Oosporogenesis and chlamydospore formation in Phytophthora capsici

Typescript.Thesis (Ph. D.)--University of Hawaii at Manoa, 1984.Bibliography: leaves [82]-88.Photocopy.Microfilm.viii, 88 leaves, bound ill. 29 cmThe sexuality of Phytophthora capsici was studied in 30 isolates. with cultures from solanaceous and nonsolanaceous hosts. including Leonian's type culture. Of the 30 isolates. 4 belonged to the Al compatibility type, 7 were A2 and 19 were infertile or AO. Fertility varied among the 11 fertile isolates from highly fertile to very low in fertility. Seven of the 11 isolates produced a few oospores in unpaired (solo) cultures. Although P. capsici has been considered a heterothallic species. oospore distribution patterns in pairings between compatible Al and A2 isolates suggested mutual induction of oospore formation. Oogonia and oospores which formed near the A2 colony were smaller than those developing near the Al colony suggesting that the smaller bodies were A2 products and the Jarger bodies were formed by the Al isolate. This was confirmed in pairings physically separated by polycarbonate membranes. Several oosporogenic pathways in P. capsici were distinguished and five categories were suggested for the genus: (1) homothallism sensu stricto. (2) induced homothallism. (3) noninduced homothallism; (4) secondary homothallism and (5) heterothallism. The optimal temperature for oospore formation in darkness was 20-24 C. whereas 31 C was distinctly inhibitory to oospore production. Light inhibition of oospore formation was found to be temperature dependent. Effect of light over the spectrum from 290 to 750 nm was minimal at 16 C, while at 24 C there was pronounced inhibition at 440-470 nm with some inhibition between 500 and 700 nm. Indirect effects of light were discovered in comparisons of several culture media used to study oosporogenesis. Clarified vegetable juice agar, oatmeal agar, and a synthetic medium, inhibited oospore formation when these were exposed to light prior to inoculation with the Al and A2 compatibility types. Rape-malt agar was not affected by light under the present test conditions. Phytophthora capsici produced abundant oospores when Difco Bacto agar was used as the solidifying agent but oospore production was greatly reduced on Seakem HGT(P) agarose, Difco Noble agar or Difco Purified agar. Chlamydospores were found in 20 of 29 isolates of P. capsici using a submerged culture method. Chlamydospores were not produced in the papaya fruit broth method developed for P. palmivora. The ready production of chlamydospores in most of these isolates of P. capsici suggested a need to expand the original description to provide for the presence of chlamydospores in some isolates