Light‐dependent Oospore Germination of Phytophthora cactorum in the Presence of Susceptible Host Plant

Abstract

Oospores of Phytophthora cactorum were produced in cleared V-8 broth supplemented with 30 mg/l b-sitosterol in the dark at 20-22°C for 2-3 months. Environmental conditions during oospore formation or maturation such as light, low temperature and also ageing could not compensate the light requirement for oospore germination. Dark grown oospores did not infect hypocotyl of susceptible safflower seedlings, an indicator plant for the pathogen, if they were not photoactivated 3-15 days or longer prior to infection. If oospores are the sole source of survival of P. cactorum in soil, then the collar region of the plant would be the main site of infection. Thus any treatment which reduce the chance of oospore germination on the soil surface may support management of this disease.

Phytophthora kernoviae oospore maturity, germination, and infection

“…Continuous light also inhibited oospore formation of the homothallic Phytophthora heveae (Brasier 1969) and a majority of other Phytophthora spp. previously tested (Banihashemi 2004;Harnish 1965;Yu et al 1981). Yu et al (1981) attributed this to inhibition to reduction of hormone production by light in heterothallic species.…”

“…require light for oospore germination. Banihashemi (2004) noted that Phytophthora cactorum needs a minimum exposure to light for photoactivation of mature oospores. Chang & Shu (1988) observed that the homothallic species, P. cactorum and P. heveae did not germinate in the dark after 3 d. However, Jimenez & Lockwood (1982) and Sneh et al (1981) observed that Phytophthora megasperma f.sp.…”

Formation and Pathogenicity Variation of Oospores of Phytophthora capsici Infecting Black Pepper

“…Observation by Banihashemi (2004) proved that P. cactorum needed dark conditions during the formation and maturation of oospores. The germination would then occur if incubated under continuous fluorescent illumination, but would not occur without the exposure to light.…”

“…Germinating oospores formed germ tubes that would develop into hyphae and mycelia or sporangia which would in turn form zoospores. According to Banihashemi (2004), oospore germination is determined by the level of maturity of oospores as the internal factor, and an external factor such as exposure to light, whose duration depended on the species of Phytophthora.…”