Evaluation of genotypes of navy and culinary bean (Phaseolus vulgaris L.) selected for superior growth and nitrogen fixation

Abstract

Levels of nitrogen fixation by navy and culinary beans (Phaseolus vulgaris L.) in Australia are low and contribute little to the N economies of the crops. As a consequence, they must be grown in highly fertile soils or fertilised with N to obtain economic yields. Eliminating the need for fertiliser nitrogen would save growers A$1 million annually. Following a 10-year program in which almost 1500 genotypes of P. vulgaris were screened for superior nodulation and nitrogen fixation, we conducted experiments at the Southedge Research Station, Mareeba, during 1995–97 to identify elite genotype(s), which could either be released as cultivar(s) or used as donor parent(s) in a breeding program. Selection criteria were plant biomass, nitrogen fixation activity assessed using the ureide method and grain yield.
The best-performing genotypes were ICA20667 and ICA21573. They produced about 20% more shoot biomass than the commercial check cultivars, Spearfelt, Gallaroy and Rainbird, and had Pfix (percentage of plant nitrogen derived from nitrogen fixation) values that were consistently about 30% higher. However, both genotypes responded strongly to fertiliser nitrogen (>200% increase in shoot nitrogen and >100% increase in grain yield at rate of 150 kg nitrogen/ha), suggesting that their nitrogen fixation capacity was inadequate. This study reinforced current recommendations that commercial crops of P. vulgaris be fertilised with nitrogen and indicated a low likelihood of release of high nitrogen-fixing cultivars to growers in the immediate future.