Occurrence of fusarium headblight of wheat in Nakuru district and its management using biocontrol agents
Abstract
Fusarium head blight (FHB) has recently re-emerged as a devastating disease of small grains
throughout the world. Different management strategies have been tried but control of the
disease has not yet been achieved. Survey for the occurrence of FHB of wheat was carried
out during the 2006 cropping season in five agro-ecological zones of Nakuru. The disease
incidence was determined as the number of blighted heads over the total number of heads in
a 10m2 while severity was determined as the proportion of the spikelets bleached. Wheat and
maize grain samples were collected from the same farms and causal fungi isolated and
identified to species level. Pathogen isolation was by plating on agar culture media. The DON
contamination was determined using competitive ELISA method.
Laboratory and greenhouse studies were also conducted to evaluate the efficacy of selected
antagonists namely, Bacillus sp, Alternaria sp, Trichoderma sp and Epicoccum sp in
management of PI-rn. The greenhouse experiments were arranged in a completely
randomised design. Data on severity was determined as the proportion of spikelets bleached
and yield was determined as ten-ear weight and yield per pot. The laboratory experiment
involved growing the pathogen and the antagonists in dual cultures. Antagonism in culture
against Fusarium graminearum was determined as reduction in colony diameter.
Most farmers used seeds from their neighbours (58%) or their own seed 25% for planting.
Most also (92%) rotated wheat with wheat or maize. Head blight was found to be highly
prevalent (88-100%) and mean incidence ranged 4 to 9%. Severity ranged from 15-37 %. The
main fungal genera isolated from wheat heads and grains were Fusarium sp, Alternaria sp
and Epicoccum sp. Fusarium sp was most prevalent (42%) in .infected wheat heads while
Epicoccum sp was most prevalent (35%) in harvested wheat grain. Only Fusarium sp and
Penicillium species were found in maize grains. Fusarium poae had the highest isolation
frequency followed by F. graminearum and F. chlamydosorium in both diseased heads and
wheat kernels. Fusarium verticilloides was the most frequently isolated (58%) from maize.
Fusarium graminearum was found in both wheat and maize. There was no significant
difference on the Fusarium species over the AEZS. There were no significant differences on
the DON levels over the AEZS. The mean DON levels were 249 and 221 ug/kg for wheat
and maize respectively. The DON in wheat ranged from 99-3691lglkg whereas that in maize
ranged from 13.6-634 ug/kg, The four antagonists significantly reduced colony diameter
with the highest reduction being in paired cultures with Trichoderma (64%) and least
effective was Epicoccum (44%) colony growth reduction. The antagonists had little or nonsignificant
reduction of disease severity. Two antagonists Alternaria and Epicoccum
significantly reduced the DON levels.
The results indicate that head blight in Nakuru district is due to a complex of Fusarium
species and that it leads to varying levels of DON over the AEZs. It showed that Fusarium
graminearum could be major causal agent of head blight in wheat and ear rot in maize. There
was indication of a possible cross contamination between maize and wheat. It is therefore
important to sensitize farmers on methods of reducing disease and DON levels and the
importance of better rotational programmes. It was also clear that the antagonists effectively
reduced colony growth in culture but little success in greenhouse tests. The reduction of DON
by Alternaria and Epicoccum species was also pronounced. More research on efficacy 'of
other antagonists should be done and determination of wheather the reduction in DON was
accompanied by an increase in other toxins.
Citation
Master of Science degree in Crop ProtectionPublisher
University of Nairobi Department of plant science and crop protection