Growth, yield and secondary metabolite production responses to microbial elicitation in Withania somnifera (L.) Dunal

Abstract

The study entitled “Growth, yield and secondary metabolite production responses to microbial elicitation in Withania somnifera (L.) Dunal.” was conducted at the Department of Plantation Crops and Spices, College of Agriculture, Vellayani, Thiruvananthapuram during 2019-2021 with a view to evaluate the effect of bacterial inoculants on seed germination, seedling vigour, growth, yield and secondary metabolite production in W. somnifera. Seeds of W. somnifera were primed with B. amyloliquefaciens (Bam), B. pumilus (Bp) and B. velezensis (Bv) at 1x 108 cfu mL-1 individually and in combination for 24 h. Among these treatments, T7, the trio combination of Bam+Bp+Bv recorded the earliest germination (5.33 days) highest germination per cent (96.67), survival per cent (92.67) seedling vigour index (958.93), basal shoot girth (0.81 cm), number of leaves (6.07), leaf area (13.38 cm2 ), shoot length (5.77cm), root length (4.16 cm) and root volume (0.54 cm3 ). All the biopriming treatments with Bacillus spp. recorded superior germination and seedling parameters over the untreated control (T9) and hydropriming (T8). The seedlings from the first phase were subjected to root dip with the respective bacterial suspension for 30 min on transplanting. The morphological and yield determining parameters such as shoot length(78.99 cm), root length (21.27cm), number of branches (8.78), number of leaves (71.00), collar girth (3.91 cm), leaf area (5146.81 cm2 ) number of flowering branches (7.89), stem fresh weight (61 .85 g plant -1 ), stem dry weight(9.78 g plant -1 ), leaf fresh weight (45.89 g plant -1 ), leaf dry weight (5.07g plant - 1 ), root fresh weight (5.47g plant-1 ), root dry weight (1.44 g plant-1 ) 100 seed weight (0.26g ) root diameter (1.33cm), root volume (5.39 cm3 ) and harvest index (0.10) were observed to be significantly higher in T7, the trio combination of (Bam+ Bp+ Bv), which was observed to be on par with T5, dual combination of (Bam+ Bv). T5 was found to be superior in shoot fresh and dry weight, berry fresh and dry weight, number of berries and 133 seed yield per plant and total dry matter production (97.48, 17.51, 8.85 and 5.32 g plant-1 , 90.56, 7.35, 18.89 g plant-1 respectively, which was observed to be on par with T7. All the said parameters were significantly lower in untreated control. Seedlings treated with bacterial suspension of B. velezensis (Bv) recorded highest chlorophyll content in the leaves of W. somnifera at the time of harvest. The highest total alkaloid content in leaves (7.86 µg 100 mg-1 ) was recorded in dual combination of Bp+Bv which was on par with the other combinantions, Bam+Bv (T5) and Bam+Bp+Bv (T7). T5 recorded the highest protein and carbohydrate content (2.96 and 23.30 mg 100 mg-1 respectively) in the roots which was on par with T7. The withanolide content was superior (7.46 µg mg-1 ) in T7, Bam+Bp+Bv which was on par with T5, Bam+Bv and T6, Bp+Bv. The yield of biochemical parameters on per plant basis viz., total leaf alkaloids, total root withanolides were the highest (397.44 µg plant-1, and 10.77 mg plant-1 respectively) in trio combination of T7 which was on par with dual combination T5. The control treatment recorded significantly lower values in all the biochemical parameters observed. In the first phase of the study, the trio combination of Bam + Bp+ Bv (T7) gave the best performance in terms of seed germination, seedling growth and seedling vigor index, In the second phase, Bam + Bp+ Bv (T7) and Bam+ Bv (T5) gave superior performance, in terms of plant growth, yield and biochemical parameters.