McLean K S, Lawrence G W
Department of Agriculture, Northeast Louisiana University, Monroe 71209.
Department of Entomology and Plant Pathology, Mississippi State University, Mississippi State 39762.
Plant Dis. 1998 Jun;82(6):711. doi: 10.1094/PDIS.1998.82.6.711A.
A premature boll rot has been observed with increasing frequency in association with cotton (Gossypium hirsutum) in the Delta region of Louisiana-Mississippi. The initial developing cotton boll, sepals, and peduncle rapidly become necrotic and mummified. A dark brown to black lesion approximately 1 cm in length develops at the base of the peduncle, extending down the petiole below the diseased cotton boll. The diseased boll and peduncle remain attached to the petiole, hanging by a small portion of peduncle tissue. In an initial survey, the symptomatic boll rot was observed in 95% of the cotton fields in the Delta in 1996. A Phomopsis sp. was isolated from 58% of the diseased bolls, 42% of the cotton boll peduncles, and 52% of the leaf petioles collected from three cotton varieties. Fusarium spp. and Alternaria alternata were isolated from the diseased bolls with a frequency of 18 and 11%, respectively. Phomopsis sp. mycelium is dense, immersed, septate, and hyaline to pale brown in color. Stromata are pulvinate, less than 5 mm in diameter and form in a ring pattern. Pycinidia are erumpet, dark brown to black, separate or aggregated, and globose with ostiolate necks. Conidia are unicellular and hyaline, with alpha conidia oblong-elliptical and biguttulate while beta conidia are filiform and hamate in shape. The ratio of alpha to beta spores varies depending on the age of the culture. Pathogenicity tests with the sterile toothpick inoculation technique were conducted in a field planted with cotton cv. DPL 50. Developing cotton bolls approximately 5 to 8 mm in diameter were inoculated with either sterile toothpicks or toothpicks infested with a Phomopsis sp. Characteristic symptoms identical to the original boll rot were observed on 80% of the inoculated bolls 7 days after inoculation. A Phomopsis sp. was reisolated from the diseased bolls, completing Koch's postulates. No symptoms developed nor was the pathogen reisolated from the controls.
在路易斯安那州 - 密西西比州三角洲地区，与棉花（陆地棉）相关的早熟棉铃腐烂现象日益频繁地被观察到。最初发育的棉铃、萼片和果梗迅速坏死并干枯成木乃伊状。在果梗基部会出现一个长约1厘米的深褐色至黑色病斑，并向下延伸至患病棉铃下方的叶柄。患病棉铃和果梗仍附着在叶柄上，仅靠一小部分果梗组织悬挂着。在初步调查中，1996年三角洲地区95%的棉田都观察到了有症状的棉铃腐烂。从三个棉花品种的58%的患病棉铃、42%的棉铃果梗和52%的叶柄中分离出了一种拟茎点霉属真菌。分别从18%和11%的患病棉铃中分离出了镰孢属真菌和链格孢。拟茎点霉属真菌的菌丝体密集、内生、有隔膜，颜色从透明到浅褐色。子座呈垫状，直径小于5毫米，呈环状排列。分生孢子器突出，深褐色至黑色，分离或聚集，球形，有孔口颈。分生孢子单细胞且透明，α分生孢子长椭圆形、具双小粒，而β分生孢子丝状、具钩状。α孢子与β孢子的比例因培养物的年龄而异。使用无菌牙签接种技术在种植棉花品种DPL 50的田间进行了致病性测试。用无菌牙签或感染了拟茎点霉属真菌的牙签接种直径约5至8毫米的发育中的棉铃。接种7天后，在80%的接种棉铃上观察到了与最初棉铃腐烂相同的特征症状。从患病棉铃中重新分离出了拟茎点霉属真菌，完成了柯赫氏法则。对照未出现症状，也未重新分离出病原体。
