Efficacy of biostimulants against Alternaria solani (Ell. and Mart.) Jones and Grout causing early blight of tomato and their impact on tomato seedling growth parameters

Early blight caused by Alternaria solani has been documented as a serious threat to tomato plants which leads to significant loss in yield in India and across the world. This study aimed to evaluate the efficacy of four biostimulants, i.e, salicylic acid, gallic acid, chitosan and Cusilano (gelatin enriched with colliadal silver and copper) against plant pathogenic fungi Alternaria solani causing early blight of tomato. Cusilano (5 µg/ml) was found most effective against A. solani under both in vitro and in vivo conditions, with maximum mycelial inhibition (60.00%) and maximum disease control (52.48%) over check. The effect of application of biostimulants was evaluated on different vegetative growth parameters of tomato after 20 days of foliar application. Seedlings treated with Cusilano and chitosan were found to have the maximum root length, i.e. 6.00 and 5.00 cm which were statistically at par with each other. The shoot length recorded for Cusilano (10.00 cm) and gallic acid (9.00 cm) were higher than salicylic acid and chitosan. Non-significant differences with respect to number of branching and stem diameter were observed among the treatments including the untreated control. Seedling fresh weight was significantly high in Cusilano treated seedlings (0.50g) followed by gallic acid (0.40g). Similar trend was observed in case of dry seedling weight. The activity of defense enzyme peroxidase (POD), polyphenol oxidase (PPO) and phenylalanine lyase (PAL) was measured in tomato leaves (cv. Avtar) challenged with A. solani. The results demonstrate a stimulatory effect of biostimulants in tomato plants against early blight and reveal that gelatin enriched with colliadal silver and copper resulted in most enhanced production of plant defense enzymes during interaction with the A. solani.