Variation in aggressiveness among isolates of Cercospora zeae-maydis inlow-, medium- and high-altitude maize agro-ecologies of Tanzania.

The objective of this study was to assess the aggressiveness and adaptation of Cercospora zeae-maydis the causal of grey leaf spot of maize in low-, mid- and high-altitude maize agro-ecologies. Field and laboratory studies were carried out to assess components of resistance, pathogen aggressiveness, sporulation, culture variations and morphological features of C. zeae-maydis isolates. Pathogen aggressiveness and morphological features differed among 30 isolates of C. zeae-maydis collected at different altitudes (p ≤ 0.05). Conidiophores per stroma between isolates ranged from 3.3 to 9.2 μ, conidiophore length 22.4–93.2 μ and colony growth rate ranged from 1.2 to 3.9 mm−1. High-altitude isolates grew 0.25 mm per day faster (9.3%), formed 1.1 cm longer lesions (25.9%), produced 1.1 × 104 more spores per cm2 of the lesion (13.6%) and formed symptoms 1 day earlier than low-altitude isolates. Prevalence of high numbers of aggressive isolates in low-altitude agro-ecologies indicates increased adaptation of C. zeae-maydis to warmer conditions. [ABSTRACT FROM PUBLISHER]