Comparative Biological Properties Of Verticillium Lecanii Conidia On Different Inert Carrier In Solid-state Fermentation

Verticillium lecanii is a well known entomopathogenic fungus with a broad range of hosts including Coleoptera, Orthopteta, Homoptera, Lepidoptera and Cucumber powdery mildew. It plays an important role in the biological control. Solid-sate fermentation has advantages such as low investment in equipments, low energy consumption, rare pollution and being easy to operate. Therefore, it is suitable for spore production of Verticillium lecanii. In this paper, on the basis of previous studies on optimization of Verticillium lecanii spore production in solid-state fermentation on sugarcane bagasse as an inert carrier, we studied growth mechanism in the inert carriers and spore characters: 1) Morphologies of mycelia and conidia of solid-state fermentation on wheat bran (control), polyurethane foam (PU) as an inert carrier, and sugarcane bagasse as an inert carrier with SEM. 2) enzymes activity of conidia. We further investigated the possible ways to shorten the growth cycle. Finally, the relationship between culturing, nutrition and sporulation cycles, spore production was explained.1. Insect rejuvenation of Verticillium lecanii CBS 102071 by infecting Bemisia tabaci and Myzus persicae, The virulence, growth and sporulation capacity of the strain of rejuvenation were restored to the original level and was used as the experimental strain.2. The method of solid-state fermentation on natural bran to produce conidia was used as a control. Chitinase and protease activities of conidia from sugarcane bagasse and PU soft foam were analyzied. The results show that the conidia from the wheat bran, sugarcane bagasse and PU foam achieved a similar activity. By comparing the producing activity cycle and sporulation cycle, we first concluded that the best time to harvest spores was just before the sporulation stability period. 3. Verticillium lecanii growth on sugarcane bagasse or PU was observed with SEM. We can see that PU had a larger pore diameter and the consensus rules of the pore space layouts were more conducive to let the aerial hyphae extend and grow in its internal free; while bagasse provided a lot of contact surface made a lot of nutritiomycelium attached to the surface of sugar cane bagasse and internal. Our analysis to be a short growth cycle and high spore production was the results of nutrition mycelium and aerial mycelium together, and a suitable inert carrier should be attacheto provide a reasonable proportion of the area and space. It is clearly evident that sugarcane bagasse was better than PU foam. Bottle-shaped conidial stalk discovery and Verticillium lecanii fungus growth pattern show that solid-state fermentation withan carrier was the better way to produce conidia. Taking into account the spore extraction, pollution and second utilization factors, we believe that bagasse is more suitable as an inert carrier.4. The liquid - solid two-phase fermentation method on a level of lab had no significant effect for shorting growth cycle of Verticillium lecanii on sugarcane bagasse fermentation. Bagasse and wheat bran powder mixture at three ratios significantly shortened the fermentation cycle to about 8~9 days. It was longer than pure wheat bran fermentation (6 ~ 8 days), but shorter than bagasse adsorbed liquid medium (10 ~ 12 days). In the eighth or ninth day, three mixed materials reached a peak of sporulation at about 5.50×109 spores / g dry matter. This production was in the middle of a pure wheat bran culture sporulation (2.40×109 spores / g dry material), and sugarcane bagasse sporulation (1.02×1010 spores / g dry matter). Its fermentation cycle was also in the middle too. There was some linear relationship between spore production and duration of fermentation cycle. We proposed that nutritional conditions and fermentation methods were the major factor to determine Verticillium lecanii spore production.