirect response (in the A seasons) was larger than the direct response for the MVA-B selections, or w h y more gain was observed for MVA-13 than for MVA-AB selections when tested in the A seasons. Since the confidence intervals overlap, the authors have chosen to simply ignore these particular issues for the moment. However, if the trends continue, explanations will have to be developed in the future. It would appear from these results that almost as much gain per year in grain yield could be achieved
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Theoret. Appl. Genetics, Vol. 44, N o . 2
F. Arboleda-Rivera and W. A. Compton : Differential Response of Maize to Mass Selection b y selection in the i n d i v i d u a l seasons (A or B) as one w o u l d achieve b y c o n t i n u o u s selection (AB). F r o m a s h o r t t e r m p o i n t of view one m i g h t still choose the c o n t i n u o u s selection a p p r o a c h o n the g r o u n d s t h a t the a d d i t i o n a l gains per y e a r were w o r t h w h a t e v e r a d d i t i o n a l costs w o u l d be i n v o l v e d . F r o m a long t e r m p o i n t of view, t h e a u t h o r s feel t h a t there is a s u b s t a n t i a l p r o b a b i l i t y t h a t higher selection limits could be reached in the more restrictive selection e n v i r o n m e n t s (either A or B i n s t e a d of AB). I t appears t h a t selection for prolificacy is more successful w h e n performed u n d e r w e a t h e r stress (MVA-B s u b p o p u l a t i o n ) . A t N e b r a s k a , m u c h of t h e increase in prolificacy w i t h mass selection for yield has n o t b e e n expressed w h e n the p o p u l a t i o n s were g r o w n u n d e r d r o u g h t stress ( G a r d n e r t969). D a t a from the p r e s e n t r e p o r t suggest t h a t selection for prolificacy u n d e r severe c o n d i t i o n s m a y result i n increases u n d e r " g o o d " c o n d i t i o n s as well, while selection for prolificacy u n d e r " g o o d " c o n d i t i o n s m a y n o t c a r r y t h r o u g h w h e n t h e m a t e r i a l is placed u n d e r d r o u g h t stress. Literature
I. Allard, R . W . , Bradshaw, A . D . : Implications of genotype-environmental interactions in applied plant breeding. Crop Sci. 4, 503--508 (1964). -- 2. Cockrem, F. R. M.: The effects of temperature on two strains of
Received J a n u a r y 1, 1973 Communicated by R. Riley
mice of different body weight and tail length. Proc. 11th Intern. Congr. Genet. a, 154 (1963). -- 3. Falconer, D. S., Latyszewski, M.: The environment in relation to selection for size in mice. J. Genet. 51, 67--80 (1952). -4. Frahm, R. R., Kojima, Ken-ichi: Comparison of selection responses on body weight under divergent larval density conditions in Drosophila pseudoobscura. Genetics 54, 625--637 (1966). -- 5. Gardner, C. O. : An evaluation of mass selection and seed irradiation with thermal neutrons on yield of corn. Crop Sci. 1, 241--245 (1961). -- 6. Gardner, C. O. : Genetic variation in irradiated and control populations of corn after ten cycles of mass selection for high grain yield. I n : Induced mutations in plants, pp. 469--477. Vienna: I n t e r n a t i o n a l Atomic E n e r g y Agency 1969. -- 7. Gorsline, G . W . , Thomas, W . I . : Transformation of plot ear corn to dry shelled grain yield. Agron. J. 55, 5 0 3 - 5 0 4 (1963). - 8. Hammond, J. : Animal breeding in relation to nutrition and environmental conditions. Biol. Rev. 22, 195--213 (1947). -- 9. Harpstead, D . D . , Sarria, D. Diaz, E.: Genetic variance estimates in a maize population subdivided into multiple and single ear type. Agronomy Abstracts. ASA. p. 11 (1967). -- 10. Jugenheimer, R. W., Williams, K. E.: Experimental corn hybrids tested in 1956. Ill. Agr. Exp. Sta. Bull. 6o6, 1--32 (1957). -11. Lonnquist, J. H.: M6todos de selecci6n riffles para mejoramiento dentrn de poblaciones. V i a Reunion Latinoamericana de Fitotecnia, Lima, Peru (1964). -12. Lonnquist, J. H.: Mass selection for prolificacy in maize. Der Ztichter 37, t85--188 (t967). -- t3. Lonnquist, J. H., Cota-A., O., Gardner, C. O. : Effect of mass selection and thermal neutron irradiation on genetic variances in a variety of corn (Zea mays L.). Crop Sci. 6, 330-- 332 (1966). -- 14. Torregroza, M., Harpstead, D. D. : Effects of mass selection for ears per p l a n t in maize. Agronomy Abstracts, ASA. p. 20 (1967).
