IDENTIFICATION OF VIRUS OF VIRUS-LIKE AGENTS CARRIED BY CITRUS PLANTS FROM DIFFERENT SOURCES IN CHINA

332 multisymptomatic or symptomless citrus samples, collected from 9 provinces,i.e. Fujian,Guangdong, Guangxi,Hainan,Zhejiang,Hunan,Yunnan, Sichuan and Guizhou, were identified for virus or virus-like agents with the help of indicator plants, electron microscopy and indirect-ELlSA.In the field conditions, citrus trees show symptoms such as green-withering or dwarfing of a whole plant, chlorotic yellow spots, mottling, uniform yellowing or nutrition-deficiency yellowing on lea-res, leaf rolling, boat-shaped or samller leaves, yellowing and corking of vein, pitting and grooving of xylem. (with a disease index of 6.7-71.1),scabious spots and tumorous proliferation of stem or trunk,"red-nose" fruit, irregular flowering, distorted flower or fruit, bark shelling of rootstock and separated bud-union, etc.The results of the identification indicate that at least 4 kinds of virus or virus-like diseases, namely, tatter leaf-citran gestunt, tris-teza, "Huanglongbin"(CYS) and exocortis,have occurred in citrus Orchards in China. In Fujian and Guangdong, tangerine cvs., Fuju, Bainianju, mandarin cvs.,Tankan,Ponkan,Sweet orange cv., Xinhui orange and Meyer lemon have been infected by TL-CSV that show chlorotic yellow spots, leaf rolling, separated budunion or show no visible symptoms The agent probably contains two components, 1. 700-850?6-15 nm infecting cowpea (Vigna sinensis (Tomer, Savi, and 2. 400-500?6-10 nm, uninfective, CTy, consisting of two strains, i. e. stem pitting strain and seedling yellow strain, has had a widespread distribution in citrus producing areas in China and grooving of xylem,yellowing and corking of vein or shows no visible symptoms on terminal branches. It usually attacks citrus trees in the existence of TL-CSV, CYS and CEV on the infected plants, but its agent can be filtered away gradually by incubation on trifoliate orange (Poncirus trifoliata (L.) Raf.) seedlings. In Fujian, 1.9-28.8% of mothet trees of a disease-free foundatioe garden have been reinfected by CTV. It has been proven rather reliable to diagnose "Huanglongbin" according to the mottling symptom in the field. A single inoculation method of sap-rub has been unsuitable for CEV detection on herbaceous indicators. The primary data imply that dwarfing and green-withering of Satsuma in Fujian and Hunan are uninfective.An approach to produce disease-free seedling in the future has been discussed in the paper.