Swart W J, Kriel W-M
Department of Plant Sciences, University of the Free State, P.O. Box 339, Bloemfontein 9300, South Africa.
Plant Dis. 2002 Jun;86(6):693. doi: 10.1094/PDIS.2002.86.6.693D.
The commercial cultivation of spineless cactus (Opuntia ficus-indica (L.) Miller) for its fruit is a relatively recent undertaking in South Africa but has been shown to possess huge export potential. To date, only one fungal pathogen, Didymosphaeria opulenta (De Not.) Sacc., has been officially reported on the genus Opuntia in South Africa, but the report is from O. stricta Haw. and not O. ficus-indica (1). The need for research on diseases of O. ficus-indica in South Africa has recently become important since local growers are increasingly reporting disease-related yield losses. Surveys conducted over a period of 3 years indicated that stems or cladodes are particularly prone to various forms of tissue necrosis, caused primarily by three fungi, which can ultimately lead to death of entire cladodes. Alternaria tenuissima was isolated from a dry superficial necrosis of the cuticle and underlying tissue as much as 3 mm deep. Symptoms include small chlorotic spots on the cuticle, which coalesce to form raised gray scabs. Fusarium sporotrichoides was isolated more commonly from dry necrotic lesions that were darker, larger, and less superficial, sometimes extending through the tissue to the opposite side of the cladode. Lasiodiplodia theobromae (teleomorph Botryosphaeria rhodina) was isolated from roundish black cankers (15 to 50 mm diameter) on cladodes and characterized by black gum exudation from the perimeter of the canker. Pycnidia were often evident on the surface of the canker. The fulfillment of Koch's postulates demonstrated that an isolate of each respective species was very aggressive in colonizing cladodes following artificial inoculations in the glasshouse. Mean lesion diameters measuring 15, 27, and 44 mm for A. tenuissima, F. sporotrichoides, and L. theobromae, respectively, were recorded 14 days after inserting wooden toothpick tips that had been colonized by the three pathogens into each of five cladodes of 18-month-old potted plants of O. ficus-indica (cv. Morado). Alternaria sp. and B. rhodina have been reported on Opuntia sp. in the United States (2), but no records of the above three fungi occurring on O. ficus-indica were found. References: (1) P. W. Crous et al. Phytopathogenic Fungi from South Africa. University of Stellenbosch, Department of Plant Pathology Press, Stellenbosch, South Africa, 2000. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989.
为获取果实而对无刺仙人掌（仙人掌属梨果仙人掌（L.）米勒）进行商业化种植，这在南非是一项相对较新的事业，但已显示出巨大的出口潜力。迄今为止，在南非，仙人掌属植物上仅官方报道过一种真菌病原体，即富氏双隔孢（De Not.）萨卡多，但该报道是关于刺梨仙人掌而非梨果仙人掌（1）。由于当地种植者越来越多地报告与病害相关的产量损失，近期对南非梨果仙人掌病害进行研究的需求变得尤为重要。一项为期3年的调查表明，茎或肉质茎特别容易出现各种形式的组织坏死，主要由三种真菌引起，最终可能导致整个肉质茎死亡。细链格孢从角质层和深达3毫米的下层组织的干性表面坏死处分离得到。症状包括角质层上的小褪绿斑点，这些斑点融合形成凸起的灰色痂。拟分枝镰刀菌更常见于颜色更深、更大且不太表浅的干性坏死病斑中，有时会穿过组织延伸到肉质茎的另一侧。可可毛色二孢（有性型为可可球座菌）从肉质茎上直径为15至50毫米的圆形黑色溃疡处分离得到，其特征是溃疡边缘有黑色树胶渗出。溃疡表面通常可见分生孢子器。科赫法则的验证表明，在温室中人工接种后，每个相应物种的一个分离株在定殖肉质茎方面极具侵袭性。将被这三种病原体定殖的木质牙签尖端插入18个月大的盆栽梨果仙人掌（品种为莫拉多）的五个肉质茎中，14天后分别记录细链格孢、拟分枝镰刀菌和可可毛色二孢的平均病斑直径为15、27和44毫米。在美国，链格孢属和可可球座菌已在仙人掌属植物上被报道过（2），但未发现上述三种真菌在梨果仙人掌上发生的记录。参考文献：（1）P. W. 克劳斯等人。《来自南非的植物病原真菌》。南非斯泰伦博斯大学植物病理学系出版社，南非斯泰伦博斯，2000年。（2）D. F. 法尔等人。《美国植物和植物产品上的真菌》。美国植物病理学会，明尼苏达州圣保罗，1989年。
