ALBERT

Notes: Genotype × environment (GE) interactions are a major problem in plant breeding programs that involve testing in diverse environments. These interactions can reduce progress from selection. Few studies have characterized the effects of weather variables on GE interactions in sorghum (Sorghum bicolor [L.] Moench). The present investigation estimated the contribution of environmental index, (Ȳ, or mean yield of all cultivars in jth environment minus Ȳ. xor overall mean yield for all cultivars and all environments), rainfall, minimum and maximum temperature, and relative humidity, to GE interaction. Yield means of 5 full-season and 10 medium-season grain sorghum hybrids grown during 1986—1988 at four locations were used in the study. The GE interaction was significant and partitioned into σ2i, components assignable to each genotype. Weather variables (covariates) were used to remove heterogeneity from the GE interaction. The remainder of the GE interaction variance was partitioned into variance components (s2i) assignable to each genotype. In both maturity groups, the environmental index removed most, although non-significant, heterogeneity from the GE interaction sums of squares. Of all weather variables, preseason and seasonal rainfall contributed most to the GE interaction sums of squares.

Notes: Preharvest aflatoxin contamination of maize (Lea mays L.) gram by Aspergillns spp. is a concern to both producers and consumers of maize. Aflatoxms are carcinogenic to animals and have been linked to liver cancer in humans. The most desirable solution for eliminating or reducing aflatoxin contamination is to identify and/or develop sources of resistance. However, only a few genetic studies, which utilized a limited amount of genetic material, have been conducted. A thorough review and consolidation of information from these studies was deemed necessary. The purpose of this paper is to present a current, critical review on aspects of infection by Aspergillus, role of insects, inoculation techniques, and sources and genetics of resistance as they relate to aflatoxin production in maize. Damage to maize kernels by insects, especially the European corn borer (Ostrinia nubilalis Hübner), fall armyworm (Spodoptera frugiperda J. E. Smith), and corn ear-worm (Helicoverpa zea Boddie), has been associated with high aflatoxin levels. Artificial inoculation techniques that damage maize kernels generally result in the highest and most consistent aflatoxin levels. Although, a relatively large amount of maize germplasm has been screened for resistance and varying levels of resistance have been identified, additional germplasm needs to be systematically evaluated. To date, there are no known genotypes with complete resistance. Results from the few genetic studies indicated that additive genetic effects controlled resist-Preharvest aflatoxin contamination of maize (Zea mays L.) gram by Aspergillns spp. is a concern to both producers and consumers of maize. Aflatoxms are carcinogenic to animals and have been linked to liver cancer in humans. The most desirable solution for eliminating or reducing aflatoxin contamination is to identify and/or develop sources of resistance. However, only a few genetic studies, which utilized a limited amount of genetic material, have been conducted. A thorough review and consolidation of information from these studies was deemed necessary. The purpose of this paper is to present a current, critical review on aspects of infection by Aspergillus, role of insects, inoculation techniques, and sources and genetics of resistance as they relate to aflatoxin production in maize. Damage to maize kernels by insects, especially the European corn borer (Ostrinia nubilalis Hübner), fall armyworm (Spodoptera frugiperda J. E. Smith), and corn ear-worm (Helicoverpa Zea Boddie), has been associated with high aflatoxin levels. Artificial inoculation techniques that damage maize kernels generally result in the highest and most consistent aflatoxin levels. Although, a relatively large amount of maize germ-plasm has been screened for resistance and varying levels of resistance have been identified, additional germplasm needs to be systematically evaluated. To date, there are no known genotypes with complete resistance. Results from the few genetic studies indicated that additive genetic effects controlled resistance to aflatoxin contamination in maize. Aflatoxin production on maize grain appeared to be greatly influence by the environment. Further genetic studies, utilizing additional germplasm, are warranted for a better understanding of the nature of resistance to asflatoxin contamination in maize. Future research needs and plans relative to resistance to aflatoxin contaminaton in maize are presented.

