Host resistance mechanisms and cultural practices for control of gray leaf spot (cercospora zeae rnaydis) of maize in Tanzania

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Sokoine University of Agriculture


Studies were carried out in selected villages of the Southern and Eastern Maize Agro- ccological Zones to assess the potential variations in isolate aggressiveness, nature and genetics of host resistance and explore cultural methods suitable for the management of gray leaf spot. Southern Zone isolates (Mbcya and Iringa) grew 0.25 mm per day faster (9.3%), formed 1.1 cm longer lesions (25.9%), produced 1.1 x 104 more spores per cm2 of the lesion (13.6%), formed symptoms 1 day earlier, caused 21.2% more disease and produced more toxins than the Eastern Zone isolates. Significantly (P<0.05) more germlings of C. zeae mayclis were established after penetration on susceptible than on resistant and moderate resistant maize genotypes. Histological studies suggest the possible involvement of inhibitory substances in host cell, a possible resistance mechanisms against C. zeae maydis in maize. Heritability and gene effect estimates for components of partial resistance to gray leaf revealed significant differences between generations, crosses and generation x cross and generation x location interactions. Results have shown that lesion size, lesion length, lesion numbers and disease severity could be used for selection of partial resistance to gray leaf spot based on field measurements. Composted cattle manure lowered gray leaf spot compared to CAN by 29. 4% at 60 kg N ha'1 and by 32.2% at 90 kg N ha’1 followed by composted poultry manure 24.5% and 22.9% and urea 17.6% and 18.2% at 60 kg N ha’1 and 90 kg N ha respectively. Grain yield in composted cattle manure, composted poultry manure and urea fertilization was 1.41 ha’1, 0.91 ha’1, 0.6 t ha1 and 4.2 t ha’1, 3.7 t ha’1, 3.4 t ha’1 higher compared to CAN and none fertilized (control) treatments respectively. There was an overall yield increase of about 41 % in the intercropping compared to non-intercropping on susceptible maize cv ‘Pannar (PAN 6549). It is recommended that breeders should consider the most aggressiveiii isolates (MBY1, MBZI, IGAW1 and NJB1) and (DOMI, MKI1 and MGTl) when screening and breeding for resistance cultivars to gray leaf spot in the Southern highlands and Eastern agro-ecological Zone respectively.



Epidemiology, Gray leaf spot, Ercospora zeae rnaydis, Taxonomy, Tanzania, Maize production, Maize production systems