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.

The question of metalaxyl resistance on late blight fungus in Estonia

E. Runno and M. Koppel

Jõgeva Plant Breeding Institute, Aamisepa St. 1, 48309 Jõgeva alevik, Estonia(Phone:+3727762790; Fax: +3727766902; E-mail: Eve.Runno@jpbi.ee)

Abstract:

Metalaxyl containing fungicides are commonly used by Estonian potato growers because of their efficiency in control of potato late blight. Metalaxyl-resistant isolates have become an important part of the Estonian population of Phytophtora infestans. The aim of the current study was to measure the frequency of metalaxyl resistance among the Estonian population of Phytophtora infestans and to test the efficacy of metalaxyl-based fungicides in controlling potato late blight. 138 isolates of Phytophtora infestans were collected from conventional, experimental and small scale growers’ fields in different parts of Estonia in 2003-2005 and were assessed for resistance to metalaxyl. Metalaxyl-resistant, intermediate and sensitive isolates were recorded at frequencies of 37.1, 45.4 and 15.1%, respectively. There were differences in frequency of metalaxyl resistance between different locations, years and different types of potato cultivations. Metalaxyl-resistant isolates were predominant (66.7%) on conventional potato fields in 2004 and 2005. Metalaxyl- resistant strains were not detected among isolates collected from the field where fungicide containing metalaxyl was not used. The increased frequency of metalaxyl-resistant isolates was detected in 2003-2005. Trials of late blight control with fungicides containing metalaxyl were performed in the same period. Metalaxyl showed lowered efficacy only in conditions of extreme late blight pressure in 2004. Therefore metalaxyl could be effectively used for control of potato late blight a maximum of two times during the growing period.

Key words: