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.