Fernando Arboleda-Rivera Insfituto Colombiano Agropecuario Programa Maiz y Sorgo Apartado aereo 51764 Medellin (Colombia) William A. Compton Associate Professor Department of Agronomy University of Nebraska Lincoln, Nebraska 68503 (USA)
Theoret. Appl. Genetics, Vol. 44, No. 2
81
Differential Response of Maize (Zea mays L.) to Mass Selection in Diverse Selection Environments 1 FERNANDO ARBOLEDA-RIVERA~ and WILLIAM A. COMPTON Department
of A g r o n o m y , U n i v e r s i t y of N e b r a s k a , Lincoln, N e b r a s k a (USA) a n d I n s t i t u t o C o l o m b i a n o A g r o p e c u a r i o , Medellln (Colombia)
Summary. The present study was designed to find what seasonal effect mass selection would render when practiced within a maize (Zea mays L.) population. Three subpopulations of "Mezcla Varietales Amarillos" population (MVA) were selected for prolificacy and grain yield in three different seasonal conditions: (i) MVA-A selected in rainy seasons (A); (ii) MVA-B selected in d r y seasons (B); (iii) MVA-AB selected under both seasonal conditions each year. Three cycles in MVA-A and,MVA-B , and six in MVA-AB were tested during three A and three B growing seasons for evaluation of progress. Mass selection in MVA-A resulted in an increase in grain yield of 10.5% per cycle when tested in the A seasons (direct response) and only 0.8% when tested in the B seasons (indirect response). For ears per p l a n t the corresponding responses were 8.8 and t.0%. The direct response in grain yield in MVA-B was only 2.5% per cycle whereas it was 7.6% when tested in the A seasons. The gain in ears per p l a n t was 11.4% in the tests in the A seasons, b u t the direct response was 4.4% per cycle. In MVA-AB, there was a gain in grain yield of 5.3 and l.t~o per cycle in the tests in A and B seasons. F o r prolificacy, the respective gains were 7.0 and 3.3% per cycle. Introduction Mass selection has been p r a c t i c e d successfully in m a i z e (Zea mays L.) b y s e v e r a l b r e e d e r s ( G a r d n e r 1961, t969, H a r p s t e a d et al. 1967, L o n n q u i s t 1964, 1967, L o n n q u i s t e t a l . t966, T o r r e g r o z a a n d H a r p s t e a d t967). All t h e r e p o r t s d e a l w i t h selection in o n l y one selection e n v i r o n m e n t . T h e a u t h o r s are n o t a w a r e of r e p o r t s in t h e l i t e r a t u r e on m a s s select i o n for p r o l i f i c a c y a n d g r a i n y i e l d in m a i z e in differe n t selection e n v i r o n m e n t s b e g i n n i n g w i t h t h e s a m e o r i g i n a l p o p u l a t i o n . S u c h s t u d i e s h a v e been done in some a n i m a l species (Cockrem 1963, F a l c o n e r a n d L a t y s z e w s k i t952, F r a h m a n d K o j i m a 1966, H a m m o n d 1947), u n d e r g o o d a n d p o o r d i e t s a n d h i g h a n d low t e m p e r a t u r e c o n d i t i o n s . T h e q u e s t i o n is w h e t h e r environmental conditions that enhance the expression of a d e s i r e d c h a r a c t e r will r e s u l t in m o r e g a i n from selection t h a n will u n f a v o r a b l e conditions. A large g e n o t y p e X e n v i r o n m e n t i n t e r a c t i o n necessit a t e s t h e d e v e l o p m e n t of v a r i e t i e s h i g h l y a d a p t e d to specific e n v i r o n m e n t s , a n d a s m a l l i n t e r a c t i o n p e r m i t s t h e d e v e l o p m e n t of v a r i e t i e s t h a t will p e r f o r m well in a b r o a d s p e c t r u m of e n v i r o n m e n t s ( A l l a r d a n d B r a d s h a w t968, C o c k r e m 1963). 1 Published as Paper No. 3452 Journal Series Nebraska Agricultural Experiment Station. 2 Rockefeller F o u n d a t i o n Fellow The authors acknowledge the cooperation of J. Antonio Rivera and L. Miguel Estrada, Agronomists, of the Corn Program of the I n s t i t u t o Colombiano Agropecuario at .Turipana Experimental Center for their invaluable help m collecting some of the data. This work was supported in p a r t b y grants from the Rockefeller Foundation to the corn program of ICA in Colombia and to the corn program at the University of Nebraska.
