Variabilidade genética em duas populações braquíticas de milho após sete ciclos de seleção massal para prolificidade
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2018-08-16
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Universidade Estadual Paulista (Unesp)
Resumo
Populações braquíticas têm sido constantemente estudadas no melhoramento de milho, o interesse por cultivares de porte baixo tem aumentado, principalmente por tolerarem plantios adensados, permitindo maior número de plantas por hectare. A prolificidade é um dos principais componentes na produção do milho que além da estabilidade de produção permite maior eficiência na utilização de nutrientes na planta. O objetivo deste trabalho foi verificar a variabilidade genética, para diferentes caracteres, presente nas populações Isanão VF-1 e Isanão VD-1 após sete ciclos de seleção massal para prolificidade. Foram avaliadas 121 progênies de meios irmãos da população Isanão VF-1 e 65 progênies da população Isanão VD-1, ambas populações de milho braquítico, na segunda safra do ano agrícola 2017 (E1) e primeira safra 2017/2018 (E2). Os caracteres avaliados para as duas épocas de semeadura foram enfezamento, tombamento, prolificidade e rendimento de espigas, e apenas para a E2 foram avaliados florescimento feminino, altura de plantas, altura de espigas e rendimento de grãos. Foram estimados parâmetros genéticos e os ganhos esperados com seleção com intensidade de seleção de 20%, para cada época e conjuntamente. Para a população Isanão VF-1 foram estimadas herdabilidades que variaram entre 37,70% e 74,82%, e ganhos de -5,11%, -10,48% para enfezamento, 19,57% e 7,13% para prolificidade, 20,75% e 15,74% para rendimento de espigas na E1 e E2 respectivamente. Para a população Isanão VD-1 as herdabilidades variaram entre 8,01% e 75,36%, e os ganhos estimados foram de -3,20% e -9,57% para enfezamento, 12,35% e 1,98% para prolificidade, 24,42% e 10,22% para rendimento de espigas, nasE1 e E2, nesta ordem. Nas análises conjuntas a interação progênies x épocas apresentou interação significativa para todos os caracteres avaliados na E1 e na E2 apenas para rendimento de espigas. Os baixos valores de herdabilidade nas análises conjuntas, associados a baixos valores de ganho estimados, sugerem que para as duas populações sejam conduzidos processo de seleção distintos para cada época. Mesmo após sete ciclos de seleção massal para prolificidade as populações avaliadas mantêm variabilidade genética suficiente para futuros ciclos de seleção.
Maize brachytic populations have been constantly studied in maize breeding, the interest for low-growing cultivars has increased, mainly because they tolerate high density of plants. Prolificacy is one of the main components of yield in maize that besides the yield stability allows higher efficiency in the use of nutrients in the plant. The objective of this work was to verify the genetic variability for different carachteres in the Isanão VF-1 and Isanão VD-1 brachytic populations after seven cycles of mass selection for prolificacy. A total of 121 open cross corn progenies from the Isanão VF-1 population and 65 open cross corn progenies from the Isanão VD-1 population, both brachytic maize populations, were evaluated in first crop 2017 (E1) and second crop 2017/2018 (E2). The evaluated traits for the two seasons were corn stunt complex, fall index, prolificacy and ear yield, and only for E2 were evaluated feminine flowering, plant height, ear height and grain yield. Genetic parameters and expected gains with selection, with 20% of intensity, were calculated for each season and jointly. For the Isanão VF-1 population, heritabilities were estimated from 37.70% to 74.82%, and expected gains of -5.11%, -10.48% for corn stunt complex, 19.57% and 7.13% for prolificacy, 20.75% and 15.74% for ear yield at E1 and E2 respectively. For the Isanão VD-1 population the heritabilities varied between 8.01% and 75.36%, and estimated gains were -3.198% and -9.565% for corn stunt complex, 12.346% and 1.982% for prolificacy, 24.423% and 10, 22% for ear yield at E1 and E2, in that order. In the jointly analyses the progenies x seasons interaction was significant for all traits evaluated in E1 and E2 only for ear yield. The low values of heritability in the jointly analyses, associated to low values of expected gains selection, suggest that for the two brachytic populations, distinct selection processes are conducted for each season. Even after seven cycles of mass selection for prolificacy, the populations evaluated maintain sufficient genetic variability for future selection cycles.
Maize brachytic populations have been constantly studied in maize breeding, the interest for low-growing cultivars has increased, mainly because they tolerate high density of plants. Prolificacy is one of the main components of yield in maize that besides the yield stability allows higher efficiency in the use of nutrients in the plant. The objective of this work was to verify the genetic variability for different carachteres in the Isanão VF-1 and Isanão VD-1 brachytic populations after seven cycles of mass selection for prolificacy. A total of 121 open cross corn progenies from the Isanão VF-1 population and 65 open cross corn progenies from the Isanão VD-1 population, both brachytic maize populations, were evaluated in first crop 2017 (E1) and second crop 2017/2018 (E2). The evaluated traits for the two seasons were corn stunt complex, fall index, prolificacy and ear yield, and only for E2 were evaluated feminine flowering, plant height, ear height and grain yield. Genetic parameters and expected gains with selection, with 20% of intensity, were calculated for each season and jointly. For the Isanão VF-1 population, heritabilities were estimated from 37.70% to 74.82%, and expected gains of -5.11%, -10.48% for corn stunt complex, 19.57% and 7.13% for prolificacy, 20.75% and 15.74% for ear yield at E1 and E2 respectively. For the Isanão VD-1 population the heritabilities varied between 8.01% and 75.36%, and estimated gains were -3.198% and -9.565% for corn stunt complex, 12.346% and 1.982% for prolificacy, 24.423% and 10, 22% for ear yield at E1 and E2, in that order. In the jointly analyses the progenies x seasons interaction was significant for all traits evaluated in E1 and E2 only for ear yield. The low values of heritability in the jointly analyses, associated to low values of expected gains selection, suggest that for the two brachytic populations, distinct selection processes are conducted for each season. Even after seven cycles of mass selection for prolificacy, the populations evaluated maintain sufficient genetic variability for future selection cycles.
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Enfezamento, Épocas de semeadura, Parâmetros genéticos, Progênies de meios irmãos, Variação genética, Zea mays, Corn stunt complex, Sowing seasons, Genetic parameters, Half sib progenies, Genetic variation