ISOZYME DIVERSITY IN PHYTOPHTHORA-PALMIVORA - EVIDENCE FOR A SOUTHEAST-ASIAN CENTER OF ORIGIN

Isozyme and morphological data were obtained for 93 isolates of P. pal mivora and six described as P. arecae. Sporangial shape for both speci es ranged from spherical to ellipsoid with a high percentage of sporan gia predominantly ellipsoid with a broad base and a short occluded ped icel less than 5 mu m in length. Fourteen enzymes stained in starch ge ls yielding 17 putative loci, II of which were monomorphic, the remain der being polymorphic (GPI, HEX2, IDH1, MDH1, PEP and SOD). Phosphoglu cose isomerase (GPI) and isocitric dehydrogenase (IDH1) were the most variable loci. Isozyme analysis of the 99 isolates revealed 18 electro phoretic types (ETs). Isolates of P. arecae clustered with P. palmivor a in ET7 and ET8, the most common ETs found in P. palmivora. Considera ble genetic diversity was found amongst P. palmivora isolates from coc onut (Cocos nucifera) with 8 ETs, durian (Durio zibethinus) with 5 ETs and other non-cacao hosts from Indonesia, Malaysia Philippines and Th ailand. Since coconut and durian are indigenous to the region, a south east Asian origin for P. palmivora seems probable. Finally, since no s ignificant differences were found in either morphology or isozymes bet ween isolates of P. palmivora and P. arecae, this study provides defin itive evidence that the two species are conspecific.