Killigrew B X, Sivasithamparam K, Scott E S
Soil Science (SEGS), The University of Western Australia, Crawley W.A. 6009, Australia.
Discipline of Plant and Pest Science, School of Agriculture and Wine, The University of Adelaide, Waite Campus, PMB 1, Glen Osmond, S.A. 5064, Australia.
Plant Dis. 2005 Jul;89(7):777. doi: 10.1094/PD-89-0777C.
Grapevine downy mildew, caused by the obligate, oomycete pathogen, Plasmopara viticola, was first recorded in Western Australia (W.A.) in 1998 (2) and has subsequently been observed in most viticultural regions of the state. Heterothallism in P. viticola was established by Wong et al. (3), whereby more than one mating type of the pathogen is required for sexual reproduction to occur. Oospores are considered to be the source of primary inoculum for this disease with further, secondary infection being advanced by asexual inoculum. However, recent research in European vineyards suggests that the majority of infection throughout the growing season arises via sexually derived (oosporic) inoculum (1). Since downy mildew is relatively new to W.A., few surveys have been conducted to study populations of the pathogen within the state. It is also noteworthy that the incidence of oospores in Australian vineyards has not been reported. The objective of this research was to assess the occurrence and type of inoculum of P. viticola in W.A. vineyards. A total of 1,266 P. viticola-infected leaf discs (LD) from eight wine-grape (775 LD), five table-grape (450 LD), and seven unknown (41 LD) cultivars grown in 16 vineyards in 10 geographically separate regions of W.A. were collected in the growing seasons of 2001-2003. These regions range from Chittering in the north to Albany in the south and received 700 to 1,200 mm annual rainfall, mostly in winter. Each LD was cleared in 1 M KOH at 60°C for 12 to 24 h and then was assessed for the presence of oospores with light microscopy. Leaves showing "mosaic"-type lesions (older infection) late in the season were collected where possible to ensure colony maturity and an increased likelihood of oospore formation. All LD from all regions were negative for the presence of oospores except for samples from a single vineyard (approximately 1,200 mm annual rainfall), where all 140 LD from six wine-grape cultivars contained oospores. The discovery that oospores were present in only one of 16 sampled vineyards provides a rare opportunity to study gene flow in field populations of the pathogen with time and to determine sources of primary inoculum where overwintering of P. viticola may not involve oospores. References: (1) S. McKirdy et al. Plant Dis. 83:301, 1999. (2) A. Rumbou et al. Eur. J. Plant Pathol. 110:379, 2004. (3) F. P. Wong et al. Plant Pathol. 50:427, 2001.
葡萄霜霉病由专性卵菌病原体葡萄生单轴霉（Plasmopara viticola）引起，1998年在西澳大利亚州（W.A.）首次被记录（2），随后在该州的大多数葡萄种植区都有发现。Wong等人（3）确定了葡萄生单轴霉的异宗配合现象，即有性繁殖需要该病原体的不止一种交配型。卵孢子被认为是这种疾病的初侵染源，进一步的二次感染则由无性接种体推动。然而，欧洲葡萄园的最新研究表明，整个生长季节的大部分感染是通过有性衍生（卵孢子的）接种体发生的（1）。由于霜霉病在西澳大利亚州相对较新，很少有调查研究该州内病原体的种群情况。同样值得注意的是，澳大利亚葡萄园卵孢子的发生率尚未见报道。本研究的目的是评估西澳大利亚州葡萄园葡萄生单轴霉接种体的发生情况和类型。在2001 - 2003年生长季节，从西澳大利亚州10个地理上分开的地区的16个葡萄园收集了总共1266个感染葡萄生单轴霉的叶片圆盘（LD），这些葡萄园种植了8个酿酒葡萄品种（775个LD）、5个鲜食葡萄品种（450个LD）和7个未知品种（41个LD）。这些地区从北部的奇廷到南部的奥尔巴尼，年降雨量为700至1200毫米，大部分降雨集中在冬季。每个LD在60°C的1 M氢氧化钾中处理12至24小时进行透明处理，然后用光学显微镜评估卵孢子的存在情况。在季节后期尽可能收集显示“花叶”型病斑（较老的感染）的叶片，以确保菌落成熟并增加卵孢子形成的可能性。除了来自一个葡萄园（年降雨量约1200毫米）的样本外，所有地区的所有LD的卵孢子检测均为阴性，该葡萄园六个酿酒葡萄品种的140个LD都含有卵孢子。仅在16个采样葡萄园中一个发现卵孢子，这为研究该病原体田间种群随时间的基因流动以及确定葡萄生单轴霉越冬可能不涉及卵孢子时的初侵染源提供了难得的机会。参考文献：（1）S. McKirdy等人，《植物病害》83:301，1999年。（2）A. Rumbou等人，《欧洲植物病理学杂志》110:379，2004年。（3）F. P. Wong等人，《植物病理学》50:427，2001年。
