Genetic Analysis of Inbred and Hybrid Grain Yield under Stress and Nonstress Environments in Tropical Maize

Abstract

of maize-based farming systems is to be sustained or increased. Drought and low soil N cause significant yield reductions in maizeMaize population improvement for drought tolerance (Zea mays L.) grown in the tropics. Understanding the genetic basis (DT) at flowering has been accomplished in source popof hybrid performance under these stresses is crucial to designing ulations by recurrent selection using managed drought appropriate breeding strategies. This study evaluates under optimal, stress (Bolañ os and Edmeades, 1993a; Edmeades et al., drought and low N stress conditions (i) the performance, combining abilities and stability of a group of tropical white inbred lines; (ii) the 1999). Recurrent selection under drought was effective genetic control and modes of gene action for grain yield; and (iii) the at increasing yield across a range of drought stress levels relationship between line per se and hybrid performance. Seventeen in all populations under evaluation (Edmeades et al., lowland white-grained tropical maize inbred lines were used in a 1999). Gains under stressed conditions were signifidiallel study. Lines and their hybrids were evaluated separately in cantly greater than those observed in conventionally trials under drought stress, low N, and optimal conditions in a total selected counterpart populations without loss of yield of 12 environments. The differences in grain yield between hybrids potential (Byrne et al., 1995). Improvements were due and inbreds (i.e., heterosis) increased with the intensity of drought to a significant reduction in barrenness and increases stress. Significant interactions were observed for combining abilities in grain number per ear and harvest index, and were under low and high N. The type of gene action appeared to be different accompanied by a reduction in the anthesis-silking interunder drought than under low N, with additive effects more important val (ASI) and a delay in leaf senescence (Bolañ os and under drought and dominance effects more important under low N. , 1993b; Edmeades et al., 1999). Improvement Edmeades The importance of additive effects increased with intensity of drought stress. This suggests the need for drought tolerance in both parentalfor drought tolerance also brought specific adaptation lines to achieve acceptable hybrid performance under severe drought. and improved performance under low N conditions sug-Inbreds derived from the population 'La Posta Sequía' exhibited the gesting that tolerance to either stress involves common highest GCA effects, stability coefficients, and frequency of dominant adaptive mechanisms (Bä nziger et al., 1999). alleles for grain yield. Good performance across stress levels can be Edmeades et al. (1997) showed that population imachieved in tropical maize hybrids.

Salt tolerance assessment of barley (Hordeum vulgare L.) genotypes at germination stage by tolerance indices

“…The interaction of specific ion and osmotic effects lead to a reduction in the number of germinated seed as well as retardation in the rate of germination (Kazemi and Eskandari, 2011). Several researchers have reported the selection of barley genotypes under favourable conditions (Betran et al, 2003). Selection by the aim of stress condition has been highly suggested too.…”

Efeitos gênicos de caracteres associados à eficiência no uso de nitrogênio em milho

“…O conhecimento dessas informações e da herança genética em condições contrastantes de disponibilidade de N é crucial para orientar o melhorista quanto ao método mais adequado de melhoramento a ser utilizado. Neste sentido, parâmetros genéticos, como capacidade geral (CGC) e específica (CEC) de combinação, são importantes para inferir sobre o controle genético de caracteres de interesse e sobre as possibilidades de melhoramento, bem como para indicação de novas cultivares de milho (Betrán et al, 2003).…”

Controle genético do teor proteico nos grãos e de caracteres agronômicos em milho cultivado com diferentes níveis de adubação nitrogenada

“…Esse fato está relacionado aos níveis de suplementação de N, que não ofereceram condições de estresse para possíveis diferenças na manifestação do controle genético da PG. A defi ciência de N tem sido relatada como de grande importância para a expressão de efeitos não aditivos e aumento da heterose quanto à produção de grãos e outros caracteres em milho (Betran et al, 2003;Medici et al, 2004). Souza et al (2008) também identifi caram importância dos efeitos aditivos em genótipos de milho, provenientes de cruzamentos entre híbridos, porém em condições mais contrastantes de adubação nitrogenada.…”