Grafting is used in vegetable production to improve plant vigour and tolerance to soil-borne diseases, yet the biological properties of the graft union remain poorly understood. Here, we investigated culturable bacteria associated with tomato (Solanum lycopersicum L.) graft unions. Bacterial populations reached 105-107 colony-forming units per gram of fresh weight (CFU g-1 FW) in graft union tissues. However, no culturable bacteria were detected from non-grafted stem samples collected from the graft union equivalent position at the corresponding sampling time (i.e. 8 days after grafting in grafted plants). The predominant bacterial genera isolated from graft unions were Microbacterium and Sphingomonas. All isolates tested negative for the hypersensitive reaction in tobacco, indicating their non-pathogenic nature. The isolates exhibited functional traits, including effects on seedling growth, phosphate solubilisation, production or degradation of N-acyl-homoserine lactones, and antibacterial activity against Ralstonia pseudosolanacearum. In addition, isolates were associated with reduced symptom development of bacterial wilt in tomato seedlings under controlled conditions. These results suggest that graft unions may provide a biologically active environment associated with the recovery of diverse culturable bacterial communities. Our findings provide insight into bacteria associated with tomato graft unions and their potential functional properties relevant to horticultural production.
Anthracnose of mango caused by Colletotrichum spp. results in quality loss, reduced shelf life, and diminished market value. Despite its economic impact, the molecular basis of mango-Colletotrichum asianum interactions remains largely unclear. This study assessed the antifungal activity of salicylic acid (SA) against C. asianum and explored its potential mechanisms. SA inhibited mycelial growth in a concentration-dependent manner, with complete arrest of spore germination at concentrations >= 2 mM. Postharvest application of 2 mM SA significantly suppressed lesion development in the fruits of 'Alphonso' and 'Banganapalli' cultivars, compared with untreated controls. Gene expression profiling at 2 mM SA was conducted in 'Gomavu' (moderately resistant) and 'Banganapalli' (susceptible) cultivars. In 'Gomavu', MRNBS-11 transcripts were markedly elevated at 6 and 12 h post-inoculation, indicating early pathogen recognition and activation of defence signalling. Additionally, SA treatment induced the expression of pathogenesis-related (PR) proteins (PR4, PR1A) and defence-related enzymes (Phenylalanine ammonia-lyase, Peroxidase), highlighting their role in restricting C. asianum infection. These findings demonstrate the potential of SA as a postharvest treatment for managing mango anthracnose and provide novel insights into the genetic basis of resistance. Further validation through field trials, and exploration of genetic improvements is recommended to strengthen disease management strategies.
