1.4.32
EXPRESSION OF PATHOGENESIS-RELATED PROTEINS IN RESISTANT AND SUSCEPTIBLE POTATO CULTIVARS AFTER INFECTION WITH PHYTOPHTHORA INFESTANS

D EVERS1 and J DOMMES2

1CRP-CU Cellule CREBS, 162A, avenue de la Faiencerie, L-1511 Luxembourg, Grand Duchy of Luxembourg; 2University of Libge, Laboratory of Plant Molecular Biology, B22-Sart Tilman, B-4000 Liege, Belgium

Background and objectives
Phytophthora infestans is the most important biotic constraint in potato production worldwide. Host-plant resistance is a primary component of integrated control of late blight. Because qualitative resistance, mediated by major R-genes, has not proved durable, quantitative resistance, mediated by minor genes and quantitative trait loci, is of increasing importance. Expanding the sources of late-blight resistance beyond Solanum tuberosum is necessary to use new genes that confer higher levels of durable resistance [1] . Here we describe the use of a population resulting from a cross between a native cultivated potato, Solanum phureja, resistant against P. infestans , and a susceptible S. tuberosum. In the present work, we will study the interaction between P. infestans and the crosses differing in their resistance characteristics. The study will be performed mainly at the RNA level in order to identify genes involved in the defence reaction of the plant. Among the markers to be used are pathogenesis-related proteins and some enzymes involved in the phenylpropanoid metabolism [2].

Materials and methods
The plant material under study results from crosses between a resistant and a susceptible cultivar. It thus consists of contrasting phenotypes and contrasting genotypes. A complex race of the fungus P. infestans is used. The investigations on the RNA level are performed by screening the different cultivars using some probes of pathogenesis-related proteins and some probes from enzymes belonging to the metabolism of phenylpropanoids. Screening is performed in the plants without and with infection by P. infestans. In a second step, we use the differential display technique to identify differentially expressed genes in non-infected plants and in infected plants in the extremes of the population. The induction of systemic acquired resistance is performed using the fungus itself, TNV or elicitors.

Results and conclusions
We will discuss preliminary results on the expression of pathogenesis-related proteins in the different resistant and susceptible cultivars before and after infection by P. infestans.

References
1. Colon LT, Budding DJ, Keizer LCP, Pieters MMJ, 1995. European Journal of Plant Pathology 101, 441-456.
2. Anfoka G, Buchenauer H, 1997. Physiological and Molecular Plant Pathology 50, 85-101.