Maize hybrid adaptability to drought stress assessed with combining ability and genotype -by -environment effects

Dryland maize (Zea mays L.) production in western Nebraska and adjacent areas is constrained mainly by water-limiting factors throughout the growing season. Nine elite single-cross (SC) hybrids and their 36 double-crosses (DC) were evaluated in western Nebraska, eastern Wyoming, and northeastern Colorado in 1998 and 1999 under different water regimes to assess differences in yield and drought-related characteristics among them, to estimate combining ability effects of these characteristics, to uncover patterns of GE interaction, and to assess the potential of indirect selection for grain yield in dryland environments based on selection under irrigated conditions. Single-cross hybrids were superior in yield to DC hybrids across all water regimes. On average, DC hybrids yielded 11% less than SC hybrids. However, the difference in yield could not be explained by differences in drought-related characteristics between SC and DC hybrids. A diallel study showed that grain yield was largely controlled by non-additive gene action, whereas drought-related characteristics were under control of additive gene action. Across all water regimes, specific combining ability (SCA) effects were more stable than general combining ability (GCA) effects. A strong association in SCA effects between yield and drought-related characteristics was observed, even under irrigated conditions. Single-cross hybrids showed a superior stability across all environments, and DC hybrids showed a better stability across harsh environments. However, SC hybrids showed superiority in yield even under the lowest-yielding conditions. Yield-component compensation and drought-escape appeared to be the mechanisms of stability among these materials. Crossover and correlated response analysis indicated that selection for grain yield in irrigated conditions for production under the dryland environments might be possible. The study suggested that screening among elite SC hybrids under irrigated environments in the area for low susceptibility to drought stress and earliness might increase the productivity of hybrid maize in the target area. Alternatively, a selection based on SCA effects for yield, which can be applied under irrigated conditions, might indirectly increase drought tolerance in hybrid maize

Separation of cotton cultivar testing sites based on representativeness and discriminating ability using GGE biplots

An important task of multienvironment trials (MET) analysis is evaluation of testing sites for megaenvironment differentiation and selection of "ideal" candidate location to improve the efficiency of cultivar selection and recommendation. The objectives of this research work were (i) to divide the Spanish cotton (Gossypium hirsutum L.) testing locations into megaenvironments and (ii) to separate the testing locations based on their distance to the "ideal" location, discriminating ability, representativeness, and uniqueness. GGE biplot was employed to analyze eight 1-yr and two multiyear (3-yr, 4-yr) balanced datasets from 1999 to 2006 cotton trials of Delta & Pine Land Co. in Spain for yield, fiber quality traits, a selection index (SI) based on yield and quality, and Verticillium wilt (Verticillium dahliae Kleb.) disease infestation level. Yearly GGE biplots revealed crossover genotype x location interactions, but not large enough to divide the area into different megaenvironments. Therefore, the Spanish cotton region may be considered as a complex megaenvironment and cultivar recommendation may be based on both mean performance and stability. Las Cabezas location was the closest to an ideal based on both yield and the SI regardless of the change from plastic to nonplastic mulching cultural practice. Aznalcazar did not provide unique information and could be dropped as a test site. The separation of test locations for their discriminating ability and representativeness provided useful information on the effectiveness of each testing location for developing and/or recommending cultivars with specific or broad adaptation. In this sense, Lebrija could be considered as trait-specific selection environment for early screening of verticillium tolerant genotypes

Grain yield and plant characteristics of corn hybrids in the Great Plains

Citation: Frank, Brian J., Alan J. Schlegel, Loyd R. Stone, and Mary Beth Kirkham. “Grain Yield and Plant Characteristics of Corn Hybrids in the Great Plains.” Agronomy Journal 105, no. 2 (2013): 383–94. https://doi.org/10.2134/agronj2012.0330.Water supply for crop use is the primary factor controlling corn (Zea mays L.) grain yield in the west-central Great Plains. With water supply varying as production systems range from dryland through irrigated, selecting hybrids for optimum yield in the anticipated water environment is vital for success. Our objective was to analyze a group of corn hybrids and determine: a) are there significant differences in identifiable plant characteristics among the hybrids and b) are there significant associations between identifiable plant characteristics and grain yield. Corn was grown near Tribune, KS, in 3 yr in two fields; one dryland and one irrigated. Hybrids (18) replicated in four blocks were grown at each field, with dryland and irrigated results analyzed separately. From linear regression, no significant correlation existed between irrigated grain yield and days to initial silking of hybrids in any of the 3 yr. The correlation between dryland grain yield and days to initial silking of hybrids was significant (P<0.05) in all 3 yr, with grain yield decreasing as days to initial silking increased. Dryland grain yield was also significantly and negatively correlated with dry stover mass in all 3 yr and with tiller population in 2 of 3 yr. Hybrids selected for dryland in the west-central Great Plains should be from the earlier 1/3 or 1/2 of the 98- to 118-d relative maturity (RM) range of our study. In addition, hybrids selected for dryland should have characteristics of smaller stature (less stover) and non-tillering plants