T h e r e are t w o p l a n t i n g seasons in t h e i n t e r m e d i a t e a l t i t u d e s a n d in t h e l o w l a n d s of Colombia. A t t h e T u r i p a n a E x p e r i m e n t a l Center, t h e s e t w o p l a n t i n g seasons h a v e v e r y d i f f e r e n t w e a t h e r c o n d i t i o n s . T h e Maize B r e e d i n g P r o g r a m of t h e I n s t i t u t o C o l o m b i a n o A g r o p e c u a r i o has f o u n d l i m i t e d p r o g r e s s from m a s s selection in m a n y p o p u l a t i o n s w h e n cycles are o b t a i n ed c o n t i n u o u s l y in e v e r y season, H o w e v e r , in t h e h i g h l a n d s , where corn can be g r o w n o n l y in one season, m a s s selection has r e s u l t e d in r a p i d p r o g r e s s in i n c r e a s i n g n u m b e r of ears p e r p l a n t a n d g r a i n yield. N o i n f o r m a t i o n is a v a i l a b l e on g e n o t y p e • season i n t e r a c t i o n in this t w o - s e a s o n selection s y s t e m . T h e p u r p o s e of this p a p e r is to r e p o r t t h e r e s u l t s of s e v e r a l cycles o b t a i n e d b y m a s s selection for prolif i c a c y a n d g r a i n y i e l d in a t r o p i c a l v a r i e t y of m a i z e in d i f f e r e n t selection e n v i r o n m e n t s .
Materials and Methods This s t u d y was carried out at Turipana Agriculture Experimental Center,of the tnstituto Colombiano Agropecuario (ICA). I t is located at t2 meters above sea level, 12 kilometers northeast of Monteria, about 80 kilometers from the Atlantic coast of Colombia. For this paper, the two planting seasons each year a t t h a t location are called A and B seasons. The A season extends from April to September and has an average rainfall of about 600 ram. I t is considered to be the more favorable cropping season. The B season extends from October to March and has an average rainfall of about 300 mm. Little or no rain usually occurs in the latter p a r t of this season and there is less cloudiness than in the A season. There also is a larger difference between d a y and night temperatures in the B season, b u t the average temperature is about the same as for the A season (29 ~ The population "Mezcla Varietales Amarillos" (MVA) was chosen for the present study due to its great diversity in genetic and geographic origin. In t96t A (season A in
78
F. A r b o l e d a - R i v e r a and W. A. C o m p t o n : Differential Response of Maize to Mass Selection
the y e a r 1961) a diallel cross was m a d e a m o n g t0 yellow flint varieties a d a p t e d to Turipana. Those varieties were :
Venezuela I,
