Effect Of Environmental Factors On The Development Of Rice False

Rice false smut is a worldwide fungal disease caused by Ustilaginoidea virens. It was firstly reported in India in1878. After that, this disease was reported in most major rice production areas in the world. Recently, rice false smut became a serious disease in Asian, Europe, Africa and South America, especially in India, Philippines, Japan and China. The disease not only decrease the yield and quality of rice, its ustiloxins also cause poisoning to human beings and animals. However, studies about rice false smut are still limited. In the present study, the effect of environmental factors on the development of false smut was evaluated under investigation of its natural occurrence and artificial inoculation.1. Arrangement of trial plots. Experiment fields were selected in the areas where the rice false smut is frequently occurred. Three treatments at three levels were adopted, i.e. cultivating densities (low, normal and high), the low cultivating densities is half of normal. But the high cultivating densities is1.5times than normal; nitrogen fertilizer levels (low, normal and high) the three different fertilizer levels are8kg/arce,15kg/acre and25kg/arce; dates of seeding (1-week early, normal and1-week late). Based on the natural occurrence, the development of rice false smut was investigated. Results showed the incidence of three dates of seed are8.15%,5.93%,2.1%; the incidence of three cultivating densities are5.28%,6.26%,4.64%; and the incidence of three fertilizer levels are6.14%,6.04%,4.00%. So the increase of cultivating density and nitrogen application at the early stage (tillering stage) did not enhance the development of the false smut disease. However, the date of seeding significantly influenced the development of this disease.2. Monitoring the meterological factors in the experimental fields. The different dates of seeding resulted in different heading stages of rice which are very crucial for the development of false smut. In order to elucidate the suitable environmental conditions, the meterological factors were site-specifically monitored. By consideration of incidence of disease on rice from different dates of seeding with corresponding meterological factors especially temperature and relative humidity, it was found that the temperature and relative humidity at rice heading stage were very important for the development of rice false smut. The temperature at20-30℃and the relative humidity over80%is suitable for the disease development, raining during the heading stage could increase severity of this disease.3. Inoculation condition experiments. Conidia and hypha suspension were used to inoculate the three different dates of seeding rice at the booting stage. Meanwhile, the meterological factors were recorded. The relation between the disease development and corresponding meterological factors, i.e. temperature and relative humidity was consistent with the observation under natural occurrence. Then the rice cultivar Wanxian98, one of the most sensitive cultivars to false smut was inoculated with different strains under the controlled conditions in greenhouse, temperature at27℃and the relative humidity over80%, Result showed that the rate of diseased panicles was above80%, indicating good development of false smut. Therefore, temperature between25～30℃and relative humidity over80%is very important for rice false smut development.