Distribution of race-specific resistance against Bremia lactucae in natural populations of Lactuca serriola

Abstract

A metapopulation approach was applied to population studies of a common weed, Lactuca serriola (prickly lettuce). Seedlings grown from seed samples collected from 752 individual L. serriola plants in 50 populations occurring along an east-to-west transect across four European countries (Czech Republic, Germany, Netherlands and United Kingdom) were screened for resistance to 10 common races of Bremia lactucae. Based on the recorded reaction patterns, host individuals were characterized into specific resistance (R-) phenotypes. Diversity of R-phenotypes, their variation and distribution among and within European populations, was evaluated at different spatial scales, i.e. from a metapopulation involving the entire European study area to individual plants occurring in local populations. Generally, European populations of L. serriola have been shown to be highly susceptible to B. lactucae. However, large variation in L. serriola resistance was found both among and within individual countries. There was a clear gradient of increasing uniformity of race-specificity moving from central to western Europe, as well as a slight decrease in the diversity of R-phenotypes. Populations in the United Kingdom were the most divergent in terms of resistance structure from other geographic regions, and also were the most homogeneous, most likely a consequence of the relatively greater degree of spatial isolation from other regions. Metapopulation, interand intra-population variation in host resistance is discussed from the viewpoint of occurrence of racespecific interactions in this wild plant pathosystem.

Morphological variability of achenes of some European populations of Lactuca serriola L.

“…Population genetic analysis by D' Andrea et al (2009) revealed that the British populations were mainly dominated by one single genotype. This also strongly supports data about variability of European L. serriola populations expressed by AFLP (Lebeda et al, 2009b) and the distribution of race-specific resistance to Bremia lactucae (Lebeda and Petrželová, 2007;Lebeda et al, 2008;Petrželová and Lebeda, 2011). In relation to the studied countries, achenes from inland (Czech and German populations) create one homological group, which is identified by shorter beaks than achenes from the Dutch and United Kingdom populations (Table 7c and Fig.…”

Distribution of downy mildew (Bremia lactucaeRegel) resistances in a genebank collection of lettuce and its wild relatives

“…Recently, a study using ten downy mildew isolates against L. serriola sampled from 50 natural populations along a transect stretching from the United Kingdom to the Czech Republic similarly showed an unequal distribution of race-specific resistances among European regions. Diversity in that study increased from west to east, while high disease incidence and high overall resistance were found only in populations from the Czech Republic (Petrželová and Lebeda, 2011). Diversity patterns on downy mildew resistance were in line with the results of molecular studies for L. serriola, revealing increasing levels of diversity from Western to Eastern Europe (Lebeda et al, 2009;van de Wiel et al, 2010).…”

Spatial variation in disease resistance: from molecules to metapopulations

“…The results show large variation both amongst and within individual populations and countries. A clear gradient of increasing uniformity of race-specificity was detected when moving from central to western Europe, as well as a slight decrease in the diversity of resistance phenotypes (Petrzelova & Lebeda 2010). Forty-five resistance phenotypes against B. lactucae were found in 16 L. serriola populations across the Czech Republic.…”