Ven. 400 and Ven. 47t. Varieties rep r e s e n t a t i v e of t h e race Coste~o g r o w n in t h e Caribbean coast of Venezuela and Colombia. Cuba 2 and Cuba 345. Collections f r o m t h e Cuba flint t y p e f r o m the Caribbean zone. ETO. A Colombia composite a d a p t e d to a l m o s t all t h e tropical areas around t h e world. Amarillo Theobromina. A collection f r o m the Colombian race Coste~o. Nari~o 330. R e p r e s e n t a t i v e of t h e corn p l a n t e d in t h e middle lands in s o u t h e r n Colombia. Ecuador 542. F r o m t h e l o w l a n d s of the coast of E c u a dor. Per(, 3309 F r o m t h e lowlands of t h e coast of Peril. Fifteen to t w e n t y disease free ears from 50-- 60 h e a l t h y cross-pollinated plants were selected f r o m each of the 45 F~'s. All ears f r o m each cross were shelled and bulked. T w o h u n d r e d seeds from each F~ were m i x e d and t h e composite was p l a n t e d in a 1/4 h e c t a r e isolation in 1962A on t h r e e dates to assure crossing of different m a t u r i t y groups. Seeds f r o m all ear-bearing plants were bulked 9 T h e p o p u l a t i o n was t h e n r a n d o m m a t e d for four generations. T h e seed of each generation was r a n d o m l y picked f r o m square isolated plots, 60X 60 hills; the hills had two plants and each hill was s e p a r a t e d 92 cm in either direction. I n t 9 6 6 A t h r e e samples of t h r e e kilos each were s e p a r a t e d f r o m t h e bulked sample of t h e fifth r a n d o m m a t e d generation 9 T h e y were called subpopulations M V A - A to be mass selected o n l y in season A, M V A - B t o be selected o n l y in season 13, and M V A - A B to be selected c o n t i n u o u s l y in b o t h seasons 9 T h e selection criteria were prolificacy (two or m o r e ears per plant) and grain yield for all three subpopulations. E a c h isolation had 42 • 52 hills s e p a r a t e d 92 cm in either direction w i t h 2 p l a n t s per hill at harvest 9 T h e selection i n t e n s i t y was 5%. E a c h grid consisted of 4 rows of 5 hills each (40 plants). A t h a r v e s t t h e ears of 6 - - t 0 prolific p l a n t s per grid were dried to c o n s t a n t m o i s t u r e and t h e t w o highest yielding plants were selected to be included in the composite for p l a n t i n g the n e x t cycle. F o r t y - t h r e e seeds f r o m each of t h e 200 selected p l a n t s were bulked together. T h r e e composites were m a d e in each cycle; one of these was for p l a n t i n g t h e n e x t cycle, one for testing purposes and one for reserve which was stored in a cold room. Yield trials were p l a n t e d in seasons t968B, 1969A, 1970A, 1970B, 1971A, and 197113. T h e first three consisted of M V A - I A and I I A , M V A - I B and l i B , MVAI A B to M V A - I V A B , MVA original, ICA V.105 and D H . 104. ICA V.105 is a c o m m e r c i a l v a r i e t y released after t w o r a n d o m m a t i n g generations of M V A - I I B . This cycle showed v e r y good a d a p t a b i l i t y and yield p e r f o r m a n c e t h r o u g h o u t t h e A t l a n t i c Coast in Colombia, based on 90 replications in t e n e n v i r o n m e n t s . T h e last three seasonal tests consisted of M V A - I A to M V A - I I I A (obtained in 1967A, 1968A, a n d 1969A, respectively), M V A - I B , to M V A - I I I B (obtained in 1966B, t967B, and 1968B, respectively), a n d M V A - I A B to M V A - V I A B (obtained in 1966B, 1967A, 1967B, 1968A, 1968B, and 1969A, respectively). T h e design used in each t e s t was a r a n d o m ized c o m p l e t e b i o c k w i t h t e n replications. Plots were t w o rows w i t h 10 hills each, w i t h hills and rows separated 92 cms in either direction 9 F i v e seeds were p l a n t e d per hill a n d later t h i n n e d to t h r e e p l a n t s per hill. A t h a r v e s t ear yields were recorded to the nearest t e n t h of a kilogram. T h e ear yields were corrected for missing hills b y t h e m e t h o d given b y J u g e n h e i m e r a n d W i l l i a m s (1957). Grain yields, a d j u s t e d to 15.5% moisture, were o b t a i n e d b y t h e m e t h o d of Gorsline and T h o m a s (t 963).
