No abstract

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% P 2 O 5 . 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 28°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 fi nal acidity produced by yeasts and the quantity of phosphate liberated.

Phosphate solubilizing fungi (PSF) were enumerated in 78 rhizosphere soil samples collected from various sites of Bhavnagar district with agro climatic zone of hot, semi-arid region of Gujarat. 81% of samples were inhabited with indigenous PSF; the count varied ranging from 0.01 to 90 × 10 3 PSF g -1 . PSF population in the rhizosphere soils were maximal at pH 7.4-8.4, electrical conductivity (EC) 1-2 dS m -1 wherein PSF population decreased with a rise in EC. Optimal moisture content ranged ≤10-30% where the abundance of PSF always decreased with increase in moisture levels while suitable organic matter content ranged from ≤0.5-4.5%. Available P range 100-300 mg kg -1 was the most suitable for occurrence of PSF as being noticed from number of soil samples harboring them in rhizosphere soils. Amongst the various rhizosphere soil properties studied, a highly signifi cant positive correlation was established between PSF and soil available P as well as pH. A signifi cant positive association observed between total fungal population and organic matter as well as soil available P. Both abundance and number of PSF were more pronounced in descending order in plant covers: oilseeds, fl owers, orchards, vegetables, pulses and cereals.