Fungal microflora causing maize ear rots in Uganda

Maize is susceptible to a number of ear rot fungi, which cause reduction in yield, quality and feed value of the grains. The most common causative agents are Fusarium moniliforme J Shed. and Stenocarpella maydis (Berk). Associated with these fungal pathogens are mycotoxins, which have adverse effects on human and animal health. This study was conducted to identify the microflora responsible for causing maize ear rots in Uganda, establish the types of mycotoxins and their levels, determine the reaction of commercial and elite maize materials to F. moniliforme and S. maydis, the two most causative agents of maize ear rot in Uganda and evaluate two methods for inoculating maize ear rot with. Fresh and stored maize samples were collected from major maize growing districts in Uganda and the kernels plated onto Malt salt agar for mould growth and subsequently mycotoxin analysis was carried out. In the freshly harvested samples Fusarium spp, Aspergillus spp, penicillium spp, phomopsis and Rhizopus were identified. Fusarium spp and Aspergillus spp were the most common moulds, with Fusarium moniliforme being the most common species isolated from from most of the plated kernels. Similar moulds were identified from stored sample but with higher level of infection than in the fresh samples. The results show that both rotten and "healthy" kernels are infected by the same moulds but with lower incidence in the "healthy". Of the healthy freshly harvested samples, 75% tested positive for aflatoxin, most having 0-5ppb but one sample had 36 ppb. All the rotten samples and 83% of the stored samples tested positive for aflatoxin. Twenty commercial varieties and 19 elite materials were inoculated at silking stage with Stenocarpella maydis and Fusarium moniliforme using infected toothpick at Namulonge in central Uganda (1120 m above sea level), Kamenyamigo in Maska (1220 m above sea level) and Kere in Kapchorwa (2155 m above sea level) to assess their reaction in different environments. S. maydis resulted in higher percentage ear rot than F. moniliforme at mid-altitude (Namulonge and Kamenyamigo) but at higher altitude (Kere), F. moniliforme was more aggressive. The proportion of rotten ears ranged from 1% in resistant H20M1 to 57.2% in susceptible SC 621 for F. moniliforme at all locations while, for S. maydis percentage ear rot ranged from 3.7% to 67.9% across all locations. Thus the reaction of a particular variety to these two pathogens is dependent on environment (altitude), and interaction of the pathogen, location and genotype was significant (P<0.001). For the evaluation of the inoculation techniques, the toothpick technique resulted in high ear rot severity than the powder technique. However, the two methods gave reproducible results.