Increasing symbiotic potentials in white clover

Abstract

Lines of white clover with higher and lower numbers of nodules were selected from a mutagenised Huia population, and seed was produced from a polycross of both lines. The progeny showed that the lines tended to have either more but smaller nodules, or fewer and larger nodules. In a further experiment, the line with fewer (larger average size) nodules, fixed more nitrogen (N) and grew bigger. Plants with fewer but larger nodules are a good model for efforts to increase the Nfixing capacity of white clover. An empirical screening method was used to obtain 15 genotypes that showed evidence of high mycotrophy. A second experiment confirmed that 5 of these genotypes gave abnormally high responses to mycorrhizal infection. Examination of the roots of these plants showed that the selections did not differ from their parent lines in terms of root length or root hair cylinder diameter. The results tend to confirm published work with spring wheat, which showed that land races and wild types respond more strongly to mycorrhizal infection than high yielding varieties do. Investigation of the mycorrhizal responses of clover ecotypes that are adapted to low phosphorus soils is a priority for future research. Keywords: mycorrhizas, nitrogen fixation, nodulation, symbioses, white clover