Ecophysiology of Alternaria alternata Causing Diseases in Litchi (Litchi chinensis)

Abstract

Alternaria alternata (Fr.) Keissl. is an important pathogen of litchi (Litchi chinensis Sonn.) that causes blight of leaf, panicle and fruits. Ecophysiological determinants favouring growth and sporulation are keys to understand the pathogen behaviour. Therefore, studies were conducted to assess the effect of different medium, carbon source, pH, temperature, relative humidity and exposure to UV radiation on growth and sporulation of A. alternata under in vitro conditions. Results showed that the maximum mycelia growth rate was on Host Leaf Extract Dextrose Agar but sporulation was the maximum on Potato Dextrose Agar medium. The mycelia growth was more with dextrose as carbon source but the maximum dry weight was recorded in maltose amended medium. Optimum pH for mycelia growth was 6.0, and below or above this pH, mycelia growth was slow. It was evident that the maximum mycelia growth rate and germination of conidia were at 30 °C. The thermal death point of A. alternata was found to be 45 °C with 10 min. exposure. The maximum mean growth rate and germination percent was recorded at 100% relative humidity. The growth rate decreased with increasing exposure time to UV‑B rays up to 20 min, but at exposure time 25 and 30 min, colony changed to profuse mycelia growth with smaller sporulating zone in the centre compared to untreated dishes. The findings of the study will be helpful in understanding epidemiology and devising management strategies of this disease.