STUDIES ON THE OCCURRENCE AND DEVELOPMENT OF POTTED CHULAN TREE LEAE-SPOT DISEASE CAUSED BY APHELENCHOIDES FRAGARIAE

Zhang Yongcun Zhang Xiujun Cheng Hurui Fang Zhongda (Section of Plant Pathology, Nanjing Agricultural University, Nanjing)

Chulan tree (Chtoranthus spicatus), Aphelenchoides fragariae

It was found for the first time during 1984-1985 that in Shexian County of Anhui Province the causal nematode of Chulan leaf-spot disease, Aphelenchoides fragariae, overwintered in Chulan buds, of which most were top buds or first and second axillary buds. Later in Nanjing of Jiangsu Province, it was also discovered that Chulan buds carried nematodes throughout the year, and the highest and lowest rate of top buds carrying nematodes (30% and 6%), together with the highest and lowest average nematode numbers per top bud (16.6 and 3), appeared in December and July, respectively. Since no pathogenic changes were observed stereomicroscopically in most contaminated buds, it was concluded that the buds were most likely the habitat and good overwintering places of the pathogenic organism.Through regular extractions of nematodes from diseased Chulan leaves excised from plants and put outside, it was confirmed that some Aphelenchoides fragariae in diseased leaves on or in soil could overwinter in Nanjing. Artificial inoculation and following staining of Chulan leaves with acid fuchsin in lectophenol made it clear that stomata were the only ways through which the nematode penetrated, and the penetration peak appeared 12 hours after inoculation.Field investigation revealed that only leaves were infected by the nematode, and earlier defoliation was the main cause of decreased flower production of Chulan. The disease was widespread in Nanjing Flowers and Trees Farm whieh grew more than 6000 pots of Chulan, diseased leaves appeared throughout the year and most frequently in March-April.