An eco-friendly approach of biocontrol of aphid (Aphis gossypii Glover) by Trichoderma harzianum

Aphid (Aphis gossypii) is one of the important pests of papaya crop. In this work, applications of Trichoderma harzianum and Beauveria bassiana (biocontrol agents) and malathion (insecticide) were conducted in vitro and in agrifields for testing their anti-aphid efficacy and compared their efficacy. Furthermore, the enzymatic mechanism of T. harzianum with respect to biocontrolling the pest was unearthed. The LD₅₀ dose of T. harzianum and B. bassiana was 1.2 × 10⁵ spores mL^-1 and 1.0 × 10⁶ spores mL^-1 respectively after 48 h of administration. The LT₅₀ of T. harzianum also exhibited a lower effective time (47.70 h) than B. bassiana (57.53 h) for the same concentration of spores applied (1 × 10⁵ spores mL^-1). The pooled data analysis of two years (2019-2020) showed that the application of T. harzianum spores in agrifields exhibited 31.75 ± 13.00a percentage of reduction of aphid population whereas malathion exhibited 23.93 ± 1.30a%, in comparison to control. The statistical analysis indicated that the application of malathion exhibited the same efficacy as T. harzianum isolate and placed in the same category. In plate detection assay, T. harzianum produced a higher hydrolytic zone for chitinase (8.0 ± 0.4 cm diameter) and protease (7.0 ± 0.4 cm diameter) enzymes, than B. bassiana (1.3 ± 0.2 cm and 1.1 ± 0.2 cm respectively). Quantitative estimation of enzymes exhibited that T. harzianum produced 299 ± 11a μg mL^-1 of chitinase, 519 ± 19a μg mL^-1 of protease, and 65 ± 12a μg mL^-1 of PR1, and on the other hand, B. bassiana yielded 124 ± 12b, 361 ± 23b, and 29 ± 18b μg mL^-1 of chitinase, protease, and PR1 respectively. It indicated that T. harzianum was superior over the B. bassiana in terms of production capacity of all three enzymes. In conclusion, all the above experimental results suggested that T. harzianum showed better aphid-killing efficacy than B. bassiana. It also suggested that T. harzianum should replace hazardous chemical pesticide (malathion) for eco-friendly biocontrol of aphids.