Aspergillus flavus ear rot and aflatoxin in Uganda and genetics of resistance in tropical maize germplasm.

Author: Sserumaga, Julius

Supervisors: James W.; George N. and Dan Makumbi

The risk of exposure to aflatoxin in tropical agricultural systems is high due to factors that favour fungal growth and toxin production. Maize is among the staple crops with high aflatoxin contamination in Uganda. An understanding of host, pathogen and resistance to infection facilitates the development of germplasm with elevated resistance to infection. The objective of the study was to contribute to maize ear rots management and the associated mycotoxins through host resistance. A various levelled testing method was utilized to haphazardly collect 247 diseased maize cob samples in maize fields in 16 districts for aflatoxin quantification and Aspergillus flavus isolations and characterization. Also, 25 SSR markers were used to fingerprint 41 inbred lines to determine genetic diversity and their relationship, 35 lines were used to evaluate aflatoxin accumulation using High-Performance Liquid Chromatography and 19 inbred lines generated 90 F1 using North Carolina Design II mating scheme to understand the gene action controlling kernel infection resistance by Aspergillus flavus and also to estimate additive and dominance genetic variances. Results showed significant differences among areas of study for A. flavus incidence and severity. Utmost incidence and severity of Aspergillus flavus was recorded in Pallisa (74.2% and 4.8, respectively). Among agro-ecological zones, the utmost incidence and severity of Aspergillus flavus were in the eastern region at 62.4% and 4.6% respectively. At all the loci, 184 alleles were recorded with an average of 7.36 and a range: 2 - 19. The gene diversity average was 0.65 and ranged from 0.18 to 0.92. Percentage heterozygosity was 4% on average and ranged from 0.0% to 2.0%. Average polymorphism information content recorded was 0.61. In understanding the inheritance of resistance to kernel infection