Suitability of phenylalanine ammonia lyase and chitinase activities as biochemical markers of soft rot resistance in Actinidia chinensis kiwifruit

Abstract

Cryptosporiopsis actinidiae causes soft rot of the kiwifruit cultivar Hort 16A (Actinidia chinensis). This paper describes measurement of phenylalanine ammonia lyase (PAL) and chitinase, with a view to identifying possible resistance markers to characterise the host/pathogen interaction. Four A. chinensis genotypes were treated pre-harvest with water or C. actinidiae spores. Fruit was stored at 1.5°C for 18 weeks to allow for disease development. Enzyme activities were measured at harvest and after storage in the area around disease lesions and in symptomless tissue. Soft rot incidence was highest in genotype 8A and equal in the other genotypes. Pre-harvest inoculation had no effect on subsequent soft rot incidence. Chitinase activities varied with genotype, and increased significantly during storage, but there was no difference between healthy versus diseased tissue. PAL expression varied with genotype, increased during storage, and was always significantly higher in the tissue around lesions. Neither enzyme measurement was a suitable resistance marker.