Copes Warren E, Rodriguez-Carres Marianela, Toda Takeshi, Rinehart Tim A, Cubeta Marc A
Agricultural Research Service (ARS) Southern Horticulture Laboratory, Poplarville, MS 39470.
Department of Plant Pathology, Center For Integrated Fungal Research, North Carolina State University, Raleigh 27695.
Plant Dis. 2011 Jun;95(6):705-711. doi: 10.1094/PDIS-11-10-0796.
Rhizoctonia web blight is an annual problem on container-grown azalea (Rhododendron spp.) in the southern and eastern United States but little is documented about the distribution or persistence of Rhizoctonia spp. in container-grown azalea. Sixty web-blight-damaged azalea plants ('Gumpo White') were collected in August 2005 and 2006 and arranged in a completely randomized design on an outdoor irrigation pad. A nylon mesh bag containing 30 necrotic leaves collected from web-blight-damaged 'Gumpo White' azalea plants were placed on the surface of the medium under the plant canopy in each container to simulate leaf litter. Ten plants were destructively sampled into eight zones by dividing stems into three zones (lengths of 0 to 2, 4 to 6, and 9 to 15 cm above the medium surface), bagged leaves into one leaf litter zone, and the medium into four zones (three horizontal layers: 1 to 3, 3 to 7, and 7 to 10 cm below the medium surface, with the middle layer further divided by removing the central 7.5-cm-diameter core) in December, February, and May. Only the three stem zones were sampled from 10 plants in early and late June and late July. Of 8,940 total isolations, 3,655 fungi with morphological characteristics of a Rhizoctonia sp. were recovered. Percent recovery differed from the eight zones (P < 0.0001) but did not differ between years (P = 0.3950) and sampling times (P = 0.1896). Frequency of recovery of Rhizoctonia spp. was highest from the lower stem and the leaf litter, and decreased with distance from the leaf litter. Recovery from stems over the six sample times was analyzed separately. Percent recovery differed between stem zones (P < 0.0001), sample times (P = 0.0478), and experiment years (P < 0.0001). In both years, mean recovery of Rhizoctonia spp. was higher from the lower stem and decreased with distance to the upper stem layer. From a subsample of 145 isolates, 95.1% were identified as binucleate Rhizoctonia (BNR) anastomosis groups (AGs)-A, -G, -K, -R, -S, and -U (-P), and 2.8 and 2.1% were Rhizoctonia solani AG-2 and an uncultured Laetisaria sp., respectively. Based on frequency analysis, recovery of BNR AGs differed by plant zone (P < 0.0001) but not over sample times (P = 0.4831). The six AGs of BNR are the predominant Rhizoctonia fungi occupying the habitat niches in container-grown azalea, with little change in population frequency and composition from fall to summer; thus, BNR pathogenic and nonpathogenic to azalea have established a mixed Rhizoctonia community on container-grown azalea.
丝核菌网斑病是美国南部和东部容器栽培杜鹃花（杜鹃花属）每年都会出现的问题，但关于丝核菌属在容器栽培杜鹃花中的分布或存活情况的记录很少。2005年8月和2006年收集了60株受网斑病损害的杜鹃花植株（‘Gumpo White’），并以完全随机设计的方式放置在室外灌溉垫上。将一个装有从受网斑病损害的‘Gumpo White’杜鹃花植株上收集的30片坏死叶片的尼龙网袋放在每个容器中植株冠层下的培养基表面，以模拟落叶层。12月、2月和5月，通过将茎干分为三个区域（培养基表面上方0至2厘米、4至6厘米和9至15厘米），将袋装叶片作为一个落叶层区域，将培养基分为四个区域（三个水平层：培养基表面下方1至3厘米、3至7厘米和7至10厘米，中间层通过移除直径7.5厘米的中心核心进一步划分），对10株植株进行破坏性采样。6月初、6月末和7月末仅从10株植株的三个茎干区域进行采样。在总共8940次分离中，回收了3655株具有丝核菌属形态特征的真菌。回收率在八个区域间存在差异（P < 0.0001），但在年份间（P = 0.3950）和采样时间间（P = 0.1896）无差异。丝核菌属的回收率在下部茎干和落叶层中最高，并随与落叶层距离的增加而降低。对六个采样时间的茎干回收情况进行了单独分析。回收率在茎干区域间（P < 0.0001）、采样时间间（P = 0.0478）和试验年份间（P < 0.0001）存在差异。在这两年中，丝核菌属的平均回收率在下部茎干中较高，并随向上部茎干层距离的增加而降低。从145株分离株的子样本中，95.1%被鉴定为双核丝核菌（BNR）融合群（AGs）-A、-G、-K、-R、-S和-U（-P），2.8%和2.1%分别为立枯丝核菌AG-2和一种未培养的拉蒂丝菌属物种。基于频率分析，BNR AGs的回收率因植株区域而异（P < 0.0001），但在采样时间间无差异（P = 0.4831）。BNR的六个AGs是占据容器栽培杜鹃花生境生态位的主要丝核菌真菌，从秋季到夏季种群频率和组成变化不大；因此，对杜鹃花致病和不致病的BNR在容器栽培杜鹃花上建立了一个混合的丝核菌群落。
