Differential Effects of Plant Growth-Promoting Rhizobacteria Used as Soil Application vis-à-vis Root Dip of Seedlings on the Performance of Onion (Allium cepa L.) in Three Distinct Agro-climatic Zones of Indian Punjab

ABSTRACT

The effects of plant growth-promoting rhizobacteria (PGPRs) vary with their mode of inoculation, location, and dose of inorganic fertilizers applied. Therefore, it is imperative to identify the proper PGPR along with its mode of inoculation for each soil–plant system. Here, six combinations of PGPRs applied through root dip of onion seedlings were used with both 75% NPK and 100% NPK. Their performance was compared with a biofertilizer commercialized by Punjab Agricultural University as soil application (T₉), two biofertilizers from Indian Agricultural Research Institute used as root dip of seedlings (T₇ and T₈), and two uninoculated controls [100% NPK (T₀) and 75% NPK (T₁₆)] at three locations of Punjab, India. Since interaction (PGPR × location) effects were significant, only one out of six PGPR treatments, viz. T₆ (100% NPK + Azotobacter + Sphingobacterium + Burkholderia), performed consistently well across locations and gave maximum 20-bulb weight, bulb yield, net returns, and benefit:cost ratio. This treatment (T₆) yielded at par with T₇ and T₈ but was superior to T₉, which in turn yielded at par with T₀ and T₁₆ at all locations. Colonization of onion roots by beneficial natural resident arbuscular mycorrhizal fungi was higher in T₆ than in control and penetration was higher when PGPRs were integrated with 75% NPK than with 100% NPK. Utilization of PGPRs with 100% NPK in light textured soils having low fertility along with poor water holding capacity and with 75% NPK in heavy textured soils having high fertility coupled with high moisture holding capacity is advocated.

KEYWORDS:

• Azotobacter
• Burkholderia
• onion
• soil texture
• Sphingobacterium

Abbreviations

N (nitrogen), P (phosphorus), K (potassium), PGPR (plant growth-promoting rhizobacteria), OC (organic carbon), PAU (Punjab Agricultural University), IARI (Indian Agricultural Research Institute), AMF (Arbuscular Mycorrhizal Fungi).

Acknowledgments

The authors are grateful to the Punjab Agricultural University, Ludhiana, India, for providing the necessary financial assistance for conducting this study.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Punjab Agricultural University, Ludhiana, India.