3. Biology of Alternaria
Conidiophores of majority of the species of Alternaria produce asexual spores (conidia) measuring between 160-
200 µm long. Under in vitro conditions, sporulation occurs at a temperature range of 8-24 ºC, where mature spores occur
after 14-24 h. Optimum temperatures are between 16 and 24 ºC where sporulation time ranges from 12 to 14 h. Moisture in
the presence of rain, dew or high humidity are essential for infection and a minimum of 9-18 h are required for majority of
the species (Humperson-Jones and Phelps, 1989). Continuous moisture of 24 h or longer practically guarantees infection
(Rangel, 1945; Chupp and Sherf, 1960). Relative humidity of 91.5% (at 20 ºC) or higher will result in the production of large
numbers of mature spores in 24 h (Humpherson-Jones and Phelps, 1989)