S14 - Session P4 - Case study of agricultural adaptation for the climate change Impact on crop diseases in Taiwan- integrated management of green onion Phytophthora blight induced by heavy rainfall

Authors: Jinhsing Huang *, Chin-Ya Yuan

Climate change has led to a significant increase in the frequency of extreme weather events. In Taiwan, the frequency of heavy rainfall has significantly increased, and that has caused various diseases of crops; most of them were caused by Phytophthora spp. In recent years, Phytophthora blight of green onion caused by P. nicotianae resulted in severe yield loss after heavy rainfall. The casual pathogens could be roughly differentiated into two strains according to the symptoms they caused- stem rot or leaf blight. The former strain caused severe stem rot but mild leaf blight symptoms; in the contrast, the latter strain caused mild stem rot but severe leaf blight symptoms. The pathogens that survived in field soil or in the seedlings were the major inoculum sources for the disease occurrence. In the artificial inoculation tests of potted green onion, high temperature ( > 24 C), shading (for more than 1 day), waterlogging, and high humidity would be helpful for disease development. Several fungicides and low-risk materials with control potential had been screened by Petri dishes tests in the laboratory and pot cultivation tests in the greenhouse. Field test results show that the application of neutralized phosphorous acid before the rainy season or/and the precise application of fungicides during the rainy season could significantly reduce the disease severity. Furthermore, applying healthy seedlings plus chemicals usage mentioned above could greatly reduce disease incidence and reduce the yield loss of green onion caused by the disease.