Abstract
Metarhizium anisopliae is a promising alternative to chemical pesticides against pine wilt disease caused by Bursaphelenchus xylophilus. Herein, we investigated the efficacy of modified atmosphere packaging (MAP) to prolong the shelf-life of the M. anisopliae conidia. The effects of various conditions on its stability were also examined. M. anisopliae-inoculated millet grains were treated in a MAP system with different packaging materials (polypropylene, PP; polyethylene terephthalate, PET; ethylene vinyl alcohol, EVOH), gas compositions (high CO2 atmosphere, ≈ 90%; high O2 atmosphere, > 95%; high N2 atmosphere, > 95%; 30% CO2 + 70% N2; 50% CO2 + 50% N2; 70% CO2 + 30% N2), and storage temperatures (4 and 25 °C). Results revealed EVOH film as the best for the preservation of gases at all concentrations for 28 days. MAP treatment in the high-barrier EVOH film under an atmosphere of 30% CO2 + 70% N2 achieved 80.5% viability of dried conidia (7.4% moisture content), with 44.2–64.9% viability recorded with the other treatments. Cold storage for technical concentrates formulation promoted extension of shelf-life of MAP-treated conidia. These results imply that MAP under optimized conditions could enhance the shelf-life of fungus-based biopesticides in fungus-colonized substrates formulations.
Highlights
Metarhizium anisopliae is a promising alternative to chemical pesticides against pine wilt disease caused by Bursaphelenchus xylophilus
At 14.3% moisture content, M. anisopliae conidia did not grow at all tested temperatures
The present study suggests that proper modified atmosphere packaging (MAP) can be effectively used to prolong the shelf-life of M. anisopliae conidia cultured on millet grains
Summary
Metarhizium anisopliae is a promising alternative to chemical pesticides against pine wilt disease caused by Bursaphelenchus xylophilus. A variety of synthetic chemical pesticides, including acetamiprid, thiacloprid, buprofezin, metham sodium, clothianidin, thiamethoxam, and fenitrothion, have been proposed to control PWD These chemicals have been limited in most developed countries due to environmental hazards, unhealthful residues, and threat to non-target species[7,8,9]. The lack of conidia stability during distribution is a critical obstacle to its widespread use and market competitiveness[11] To overcome this issue, several research efforts, such as designed formulations, pre-incubation, and adjuvant, have been s uggested[11,13,14]; constraints of high installation cost and obstacle of scaling up still limit commercial applications of these treatments. Little information exists on the application of MAP to M. anisopliae, despite many previous studies on other genera, such as Beauveria[13,15,16,18]
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