Chlamydospore formation in ‘ Phytophthora palmivora’ MF4

Abstract

Six of the 29 isolates of ‘P. palmivora’ MF4 examined formed abundant chlamydospores in agar media and/or on mycelial mats submerged in water. Our data revealed the hitherto unreported formation of chlamydospores in the macadamia isolate which was named P. capsici by Kunimoto et al. The mean chlamydospore diam of the six isolates ranged from 27 to 29 μm. Viability of chlamydospores ranged from 92 to 97%, but germination of viable spores was low in most media tested. The postgrowth incubation temperatures greatly affected chlamydospore production, with 15°C being the optimum. Like the majority of the ‘P. palmivora’ MF4 isolates examined, none of the 25 P. capsici isolates tested produced chlamydospores. If ‘P. palmivora’ MF4 is indeed P. capsici as considered by some workers, our data constitute the first report of chlamydospore formation in this species and the species description of P. capsici should be revised. It also suggests that the absence of chlamydospores can no longer be viewed as an important criterion for merging ‘P. palmivora’ MF4 with P. capsici, for positive identification of P. capsici, or for distinguishing it from other morphologically similar species.