Survey of Wild Actinidia Species in the Jinggang Mountains of China and Identification of Associated Bacteria

Y Bacterial canker caused by a virulent strain of Pseudomonas syringae pv. actinidiae (Psa biovar 3) has a significant impact on kiwifruit vine health and results in loss of production worldwide. Psa was first recorded in China in 1986 in commercial crops of Actinidia deliciosa in Hunan province. From 2008, outbreaks of Psa in Italy and New Zealand have been devastating for Actinidia chinensis cultivars, which are generally more susceptible to the disease than those of A. deliciosa. Kiwifruit germplasm varies in its susceptibility to Psa, with some showing an apparent tolerance to the disease. Identification of resistant cultivars in breeding programmes is an important strategy for disease control. There is little knowledge of the importance of wild repositories of kiwifruit species and the possibility of endemic Psa. The objective of this work was to find wild Actinidia species distributed in the large area of the Jinggang mountainous region of Jiangxi province and to isolate and identify bacteria associated with the vines. Many species of Actinidia have been sourced from this area for breeding programmes at the Sichuan Provincial Academy of Natural Resource Science in Chengdu. Twenty-nine vine samples were collected, including A. chinensis, Actinidia eriantha, Actinidia callosa var. henryi and an unknown species, from 406-1414 m above sea level. The GPS position of each vine was noted. Only suspected die-back symptoms of Psa were observed on vines in this survey. Vine tissue from the 29 Actinidia samples was transferred to plates of bacterial medium (KBC). One hundred and thirty isolates were recovered from the wild and 25 isolates from the cultivar 'Hongyang' in eight commercial orchards and purified on plates, and DNA was then extracted for PCR analysis. Neither Psa biovar 3 nor P. syringae pv. actinidifoliorum (Pfm) were detected from Actinidia vines collected in the Jinggang mountain region, whereas Psa biovar 3 was detected in 11 isolates from four 'Hongyang' orchards.