Plant growth-promoting rhizobacteria (PGPR) is a microbial population found in the rhizosphere of plants that can stimulate plant development and restrict the growth of plant diseases directly or indirectly. In this study, 90 rhizospheric soil samples from five agro climatic zones of chilli (Capsicum annuum L.) were collected and rhizobacteria were isolated, screened and characterized at morphological, biochemical and molecular levels. In total, 38% of rhizobacteria exhibited the antagonistic capacity to suppress Ralstonia solanacearum growth and showed PGPR activities such as indole acetic acid production by 67.64% from total screened rhizobacteria isolates, phosphorus solubilization by 79.41%, ammonia by 67.75%, HCN by 58.82% and siderophore by 55.88%. We performed a principal component analysis depicting correlation and significance among plant growth-promoting activities, growth parameters of chilli and rhizobacterial strains. Plant inoculation studies indicated a significant increase in growth parameters and PDS1 strain showed maximum 71.11% biocontrol efficiency against wilt disease. The best five rhizobacterial isolates demonstrating both plant growth-promotion traits and biocontrol potential were characterized and identified as PDS1—Pseudomonas fluorescens (MN368159), BDS1—Bacillus subtilis (MN395039), UK4—Bacillus cereus (MT491099), UK2—Bacillus amyloliquefaciens (MT491100) and KA9—Bacillus subtilis (MT491101). These rhizobacteria have the potential natural elicitors to be used as biopesticides and biofertilizers to improve crop health while warding off soil-borne pathogens. The chilli cv. Pusa Jwala treated with Bacillus subtilis KA9 and Pseudomonas fluorescens PDS1 showed enhancement in the defensive enzymes PO, PPO, SOD and PAL activities in chilli leaf and root tissues, which collectively contributed to induced resistance in chilli plants against Ralstonia solanacearum. The induction of these defense enzymes was found higher in leave tissues (PO—4.87-fold, PP0—9.30-fold, SOD—9.49-fold and PAL—1.04-fold, respectively) in comparison to roots tissue at 48 h after pathogen inoculation. The findings support the view that plant growth-promoting rhizobacteria boost defense-related enzymes and limit pathogen growth in chilli plants, respectively, hence managing the chilli bacterial wilt.

The polyphagous insect-pest, Helicoverpa armigera, is a serious threat to a number of economically important crops. Chemical application and/or cultivation of Bt transgenic crops are the two strategies available now for insect-pest management. However, environmental pollution and long-term sustainability are major concerns against these two options. RNAi is now considered as a promising technology to complement Bt to tackle insect-pests menace. In this study, we report host-delivered silencing of HaAce1 gene, encoding the predominant isoform of H. armigera acetylcholinesterase, by an artificial microRNA, HaAce1-amiR1. Arabidopsis pre-miRNA164b was modified by replacing miR164b/miR164b* sequences with HaAce1-amiR1/HaAce1-amiR1* sequences. The recombinant HaAce1-preamiRNA1 was put under the control of CaMV 35S promoter and NOS terminator of plant binary vector pBI121, and the resultant vector cassette was used for tobacco transformation. Two transgenic tobacco lines expressing HaAce1-amiR1 was used for detached leaf insect feeding bioassays. Larval mortality of 25% and adult deformity of 20% were observed in transgenic treated insect group over that control tobacco treated insect group. The reduction in the steady-state level of HaAce1 mRNA was 70–80% in the defective adults compared to control. Our results demonstrate promise for host-delivered amiRNA-mediated silencing of HaAce1 gene for H. armigera management.

Cold-induced sweetening (CIS) is an unwanted physiological phenomenon in which reducing sugars (RS) get accumulated in potato (Solanum tuberosum) upon cold storage. High RS content makes potato commercially unsuitable for processing due to the unacceptable brown color in processed products like chips, fries, etc., and the production of a potential carcinogen, acrylamide. UDP-glucose pyrophosphorylase (UGPase) catalyzes the synthesis of UDP-glucose towards the synthesis of sucrose and is also involved in the regulation of CIS in potato. The objective of the present work was RNAi-mediated downregulation of the StUGPase expression level in potato for the development of CIS tolerant potato. Hairpin RNA (hpRNA) gene construct was developed by placing UGPase cDNA fragment in sense and antisense orientation intervened by GBSS intron. Internodal stem explants (cv. Kufri Chipsona-4) were transformed with hpRNA gene construct, and 22 transgenic lines were obtained by PCR screening of putative transformants. Four transgenic lines showed the highest level of RS content reduction following 30 days of cold storage, with reductions in sucrose and RS (glucose & fructose) levels of up to 46% and 57.5%, respectively. Cold stored transgenic potato of these four lines produced acceptable chip colour upon processing. The selected transgenic lines carried two to five copies of the transgene. Northern hybridization revealed an accumulation of siRNA with a concomitant decrease in the StUGPase transcript level in these selected transgenic lines. The present work demonstrates the efficacy of StUGPase silencing in controlling CIS in potato, and the strategy can be employed for the development of CIS tolerant potato varieties.