Evaluation the Population of Citrus Root Nematode (Tylenchulus semipenetrans Cobb, 1913) and semi fungus Phytophthora nicotianae (Breda de Hann, 1896) in Healthy and Declining Citrus Trees in South of Kerman Provine

Citrus production is very important in term of economical and productivity in south of Kerman province, Iran. During recent years, occuring a new decline disease caused sever threat in citrus orchards in south part of Iran. The disease symptoms starting with significant growth retardation of infected plants. Sever  root rot can be seen easily on infected trees. In this research, the partial distribution of citrus declining disease, the population of citrus root nematode (Tylenchulus semipenetrans) and Phytophthora nicotiana were counted in bouth healthy and infected trees. The partial distribution of citrus decline was 76 percent. The results showed that the investigated samples were infected to citrus root nematode moderate to sever level. The mean of female nematode population per gram root of infected and healthy plant reported 210 and 11 respectively. The mean of 2nd larva populations per 200cm3 soil samples of infected and healthy plants were calculated 2573 and 183 respectively. The numbers of propogules of P. nicotiana in one gram soil rhizosphere of infected and healthy trees reported 13.5 and four respectively. Inoculations of bakraee seedling (rootstock) with nematode and Phyophthora showed sever root rot and nematode infection and finally death of plants. Based on the results of this research, a complex of Phytophthora and citrus nematode are involved in citrus decline disease and can affect the disease severity in south of Kerman.