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The gains per cycle based on both seasons (a total of six) were 4.9% for MVA-A, 4.7% for MVA-B, and 2.9% for MVA-AB. Total gains as estimated from the above rates were 3 (4.9%) = t4.7% for MVA-A, 3(4.7%) = 14.1% for MVA-B, and 6(2.9%) = 17.4% for MVA-AB. From a combined analysis of variance, the MVA-A cycles by A season interaction showed significance (P = .01) whereas the MVA-A cycles by B season interaction showed no significance. Also the MVA-B by A season interaction was significant (P = .05) while no significance was shown by the MVA-B b y B
80
F. Arboleda-Rivera and W. A. Compton : Differential Response of Maize to Mass Selection
season interaction. The interaction of MVA-AB subpopulation was non-significant in either season.
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The results of seasonal mass selection on prolificacy are summarized in Table 2. The MVA-A subpopulation showed an increase of 8.8% per cycle when tested in the A seasons but only ~.0% in the B season tests. The MVA-B subpopulation showed a substantial increase per cycle of ~ t.4% when tested in the A and 4.4% when tested in the 13 seasons. In the MVA-AB selections a gain of 7.0% and 3.3% per cycle were obtained when tested in A and 13 seasons, respectively. Based on the overall means, the gain per cycle in ears per plant was larger in the MVA-13 selections (7.4%) than in the other two selected sub-populations (4.3% for MVA-A and 4.9% for MVA-AB). Total gains after three cycles in MVA-A and MVA-B, and six cycles in MVA-AB were 12.9%, 22.2%, and 29.4% over the original MVA population, respectively. The lVlVA-B selection cycles by A season interaction was significant (P = .01) for prolificacy whereas no other interactions were significant for the other subpopulations when tested in either season.
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Discussion The results reported in this paper are in agreement with other studies in different populations of maize when mass selection either for prolificacy or for yield was made within each subpopulation in only one selection environment (Gardner ~96~, ~969, Harpstead et al. ~967, Lonnquist 1964, ~967, Lonnquist et al. ~966, Torregroza and Harpstead a967). Although genetic variance studies have not been performed in the MVA population and its subpopulations, the data suggest that, because of the upward linear trend in both traits, the seasonal mass selection practiced had successfully increased the frequency of favorable genes. In a two-season per year breeding program, such as the one in Colombia, the results obtained in this study are of importance. It appears that more gain per cycle is achieved by selecting for grain yield in either the A or in the B seasons under similar environmental conditions, than when selecting in both seasons continuously. It is not clear w h y the indirect response (in the A seasons) was larger than the direct response for the MVA-B selections, or w h y more gain was observed for MVA-13 than for MVA-AB selections when tested in the A seasons. Since the confidence intervals overlap, the authors have chosen to simply ignore these particular issues for the moment. However, if the trends continue, explanations will have to be developed in the future. It would appear from these results that almost as much gain per year in grain yield could be achieved
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Theoret. Appl. Genetics, Vol. 44, N o . 2
