Pathogenic Diversity in and Sources of Resistance to Uromyces appendiculatusin Southern Africa

摘要

The reaction of the first (1983) common bean internationaldifferential set and other germplasm to 248 singlepustule isolates of the rust fungus Uromycesappendiculatus, collected from various southern Africancountries, was evaluated. Eleven of the mostimportant isolates were re-purified and re-inoculated,this time also on the second (2002) revised and smallerinternational differential set. The 248 isolatescould be grouped into 44 race-groups. These weresubjected to principal coordinates analysis (PCoA).A second PCoA was carried out using 25 of the mostimportant of the 44, together with 34 African racesreported by previous authors. Isolates were generallyavirulent on accessions with the resistance genesUr-3+, -5 or -11, as well as Compuesto Negro Chimaltenango(CNC) and A 286, all small seeded, andthe most useful sources were accessions carrying bothUr-3 and Ur-11, for instance BelMiNeb-RMR-7,BelDakMi-RMR-14 and -18. Isolates were generallyvirulent on large seeded accessions (with, among othersUr-4, -6 or -9), reflecting the preference for largeseeded beans in southern Africa and co-evolution ofhost and pathogen. No large seeded accessionsshowed broad resistance. The least susceptible wasPlant Introduction 260418, which rated resistant tomoderately susceptible to the 11 races. These observationswere confirmed by field ratings on the sameaccessions over multiple seasons. According to thePCoA, which proved useful for the identification ofdifferentiating accessions, southern African isolatesfell into three main clusters, for which Redlands Pioneerand the South Africa cultivar Teebus were themost discriminating differentials. Other accessionsthat showed particularly useful differentiating abilitywere Olathe and 51051. Of these, only Redlands Pioneerhas been included in the 2002 differential set.The PCoA grouping of the African races was similarto that of the southern African race-groups.