【作者】 刘淑芬；

【导师】 刘大群； 陈森玉；

【作者基本信息】 河北农业大学 ， 植物病理， 2004， 博士

【摘要】 食线虫真菌Hirsutella minnesotensis和Hirsutela rhossiliensis是大豆孢囊线虫(Heterodera glycines)二龄幼虫(J2)的两种内生寄生物。在实验室，温室，和明尼苏达大豆田对两种真菌的生物学和生态学特性进行了调查。Hirsutella minnesotensis是最近分离的大豆孢囊线虫的病原菌，该菌在接种后7天开始产孢，接种后13或14天在菌丝体上的孢子数量达到高峰，平均39／J2。产孢高峰后，在菌丝体上的孢子数量很快降低，接种后38天观察仅几个或无任何孢子。用琼脂平板测定，分生孢子从孢子梗上脱落后显然失去侵染性。然而，当脱落的孢子和二龄幼虫被培育在土壤两天，有7.5％到9.7％的J2被真菌孢子附着。真菌孢子转移到J2的百分比与起初加到土壤的真菌定殖的J2的数成正相关。每25克土壤中，以4，800真菌定殖的J2接种水平，在加定殖的J2后9天，孢子的转移率可达75％。此菌在土壤有弱的腐生生长能力。菌丝或孢子加入土壤，最初能产生侵染孢子，但寄生性随着时间的延长而衰弱，在加真菌后35天，对测定J2仅有有限的寄生性。当真菌定殖的J2加到微波处理的土壤后367天，可检测到孢子的侵染性，但在450天，观察无任何侵染性。Hirsutella minnesotensis的线虫寄主范围比较宽，包括植物寄生线虫，食昆虫线虫，食真菌线虫和食细菌线虫。 在温室研究测定，与土壤对照和玉米渣空白对照相比，无论用液体培养物以每盆0.2，0.4和0.8克菌丝体接种水平还是以1％玉米渣固体培养物接种水平，Hirsutella minnesotensis和Hirsutella rhossiliensis在灭菌的和未处理的土壤，均能有效地减少线虫群体密度。土壤pH，土壤结构和有机质均影响H．minnesotensis和H．rhossiliensis对J2的寄生性，这取决于真菌种，真菌接种水平和接种天数。土壤pH，土壤结构和有机质也影响两个真菌对大豆孢囊线虫的生防效果，这取决于真菌种和真菌接种水平。琼脂平板测定pH对H．minnesotensis和H．rhossiliensis生长和产孢的影响，结果表明，两个真菌的菌落直径与pH的关系符合立方模型。两个真菌的菌落生长的最适pH为6.2。当pH降低到4，两个真菌的菌落生长显著受抑制。当pH逐渐增加从最适pH到pH10，生长逐渐受抑制。两个真菌的最适产孢pH类似于最适生长pH。当pH降低到4或pH高为9和10，产孢量会减少。 于2002和2003年，在玉米和大豆田调查了耕地处理是否影响H．minnesotensis和H．rhossiliensis对J2的寄生性。两年的数据表明，在不同的样品日在玉米田或大豆田，在2002年，耕地处理与免耕相比，无任何差异对两种菌的寄生性。然而在2003年的春季和收获季节，大豆田的J2被Hirsutella spp．寄生的百分比在免耕处理显著高于在常规耕作处理。Hirsutella spp．寄生二龄幼虫的百分比，大豆田显著高于玉米田。季节影响真菌的寄生性，Hirsutella spp．寄生二龄幼虫的百分比在中期季节高于种植和收获季节。 用真菌悬浮液处理大豆种子，营养菌落接种土壤，在温室条件下，H．minnesotensis和H．rhossiliensis均能侵染和定殖根，但不引起根部病害。用营养菌落接种土壤，H．rhossiliensis能促进大豆根生长在灭菌和自然土壤，然而，H．minnesotensis仅促进大豆根生长在灭菌土壤。更多还原

【Abstract】 Nematophagous fungi Hirsutella minnesotensis and Hirsutella rhossiliensis are two endoparasites of second-stage juveniles (J2) of the soybean cyst nematode (SCN), Heterodera glycines. Ecology and biology of the two fungi were investigated in laboratory and greenhouse and Minnesota soybean field. Hirsutella minnesotensis is a recently isolated pathogen of the SCN. The fungus started sporulation 7 days after inoculation (DAI), and the number of spores on the mycelium reached a peak, average 39 (range 5 to 120) spores/J2, at 13 or 14 DAI. After the peak, the number of spores on the mycelium decreased quickly. At 38 DAI, only a few or no spores were observed on the mycelium. On water agar test, spores detached from phialides appeared to lose infectivity. However, when the detached spores and J2 were incubated in soil for two days, there were 7.5% to 9.7% of the J2 attached by fungal spores. The percentage of J2 transmitted by the fungus was positively related with the number of fungus-colonized J2 initially added into the soil. At 4,800 fungus-colonized J2 (= 72,000 spores) per 25 grams of soil, approximately 75% of assay J2 were transmitted 9 days after adding the colonized J2. The fungus has a weak ability of saprophytic growth in soil. Mycelium or spores added into soil could produce infective spores initially, but parasitism declined over time, and at 35 days after adding the fungus only limited parasitism was observed by adding assay J2. When fungus-colonized J2 were added into soil treated with microwave heating, infective spores were detected up to 367 days, but no infectivity was observed at 450 day after adding the J2. Nematode host range of H. minnesotensis was wide including plant-parasitic nematodes, entomophilic nematodes, fungal-feeding nematodes, and bacteria-feeding nematodes.In greenhouse studies, both liquid culture at 0.2, 0.4 and 0.8 g of mycelium/pot and solid culture at 1% of corn-grits culture of the two fungi effectively reduced nematode population densities in both autoclaved and untreated soils. Four soils with different pH, texture and organic matter influenced parasitism of J2 and biocontrol effectiveness of the two fungi.The effect of pH on growth and sporulation Hirsutella rhossiliensis and Hirsutella minnesotensis on agar plate was investigated. The optimum pH for the colony to grow on agar was approximately 6.2 for both fungi. The growth of both species was reduced drastically when pH was reduced to 4, and reduced gradually when pH increased from the optimum pH up to pH 10. Optimum pH for sporulation of the two fungi was similar to the optimum pH for growth, and the sporulation was greatly inhibited by either low pH at 4 or high pH at 9 and 10.The effect of tillage on parasitism of Heterodera glycines J2 by the two fungi was investigated in soybean and corn fields in Minnesota during 2002 and 2003. Two years data indicated that there were no differences between conventional tillage and no-till for the parasitism of Hirsutella spp. at the different sampling dates either in soybean field or corn field in 2002. In 2003, however, the percentage of J2 parasitized by Hirsutella in no-till was significantly higher than that in conventional tillage in spring and at harvest in the soybean field. In soybean field, the percentage of J2 parasitized by Hirsutella spp. was higher than that in corn field. The seasonaffected the parasitism of the fungus Hirsutella spp.; the percentage of J2 parasitized by Hirsutella spp. at middle season was higher than that at planting and harvest season.On water agar and soil tests, H. rhossiliensis and H. minnesotensis were able to infect and colonize root, but symptoms of root disease were not observed. Hirsutella rhossiliensis promoted soybean growth in autoclaved soil and natural soil, however, H. minnesotensis only promoted soybean growth in autoclaved soil.更多还原