Foliar Resistance to Phytophthora infestans (Mont.) de Bary (US-8) in 13 Mexican and South American Solanum Species Having EBNs of 1, 2, and 4 and Implications for Breeding
Zlesak. D. C Thill. C. A
American Journal of Potato Research ; 2004 [Vol.81] Pages:421-429
Abstract
The recent US-8 clonal lineage of Phytophthora 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 American Solanum species having an Endosperm Balance Number (EBN) of 1, 2, or 4, and one species with an mtknown EBN. Species evaluated were 2x(1EBN) S. bulbocastanum, S. cardiophyUum, S. commersonii, S. pinnatisectum, and S. trifidum; 2x(2EBN) S. berthaultii, S. megistacrolobum, S. microdontum, and S. verrucosum; 4x(2EBN) S. fendleri and S. stolon~erum; 6x(4EBN) S. guerreroense; 2x unknown EBN S. polyadenium; as well as 4x 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 EBN (1888) species. AUDPC ranged among species from 555 (S. cardiophyllum) to 1932 (S. megistacrolobum) and among PIs within a species most widely for S. bulbocastanum (267-1007) and least widely for S. polyadenium (1019-1179). In 1999 LB symptoms were not observed on the species before an early freeze; however, all 1999 S. 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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