Infection efficiency of Phaeoisariopsis personata and the influence of different wetness patterns on germ-tube growth of the pathogen

Controlled environment studies with P. personata [Mycosphaerella berkeleyi], the causal agent of late leaf spot disease of groundnut, showed that infection is enhanced if leaves are exposed to alternate wet and dry periods (intermittent wetness) compared with continuous wetness. Detailed investigations to elucidate this phenomenon revealed more germ tubes per conidium and more branching of germ tubes with intermittent wetness than with continuous wetness. With intermittent wetness there was clear evidence of tropic growth of germ tubes and branches towards stomata and subsequent penetration. With continuous wetness, germ tube growth did not appear to be directional and germ tubes commonly passed over the stomatal guard cells, therefore leading to relatively few stomatal penetrations. For both wetness regimes, stomatal penetrations continued to increase with increased leaf wetness for at least 6 d after inoculation and there was a linear relationship between the number of stomatal penetrations and the number of resultant lesions. Infection efficiency was markedly increased when the spore load was reduced to 0.1 conidia/cm² (c. 1 spore/leaflet)

Relationships between temperature and latent periods of rust and leaf-spot diseases of groundnut

The effect of temperature on the latent periods of rust, late leaf spot and early leaf spot diseases of groundnut caused by Puccinia arachidis, Phaeoisariopsis personata and Cercospora arachidicola. respectively, was studied. The latent periods (LP) of rust, late leaf spot and early leaf spot ranged from 12-49 days, 13-38 days and 13-39 days, respectively, between 12 C and 33 C An equation relating the rate of pathogen development (1/LP) to temperature was fitted using daily mean temperatures to provide three cardinal temperatures: the minimum (7"m,n), optimum (r^pc), and maximum (Tm,,). T^,^ was about I2°C for rust and about 10°C for the two leaf-spot diseases. Top, for all three diseases was close to 25 C. 7"max was Bl'C for early leaf spot, and extrapolated values for late leaf spot and rust were about 35 and 40°C, respectively