BIODIVERSITY FOR DISEASE RESISTANCE, AND POTENTIAL FOR IN SITU CONSERVATION OF PHASEOLUS VULGARIS LANDRACE MIXTURES IN THE SOUTHERN HIGHLANDS OF TANZANIA
DM TEVERSON1, JD TAYLOR2, CS MUSHI3, SZ BISANDA4 and JM LENNE1
1Natural Resources Institute, Chatham Maritime, Kent ME4 4TB, UK; 2Horticulture Research International, Wellesbourne, Warwick CV35 9EF, UK; 3Selian Agriculture Research Institute, Arusha, Tanzania; 4Ministry of Agriculture Research and Training Institute, Mbeya, Tanzania
Background and objectives
Wild relatives and landraces of crop species have long been recognised as important sources of useful genes for breeding improved crop cuitivars. Concern over the apparent loss of wild plants and landraces has been the driving force behind the conservation of genetic resources. However, comprehensive studies of useful characteristics in such populations are often lacking, and the justification for random collecting and preserving germplasm in ex situ collections is not always clear. The aim of the present study was to dissect and quantify biodiversity in traditional Tanzanian bean (Phaseolus vulgaris) landraces in respect of resistance to the major biotic stress: plant disease.
P. vulgaris is subject to a wide range of diseases caused by bacterial, fungal and viral pathogens. For this study we identified five priority pathogens: angular leaf spot (Phaeoisariopsis griseola), anthracnose (Colletotrichum lindemuthianum), common bacterial blight (Xanthomonas campestris pv. phaseoli), halo blight (Pseudomonas syringae pv. phaseolicola), and bean common mosaic virus (BCMV), all of which are widely distributed throughout the bean-growing areas of Africa and worldwide. A common feature of these pathogens is the existence of races/strains, which show pathogenic variation in respect of the host species and cultivars they attack. The existence of races (pathogenic variants) is a major limiting factor in breeding for resistance.
Since African bean landraces survive despite the 'massed ranks' of pathogens and all their variants, and without pesticide inputs, the prime objective of this study was to examine landrace diversity for disease resistance and to address the questions: do landraces represent unique collections of resistance genes (lacking in most modern cultivars) and if so, is a greater effort to conserve landraces necessary and how might this be achieved?
Results and conclusions