F. Arboleda-Rivera and W. A. Compton : Differential Response of Maize to Mass Selection b y selection in the i n d i v i d u a l seasons (A or B) as one w o u l d achieve b y c o n t i n u o u s selection (AB). F r o m a s h o r t t e r m p o i n t of view one m i g h t still choose the c o n t i n u o u s selection a p p r o a c h o n the g r o u n d s t h a t the a d d i t i o n a l gains per y e a r were w o r t h w h a t e v e r a d d i t i o n a l costs w o u l d be i n v o l v e d . F r o m a long t e r m p o i n t of view, t h e a u t h o r s feel t h a t there is a s u b s t a n t i a l p r o b a b i l i t y t h a t higher selection limits could be reached in the more restrictive selection e n v i r o n m e n t s (either A or B i n s t e a d of AB). I t appears t h a t selection for prolificacy is more successful w h e n performed u n d e r w e a t h e r stress (MVA-B s u b p o p u l a t i o n ) . A t N e b r a s k a , m u c h of t h e increase in prolificacy w i t h mass selection for yield has n o t b e e n expressed w h e n the p o p u l a t i o n s were g r o w n u n d e r d r o u g h t stress ( G a r d n e r t969). D a t a from the p r e s e n t r e p o r t suggest t h a t selection for prolificacy u n d e r severe c o n d i t i o n s m a y result i n increases u n d e r " g o o d " c o n d i t i o n s as well, while selection for prolificacy u n d e r " g o o d " c o n d i t i o n s m a y n o t c a r r y t h r o u g h w h e n t h e m a t e r i a l is placed u n d e r d r o u g h t stress. Literature
I. Allard, R . W . , Bradshaw, A . D . : Implications of genotype-environmental interactions in applied plant breeding. Crop Sci. 4, 503--508 (1964). -- 2. Cockrem, F. R. M.: The effects of temperature on two strains of
Received J a n u a r y 1, 1973 Communicated by R. Riley
mice of different body weight and tail length. Proc. 11th Intern. Congr. Genet. a, 154 (1963). -- 3. Falconer, D. S., Latyszewski, M.: The environment in relation to selection for size in mice. J. Genet. 51, 67--80 (1952). -4. Frahm, R. R., Kojima, Ken-ichi: Comparison of selection responses on body weight under divergent larval density conditions in Drosophila pseudoobscura. Genetics 54, 625--637 (1966). -- 5. Gardner, C. O. : An evaluation of mass selection and seed irradiation with thermal neutrons on yield of corn. Crop Sci. 1, 241--245 (1961). -- 6. Gardner, C. O. : Genetic variation in irradiated and control populations of corn after ten cycles of mass selection for high grain yield. I n : Induced mutations in plants, pp. 469--477. Vienna: I n t e r n a t i o n a l Atomic E n e r g y Agency 1969. -- 7. Gorsline, G . W . , Thomas, W . I . : Transformation of plot ear corn to dry shelled grain yield. Agron. J. 55, 5 0 3 - 5 0 4 (1963). - 8. Hammond, J. : Animal breeding in relation to nutrition and environmental conditions. Biol. Rev. 22, 195--213 (1947). -- 9. Harpstead, D . D . , Sarria, D. Diaz, E.: Genetic variance estimates in a maize population subdivided into multiple and single ear type. Agronomy Abstracts. ASA. p. 11 (1967). -- 10. Jugenheimer, R. W., Williams, K. E.: Experimental corn hybrids tested in 1956. Ill. Agr. Exp. Sta. Bull. 6o6, 1--32 (1957). -11. Lonnquist, J. H.: M6todos de selecci6n riffles para mejoramiento dentrn de poblaciones. V i a Reunion Latinoamericana de Fitotecnia, Lima, Peru (1964). -12. Lonnquist, J. H.: Mass selection for prolificacy in maize. Der Ztichter 37, t85--188 (t967). -- t3. Lonnquist, J. H., Cota-A., O., Gardner, C. O. : Effect of mass selection and thermal neutron irradiation on genetic variances in a variety of corn (Zea mays L.). Crop Sci. 6, 330-- 332 (1966). -- 14. Torregroza, M., Harpstead, D. D. : Effects of mass selection for ears per p l a n t in maize. Agronomy Abstracts, ASA. p. 20 (1967).
Fernando Arboleda-Rivera Insfituto Colombiano Agropecuario Programa Maiz y Sorgo Apartado aereo 51764 Medellin (Colombia) William A. Compton Associate Professor Department of Agronomy University of Nebraska Lincoln, Nebraska 68503 (USA)
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