Estabilidade de produção de híbridos simples e duplos de milho oriundos de um mesmo conjunto gênico Yield stability in single and double crosses of maize originated from the same gene pool

O presente trabalho foi realizado com o objetivo de comparar a estabilidade de híbridos simples e híbridos duplos de milho oriundos de um mesmo conjunto gênico. Foram avaliados 55 tratamentos, sendo dez híbridos simples comerciais, utilizados como parentais e 45 híbridos duplos resultantes de um dialelo completo. As sementes dos híbridos duplos foram obtidas na área experimental do Departamento de Biologia da Universidade Federal de Lavras (DBI/UFLA). Os experimentos foram desenvolvidos em 15 ambientes, no ano agrícola de 2005/2006, em propriedades de agricultores e estações experimentais. O delineamento experimental utilizado foi o de blocos casualizados com três repetições e o caráter avaliado foi a produtividade de espigas despalhadas (kg ha-1), corrigida para 13% de umidade. Obteve-se a contribuição de cada híbrido para a interação genótipos x ambientes e o desvio em relação ao desempenho máximo em cada ambiente utilizando a estatística não-paramétrica por meio da soma de postos. Os híbridos duplos foram, em média, mais estáveis, contudo, identificaram-se híbridos simples tão estáveis quanto os duplos.<br>The objective of the present work was to study the adaptability and stability of single and double-crosses of maize originated from the same gene pool. Ten commercial single-crosses and all possible double-crosses, obtained from a complete diallel, were evaluated. Seeds of the double-crosses were obtained in an experimental area of the Biology Department at Universidade Federal de Lavras (DBI/UFLA). The experiments were conducted in 15 environments in the 2005/06 growing season, on farms and in experimental stations. The cultural practices were the ones normally used by farmers or experimental stations for maize. The entries were evaluated in randomized complete blocks design with three replications per environment. The trait under study was husked ears yield (kg ha-1), corrected to 13% of moisture content. Nonparametric statistics were used to study hybrids adaptability and stability. The contribution of each hybrid to the genotype-by-environment interaction and the deviation in relation to the maximum performance in each environment was determined. The double-crosses were on average more stable, although some single-crosses were as stable as the double-crosses

Interrelationship among and repeatability of seven stability indices estimated from commercial cotton (Gossypium hirsutum L.) variety evaluation trials in three Mediterranean countries

Multi-environment trial data are required, to obtain variety stability performance parameters as selection tools for effective cultivar evaluation. The interrelationship among seven stability parameters and their association with mean yield, along with the repeatability of these parameters across consecutive years was the objective of this study. Cottonseed yield data of 31 cotton cultivars, proprietary of Delta and Pine Land Co and other companies, evaluated in 20 locations over the 1999-2005 year period in Greece, Spain and Turkey were used for combined analysis of variance in four datasets. Across locations in a single evaluation year (dataset A), across locations in each of two single consecutive evaluation year (dataset B), across locations and two consecutive years (dataset C) and across locations and three consecutive years (dataset D). For each dataset, cultivar phenotypic variance (sigma(2)(p)) was appropriately partitioned in its components and the h(2) and sigma(2)(ge) component estimated. Furthermore, following the appropriate stability analysis b(i); sd(i)(2), sigma(2)(i); YS(i) and AMMI1 along with the GGE Biplot distance (GGED) and instability (GGEIN) parameters were obtained. The interrelationship among the parameters and their association with mean yield based on Spearman rank correlation was studied in each of the seven single evaluation years (dataset A). Rank correlation coefficients were also used as estimates of the repeatability of these stability parameters across consecutive year combinations (dataset B, C and D). The parameters GGED and YS(i) were consistently highly correlated with each other and mean yield in five out of seven single evaluation years. The data provided evidence that single year evaluation across locations might be sufficient to reliably rank cotton cultivars, based on mean yield along with GGED and YS(i). Combined analysis across two consecutive years (dataset C) was more effective as compared to single year evaluation. GGED was relatively more repeatable than YS(i) and mean yield in single (dataset B) and 2-year comparisons (dataset C). Although GGED is an index depended and proportional to yield, provides a superior way to integrate mean performance and stability into a single measure, which can be assessed visually on biplots. Regarding the other stability parameters, the results were contradicting and of low repeatability across single years and two consecutive years. Cultivar evaluation combined across locations in 3 years did not improve the repeatability of cultivar variance effects but resulted in very high repeatability of GGED, YS(i) and mean yield