Resistance of kiwifruit cultivars to ceratocystis wilt: An approach considering the genetic diversity and variation in aggressiveness of the pathogen

Kiwifruit (Actinidia spp.) is native to southern China, but was first cultivated in New Zealand and then spread worldwide. Emerging diseases such as ceratocystis wilt have attracted the attention of kiwifruit growers due to the great losses observed in southern Brazil. Effective control can be achieved by screening for resistance, but the genetic variability of the pathogen must be considered. Thus, this study aimed to assess the genetic diversity and variation in aggressiveness of Ceratocystis isolates from kiwifruit in southern Brazil and then evaluate the resistance of kiwifruit cultivars with the most aggressive isolates. A collection of 46 isolates were obtained from southern Brazil and 14 simple‐sequence repeat (SSR) markers was successfully used for genotyping. Out of 14 markers, 13 were polymorphic and identified 26 genotypes. Fourteen distinct genotypes were tested on a susceptible cultivar to select the most aggressive ones. Finally, inoculation with an equal mixture of five of the most aggressive isolates was used to evaluate the resistance of seven kiwifruit cultivars: Red Arguta, Green Arguta, Allison, Chieftain, Hayward, Monty, and Tomury. Cultivars varied in levels of susceptibility, with disease severity ranging from 40% to 100%. Considering the length of stem lesions, Chieftain showed the lowest level of severity at 40%, while no wilt symptoms were observed at 45 days after inoculation. In addition to the seven cultivars, a half‐sibling progeny with 618 plants of the rootstock cv. Bruno was also assessed, but only seven individuals were resistant. These seven plants can be cloned and used as resistant rootstocks in commercial orchards. Populations of Ceratocystis fimbriata on kiwifruit from southern Brazil showed high genetic and physiological diversity. Inoculations using the most aggressive isolates successfully identified resistant kiwifruit cultivars.