Foliar resistance toPhytophthora infestans (Mont.) de Bary (US-8) in 13 Mexican and South AmericanSolarium species having EBNs of 1, 2, and 4 and implications for breeding |
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| Authors: | David C Zlesak Christian A Thill |
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| Institution: | 1. Department of Horticultural Science, University of Minnesota, 305 Alderman Hall, 1970 Folwell Avenue, 55108, St. Paul, MN
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| Abstract: | The recent US-8 clonal lineage ofPhytophthora infestans, the pathogen causing late blight (LB) disease, is one of the most widespread and difficult to control. Sources of foliar resistance to US-8 were evaluated in 1927 seedling genotypes by sampling 49 plant introductions (PIs) representing 13 Mexican and South AmericanSolanum species having an Endosperm Balance Number (EBN) of 1, 2, or 4, and one species with an unknown EBN. Species evaluated were 2x(1EBN)S. bulbocastanum, S. cardiophyllum, S. commersonii, S. pinnatisectum, andS. trifidum; 2x(2EBN)S. berthaultii, S. megistacrolobum, S. microdontum, andS. verrucosum; 4x(2EBN)S. fendleri andS. stoloniferum; 6x(4EBN)S. guerreroense;2x unknown EBNS. polyadenium; as well as4x S. tuberosum families as controls. Foliar resistance in the field was monitored in 1998 and 1999. Resistance differed relative to species geographic origin, EBN, species themselves, PIs within a species, and genotypes within a PI. In 1998 Mexican germplasm had a lower area under the disease progress curve (AUDPC, 1140) and greater resistance than South American germplasm (1601), while the 1EBN (1119) and unknown EBN (1075) species had greater resistance than 2EBN (1470) and 4EBN (1888) species. AUDPC ranged among species from 555 (S. cardiophyllum) to 1932 (S. megistacrolobum) and among PIs within a species most widely forS. bulbocastanum (267–1007) and least widely forS.polyadenium (1019–1179). In 1999 LB symptoms were not observed on the species before an early freeze; however, all 1999S. tuberosum families showed LB symptoms and segregated for resistance, pointing to greater resistance in the species than in cultivated germplasm. Resistance found in diploid 2EBN germplasm is more accessible due to greater crossability with cultivated germplasm; however, though more difficult to introgress, resistance found in some of the more reproductively isolated 1EBN germplasm is worth pursuing. |
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