Use of almond mesocarp for production of the entomopathogenic fungus <I>Verticillium lecanii</I>

Abstract

Almond mesocarp (AM) has been evaluated for production of Verticillium lecanii. Microbial flora of AM has been studied. After ground AM dilution plating, 5.3 x 10(5) +/- 2.6 x 10(4) fungal CFU.g-1 of dry AM were found. Common fungal saprophytes (Rhizopus sp. and Alternaria spp.) were found in more than 80% of the samples. Aspergillus sp. and yeasts were found less commonly. Rhizopus sp., Alternaria spp., and Aspergillus sp. inhibited growth of several V. lecanii; therefore, AM was treated with sterilization agents to eliminate endogenous mycoflora. Small samples (10 g) of AM saturated in distilled water treated with steam (120 degrees C and 100 kPa) were completely sterilized after 15 min. Ground AM incorporated on agar increased the biomass of V. lecanii compared with controls. This suggested AM as suitable substrate for the production of the fungus. In petri dishes, 9.7 x 10(7) +/- 2.9 x 10(7) conidia.g-1 of dry AM were produced after inoculating 10 conidia.g-1 of AM and incubating for 2 weeks. Viability of conidia produced was more than 90%. These conidia (5 x 10(4) conidia per larvae) caused Galleria mellonella mortality, calculated as median lethal time (LT50 5.3 +/- 1.6 days), that was significantly higher (F = 10.93; P < 0.05) than untreated controls (LT50 11.3 +/- 1.1 days). Larger scale tests have to be optimized before mass production.