Breeding for drought tolerance by integrative design: the case of common bean (Phaseolus vulgaris L.) in Ethiopia

Keywords: Decentralized breeding, drought stress, farmer preference, genetic diversity, participatory variety selection, population structure, quantitative trait loci Drought stress is the most important limitation facing crops now and in the future. This makes improving adaptation to drought stress a major objective of crop breeding. Breeding efforts in common bean developed drought tolerant genotypes but the genetics and preferences of farmers for drought tolerance are largely un-studied. This study assessed genetic, physiological and social aspects of drought tolerance in common bean breeding. More specifically the study was envisioned as developing common bean varieties with increased levels of drought tolerance in farmers’ preferred grain typesfor southern Ethiopia. Multiple approaches that combine laboratory, greenhouse and field level analysis with participatory experimentation deploying tools in the biological and social science arenas were used. The findings demonstrate that farmer use and management of common bean seed and varieties in southern Ethiopia are characterized by varying conditions, varying practices and the dynamics of a changing climate and market. Farmers recognize that climate is changing but only half of them have adapted some of the cropping practices. Marginality of production ecology related with climate change, market dynamics, cropping system and culinary preferences make common bean farming at farmer level a series of moving targets that are problematic for a drought breeding program to hit simultaneously. Moreover, exposure to new variety types influence farmers’ preferences. In addition to this diversity in production environments and variation in farmers’ preferences, the plant’s response to drought stress is complex and diverse. Targeting specific plant responses to target areas is a difficult challenge for common bean breeders as shown by the quantitative trait loci (QTL) analysis. But, this study has generated information for specific qualitative and quantitative targets in the breeding design. These include: 1) farmers’ preferences are not static nor are they consistent across gender, location, individual and co-evolve with exposure; 2) original differences in introduced germplasm from the primary centers of domestication were the base for East African common bean diversity and there are distinct germplasms at national or regional level; 3)the relevance of continued photosynthate accumulation as a trait for common bean drought tolerance; 4) root based QTL can be identified but may not be compatible with yield related traits although their selection can benefit from tightly linked markers; 5) only a few major QTLs with high QTL×E interaction were detected whereas a large proportion of genetic variance remained unexplained by the QTLs for traits related to drought avoidance, photosynthate accumulation and (re)mobilization, highlighting the difficulty in detecting QTL in drought studies in common bean; and 6) exposing farmers to new drought-tolerant variety types makes them aware of drought selection traits and creates new market niches for new products. Hence, more drought-tolerant common bean genotypes for a range of farmer conditions, markets and preferences can only be developed on the basis of an integrated understanding of farmers’ production conditions, existing seed system practices and different physiological processes that regulate drought tolerance in the plant. In general, the results from the present work contribute to integrative breeding strategies that incorporate participatory, physiology and marker-aided selection to breed new varieties of drought-tolerant common bean that combine a range of mechanisms in farmers’ preferred grain types.

Bibliographic Details

Main Author:	Asfaw, A.
Other Authors:	Struik, Paul
Format:	Doctoral thesis biblioteca
Language:	English
Subjects:	drought resistance, farming systems research, genetic diversity, phaseolus vulgaris, plant breeding, quantitative trait loci, bedrijfssystemenonderzoek, droogteresistentie, genetische diversiteit, loci voor kwantitatief kenmerk, plantenveredeling,
Online Access:	https://research.wur.nl/en/publications/breeding-for-drought-tolerance-by-integrative-design-the-case-of-
Tags:	Add Tag No Tags, Be the first to tag this record!