Role of pink pigmented facultative methylotrophic bacteria in promoting growth and yield of greengram (Vigna radiata L.)

Introduction

The rapid increase in global population has intensified the demand for food, leading to the indiscriminate use of chemical fertilizers. While these inputs initially boost crop productivity, their overuse has resulted in soil degradation and environmental concerns. Hence, sustainable strategies that enhance yield without compromising soil health are urgently needed. Bioinoculants, which are microbial formulations containing single or consortia of beneficial microorganisms, have gained importance as eco-friendly alternatives to chemical fertilizers. They promote plant growth, improve nutrient availability, and help in reducing environmental impacts. Among bioinoculants, methylotrophic bacteria-particularly Pink Pigmented Facultative Methylotrophs (PPFM)-have shown promise in sustainable agriculture. These bacteria colonize both rhizosphere and phyllosphere, where they enhance plant growth by producing phytohormones such as cytokinins and auxins, solubilizing phosphorus, producing siderophores, and inducing resistance against pathogens (Mandhiyan et al., 2004) [5] . Different studies have reported that PPFM application, either as seed inoculants or foliar sprays, improves soil microbial activity, nutrient availability, seed germination, and crop yields (Jeya Jyothi et al., 2014; Raghavendra et al., 2019) [1,10] . Considering these advantages, the present study was conducted to evaluate the effect of PPFM on the growth and yield of greengram, hypothesising that seed treatment coupled with foliar application would positively influence crop performance. to evaluate the effect of PPFM on greengram (var. WGG-42). The experiment was designed with nine treatments and three replications in a simple randomized block design. Treatments included seed treatment with Rhizobium (T₁), seed treatment with 1% PPFM (T₂), Seed treatment with 2% PPFM (T3) seed imbibition with water (T4), Foliar spray of 1% PPFM at flower initiation and pod formation stages (T5), foliar spray of 2% PPFM at flowering and pod formation (T6), Seed treatment with 1% PPFM + Foliar spray of 1% PPFM at flower initiation and pod formation stages(T7), Seed treatment with 1% PPFM + Foliar spray of 2% PPFM at flower initiation and pod formation stages (T8), and Water spraying at flower initiation and pod formation stages (T9)-The experimental field was neutral in condition (pH 7.1), low in nitrogen content (233.7 kg ha⁻¹), high in phosphorus content (32.7 kg ha⁻¹), and medium in potassium content (334.2 kg ha⁻¹). The experimental crop was sown on 25 th October 2023 with 30 × 10 cm spacing apart. Pendimethalin was applied as a pre-emergence herbicide within 24 h of sowing, and a uniform basal dose of fertilizers was applied for all the treatments. PPFM inoculation and foliar sprays were imposed as per treatments. The crop was harvested on 17 th January 2024. The biometric observations were recorded by selecting five plants randomly per treatment, and treatment means were used for analysis.

Material and Methods

Results and Discussion

Growth and Yield of green gram

The different treatment combinations like seed treatment, seed imbibition, and foliar spray did not significantly influence plant height; however, dry matter production varied markedly. Seed treatment with 1% PPFM combined with foliar spray of 2% PPFM at flowering and pod formation stages recorded the highest dry matter accumulation, statistically on par with seed treatment with 1% PPFM and foliar spray of 1% PPFM at the same stages. The enhanced dry matter production can be attributed to the ability of methylotrophic bacteria to promote seed germination and seedling growth through synthesising phytohormones such as cytokinins and auxins (Long, 2000) [3] and their role in atmospheric nitrogen fixation. The lowest dry matter production was observed in the seed imbibition with water treatment, corroborating the earlier findings of Mandhiyan et al. (2004) [5] . Foliar application of 2% PPFM at flowering and pod formation and seed treatment also resulted in a significant increase in yield attributes, grain yield, and haulm yield. This treatment was on par with seed treatment with 1% PPFM and foliar spray of 1% PPFM at the same growth stages. The improvement may be due to enhanced nutrient availability and uptake. Similar positive effects of methylotrophs on germination, plant growth, and yield have been reported in barnyard millet (Poorniammal et al., 2020) [9] , while Mandhiyan et al. (2004) [5] and Om base et al. (2003) [7] also documented increased seedling vigour, dry matter accumulation, and yield with PPFM inoculation.

Correlation among yield attributes and yield

Correlation analysis was carried out between the different parameters like plant height, number pods per plant, number of seeds per pod, 100 seed weight, plant drymatter and grain yield to determine the relationship among the various parameters studied (Fig. 1). The results shows that all the parameters are positively correlated with grain yield and Haulm yield. A significant correlation (p<0.05) was also observed between between grain yield and plant dry matter, pod per plant, seeds per pod. The results are in conformity with Narayanan Vijayanand et al., 2021 [8] .

Economics Cost of cultivation:

The maximum cost of cultivation was observed with treatment of seed treatment and foliar spray of 2% PPFM (₹37,616 ha⁻¹), followed by seed treatment and foliar spray of 1% PPFM (₹37,316 ha⁻¹). The lowest cost was recorded with seed imbibition with water (₹26,866 ha⁻¹).

Gross returns: Gross returns of different treatments varied across, with the highest being recorded in seed treatment + foliar spray of 2% PPFM (₹115,430 ha⁻¹), followed by seed treatment + foliar spray of 1% PPFM (₹94,055 ha⁻¹). The lowest gross return was noted in seed imbibition with water (₹43,945 ha⁻¹). These results are in tune with the findings of Vigneshwarraj et al. (2020) [12] .

