Maize Cultivar Performance under Diverse Organic Production Systems

Maize (Zea mays L.) performance can vary widely between different production systems. The need for high-performing hybrids for organic systems with wide adaptation to various macroenvironments is becoming increasingly important. The goal of this study was to characterize inbred lines developed by distinct breeding programs for their combining ability and hybrid yield performance across diverse organic environments. Parent lines were selected from five different breeding programs to give a sample of publically available germplasm with potential for use in organic production systems with expired plant variety protection (Ex-PVP) and current commercial inbreds as benchmarks. A North Carolina Design II mating design was used to produce all possible cross combinations between seven lines designated as males and seven lines designated as females. A significantly positive general combining ability for the female inbred UHF134 suggests that it performs well in hybrid combination. Significant general combining ability was not observed for any male inbred line in this study. Several significantly positive specific combining abilities suggest that nonadditive genetic effects play an important role in determining yield in this germplasm. Further analysis revealed that hybrids containing either an Ex-PVP line or a commercial inbred line were on average superior to hybrids containing only inbreds developed by the cooperators of this study. This demonstrates the utility of testing inbreds from diverse sources when developing hybrids for organic production systems

Herança da senescência retardada em milho Inheritance of the delayed senescence in maize

O objetivo deste trabalho foi estudar a herança da senescência retardada em milho. Foram realizados cruzamentos dialélicos parciais entre 50 linhagens e cinco testadores. Os 250 cruzamentos resultantes, além de seis híbridos comerciais utilizados como testemunhas, foram avaliados em oito ambientes, no delineamento látice simples 16x16, com duas repetições por ambiente. Os cruzamentos dialélicos foram analisados utilizando o método 4 do modelo 1 de Griffing, adaptado para múltiplos ambientes. A contribuição da capacidade geral de combinação (CGC) para a expressão do caráter "stay-green" (69,06%) foi maior que a da capacidade específica de combinação (CEC) (30,94%), evidenciando que os efeitos aditivos são mais importantes que os efeitos não aditivos na expressão deste caráter. Tanto a CGC como a CEC interagiram significativamente com o ambiente, indicando que a seleção para este caráter deve ser realizada com base nas médias de experimentos em diversos ambientes.<br>The objective of this research was to study the inheritance of delayed senescence in maize. Partial diallel crosses among 50 inbred lines and five testers were made. The 250 crosses, along with six commercial hybrids used as checks, were evaluated at eight environments in lattices 16x16 with two replications per environment. The diallel crosses were analyzed following the method 4 model 1 of Griffing, extended to multiple environments. The contribution of the general combining ability (CGA) for the expression of the stay-green trait (69.06%) was greater than the specific combining ability (SCA) (30.94%), showing that additive effects are more important than non-additive effects for the expression of this trait. Both GCA and SCA interacted significantly with the environments, indicating that the selection for this trait should be based on the means across environments

Gene effects for specific leaf area and harvest index in three crosses of groundnut (Arachis hypogaea)

Groundnut productivity is low in the semiarid tropics mainly because of drought caused by low and erratic rainfall. Genotypes that have ability to use limited available water efficiently are required to enhance productivity of the crop. In groundnut, water use efficiency (WUE) is correlated with specific leaf area (SLA). The latter can be used as a surrogate trait for selecting for WUE. Partitioning of assimilates as measured by the harvest index (HI) has the greatest effect on pod yield. In order to improve SLA and in turn WUE and HI, a good knowledge of genetic systems controlling the expression of these traits is essential for the choice of an efficient breeding procedure. This study was conducted to investigate inheritance of SLA and HI in three crosses involving Chico, TMV 2 NLM, and ICGV 86031 groundnut genotypes. The crosses used were Chico × TMV 2 NLM, Chico × ICGV 86031 and TMV 2 NLM × ICGV 86031. The study included parents, F1, F2, and backcross generations. Generation means analysis indicated that the additive effects were more important than the dominance effects in the expression of SLA and HI. In addition to additive and dominance effects, additive × additive type of epistasis, which can be fixed in groundnut (a self pollinated crop), was also significant for SLA in all the three and for HI, in two crosses (Chico × TMV 2 NLM and Chico × ICGV 86031). The selection for SLA and HI can be effective in early generations in some crosses and to exploit the additive × additive type of interaction, it can be done in large populations of later generations