Abstract
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 48h of administration. The LT50 of T. harzianum also exhibited a lower effective time (47.70h) than B. bassiana (57.53h) 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 ± 0.4cm diameter) and protease (7.0 ± 0.4cm diameter) enzymes, than B. bassiana (1.3 ± 0.2cm and 1.1 ± 0.2cm 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.
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