Department of Plant Pathology, 1630 Linden Drive, University of Wisconsin-Madison, Madison, Wisconsin 53706.
Appl Environ Microbiol. 1990 Mar;56(3):713-8. doi: 10.1128/aem.56.3.713-718.1990.
We explored the potential of biological control of alfalfa (Medicago sativa L.) seedling damping-off caused by Phytophthora megasperma f. sp. medicaginis by screening root-associated bacteria for disease suppression activity in a laboratory bioassay. A total of 700 bacterial strains were isolated from the roots of field-grown alfalfa plants by using Trypticase soy agar. A simple, rapid assay was developed to screen the bacteria for the ability to reduce the mortality of Iroquois alfalfa seedlings that were inoculated with P. megasperma f. sp. medicaginis zoospores. Two-day-old seedlings were planted in culture tubes containing moist vermiculite, and each tube was inoculated with a different bacterial culture. Sufficient P. megasperma f. sp. medicaginis zoospores were added to each tube to result in 100% mortality of control seedlings. Of the 700 bacterial isolates tested, only 1, which was identified as Bacillus cereus and designated UW85, reduced seedling mortality to 0% in the initial screen and in two secondary screens. Both fully sporulated cultures containing predominantly released spores and sterile filtrates of these cultures of UW85 were effective in protecting seedlings from damping-off; filtrates of cultures containing predominantly vegetative cells or endospores inside the parent cell had low biocontrol activity. Cultures grown in two semidefined media had significantly greater biocontrol activities than cultures grown in the complex tryptic soy medium. In a small-scale trial in a field infested with P. megasperma f. sp. medicaginis, coating seeds with UW85 significantly increased the emergence of alfalfa. The results suggest that UW85 may have potential as a biocontrol agent for alfalfa damping-off, thus providing an alternative to current disease control strategies.
我们通过实验室生物测定筛选根际相关细菌的防病活性，探索利用生物防治控制大丽轮枝菌（Phytophthora megasperma f. sp. medicaginis）引起的紫花苜蓿（Medicago sativa L.）幼苗猝倒的潜力。从田间生长的紫花苜蓿植物根系中分离出 700 株细菌，使用胰蛋白酶大豆琼脂。开发了一种简单、快速的测定方法，筛选具有降低接种大丽轮枝菌游动孢子的伊洛魁苜蓿幼苗死亡率的能力的细菌。将两天大的幼苗种植在含有湿润蛭石的培养管中，每个管中接种不同的细菌培养物。向每个管中添加足够的大丽轮枝菌游动孢子，以使对照幼苗的死亡率达到 100%。在测试的 700 个细菌分离物中，只有 1 个被鉴定为蜡状芽孢杆菌，并命名为 UW85，在最初的筛选和两次二次筛选中均将幼苗死亡率降低至 0%。含有主要释放孢子的完全孢子化培养物和这些 UW85 培养物的无菌滤液均有效地保护幼苗免受猝倒；含有主要是营养细胞或母细胞内内生孢子的培养物滤液的生物防治活性较低。在两种半定义培养基中生长的培养物的生物防治活性明显高于在复杂胰蛋白酶大豆培养基中生长的培养物。在受大丽轮枝菌侵染的田间进行的小规模试验中，用 UW85 包衣种子显著增加了苜蓿的出苗率。结果表明，UW85 可能具有作为苜蓿猝倒病生物防治剂的潜力，从而为当前的疾病控制策略提供了一种替代方法。
