Lebeda, Ales*; Petrželová,  I; Maryška , Z.  Comparative analysis of variation and dynamics of virulence of Bremia lactucae populations on Lactuca sativa and Lactuca serriola. In: International Meeting on "Population and Evolutionary Biology of Fungal Symbionts", Ascona, Switzerland, 2007. AB-27. Click here to download the presentation on pdf format.

Bremia lactucae Regel is highly variable and worldwide distributed oomycete pathogen which attacks cultivated lettuce (Lactuca sativa) and many other species from the family Asteraceae (Lebeda et al., 2002). There is only limited information about recent distribution, variation and dynamics of virulence in B. lactucae populations (Lebeda and Zinkernagel, 2003; Lebeda and Petrželová, 2004; Petrželová and Lebeda, 2004). The present paper brings more information about this topic, including comparative study of wild- and crop-pathosystem and possible pathogen and gene flow between both pathosystems.

Populations of B. lactucae occurring on L. sativa and L. serriola in the Czech Republic were studied during period 1998-2005. The aim was to determine variation in virulence in populations of B. lactucae, catch its temporal and spatial dynamics, and compare pathogen populations in crop (L. sativa) and wild (L. serriola) pathosystem. Isolates obtained from naturally infected Lactuca spp. plants were used for virulence analysis. Totally 86 isolates were collected from L. sativa and 253 isolates from L. serriola. Virulence of isolates was examined by screening on differential set of 56 L. sativa and L. serriola genotypes with well characterized resistance background (Dm-genes or R-factors) and allowing determination of 32 virulence factors (v-factors).

Both in crop and wild pathosystem broad variation of virulence of B. lactucae was recorded. However, the virulence structure and v-phenotype composition of pathogen populations in both pathosystems differed considerably. Isolates originating from cultivated lettuce displayed mostly highly complex response to L. sativa differentials (v-factors v1-v14, v16 and partially also v18, v36, v38), while isolates from L. serriola were virulent mostly on L. serriola and/or L. sativa differentials with resistance derived from L. serriola (e.g. v5/8, 7, 11, 15, 16, 17 and 23-30). Only occassionaly, isolates with combined response were recorded.

Totally 73 different v-phenotypes were determined in wild populations of B. lactucae (occurring on L. serriola) during the studied period. However, the v-phenotype composition was changing from year to year. Each year a large diversity of v-phenotypes was recorded, but only with a few prevailing ones. The results demonstrated that numerous v-phenotypes may persist in the pathogen populations and they were recorded in several successive years. However, the frequency of their occurrence fluctuated among years.

Large diversity of v-phenotypes was recorded also in populations of B. lactucae on L. sativa. However, most of the v-phenotypes were unique and did not appear repeatedly in other populations or in subsequent years. In 1999 was recorded extremely high variation in virulence even among isolates originating from one locality (Petrželová and Lebeda, 2000). Nevertheless, the numbers of isolates obtained from L. sativa in individual years are not so high to make any general conclusions about the pathogen populations. However, the results of analysis are giving clear evidence about some shift in virulence structure (e.g. increasing frequency of occurrence of isolates and v-factors overcoming newly introduced r-factor R36 (derived from L. saligna) and R38 (from L. serriola) during the studied period).

*Institution: Palacký University in Olomouc, Faculty of Science, Department of Botany, Šlechtitelů 11, 783 71 Olomouc, Czech Republic

E-mail: lebeda@upol.cz

Acknowledgements: This research was supported by grants: MSM 6198959215 (Ministry of Education, Youth and Sports of the Czech Republic); QD 1357 and  „National Programme of Genepool Conservation of Microorganisms and Small Animals of Economic Importance“ (Ministry of Agriculture of the Czech Republic).