Production of Phytophthora infestans oospores in planta and inoculum potential of in vitro produced oospores under temperate highlands and subtropical plains of India

Abstract

High moisture content of the host tissue (≤ 88%) and low ambient r.h. (50-54%) favoured oospore formation under controlled environments. It took 14-16 days for oospores to develop; thereafter the number of oospores increased with time and decreased with moisture content of host tissue. High ambient r.h. (> 80%) did not favour oospore formation under field or controlled conditions. Oospore formation was detected in inoculated plants grown in the field when the ambient r.h. declined to ≤ 74% and moisture content of host tissue decreased to 83.7-85.6%. It took 8 days (cv. Kufri Chandramukhi) to 13 days (cv. Kufri Jyoti and Kufri Badshah) for oospores to develop. Cultivars also differed in their response to oospore production, cv. Kufri Chandramukhi being more responsive (4800 oospores g -1 f wt) than cv. Kufri Jyoti and Kufri Badshah (1320 and 390 oospores g -1 f wt respectively). Oospores produced in vitro remained viable when buried in soil in the temperate highlands of Himachal Pradesh and sub-tropical plains of Uttar Pradesh, India for more than 150 days, i.e. beginning of the next crop season. The oospores germinated and initiated late blight infection at the base of the stems after 21-30 days of incubation of the potato plants raised in oospore-infested soil. It took 2 days for newly formed oospores to germinate and this delay time increased to 75-77 days after 180-days burial. It took 15 days for their germination (47%) in soil extract as compared to 50 days in sterilised distilled water.

Oospores of Phytphthora infestans in soil provide an important new source of primary inoculum in Finland

“…It is confusing that we did not observe lesions on stem bases, which are typical for oospore-derived infections in Mexico and India (Fernández-Pavia et al 2004, Singh et al 2004. Perhaps the soil temperature during the early stage of potato development is too low in Finland, usually around 10ºC, limiting or reducing oospore germination.…”

Land‐use changes influence the sporulation and survival of Phytophthora agathidicida, a lethal pathogen of New Zealand kauri (Agathis australis)

“…Many abiotic (e.g., temperature, water availability, pH) and biotic (e.g., microbial metabolites, antagonism) factors have been demonstrated to affect sporangia/oospore formation in Phytophthora species (Duniway, ; Schmitthenner & Canaday, ; Weste, ). Further examples such as host resistance (Hanson & Shattock, ), fungicide application (Groves & Ristaino, ), drought conditions (Singh, Gupta, Roy, & Rana, ) and high humidity (Cohen, Farkash, Baider, & Shaw, ), and the variable or contradictory response of sporangia/oospore formation to these stressors results in complex patterns of asexual/sexual reproduction (Duniway, ; Schmitthenner & Canaday, ). Moreover, the importance of these factors varies with Phytophthora species, and even within isolates of the same species (Ribeiro, ), suggesting that a comprehensive assay of P. agathidicida for its response to variations in these environmental factors is required.…”

Phytophthora kernoviae oospore maturity, germination, and infection

“…Oospores were formed and released from the mycelia by following a modified method described by Singh et al (2004). Five 6-mm-diameter plugs of clarified 20 % V8 agar containing mycelia from the edge of an actively growing colony of Phytophthora kernoviae isolates PK-1, PK-2, PK-3, and PK-4 (isolate PK-5 was not available during this test) were transferred to a Petri dish (100 Â 15 mm) containing approximately 20 ml of sterile, clarified 20 % V8 broth.…”