Distribution of mating types, metalaxyl sensitivity and virulence races of Phytophthora infestans in Estonia

E. Runno-Paurson*, R. Kiiker, A. Aav, M. Hansen and I.H. Williams

Estonian University of Life Sciences, Institute of Agricultural and Environmental
Sciences, Department of Plant Protection, Kreutzwaldi 1, EE51014 Tartu, Estonia
*Correspondence: eve.runno-paurson@emu.ee

Abstract:

Potato late blight, caused by the oomycete Phytophthora infestans, is a destructive potato disease, causing considerable crop loss worldwide. As the late blight pathogen population is diverse and variable in Estonia, changes in the population should be monitored regularly. In this study, the Estonian population of P. infestans was characterised with mating type, sensitivity to metalaxyl and virulence on potato R-gene differentials. During the growing season 2013, 110 isolates were collected from nine potato fields. The frequency of A2 mating type was on average 29%, and varied significantly between different fields from 7% to 78% (p = 0.001). On all studied potato fields, both mating types were recorded, suggesting continuous sexual reproduction of P. infestans and possible risk of oospore production and early attacks of late blight in Estonian potato fields. The prevalence of metalaxyl sensitive isolates in the population (64%) differed from results from previous research. Thus changes have occurred in the P. infestans Estonian population. There were no significant differences in metalaxyl sensitivity between studied fields (p = 0.073). The Estonian race structure was highly diverse and complex, on average 7.2 virulence factors per isolate, but varied between fields from 5.6 to 9.0. 42 virulence races were found; the four most common were 1.2.3.4.5.6.7.8.10.11, 1.2.3.4.6.7.8.10.11, 1.2.3.4.7.10.11 and 1.2.3.4.7.8.10.11, which comprised 46% of the population. The overall normalized Shannon’s diversity index was 0.69, confirming the high diversity of the population. Continuous pathogen population studies describing the contemporary P. infestans population are essential in order to advise potato breeders and growers accordingly.

Key words:

mating type, metalaxyl, Phytophthora infestans, population variation, potato late blight, virulence testing.

NegFry – DSS for the chemical control of potato late blight – results of validation trails in Tartu

V. Eremeev, A. Lõhmus and J. Jõudu

Institute of Agricultural and Environmental Science (IAES), Estonian University of LifeScience, Kreutzwaldi St. 64, EE51014 Tartu, Estonia; e-mail: Viacheslav.Eremeev@emu.ee

Abstract:

Potato late blight, caused by the oomycete fungus Phytophthora infestans (Mont.) de Bary is the most destructive disease affecting the potato worldwide. For controlling the disease, most manuals recommend that growers apply fungicides at regular intervals of 8–10 days from the time of row closing until the end of the growing season. The NegFry model was used for timing the chemical control of potato late blight. The NegFry model is based on two existing models, the ‘negative prognosis’, for forecasting the risk of primary attacks, and a model for timing subsequent fungicide applications during the season. The main objective of NegFry is to get high yield and quality with minimum use of fungicides.Present work underscores that NegFry has given a positive result by timing the firstspraying for anticipation of the infection and by optimizing the number of treatments for late blight control.

Key words: