FORMATION OF CHLAMYDOSPORES IN Phytophthora parsiana in vivo AND in vitro AS SURVIVAL PROPAGULES

The formation of chlamydospores of Phytophthora parsiana, a newly described high temperature tolerant pathogen of woody plants, were investigated in culture media and in infected roots of susceptible host plants. Different solid agar media and cleared V-8 juice broth were inoculated with different isolates of P. parsiana and incubated for four days at room temperature before they were transferred to 4°C in the dark. Chlamydospore formation was monitored during twelve months. Infected almond and pistachio roots inoculated with the pathogen under greenhouse conditions were removed from soil, washed thoroughly and incubated within moist sterilized sand in plastic bags at 4°C for twelve months and examined monthly using light microscope. Chlamydospores were observed only on carrot agar two weeks after incubation and after four months in infected pistachio and almond roots . No chlamydospores were produced on other solid media and in CV8 juice during 12 months incubation.The average diameter of chlamydospore in culture and in roots were 29.7 and 32.47μm with wall thickness 1.7 and 2.07 μm, respectively. Frozen culture medium and root containing chlamydospores at 20°C for 72 hours resumed growth after thawing on Phytophthora selective medium. Sterilized non inoculated root segments colonized internally by the pathogen did not resume growth after freezing. The isolates did not produce oospores in single or dual cultures with P. capsici mating types. It is concluded that under natural conditions chlamydospore is a survival propagule of the pathogen.