Abstract
A radish variety named Tasaki Mula was used to investigate the effect of climatic factors on the development of Alternaria disease under field conditions. The average data of 2 crop seasons (2004/05-2005/06) revealed that 20-day-old plants transplanted on 20 December showed less number of spots and conidia, and their numbers increased with the age of the plants. The conidia and spot ratio was 290:1-593.10:1 from disease initiation to final assessment in 50-day-old plants. Correlation analysis of the association of the number of conidia landing and numbers of spots per leaf with weather factors at different growth stages revealed that maximum (23.48°C) and minimum (11.14°C) temperatures and sunshine hours (5.00 h) had significant positive correlation, while relative humidity (78.28%) and fog hours (4.39 h) had significant negative correlation with conidia landing and number of spots per leaf in 50-day-old transplanted plants. Total rainfall and number of rainy days had no significant association with conidia landing and number of spots per leaf. Prediction equations were developed for 4 different observations. The R2 values for the association of weather factors with number of conidia landing and number of spots per leaf showed variation of 54-93% and 44-81%, respectively, in radish seed crop infected with Alternaria brassicae. This indicated that some unknown factors might be involved in conidia production and number of spot formation, and some climatic factors played a significant role in disease development.
