Effect of Penicillium bilaii inoculation and phosphorus fertilisation on root and shoot parameters of field-grown pea

The mechanisms underlying the stimulating effect of Penicillium bilaii inoculation on the growth of crop plants are not clear. The effect of P. bilaii inoculation on root morphology [dry weight (DW), length and specific root length) and other root and shoot parameters of pea were investigated at two field sites in western Canada in 1996. Pea (Pisum sativum L.) was grown at three levels of P fertilization (0, 6.4 and 19.3 kg ha–1) at Ellerslie, AB, and Outlook, SK. Shoot dry matter, P concentrations, P content and nodulation were also measured in pea plants harvested at the seven- to nine-node stage. Soil cores were used to sample roots. Although plants were responsive to P fertiliser at both sites, P. bilaii inoculation affected pea growth at the Ellerslie site only. At this site, P. bilaii inoculation increased root length by 48%, specific root length (m g–1 root DW) by 21%, root DW by 13%, and shoot P concentration by 13% in treatments that received no P fertiliser. We suggest that the stimulating effect of P. bilaii inoculation on crop P nutrition is partly explained by increases in root absorptive capacity in the presence of the fungus. However, this effect was only significant under P-limited conditions. Key words: Microbial inoculants, Pisum sativum, Penicillium bilaii, phosphorus, root length, root morphology