Notes: Previous genetic studies on resistance to aflatoxin production in maize (Zea mays L.) only used a limited amount of germplasm. The objective of this study was to determine general (GCA) and specific combining abilities (SCA) for resistance to prehar-vest aflatoxin accumulation in grain, utilizing A619 Lfy syn, A632 Lfy syn, B73 Lfy syn, Hy Lfy syn, Mol7 Lfy syn, Wf9 Lfy syn, and 914 Lfy syn. We evaluated 21 F1 crosses (diallel) for aflatoxin accumulation in grain in three environments. Twenty-one days after mid-silk, ears were slash-inoculated with Aspergillus parasiticus (Speare). Samples were analyzed for aflatoxins Bl B2, G1 and G2. Significant differences for aflatoxin accumulation were detected among environments, with the environment that experienced drought stress showing the highest concentration for all four aflatoxins. The GCA and crosses mean squares were not significant for any aflatoxin and the SCA mean square was significant (P = 0.1) only for aflatoxin G2. Relatively small quantities of aflatoxin accumulation on, and nonsignificant differences among the 21 F1 crosses might be indicative of their inherently high resistance levels. The SCA sums of squares constituted two thirds or more of crosses sums of squares, which indicated a preponderance of dominance and/or epistatic effects for aflatoxin accumulation. The Hy Lfy syn GCA effect tended to increase aflatoxin Bl and Wf9 Lfy syn tended to reduce aflatoxin accumulation as it showed a significant (P = 0.1), negative GCA effect for aflatoxin G1. The F1 cross Wf9 Lfy syn × 914 Lfysyn showed significant, negative SCA effect for af-latoxins B1 and G1, whereas A619 Lfy syn × 914 Lfy syn and Mo17 Lfy syn × Wf9 Lfy syn tended to increase one or more aflatoxins. For aflatoxin Br, a significant environments (E) × crosses (C) interaction was largely due to E × GCA interaction, which, in turn, was due to an interaction of the B73 Lfy syn GCA effect with E. This interaction effect tended to reduce aflatoxin BS. The E × C interaction for aflatoxin G2 was due to both E × GCA and E × SCA interactions. B73 Lfy syn GCA × E tended to reduce aflatoxin G, and Mo17 Lfy syn GCA × E tended to increase aflatoxin G. Additive genetic correlations based on GCA effects among the four aflatoxins were significant (0.76 to 0.96), except the correlation between aflatoxins B, and G2 (0.43), suggesting that, in general, increasing resistance to one toxin may lead to resistance to the other three toxins.

Notes: Summary Genotype x environment (GE) interaction encountered in experiments complicates genotype selection and varietal recommendation. The integration of yield and stability of genotypes into a single parameter may make selection and recommendation easier. Kang developed a rank-sum method that allows selection for both yield and the stability variance statistics (σ i 2 or s i 2 ) of Shukla. The objective of this research was to compare the rank-sum selection method to selection based on yield alone in five international maize (Zea mays L.) yield trials. Ranks were assigned for yield (the highest mean yield received a rank of 1) and for σ i 2 and s i 2 (the lowest value received a rank of 1). The yield and σ i 2 ranks and/or the yield and s i 2 ranks for each genotype were summed. Each trial contained two reference entries (REs). Yield rank or rank-sum of each genotype was compared to yield rank or rank-sum of the best RE (BRE). GE interaction was significant for all trials. Heterogeneity in the GE interaction due to the linear effect of a covariate (differences in fertility and/or cultural practices) was significant in Trials 1, 2, and 5. Overall, in all trials, 29 genotypes were selected on the basis of yield alone. On the basis of σ i 2 and yield rank-sum, 32 genotypes were identified, with 11 being lower yielding than the 29 yield-based selections. On the basis of s i 2 and yield rank-sum, 31 genotypes were selected, with 11 being lower yielding than the yield-bases selections. Obviously, yield is sacrificed when the rank-sum method is used in the selection process. However, selection based on yield alone may not be adequate when GE interaction is significant because of testing in diverse environments.

Notes: Summary Aspergillus flavus Link ex Fries spores are commonly used as inoculum for screening maize (Zea mays L.) genotypes for resistance to aflatoxin accumulation on grain. Occasionally, A. parasiticus Speare is also used for this purpose. However, only limited data are available on whether one species is as effective as the other for identifying aflatoxin-resistant genotypes. Our objective was to determine relative aflatoxin accumulation on kernels of maize containing the leafy (Lfy) gene in response to A. flavus and A. parasiticus. Aflatoxin production by A. flavus and A. parasiticus on grain of seven maize synthetics containing the Lfy gene, viz., A619, A632, Mo17, B73, HY, Wf9, and 914, was examined in three environments in Louisiana. Ears were doubly inoculated at 14 and 21 days after mid-silk by atomizing over external silks a 2 ml suspension containing 2.0×107 spores ml-1 of either A. flavus or A. parasiticus. All genotypes responded similarly in the three environments to both the fungal species. Aflatoxin B1 and B2 production did not differ in the three environments. The seven genotypes did not differ in levels of aflatoxin accumulation in response to either A. flavus or A. parasiticus. Aflatoxin production by A. flavus was detected in maize samples from all three environments, but aflatoxin production by A. parasiticus was found only in samples from Winnsboro, where moisture stress occurred. Mean B1 and B2 production by A. flavus from the three environments was, respectively, four and one-half times and two times more than that by A. parasiticus.