Deploying root traits for African bean breeding.

摘要

Common bean is the most important grain legume for direct human consumption in the world. It provides dietary protein and minerals for millions of people in developing countries. Low Phosphorus (P) availability and drought are major constraints to bean production in many productions region in Africa and Latin America. Genotypic adaptation to drought and low soil P availability is associated with phenotypic variation in root architecture. Plants evolved a wide range of adaptations to enhance P and water acquisition from the soil. In this dissertation, we describe the importance of root traits for resource acquisition and the used of root phenotyping and selection as an alternative for improving crop adaption to drought and low P stresses. Chapter 1 presents the general introduction of common bean as a legume crop with emphasis on the importance of root architecture for water and nutrient uptake from the soil, and the genetic basis of some root traits. In Chapter 2 we developed a rapid, simple and inexpensive method for field phenotyping of root phenes of common bean. With this method twelve architectural root phenes from one root crown can be evaluated in two minutes. The field phenotyping method we developed, Shovelomics, should have utility for bean breeding for low P and drought tolerance in developing countries of Africa and Latin America. In chapter 3, we describe a large and diverse genetic variation in root phenes of common bean from Andean and Mesoamerican gene pools. Large variation among genotypes within gene pools, genotypes within race, and genotypes within country of origin were detected. Genotypes with root traits associated with adaptation to low P availability were found in both gene pools, while traits associated with adaptation to drought stress were mostly found in the Mesoamerican gene pool. Our findings indicate that useful root traits for breeding for edaphic stresses were identified in both Andean and Mesoamerican gene pools. In Chapter 4, we worked with root hair traits, and longer and denser root hairs are associated with P efficiency in crops. We found large genetic variation in root hair length from basal roots within bean populations derived from parents contrasting in root hair traits. In addition, we estimated the heritability of root hair length from basal roots using parent-offspring regression analysis, and we found moderately high heritability of root hair length in two populations. This result has implications for strategies used for selection for longer and denser root hairs. The relatively high heritability suggests that considerable progress may be expected from selection for longer root hairs in segregating bean populations. Breeding for longer and denser root hairs could enhance acquisition of P in low P soils in Africa and Latin America. Breeding for multiple root phenes could enhance acquisition of multiple soil resources.