Zazzerini A, Tosi L
University of Perugia, Istituto di Patologia vegetale, Borgo XX Giugno, 74, 06121 Perugia, Italy.
Plant Dis. 1998 Feb;82(2):263. doi: 10.1094/PDIS.1998.82.2.263D.
During a survey in the spring of 1997, sunflower (Helianthus annuus L.) plants with characteristic symptoms (stunting and veinal chlorosis of leaves) of downy mildew caused by Plasmopara helianthi Novot. were observed in two experimental fields in the central Italian region of Umbria. In the first field, used to evaluate 58 commercial sunflower hybrids, fewer than 1% of plants displayed typical downy mildew symptoms. In a second field, planted with the old susceptible cultivar Ala, disease incidence was 12%. The inoculum of P. helianthi (one isolate from each field) was obtained either from downy mildew-infected leaves or infested soil (from around the roots of diseased plants). All were collected according to a random distribution. From this collection, two isolates were identified as race 2 by the whole-seedling immersion technique (2) with differential cultivars: HA 89, AD 66, CM 90 RR, RHA 265, RHA 274, HIR 34, DM-2, and HA 335. All differential lines were tested twice with 30 seeds per replicate (four replicates per line). Two weeks after inoculation the percentage of susceptible seedlings (showing sporulation on cotyledons and/or first true leaves) was determined. Race 2 has long occurred in some European countries, but this is the first report of this race from Italy. Extensive field surveys carried out in the last 10 years revealed that race 1 is the only one occurring in central Italy. An isolate apparently comparable to race 2 was reported in experimental plots in 1975 (1) where only Pl1 cultivars were susceptible. Differential lines, at that time, were not available and race identification was not carried out. Italy imposes importation regulations for sunflower seed that include treatment with metalaxyl. In greenhouse trials we have not observed a reduction in sensitivity to this systemic fungicide used as seed treatment against P. helianthi race 2. Consequently, the susceptibility of some commercial hybrids, indicated as resistant to downy mildew by importers, could be attributed to irregularity in the production of seeds. Also, an insufficient seed dressing with metalaxyl does not completely control the pathogen. References: (1) M. D'Armini et al. Atti Giornate Fitopatol. 1:659, 1975. (2) T. J. Gulya et al. Helia 14:11, 1991.
1997年春季的一项调查中，在意大利中部翁布里亚地区的两块试验田中，观察到了具有向日葵霜霉病特征症状（植株矮化和叶片叶脉黄化）的向日葵（Helianthus annuus L.）植株。向日葵霜霉病由Novot.的Plasmopara helianthi引起。在第一块用于评估58个商业向日葵杂交种的试验田中，表现出典型霜霉病症状的植株不到1%。在第二块种植了旧的感病品种Ala的试验田中，发病率为12%。向日葵霜霉病菌的接种体（从每块田分离得到一个菌株）取自感染霜霉病的叶片或染病土壤（染病植株根部周围）。所有样本均按随机分布采集。通过全苗浸渍技术（2），使用鉴别品种HA 89、AD 66、CM 90 RR、RHA 265、RHA 274、HIR 34、DM - 2和HA 335，从这些样本中鉴定出两个菌株为2号小种。所有鉴别品系均进行了两次测试，每次重复用30粒种子（每个品系四个重复）。接种两周后，测定感病幼苗（子叶和/或第一片真叶上出现孢子）的百分比。2号小种在一些欧洲国家早已存在，但这是该小种在意大利的首次报道。过去10年进行的广泛田间调查显示，1号小种是意大利中部唯一出现的小种。1975年（1）在试验田中报道了一个显然与2号小种相当的菌株，当时只有Pl1品种感病。那时没有鉴别品系，也未进行小种鉴定。意大利对向日葵种子实施进口规定，包括用甲霜灵处理。在温室试验中，我们未观察到作为种子处理剂用于防治向日葵霜霉病菌2号小种的这种内吸性杀菌剂的敏感性降低。因此，一些被进口商标明对霜霉病有抗性的商业杂交种的感病性，可能归因于种子生产的不规范。此外，甲霜灵拌种不足不能完全控制病原菌。参考文献：（1）M. D'Armini等人，《植物病理学会议论文集》1:659，1975年。（2）T. J. Gulya等人，《Helia》14:11，1991年。
