Pathogens identification and resistance evaluation on bacterial canker in Actinidia arguta germplasm

Abstract

Pathogen isolation and identification were performed on Actinidia arguta ‘Longcheng No. 2’ occurring bacterial canker from Liaoning Province, China. The pathogenic bacteria were identified as Pseudomonas syringae pv. actinidiae (Psa) by the analysis of morphology,16S rRNA and gyrB sequence, which were identified as Psa biovar 2 by Psa-specific primer sequence analysis. The pathogenicity tests were carried out with the isolate ‘R12’ and type strain ‘M228’ (biovar 3) as a control; the results showed that the phloem of green stems in A. arguta ‘Kuilv’ could be infect rapidly by R12, and milky mucus flowed from wounds, then the phloem turned black-brown, but it had strong resistance to Psa M228. In order to evaluate the resistance on Psa R12, 54 A. arguta germplasm resources were infected by artificial inoculation of stems, with A. deliciosa cv. ‘Hongyang’ and A. chinensis cv. ‘Xuxiang’, as control plant material, and their resistance levels were classified according to the disease index. The 54 tested materials exhibited differences in resistance to Psa R12, but no immune materials were found. In general, the germplasms were divided into five disease resistance categories, including 2 accessions with high resistance ‘Jianfengkuilv’ and ‘TL20013’, accounted for 3.70% of all the inoculated accessions; there were 11 resistant accessions, 15 tolerant accessions, 21 susceptible accessions, 5 highly susceptible accessions among them, accounted for 20.37%, 27.78%, 38.89% and 9.26%, respectively. In this study, the screening of disease-resistant germplasms could lay a foundation for further research on gene mapping, resistance mechanisms and breeding-resistant varieties of A. arguta to Psa.