Effect of plant growth promoting rhizobacteria on root morphology of Safflower (Carthamus tinctorius L.)

Abstract

Rooting characteristics significantly affect the water-use patterns and acquirement of nutrient for any plant species. Plant growth promoting rhizobacteria improve the plant growth by a variety of ways like the production of phytohormones, nitrogen fixation, phosphate solubilization and improvement in root morphology etc, and are also useful in cutting down the cost of chemical fertilizers. The present investigation was carried out to determine the comparative effect of plant growth promoting rhizobacteria (PGPR), Azospirillum brasilense, Azotobacter vinelandii and Pseudomonas stutzeri, either alone or in combination with different doses of chemical fertilizers [full dose (Urea at 60 kg ha^-1 and DAP at 30 kg ha^-1), half dose (Urea 30 kg ha^-1 and DAP 15 kg ha^-1) and quarter dose (Urea 15 kg ha^-1 and DAP 7.5 kg ha^-1)] on root morphology and root distribution pattern of safflower (Carthamus tinctorius L.) viz. cvv. Thori and Saif-32 in the soil. The PGPR were applied as seed inoculation at 106 cells/ml prior to sowing. P. stutzeri either alone or in combination with full dose of chemical fertilizers, was highly effective in increasing the root area in cv. Saif-32, whereas, the percent increase due to A. brasilense was comparable to that of treatment with full dose of chemical fertilizers. P. stutzeri inoculation resulted in significantly higher root length in both the cultivars. Significantly, higher root width (54%) of cv. Thori was observed in treatment receiving inoculation with A. vinelandii and supplemented with half dose of chemical fertilizers, whereas maximum root width of cv. Saif-32 was recorded in treatment supplemented with half dose of chemical fertilizers. It is inferred that PGPR inoculation especially those of A. brasilense and P. stutzeri either alone and more so in combination with half dose of chemical fertilizers, are highly effective in improving root morphology and growth in safflower.

Key words: Root area, safflower, plant growth promoting rhizobacteria (PGPR), root growth, chemical fertilizers.