Genetics of resistance to Stenocarpella maydis ear rot of maize

[摘要] The objective of this study was to determine if germplasm available in South Africaand elsewhere, have sufficient variation in resistance to be used for the improvement ofresistance to Stenocarpella maydis, and to assess the viability of using recurrentselection as a breeding method under conditions of artificial infection with thepathogen. The study attempted to provide a better understanding of effective methodsto screen for resistance without sacrificing other favorable agronomic traits. Theinheritance and combining ability of resistance, as well as genetic and phenotypiccorrelation of resistance parameters with other characteristics, were investigated.The study comprised of three experiments. The first experiment was a complete diallelcross containing 10 commercial and experimental inbred lines, ranging from resistantto susceptible. Five South African developed inbreds, four USA developed and oneBrazilian inbred were used. The diallel was evaluated during the 1999/2000 season atthree environments across the South African maize growing area. Plants wereartificially inoculated twice, two weeks prior to anthesis. Different S. maydis relatedand agronomic characteristics were measured. The second experiment was a trialcontaining both South African developed hybrids and hybrids derived from crossesbetween South African developed germplasm and those of exotic and temperate origin.The trial was evaluated at one environment in the South African maize growing area.Again, plants were artificially inoculated twice, two weeks prior to anthesis.Flowering data were taken along with S. maydis incidence and grain moisture atharvest. The third experiment involved the evaluation of a recurrent selectionprogram, using three previously identified resistant inbreds as donor parents for thedevelopment of new genotypes with superior resistance to S. maydis. Selection wasdone on an ear-to-row basis over three years, using the segregating progenies derivedfrom crosses between the three inbreds.Highly significant differences were obtained between genotypes for all characteristicsmeasured, indicating variation for resistance in germplasm used in local breedingprograms. Across all three environments, the general combining ability (GCA) andspecific combining ability (SeA) effects were significant. Inbreds D0620Y, MON1and F2834T had the greatest negative GCA effects for S. maydis related characteristicsthat contributed towards resistance, with MONI being heterotically unique, combiningto all the other inbreds. PI combinations with inbred B37 had the greatest negativeSeA effects of all genotype combinations evaluated. GCA:SCA ratio's indicated thatresistance is controlled by additive gene effects, with low dominance and interactioneffects. Genetic correlations existed between the S. maydis related characteristics,with very high heritability and high correlated response between them. Due to it'ssimplicity, percentage rotted ears was the best method to measure resistance. Uprightears were found to result from S. maydis infection, rather than to predispose ears tothe disease.Significant differences were found between maturity classification and S. maydisincidence for South African developed germplasm crossed to temperate and tropicalgermplasm. Later flowering hybrids showed less S. maydis infection compared toearlier hybrids. Using resistant parents in breeding populations, superior genotypescould be selected by applying artificial inoculation and recurrent selection on an ear-torowbasis.

[发布机构] University of the Free State