PHYTOPHTHORA RESISTANCE IN CACAO (THEOBROMA-CACAO) - INFLUENCE OF PODMORPHOLOGICAL-CHARACTERISTICS

Twelve diverse cacao (Theobroma cacao) genotypes were assessed for pod resistance to Phytophthora palmivora at the penetration and post-pene tration stages of infection using two inoculation methods. Correlation analysis between a number of pod characteristics (stomatal frequency, stomatal pore length, surface wax, thickness of exocarp/endocarp, har dness of exocarp/mesocarp, moisture content) and resistance indicated a strong relationship between resistance to lesion establishment (lesi on frequency) and the joint effect of stomatal frequency and pore leng th. The epidermal impressions of the pod surfaces bearing germinating zoospores of P. palmivora provided evidence that penetration occurs th rough stomata, epidermal hair base, scar and by direct penetration. A poor correlation was obtained between the pod characteristics studied and post-penetration resistance, suggesting that this resistance, asse ssed by lesion size, is not governed by morphological or physical char acteristics of the pod, but probably by biochemical factors. The impor tance of these findings in breeding of cacao for resistance to P. palm ivora is discussed.