OCCURRENCE OF F U S A R I U M HEAD BLIGHT, ASSOCIATED MYCOTOXINS AND RESISTANCE OF WHEAT GERMPLASM OLIVER OTIENO OKUMU (B.Sc. Agriculture, University of Nairobi) THESIS SUBMITTED IN PARTIAL FULFILLMENT OF T H E REQUIREMENT FOR T H E DEGREE OF MASTER OF SCIENCE IN CROP PROTECTION DEPARTMENT OF PLANT SCIENCE AND CROP PROTECTION F A C U L T Y OF AGRICULTURE UNIVERSITY OF NAIROBI 2014 DECLARATION This is my original work and it has not been submitted for award of a degree in any other University Oliver Otieno Okumu Signature: Date: This thesis has been submitted for examination with our approval as University supervisors Prof. James W. Muthomi Department of Plant Science and Crop Protection University of Nairobi Signature: - - - C M . Date: S^Stl!^ Dr. Maina Wagacha School of Biological Sciences University of Nairobi 7 Signature: Date Dr. Charity Mutegi International Institute of Tropical AgricultHfe (IITA), Nairobi Date:-J-^3.1MH Signature:^^^ ii ABSTRACT F u s a r i u m head blight (FHB) is an important disease of wheat that reduces yield and quality through contamination with mycotoxins detrimental to human and livestock health. Major wheat varieties grown in Kenya are susceptible to F H B and there is no known source of resistance to the disease available. This study was carried out to determine the occurrence of F u s a r i u m head blight, associated mycotoxins and the level of susceptibility of wheat germplasm to FHB and deoxynivalenol (DON) contamination. A survey was carried out during the 2013 cropping season in four agro-ecological'zones (AEZ) in Nakuru County to determine wheat production practices and incidence and severity of FHB in each farm. F u s a r i u m species and mycotoxins DON and T2-toxin were determined in wheat heads and kernels. Nine wheat varieties and four C I M M Y T lines were evaluated for susceptibility to F H B in field experiments at diverse agroecolgical zones in Nakuru and Narok Counties and in the greenhouse. After inoculation with F . g r a m i n e a r u m susceptibility was determined based on FHB severity, reduction in grain yield, kernel infectionand DON contamination in kernels. Majority (47.4%) of the farmers used certified wheat seeds and variety Njoro BW2 was the most widely grown. Most (63.4%) of the farmers used wheat straw to make hay for livestock feed, applied soil amendments (100%), practiced crop rotation (81.3%) while only 6.5% of the farmers practiced mixed cropping. Rust was the most important disease in all the farms surveyed. Head blight was prevalent (100%) in all the agro-ecological zones and mean incidence and severity ranged from 10.6 to 12.5% and 12.9 to 2 0 . 9 % , respectively with the highest incidence and severity in agro-ecological zone LH3. F u s a r i u m spp were F . g r a m i n e a r u m , F . avenaceum contaminated with mycotoxins DON The most frequently isolated and F . p o a e . Most wheat samples were and T-2 toxin upto 182ng/g and 37ng.g respectively. XV Ninety eight percent of the samples contained T-2 toxin above the limit of detection of 3.5ng/g while 46% of the samples contained DON above the limit of detection of 18.5ng/g. Wheat varieties and lines varied in susceptibility to F . g r a m i n e a r u m with variety Kwale showing least susceptibility while line 10155 was the most susceptible. Variety sunbird had the highest mean F H B severity and A U D P C in Nakuru while line 10155 had the highest mean severity and A U D P C in both the greenhouse and Narok trials. In Nakuru variety Kenya Hawk had the highest yield of 878g while Kenya wren had the lowest (167g). In Narok, Kibis had the highest grain yield of 128g while line 957 gave the lowest yield of 59g. A l l the wheat varieties and lines accumulated DON with variety Chiriku having the least concentration of 457ng/g while line 10155 had the highest concentration of 748ng/g. Deoxynivalenol accumulation in grain samples from the greenhouse was lower compared to the samples from the field trials. Most grain samples were contaminated with DON and T-2 toxin. Mycotoxin levels varied depending on the A E Z and the pre-dominant F u s a r i u m species isolated from a region. Variety selection and crop rotation influenced the occurrence of FHB in the different agro- ecological zones. Although host resistance is the best option in the management of FHB, the varieties currently available do not confer resistance to both the FHB and DON accumulation. Therefore, more research on developing resistant varieties should be done in the country. Key words: Deoxynivalenol, F u s a r i u m , head blight, mycotoxins, T-2 toxin. xvi