| Birdseye speedwell (Veronica persica Poir) is a major weed worldwide that significantly reduces yield of many different crops. In the search for biological control methods for birdseye speedwell, Colletotrichum gloeosporidies Penz. f.sp. veronicae S.Qiang et Q.Zeng, isolated from naturally infected birdseye speedwell, was virulent to the Veronica species but was safety to such crops as wheat, rape, soybean, cotton and com under laboratory or greenhouse conditions, which had the potential to be developed as mycoherbicide for birdseye speedwell. The aim of this study was to evaluate and improve the some related techniques for the commercialization of Collectotrium gloeosporiodies f.sp. veronicae as a potential mycoherbicide for birdseye speedwell.Firstly, the studies on fermentation methods, kinds, pH and water content of cultural media, and cultural time were conducted in order to develop a technique of mass-production of conidia of Collectotrichum gloeosporioides as a biological agent for Veronica persica. The research results showed that the conidia of this fungus could be mass-produced in both of submerged and solid substrate, but the highest harvest of conidia was made under the fermentation combined mycelia produced in submerged substrate and conidia sporulated in solid substrate. The wheat-bran and bean-cake substrate was the best one selected from the solid media tested, which all were suitable for the culture of this fungus. The highest yield at 8.30 x 109 conidia g-1 dry weight was obtained under pH 6.5-7.5 and water content equaled to 1.2 time dry-weight of solid media and after six-day culture. The addition of Veronica persica powder could promote to sporulate in solid media.The raw conidia powder produced by combined liquid-solid substrate fermentation contains abundant conidia (nearly 1010 conidia g-1 dry weight) , and it can be stored with simple equipment. While the fresh conidial powder of Collectotrichum gloeosporioides Penz. f.sp. veronicae Sheng Qiang et Qing Zeng was stored at 4癈 and room temperature in open or close capsule, germination rates and length of germ tube of conidia wereexamined at 15 and 60 days intervals, respectively. Results showed that there were no significant differences in germination rates and length of germ tube of conidia stored at 4 癈 and room temperature within 6 months. However, the germination rates and length of germ tube of conidia decreased significantly after storage for over 10 months at 4C or room temperature. In general, the conidia viability were most stable when the conidia powder with 4.0% water content was stored closely at 4C because the germination rates were 70.4% and the length of germ tube decreased only by 43.2% by the end of 420 days comparing to that by 60 days. Whereas, the conidia powder with 9.6% water content stored openly at room temperature were declined the most obviously, the corresponding values were 35.5% and 12.7% respectively. Therefore, storage temperature and water content of conidia were two key factors, influencing the shelf-life of Collectotrichum gloeosporioides f.sp. veronicae conidia. The conidia were heat-treated in oven at 40~60 C for 15~120 min to observe tolerance to high temperature of conidia. Results showed that the conidia powder was partly tolerant to temperature, while the susceptivity increased obviously with temperature rising. A regression analysis showed that the length of germ tube of conidia were decreased by 50% when heat-treated at 60C for 6 min comparing with that of control.The compatibility of Collectotrichum gloeosporioides conidia with six widely used herbicides was investigated by comparing germination rates and germ tube length of conidia in liquid containing 0.1-1.0 fold of concentration recommended for field spray. The results showed that the conidia germinated well in herbicides tested, even at the field-spray concentration recommended, the germination rate was more than 78.3%. The results also showed that negative effect of herbicide on the growth of conidia germ tube increased signific... |
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