Costa J L da S, de Oliveira V C
Rice and Beans Research Institute (Embrapa), P.O. Box 179, 75375-000 Santo Antônio de Goiás, GO, Brazil.
Catholic University of Goiás, P.O. Box 86, 74605-010 Goiânia, GO, Brazil.
Plant Dis. 1999 May;83(5):486. doi: 10.1094/PDIS.1999.83.5.486A.
In September 1997, after the tropical winter season and following a long warm (28 to 33°C) and rainy (27 mm) period, smut symptoms were observed on two dry-bean (Phaseolus vulgaris) fields in Brazil. Brownish to blackish powdery masses of spores were observed on stems, pods, and roof green and senescent plants. No galls were observed. Hyphae in infected tissue were intercellular; no clamp connections were observed. Typical globose teliospores were observed that measured 7 to 11 μm. Spores were uninucleate or binucleate; predominantly brownish with flattened poles and equatorial band; the exospore wall was thick and surface ornamented (echinulate-type). Teliospores incubated in water drops generated transversely septate promycelia, unbranched, producing terminal and lateral basidiospores. The fungus did not grow well on potato dextrose agar (PDA) medium, generating yeastlike colonies. To confirm pathogenicity of a Ustilago sp., spores collected from field-infected plants were inoculated on 8- and 20-day old seedlings of dry-bean cultivars Rosinha and Perola. Spore suspensions of 10 teliospores were sprayed all over the plants. After inoculation, plants were kept in a moist chamber (relative humidity [RH] 100%) for 2 days. At the third day, inoculated plants were covered with clear polyethylene bags and transferred to the greenhouse (RH 50%, temperature 25 ± 2°C). Noninoculated controls were included for comparisons. Within 2 weeks, all inoculated plants reproduced field symptoms of darkened tissues covered by profuse sori containing teliospores and basidiospores. Eight-day-old plants died 2 weeks after inoculation. Noninoculated plants did not develop any symptoms. Teliospores obtained from dead plants were identical to those used for inoculation, thus completing Koch's postulates. Fischer (1), and later Fischer and Shaw (2), proposed a species concept for Ustilago based on morphology (primarily of the teliospore), symptomatology, and host specialization at the host-family level. Although the teliospores found on dry-beans, in Brazil, are much like those of Ustilago maydis, the fungus did not cause galls on plants, was able to infect roots and kill seedlings. and is very well adapted to a legume plant. Cross inoculation tests indicated that spores from dry-beans cannot cause disease symptoms on maize. We therefore regard the bean smut as a new species. We are not aware of any other Ustilago sp. being reported on a legume host. References: (1) G. W. Fischer. 1953. Manual of the North America Smut Fungi. (2) G. W. Fischer and C. G. Shaw. Phytopathology 43:181, 1953.
1997年9月，在热带冬季过后，经历了一段漫长温暖（28至33°C）且多雨（27毫米）的时期后，巴西的两块干豆（菜豆）田出现了黑粉病症状。在茎、豆荚以及绿色和衰老植株的顶部观察到了从褐色到黑色的粉状孢子团。未观察到瘤瘿。受感染组织中的菌丝存在于细胞间；未观察到锁状联合。观察到典型的球形冬孢子，直径为7至11微米。孢子单核或双核；主要呈褐色，两极扁平且有赤道带；外孢壁厚，表面有纹饰（小刺状类型）。在水滴中培养的冬孢子产生横向分隔的先菌丝，不分枝，产生顶生和侧生担孢子。该真菌在马铃薯葡萄糖琼脂（PDA）培养基上生长不佳，形成酵母样菌落。为了确认一种黑粉菌属真菌的致病性，将从田间感染植株上收集的孢子接种到8日龄和20日龄的干豆品种罗西尼亚和佩罗拉的幼苗上。将含有10个冬孢子的孢子悬浮液喷洒在整株植物上。接种后，将植株置于湿度箱（相对湿度[RH]100%）中2天。第三天，对接种的植株用透明聚乙烯袋覆盖，并转移到温室（RH 50%，温度25±2°C）。设置未接种的对照进行比较。在2周内，所有接种的植株都出现了田间症状，即组织变黑，覆盖着大量含有冬孢子和担孢子的孢子堆。8日龄的植株在接种后2周死亡。未接种的植株未出现任何症状。从死亡植株上获得的冬孢子与用于接种的冬孢子相同，从而完成了柯赫氏法则验证。菲舍尔（1），以及后来的菲舍尔和肖（2），基于形态学（主要是冬孢子的形态）、症状学以及寄主科水平上的寄主专一性，为黑粉菌属提出了一个物种概念。尽管在巴西干豆上发现的冬孢子与玉米黑粉菌的冬孢子非常相似，但该真菌不会在植物上引起瘤瘿，能够感染根部并杀死幼苗，而且非常适应豆科植物。交叉接种试验表明，来自干豆上的孢子不会在玉米上引起病害症状。因此，我们将这种豆类黑粉病视为一个新物种。我们不知道有任何其他黑粉菌属物种在豆科寄主上被报道过。参考文献：（1）G. W. 菲舍尔。1953年。《北美黑粉菌手册》。（2）G. W. 菲舍尔和C. G. 肖。《植物病理学》43:181，1953年。
