Rock phosphate dissolution by specific yeast

Phosphate solubilizing yeast (PSY) were isolated from rhizosphere, non-rhizosphere and fruits from Bhavnagar district. The potential of 25 yeasts were analyzed on the basis of phosphate solubilizing zone to growth on solid medium denoted as solubilization index (SI) which ranged from 1.10 to 1.50. Among 25 yeast isolates, 6 yeast belonging to genus Saccharomyces (2), Hansenula, Klockera, Rhodotorula and Debaryomyces exhibited highest SI (1.33-1.50) were further examined for in vitro tricalcium phosphate (TCP) and low grade rock phosphate (RP) solubilization. TCP proved superior to RP with all the yeasts. Within low grade RPs tested, except isolate Y5, all isolates showed maximum solubilization with Hirapur RP (HRP) ranging from 7.24 to 19.30 mg% P2O5. Among six PSY screened, Debaryomyces hansenii showing maximal HRP solubilization was chosen for further physiological studies. Maximum HRP solubilization was expressed in following condition: pH optima 7.0, temperature optima 28A degrees C and optimal period of incubation were 15 days. Acidic pH of the spent media was a constant feature in all the cases. No correlation could be established between final acidity produced by yeasts and the quantity of phosphate liberated.