Foliar Resistance to Phytophthora palmivora as an Indicator of Pod Resistance in Theobroma cacao

Abstract

Resistance to Phytophthora palmivora was assessed in leaves and pods of 12 diverse cacao genotypes at the penetration and post-penetration stages of infection to determine the relationship of resistance between stages and sites of infection. Penetration resistance was based on the frequency of lesions, whereas lesion size was used as a measure of post-penetration resistance. We observed significant clonal differences for leaf and pod resistance at the two stages of infection. A poor correlation between resistance at the penetration and post-penetration stages in both leaves and pods indicated that these two forms of resistance are independent and governed by different mechanisms. Correlation between resistance of leaves and pods was not significant at the penetration stage, whereas that of post-penetration resistance was positive and significant. This shows that internal or tissue resistance is common between leaf and pod and indicates that leaf resistance at the post-penetration stage of infection could be used to predict pod resistance; however, resistance of leaves at the penetration stage cannot be used to predict penetration resistance in pods. A high positive correlation obtained between attached leaves and pods with their detached counterparts showed that detached organs can be used for the prediction of resistance in attached leaves and pods.