Low phosphorus (P) stress limits soybean production. A population of 152 recombinant inbred lines (RILs) derived from a cross between ÔBogaoÕ (P sensitive variety) and ÔNannong 94-156Õ (P tolerant variety) and 248 markers were used to map quantitative trait loci (QTLs) for low-P tolerance. Two pot culture trials were conducted and low-P tolerance evaluated using flower and pod abscission rate under low P and normal P. Conditional QTLs and epistasis for tolerance to low P were also analysed. A conditional QTL (near Satt274) on linkage group D1b+W was identified which conferred low-P tolerance epistatic effects and coincided with previously discovered QTLs. An additive QTL, qFARLPG-07, for flower abscission rate under low P was detected with a LOD score of 7.79 and explained 32.3% of phenotypic variation. It was detected at the same interval of the corresponding QTL for other traits across years. This region coincided with two conditional QTLs (cqFARLPG-07 and cqPARLPG-07), from the P-tolerant parent ÔNannong 94-156Õ related to low-P tolerance. These results will provide a basis for further fine mapping and eventual cloning of the P-efficiency genes in soybean.

Chlorophyll variation mutants are important materials for studying chlorophyll metabolism, photosynthesis, chloroplast biogenesis and related physiological processes. In this study, a chlorophyll-deficient soybean mutant (cd1) was isolated by screening M 2 progenies of cultivar ÔNannong 86-4Õ treated with 0.4% ethyl methanesulfonate. cd1 displayed yellow-green leaves from seedling stage V1 to fully flowering stage R2, abnormal chloroplasts, lower total chlorophyll content (30-66% reduction), lower plant height and lower seed yield compared to its wild-type control. Genetic analysis demonstrated that the visible yellow-green trait was controlled by a single recessive nuclear gene. Subsequently, the cd1-mutant gene was mapped at a 6.9-cM interval on chromosome 10, flanked by two simple sequence repeat markers Satt633 and Sat_291. These results provide us with the opportunity to study a novel gene regulating chlorophyll synthesis.