Components of coconut fruit susceptibility to <em>Phytophthora katsurae</em> (Pythiaceae) in Côte d’Ivoire

Abstract

The present study was to evaluate the susceptibility of coconut fruit to Phytophthora katsurae (Ko and Chang) according to their age and the position of lesions. The infection rates of nuts under natural conditions and by inoculation techniques on wounds and deposition of inoculum on the pericarp were compared. Under natural conditions, immature adult nuts between 8 and 11 months old are the most susceptible stage to infection by P. katsurae. The rounder part is the most receptive site. The proximal part is most liable to attack in young 4-8 months old fruits, which are less numerous in the susceptible host stage. Ripe nuts of at least 12 months old are totally immune to infection. The distal part of all categories of nuts is not invaded by the lesions. There is a highly significant difference between the susceptibility of the proximal zone of young and adult wounded nuts at 1% significance level. A non responsiveness of the distal zone of the young nuts was observed on nuts not wounded. Based on artificial inoculations on fruit of different ages, the resistance mechanism in the fruit seems to be much more physically linked to nut anatomy than chemically.

Keywords: Immature nutfall, field infection, rough and gentle inoculation, success rate, physical penetration