Colonization and persistence of different strains of Beauveria bassiana and Metarhizium anisopliae as endophytes in cabbage for management of diamond back moth Plutella xylostella L

Abstract

The present study was taken up to identify the promising entomofungal pathogens newlineagainst cabbage pest Diamond back moth, Plutella xylostella (L.) through endophytic newline newlineestablishment. ICAR-NBAIR collection of Beauveria bassiana (Bals.) Vuillemin (ICAR- newlineNBAIR 20 isolates) and Metarhizium anisopliae (Metsch.) Sorokin (ICAR-NBAIR 20 isolates) newline newlineat the concentration of 1×107 conidia/ml were tested against the larvae of Plutella xylostella newline(2nd instar) using larval dip method through laboratory bioassay. Based on the laboratory newlinebioassay, four promising isolates were identified against P. xylostella with significant percent newlinemortality (51.14-88.85%). Among the four isolates, ICAR-NBAIR Ma-4 showed 88.85%, newlineICAR-NBAIR Ma-35 of 81.44%, ICAR-NBAIR Bb-5a of 77.36% and ICAR-NBAIR Bb-45 newlineof 51.14% mortality respectively. These 4 isolates were selected further for endophytic as well newlineas other studies. newlineDose mortality studies with these four promising isolates were conducted at the five newlinedifferent concentrations (104 newline, 105 newline, 106 newline, 107 and 108 conidia / ml) on Plutella xylostella (2nd instar) newline newlineby larval dip method showed LC50 value in the range of 2.6×104 newline-1.9 × 106 newline newlineconidia/ml. In the newlinefour isolates tested, NBAIR Ma-35 isolate showed LC50 of 2.6 x 104 conidia/ml, NBAIR Ma-4 newlineat 5.3 x 104 newline newlineconidia/ml, NBAIR Bb-5a at 1.3 x 105 conidia/ml and NBAIR Bb-45 at 1.9 x 106 newlineconidia/ml respectively. Time mortality studies of four isolates at concentration of 1 x 108 newlineconidia/ml showed LT50 of 86.6-156.64 hours against P. xylostella. In the four promising newlineisolates, NBAIR Ma-35 isolate showed LT50 at the time of 86.6 hours, NBAIR Ma-4 at 121.30 newlinehours, NBAIR Bb-5a at 100.32 hours and NBAIR Bb-45 at 156.64 hours respectively. newlineIn second laboratory bioassay method, four promising isolates were evaluated against newlinesecond instar larvae of P. xylostella at 1 x 108 conidia/ml by feeding method. In the four isolates newlinetested, NBAIR Ma-35 isolate showed 74%, NBAIR Ma-4 of 70.8%, NBAIR Bb-5a of 62.4% newlineand NBAIR Bb-45 with 52% mortality. newlineThese four promising isolates were studied for their ability to establish as endophytes newlinein cabbage through different application methods i.e., seed treatment, root inoculation and newlinefoliar application at the concentration of 1 × 108 newline newlineconidia/ml under glasshouse conditions in newline2017 and 2018 period. The colonization of B. bassiana and M. anisopliae in cabbage leaf, stem, newlineand root tissues were confirmed through plating technique, PCR studies using specific primers newlineof B. bassiana and M. anisopliae. All four isolates were able to colonize the cabbage leaves, newlinestems, and roots with varying percentage of colonization and persistence during 15 days after newlinetreatment (DAT), 30, 45 and 60 DAT in all three methods tested by plating method and PCR newlinestudies. In untreated control, colonization of endophytic fungus was not noticed from the newline newlinecabbage plant tissues by plating and PCR studies. In all the three applications, all the four newlineisolates showed higher colonization in cabbage leaves by foliar application method. Further newlineendophytic studies with these promising isolates were carried using foliar application method newlinein cabbage. The Scanning and Transmission electron microscopic studies were conducted for newlineconfirmation of endophytic establishment in cabbage leaves. All the four isolates showed newlinegermination, penetration and internal colonization in the cabbage leaves by foliar application newlinemethod. Based on the laboratory bioassay, endophytic studies, efficacy studies and formulation newlinestudies, NBAIR Ma-35 was found as a potential endophytic isolate for the control of cabbage newlinepest P. xylostella which can be used for further field studies. newline