The role of root growth traits in resistance to the biotic stress, fusarium root rot and the abiotic stress, low soil phosphorus in common bean (Phaseolus vulgaris L.).

摘要

Genetic and environmental variability for root architecture has been identified in common bean. The overall objective of this research was to determine if root architecture traits are an adaptation against an abiotic and a biotic stress. The stresses compared in this study were the fungal disease. Fusarium root rot caused by Fusarium solani f.sp. phaseoli (Fsp) and phosphorus deficient soils, both significantly reduce yield in major bean production regions.;Fusarium root rot is greatly influenced by environmental conditions that stress plant roots, which has hindered progress in breeding resistant bean cultivars. The first objective was to determine if Fusarium root rot resistance is conferred by genes expressed in the root or shoot and if root architecture plays a role in resistance. Reciprocal grafting of a resistant (FR266) and susceptible (Montcalm) bean cultivar was used to study resistance to Fsp in two root growth environments, one without additional stress (Experiment 1) and one with the additional stress of a compacted soil layer (Experiment 2). Reciprocal grafting revealed that root rot incidence was controlled by genes expressed only in the roots in Experiment 1. Variability for root architecture was present, but it did not affect root rot incidence. In Experiment 2, root and shoot genotype both dictated root rot incidence and root traits including root length and root dry weight appeared to be related to root rot incidence.;Root architecture traits have been shown to be related to P uptake and influence tolerance to low P soils. The second objective was to study the relationship between root architecture and P uptake in an Andean recombinant inbred line (RIL) population developed from a cross between a low P tolerant (G19833) and susceptible (AND696) bean line. The RILs also varied in plant growth habit and this was examined in relation to root architecture and yield. The population was field-grown under both high and low P levels and root architecture traits, P uptake and seed yield were measured. A linkage map was developed and a QTL study was conducted to determine which regions of the genome controlled these traits. Two QTL for root length density were identified that explained nearly 40% of the phenotypic variation, but root traits were not important for low P tolerance as measured by P uptake and seed yield. Growth habit influenced yield differently across soil treatments and indeterminate RILs had higher root length density than determinate RILs in the high P treatment.;The third objective was to examine the relationship between tolerance to low P soil and seed P, Fe, and Zn levels and identify QTL controlling these traits in the population. Iron and Zn are important to human nutrition and interact with P stored as phytic acid. Variability for seed Fe and Zn levels related to seed P was detected and QTL for these traits co-localized to linkage group B01 near the region of the gene that controls determinate plant growth habit.