Resistance to Aspergillus ear rot and aflatoxin

In 1991, 1,041 and 949 crosses with the susceptible corn (Zea mays L.) inbreds Mo17 and B73, respectively, were evaluated for resistance to ear rot caused by Aspergillus flavus using a pinboard inoculator developed at the University of Illinois. Inbreds used in development of F$\sb1$ hybrids included agricultural experiment station releases, and inbreds from Canada, Europe, Mexico, India, China, and South Africa. The F$\sb1$ crosses were evaluated with a susceptible inbred to identify sources of resistance with alleles not found in B73 or Mo17 for incorporation into widely grown hybrids. From the F$\sb1$ crosses, 18 inbreds crossed with B73 and 17 inbreds crossed with Mo17 were selected (35 total F$\sb1$'s) and analyzed for aflatoxin content. In 1992, inheritance of resistance to A. flavus ear rot was studied in the 35 crosses involving the parental, F$\sb1$, F$\sb2$, and backcross to the susceptible parent generations. The F$\sb3$ generations were also evaluated for ten of the crosses. In 1993, 11 of the crosses were revaluated using the parental, F$\sb1$, F$\sb2$, F$\sb3$, and backcross to the susceptible and to the resistant generations. Five F$\sb2$ and three F$\sb3$ populations selected from the 35 F$\sb1$ crosses were evaluated for A. flavus ear rot and for aflatoxin in 1992 and 1993, respectively. Aflatoxin values from individual F$\sb2$ plants and F$\sb3$ families were separated into classes to study frequency distributions. In separate experiments, the 32 inbreds per se and 35 F$\sb1$ crosses were reevaluated for A. flavus ear rot, kernel infection, and aflatoxin in 1992 and 1993. Also, 20 selected F$\sb1$ crosses were evaluated in Starkville, Mississippi during 1993 for A. flavus ear rot and aflatoxin content.Additive and dominance gene action were of primary importance in resistance to A. flavus ear rot. Additive gene effects were of primary importance in the crosses B73 x LB31, B73 x CI2, and Mo17 x Tex6, whereas, genic dominance was of primary importance in B73 x L317, Mo17 x OH513, and B73 x 75-R001. Crosses Mo17 x 75-R001 and Mo17 x H103 were non-significant in the additive dominance model. Crosses containing Mo17 as the susceptible parent were generally more resistant to A. flavus ear rot and aflatoxin accumulation. When aflatoxin content frequency distributions of F$\sb2$ plants and F$\sb3$ families of the Mo17 x Tex6 and B73 x LB31 populations were examined, F$\sb2$ plants and F$\sb3$ families were highly scewed toward the resistant parents. The F$\sb2$ and F$\sb3$ generations indicated various levels of transgressive segregation for resistance to both A. flavus ear rot and aflatoxin.Inbreds Tex6, LB31, and CI2 consistently had the highest levels of resistance to A. flavus ear rot, kernel infection, and aflatoxin content as inbreds per se and in F$\sb1$ hybrid combinations. Inbreds OH513, OH516, and N6 had moderate levels of resistance to A. flavus ear rot and aflatoxin content. Pearson correlation coefficients were significant between ear rot ratings and aflatoxin values and ranged from 0.52 to 0.80 in the inbred and F$\sb1$ hybrid experiments, but were non-significant between ear rot ratings and kernel infection values and kernel infection and aflatoxin values. Consequently, ear rot ratings were a more accurate indicator of aflatoxin production.U of I OnlyETDs are only available to UIUC Users without author permissio