Schroeder K L, Paulitz T C
Department of Plant Pathology, Washington State University, Pullman 99164-6430.
USDA-ARS, Pullman, WA 99164-6430.
Plant Dis. 2012 Apr;96(4):584. doi: 10.1094/PDIS-09-11-0809-PDN.
Canola (Brassica napus L) production has gained renewed interest in Washington State over the past few years, primarily for the purpose of producing biofuel. Plants were observed to be showing symptoms of Rhizoctonia root rot and postemergence damping-off. In many cases, this was due to Rhizoctonia solani AG-2-1, which was previously documented (4). However, additional plants were occasionally observed that were stunted and had reduced vigor, but lacked the distinctive severe stem damage and postemergence damping-off, which are both symptoms of infection with R. solani AG-2-1. Isolates of R. solani AG-10 were collected from symptomatic plants or baited from root zone soil at various dryland production locations in eastern Washington, including sites near Colfax, Pullman, and Walla Walla. Initial identification was determined by quantitative (Q)-PCR using R. solani AG-10 specific primers (3). The identity was verified by sequencing random isolates identified by Q-PCR (GenBank Accessions Nos. JQ068147, JQ068148 and JQ068149). All sequenced isolates had 99% identity to previously reported isolates of R. solani AG-10. Six isolates were chosen to test pathogenicity on canola plants in the greenhouse. Sterilized oats were inoculated with each of six isolates of R. solani AG-10 and grown for 4 weeks. The soil was infested with ground oat inoculum (1% wt/wt) and spring canola cv. Sunrise was seeded into 3.8 × 21-cm containers. After 3 weeks of incubation at 15°C, plants were harvested and assessed. Emergence was reduced in the infested soil with 73 to 93% (average 81%) emergence compared with 100% emergence in the noninfested soil. There was no evidence of postemergence damping-off. However, all six isolates of R. solani AG-10 significantly reduced the plant height and top dry weights compared with the noninfested controls. The plant height in infested soil was 28 to 42% (average 34%) shorter and top dry weights were 37 to 70% (average 54%) lower than in noninfested soil. Roots of infected plants had a light brown discoloration along with reduced length and fewer lateral roots. Additional host plants were tested, including wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), pea (Pisum sativum L.), chickpea (Cicer arietinum L.), and lentil (Lens culinaris Medik.). There was no significant reduction in plant height or plant dry weight for any of these hosts. R. solani AG-10 was previously found to be weakly virulent on canola and other cruciferous hosts in Australia (1,2). To our knowledge, this is the first report of R. solani AG-10 causing disease on canola in Washington State. Reference: (1) R. K. Khangura et al. Plant Dis. 83:714, 1999. (2) G. C. MacNish et al. Australas. Plant Pathol. 24:252, 1995. (3) P. A. Okubara et al. Phytopathology 98:837, 2008. (4) T. C. Paulitz et al. Plant Dis. 90:829, 2006.
在过去几年里，华盛顿州对油菜（甘蓝型油菜）生产重新产生了兴趣，主要目的是生产生物燃料。人们观察到一些植株出现了立枯丝核菌根腐病症状和出土后猝倒现象。在许多情况下，这是由立枯丝核菌AG-2-1引起的，此前已有相关记录（4）。然而，偶尔也会观察到其他植株生长发育不良、活力下降，但没有立枯丝核菌AG-2-1感染所特有的严重茎部损伤和出土后猝倒症状。从华盛顿州东部不同旱地生产地点的有症状植株上采集了立枯丝核菌AG-10的分离株，或从根际土壤中诱捕得到，这些地点包括科尔法克斯、普尔曼和沃拉沃拉附近的地区。最初的鉴定是通过使用立枯丝核菌AG-10特异性引物的定量（Q）-PCR进行的（3）。通过对Q-PCR鉴定出的随机分离株进行测序（GenBank登录号为JQ068147、JQ068148和JQ068149）来验证其身份。所有测序的分离株与先前报道的立枯丝核菌AG-10分离株具有99%的同源性。选择了六个分离株在温室中对油菜植株进行致病性测试。用立枯丝核菌AG-10的六个分离株分别接种灭菌燕麦，培养4周。土壤用磨碎的燕麦接种物（1%重量/重量）侵染，春油菜品种Sunrise播种到3.8×21厘米的容器中。在15°C下培养3周后，收获并评估植株。与未侵染土壤中100%的出苗率相比，侵染土壤中的出苗率降低了73%至93%（平均81%）。没有出土后猝倒的迹象。然而，与未侵染的对照相比，立枯丝核菌AG-10的所有六个分离株均显著降低了植株高度和地上部干重。侵染土壤中的植株高度比未侵染土壤中的短28%至42%（平均34%），地上部干重比未侵染土壤中的低37%至70%（平均54%）。受感染植株的根系有浅褐色变色，长度缩短，侧根减少。还对其他寄主植物进行了测试，包括小麦（普通小麦）、大麦（大麦）、豌豆（豌豆）、鹰嘴豆（鹰嘴豆）和小扁豆（兵豆）。这些寄主植物的株高或植株干重均没有显著降低。立枯丝核菌AG-10此前在澳大利亚被发现对油菜和其他十字花科寄主的致病性较弱（1,2）。据我们所知，这是立枯丝核菌AG-10在华盛顿州引起油菜病害的首次报道。参考文献：（1）R.K.Khangura等人，《植物病害》83:714，1999年。（2）G.C.MacNish等人，《澳大利亚植物病理学》24:252，1995年。（3）P.A.Okubara等人，《植物病理学》98:837，2008年。（4）T.C.Paulitz等人，《植物病害》90:829，2006年。
