Selection Of Molecular Markers Linked To Potato Horizontal Resistance To Phytophthora Infestans Via Candidate Gene Strategy

Potato (Solarium tuberosum L.) is the fourth among the food crops in the world. Although it has importance to agriculture and industry in both China and the world, the potato is subject to many pests and diseases, among which late blight caused by Phytophthora infestans is most notable. Vertical resistance of potato to P. infestans is nondurable, since new races of the pathogen could occur and soon overcome this monogenic resistance. On the contrary, horizontal resistance controlled by multigenes is race-nonspecific and has become more durable. Horizontal resistance of potato is one of the most important goals in breeding programs. Unfortunately, tetrasomic inheritance of potato and complex interactions among the host genes, the pathogen and environment make it very difficult to evaluate and select potatoes with horizontal resistance.The candidate gene strategy is adopted to identify markers significantly associated with horizontal resistance to P. infestans in a segregation population derived from the B population constructed in the International Potato centre. The main results are as following:1. There were 122 individuals selected randomly from the B population derivals the segregation population for the present research. The leaflets of each clone were inoculated with the mixture of P. infestans races, which exhibited a normal distribution in the population.2. Following the markers mapped previously, those associated with QTLs of late blight resistance and/or proved to possess NBS-LRR structure were selected , together with the selected ESTs related to the horizontal resistance, were taken as the candidate genes for the specific primer design. Up to 38 combinations of the simple PCR primers were screened and 8 markers, BA228d23₉₀, grol-2-P40₅₀₀, NL27₂₅₀, GP23₆₀₀, GP23₁₂₀₀, R×1₃₀₀, GP179₅₇₀, prp1₈₀₀, showed a significant relationship to the resistance by stepwise analysis.3. The specific primers and their nest primers were designed according to the selected EST sequences and those derived from the LM-PCR primer sequences for the TRAP amplification. Among the bands produced, 1-1650, 1-1360, 2-1820, 2-1380, 3-1500, 3-1380, 3-480, 5-1670, 5-1300, 5-1100, 6-820, 7-1180, 7-640, 8-1740, 8-1360, 8-260, 9-420, 14-1360, 14-220, 13-1360, 13-1100 and 13-410 were significantly associated with the resistance.4. Analysis of molecular marker-assistant selection confirmed that the efficiency of selection by multi-markers is higher than that of selection by single marker.5. A high efficiency of candidate gene strategy was demonstrated in this study to identify the markers significantly associated with horizontal resistance of potato to P. infestans.