Conn Kenneth L, Leci Edlira, Kritzman Giora, Lazarovits George
Agriculture and Agri-Food Canada (AAFC), Pest Management Research Center (PMRC), 1391 Sandford St., London, Ontario, Canada N5V 4T3.
Department of Plant Pathology, ARO, The Volcani Center, Bet Dagan 50 250 Israel.
Plant Dis. 1998 Jun;82(6):631-638. doi: 10.1094/PDIS.1998.82.6.631.
A procedure is described for estimating Streptomyces populations in soil. Soils are air-dried, 10g quantities are shaken in plastic bags containing 0.1% water agar and homogenized with a Stomacher homogenizer, serial dilutions are plated on a semi-selective culture (STR) medium and incubated for 2 weeks at 22°C, and the Streptomyces colonies are enumerated. Use of STR medium reduced the bacterial and fungal colonies recovered from soil to levels below that of the Streptomyces spp. while not affecting the number of Streptomyces colonies compared with those enumerated on yeast malt extract medium. A procedure for screening large numbers of Streptomyces strains for thaxtomin production, a phytotoxin recognized as a virulence marker in S. scabies, is also described. Strains are grown on oatmeal medium, and the thaxtomin is extracted from the medium by facilitated diffusion and detected by miniature thin layer chromatography. S. scabies and S. acidiscabies strains (approximately 130 from Ontario and 70 from other locations in North America) that produced thaxtomin did not form aerial mycelia or sporulate on STR medium within 2 weeks at 22°C. Ontario S. scabies strains that produced thaxtomin A also produced melanin on STR medium. All S. scabies strains from scab lesions that produced thaxtomin A had this colony morphology, whereas only 4 to 9% of strains from soil with this colony morphology produced thaxtomin A. Using these procedures, we determined that the population of thaxtomin-producing S. scabies in soil from a potato field in Ontario with a history of potato scab was about 20,000 CFU/g soil.
本文描述了一种估算土壤中链霉菌种群数量的方法。将土壤风干，称取10克土壤置于含有0.1%水琼脂的塑料袋中振荡，并使用Stomacher均质器进行均质处理，然后进行系列稀释，接种于半选择性培养基（STR）上，在22°C下培养2周，最后对链霉菌菌落进行计数。与在酵母麦芽提取物培养基上计数的结果相比，使用STR培养基可将从土壤中回收的细菌和真菌菌落数量降低至低于链霉菌属的水平，同时不影响链霉菌菌落的数量。本文还描述了一种筛选大量链霉菌菌株以检测其是否产生硫代米星的方法，硫代米星是一种植物毒素，被认为是疮痂链霉菌的毒力标记。将菌株接种于燕麦片培养基上培养，通过促进扩散从培养基中提取硫代米星，并使用微型薄层色谱法进行检测。在22°C下培养2周后，产生硫代米星的疮痂链霉菌和酸疮痂链霉菌菌株（约130株来自安大略省，70株来自北美其他地区）在STR培养基上不形成气生菌丝或孢子。在安大略省产生硫代米星A的疮痂链霉菌菌株在STR培养基上也产生黑色素。所有从疮痂病变中分离出的产生硫代米星A的疮痂链霉菌菌株都具有这种菌落形态，而具有这种菌落形态的土壤菌株中只有4%至9%产生硫代米星A。使用这些方法，我们确定安大略省一块有马铃薯疮痂病史的马铃薯田土壤中产生硫代米星的疮痂链霉菌种群数量约为20,000 CFU/克土壤。