Net returns: Seed treatment with 1% PPFM + foliar spray of 2% PPFM contributed the maximum net returns (₹77,814 ha⁻¹), closely followed by seed treatment + foliar spray of 1% PPFM (₹76,363 ha⁻¹). The operations of seed treatments and other special practices helped reduce the cost of cultivation, which confirms with Narendar et al., 2023 [6] .

Benefit-Cost (B:C) ratio:

The highest B:C ratio was obtained with seed treatment + foliar spray of 1% PPFM (2.34), followed by foliar spray of 2% PPFM (2.32) and seed treatment with 2% PPFM (2.07). The lowest B:C ratio (1.64) was recorded in seed imbibition with water, supporting the earlier results of Sekar et al. (2010) [11] .

Conclusion

The present investigation indicated that the number of pods, and seeds per plant significantly impacted the grain yield and Haulm yield of greengram. The highest grain yield was observed with Seed treatment with 1% PPFM and 2%foliar spray of PPFM at critical stages however, the seed treatment followed by foliar spray with 1% PPFM recorded secondbest yield at par. Foliar spray of PPFM two times also gave a good yield at par with the highest grain yield treatments. The treatment of PPFM 1% seed treatment and 1% foliar spray at critical stages recorded the highest benefit-cost ratio.

Acknowledgement

AcknowledgementThe authors are highly thankful to the Director of Research, Professor Jayashankar, Telangana Agricultural University (PJTAU), Hyderabad, for providing facilities for conducting the experiment.

References

1. T1-Seed treatment with Rhizobium 25.7 2478 889 1589 T2-Seed treatment with 1% PPFM 25.3 2650 925 1798 T3-Seed treatment with 2% PPFM 25.9 2871 1070 1851 T4-Seed imbibition with water 24.9 2367 833 1533 T5-Foliar spray of 1% PPFM at flower initiation and pod formation stages 28.9 2953 1093 1893 T6-Foliar spray of 2% PPFM at flower initiation and pod formation stages 29.0 2975 1107 1937 T7-Seed treatment with 1% PPFM + Foliar spray of 1% PPFM at flower initiation and pod formation stages 29.2 3528 1282 2245 T8-Seed treatment with 1% PPFM + Foliar spray of 2% PPFM at flower initiation and pod formation stages 30.3 3779 1358 2420 T9-Water spraying at flower initiation and pod formation stages 25.4 2632 853 1625 SE.m ± 2.00 305 115 193 CD NS 914 344 580 Table 2: Effect of pink-pigmented facultative methyl bacterium on grain yield and economics of greengram Treatments Grain yield (kg ha -1 )
2. Jeyajyothi R, Subhalakshmi L, Nallaiah D. Effect of PPFM application on microbial population in transplanted rice. Trends Biosci. 2014;7:3573-3574.
3. Kumar M, Tomar RS, Lade H, Paul D. Methylotrophic bacteria in sustainable agriculture. World J Microbiol Biotechnol. 2016;32:120-128. doi:10.1007/s11274-0162074.
4. Long RL. tRNA is the source of cytokinin secretion by plant-associated members of the genus Methylobacterium. [PhD dissertation]. University of Missouri-Columbia; 2000.
5. Madhiyan M, Reddy BS, Anandham R, Senthil Kumar M, Poonguzhali S, Sundaram SP, et al. Plant growthpromoting Methylobacterium induces defense responses in groundnut (Arachis hypogaea L.) compared with root pathogens. Curr Microbiol. 2006;53(4):270-276.
6. Madhiyan M, Poonguzhali S, Senthil Kumar M, Seshadri S, Chung J, Yang S, et al. Growth promotion and induction of systemic resistance in rice cultivar CO-47 (Oryza sativa L.) by Methylobacterium spp. Bot Bull Acad Sin. 2004;45:315-324.
7. Narendar G, Madhushekar BR, Avil Kumar K, Goverdhan M. Impact of frontline demonstrations on redgram yield, economics and yield gap analysis in Telangana. Environ Ecol. 2023;41(4C):2814-2819.
8. Ombase AR, Andsule RN, Amrutsagar VM. Influence of foliar spray of methanol on growth, nutrient uptake and yield of summer groundnut. J Maharashtra Agric Univ. 2003;28(3):262-265.
9. Vijayanand N, Subramanian SR, Ponnerulan B, Saminathan E, Veerenan U, Kathiresan D, et al. Potential of pink pigmented methylotrophic bacteria on growth and physiology of clusterbean and soil microbial community. Biocatal Agric Biotechnol. 2021;37:102161. doi:10.1016/j.bcab.2021.102161.
10. Poorniammal R, Prabhu S, Senthilkumar M, Anandhi K. Effect of phyllosphere application of Methylobacterium on growth and yield of barnyard millet (Echinochloa frumentacea var. COKV 2). Int J Curr Microbiol Appl Sci. 2020;9(4):1860-1866.
11. Raghavendra J, Santhosh G, Mahadevaswamy P, Shubha S, Ravi MV. in vitro screening of pink pigmented facultative methylotrophs based on their functional characteristics. Int J Pure Appl Biosci. 2019;7(1):553-562.
12. Sekar S, Amanullah M, Manoharan M, Muthukrishnan KS, Subramanian S, Vincent S. Influence of fertilizer levels and growth substances on yield and economics of hybrid maize. Madras Agric J. 2010;97(1-3):58-61.
13. Vigneshvarraj D, Elayaraja A, Arivukkarasu K, Jawahar P. Influence of INM on nodulation, yield, quality and economics of greengram in coastal saline sandy soil. Plant Arch. 2020;20(2):5310-5314.