Viability of oospores ofPhytophthora infestansunder field conditions in northeastern North America

Abstract

Studies were conducted in potato fields on Prince Edward Island (PE) and New Brunswick (NB) to determine the overwintering viability, germination, and infectivity of oospores of Phytophthora infestans. Oospore viability was determined using plasmolysis (4 M NaCl) and tetrazolium bromide (MTT) tests. After seven months exposure to winter conditions in potato fields, the viability of oospores buried on PE and NB ranged from 2.5 to 13% and from 1 to 28%, respectively, with the plasmolysis test and from 13 to 44% and from 2.5 to 40%, respectively, with the MTT test. In other studies on PE, oospore viability ranged from 5 to 15% 12 months after burial. In laboratory studies, oospores exposed to temperatures of -20 and -50°C for up to 90 days had viabilities greater than 50%, whereas exposure to 0, 4, or 15°C resulted in average viabilities from 23 to 36%. The lowest viability, 22%, was recorded at the highest temperature tested, 36°C. Oospore germination was low, ranging from 6 to 19%. However, this level was sufficient to demonstrate that oospores could be a source of inoculum. A potato soil leachate medium was superior to others for stimulating oospore germination. Oospores of P. infestans present in potato stems and infested farm soil, maintained underground for seven months, were able to infect potato leaf discs in the laboratory. Although all studies were conducted in essentially gnotobiotic conditions, they demonstrate that oospores cannot only survive the winter conditions in northeastern North America but can also germinate and infect new potato tissue in the following growing season. While it would be useful to confirm these findings with new studies under native soil conditions, this is not practical at this time. The presence of oospores also poses a new disease risk that needs to be addressed in future late blight management strategies.Résumé : Des études ont été menées a l'Ile du Prince Édouard (IPE) et au Nouveau-Brunswick (NB), Canada, pour determiner la viabilité hivernale, la germination et Ie pouvoir infectieux d'oospores de Phytophthora infestans. La viabilité des oospores a été déterminée sur la base de deux tests : la plasmolyse dans NaCl 4 M et la coloration au bromure de tetrazolium (MTT). Après sept mois dans des conditions hivernales, la viabilité des oospores enterrées a PIPE et au NB était respectivement de 2,5 a 13% et de 1 a 28% sur la base du test de plasmolyse. Sur la base du test MTT, la viabilité des oospores était respectivement de 13 a 44% et de 2,5 a 40% a 1TPE et au NB. Les oospores enterrées pendant 12 mois a 1TPE avaient une viabilité de 5 a 15%. Les oospores exposées a des temperatures entre -20 et -50°C au laboratoire pour une période allant jusqu'a 90 jours avaient une viabilité supérieure a 50%, alors que celles exposées a 0, 4 ou 15°C avaient une viabilité entre 23 et 36%. La viabilité la plus faible, 22%, a été trouvée parmi les oospores exposées a 36°C. Même si la germination des oospores était faible (6-19%), celles-ci pourraient servir de source initiale d'inoculum. Parm...

Potential of sexual reproduction among host‐adapted populations of Phytophthora infestans sensu lato in Ecuador

“…After 21 days of incubation, oospores and hyphae of each cross were mechanically separated by blending the mycelia in 50 mL sterile deionized water (SDW) for 1 min. One mL 1% lysing enzyme (Sigma, L‐2665, St Louis, MO, USA) was added to 9 mL oospore suspension to eliminate mycelia and remaining sporangia (Medina & Platt, 1999). Samples were incubated at 20°C for 48 h, mixed with an equal volume of freshly prepared 0·5% KMnO 4 solution (Chang & Ko, 1991), and afterwards agitated for 15 min.…”

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

“…Viability was highest in the newly formed, as compared to the buried, oospores declining over time after burial. Pittis & Shattock (1994), Drenth et al (1995), Zarzycka & Sobkowiak (1997), Medina & Platt (1999) and Mayton et al (2000) also recorded adverse effects of burial period on oospore viability. In reported studies, the extent of viability varied from region to region, being 7.8% after 10-months burial in UK (Pittis & Shattock, 1994) and 5-15% after 12 months in Prince Edward Island, Canada (Medina & Platt, 1999).…”

“…It is now well known that the two mating types when inoculated either in equal proportion or in proportions ranging up to 19:1 on host tissue produce oospores in abundance (Frinking et al, 1987;Mosa et al, 1991;Drenth et al, 1995;Cohen et al, 1997;Turkensteen et al, 2000). Recent investigations have shown that P. infestans produces oospores naturally in host tissue where the two mating types are present (Flier & Turkensteen, 1999;Medina & Platt, 1999;Gavino et al, 2000). The present paper describes (i) the role of ambient r.h. and moisture content of host tissue on oospore production, (ii) oospore survival and germination under natural conditions, and (iii) the role of oospores as primary inoculum for late blight in the temperate highlands and sub-tropical plains of India.…”

Pre and Post Harvest Diseases of Potato and Their Management

“…Occurrence of both A 1 and A 2 strains at the same location has also opened up the possibility of development of thick walled oospores which could survive extreme winter (Medina and Platt 1999 ) or summer conditions. The oospores may act as an another source of primary inoculum, in addition to the already known sources such as infected seed tubers, waste heaps and volunteer plants etc.…”