Comparisons of Single-Oospore Isolates of Phytophthora Species from Naturally Infected Cocoa Pods in Brazil

ABSTRACT

Soil, mummified cocoa pods on trees, and pods from husk piles were examined for species of Phytophthora in several experimental cocoa field plots in Brazil. Phytophthora capsici and P. citrophthora were recovered from soil and from husk piles. Compatibility types A1 and A2 of P. capsici were isolated from a single pod. Plerotic oospores of Phytophthora with amphigynous antheridia still attached to the oogonial stalk were found in pods from husk piles. Fifteen percent of the oospores removed from pods germinated. Twenty single-oospore isolates were compared with respect to colony and sporangia morphology, sporangium production, stalk lengths, and compatibility type. Most cultures from germinated oospores resembled P. capsici but some had unique characteristics that included noncaducous sporangia and large (>50 μm in length) sporangia. The majority of single-zoospore isolates from single-oospore cultures were similar to their respective parent cultures. However, some differed with respect to size of sporangia, caducity of sporangia, and compatibility type.

Key Words:

• cocoa
• Phytophthora
• black pod disease