Induction of innate immunity and plant growth promotion in tomato unveils the antiviral nature of bacterial endophytes against groundnut bud necrosis virus.

Abstract

Tomato is an important crop worldwide, but groundnut bud necrosis virus (GBNV) often hampers its growth. This study investigates the antiviral potential of bacterial endophytes, including Brucella melitensis CNEB54, Bacillus licheniformis CNEB4, Bacillus velezensis CNEB26, and Bacillus vallismortis BAVE5 against GBNV, as well as their ability to enhance immunity and growth in tomato. All four bacterial isolates demonstrated a significant delay in GBNV symptom development 10 days post-inoculation, with disease incidence ranging from 18% to 36% compared to 84% in control. DAC-ELISA results indicated a noteworthy reduction in virus titer (0.32-0.96 OD) in treated tomato plants versus the control (3.26 OD). In addition, qPCR analysis revealed decreased viral copy numbers in plants treated with bacterial endophytes (1.3-3.1 × 10⁵) as against in untreated inoculated control (2.4 × 10⁶). Furthermore, these endophytes upregulated the expression of defense-associated genes, such as MAPKK1, PAL, PPO, LOX1, JAR1, and PDF 1.2. Field experiments with the application of B. melitensis and B. velezensis exhibited improved growth, with an average plant height of 123.70 cm, 14.87 flowers per plant, and a fruit weight of 549.3 g per plant, with a disease incidence of 18.1%. In comparison, the untreated control plants only reached a height of 104.73 cm, produced 11.17 flowers per plant, and yielded 267 g of fruit per plant, with a disease incidence of 30.1%. These findings strongly support the use of bacterial endophytes to reduce disease incidence and severity, enhance plant immunity and promote plant growth, resulting in overall crop productivity in sustainable agriculture.IMPORTANCEThe infection of GBNV in crops such as tomatoes, peanuts, and pulses leads to significant yield loss. Applying insecticides to control vector populations, can limit the spread of viruses carried by these vectors. The present study envisages a novel strategy to combat GBNV, with the help of bacterial endophytes. These bacterial endophytes have tremendously reduced the symptom expression of GBNV, induced the expression of defense genes during the tri-trophic interaction and promoted plant growth in tomatoes under field conditions. Hence, these bacteria are identified to be involved in immunity boosting, viral suppression and growth promotion.