Plant growth promoting characteristics of soil yeast ('Candida tropicalis' HY) and its effectiveness for promoting rice growth

Compared with bacteria and mycorrhizal fungi, the potential to use yeasts as plant growth promoting agents has been under-exploited. We investigated the ability of the soil yeast 'Candida tropicalis' HY (CtHY) to stimulate rice seedling growth and some of the possible mechanisms by which plant interaction may occur. Laboratory culture experiments found that CtHY produces small quantities of indole acetic acid (IAA), but grows rapidly on aminocyclopropane-1-carboxylate (ACC) as a sole source of nitrogen, indicative of high ACC deaminase activity. The strain also tested positive for polyamine and phytase production, and mobilized phosphate from insoluble tri-calcium phosphate. CtHY rapidly colonized the roots of rice seedlings and maintained high numbers for at least 3 weeks, increasing the dry weight of inoculated roots by 16-35% compared to non-inoculated control seedlings. These results validate the inclusion of CtHY in the commercial biofertiliser product BioGro, which has previously been demonstrated to increase the nutrition, growth and yield of paddy rice.