Key Laboratory of Integrated Pest Management on Crops in Southwest

Chengdu, China

Key Laboratory of Integrated Pest Management on Crops in Southwest

Chengdu, China
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Xue L.H.,Sichuan Academy of Agricultural Science | Xue L.H.,Lanzhou University | Xue L.H.,Key Laboratory of Integrated Pest Management on Crops in Southwest | Liu Y.,Sichuan Academy of Agricultural Science | And 8 more authors.
Plant Disease | Year: 2017

Aconitum carmichaelii Debeaux is a member of Aconitum, and its lateral root is the unique source of the famous “Fuzi” herb, officially named Radix Aconiti Lateralis Praeparata or Prepared Common Monkshood Daughter Root (Zhou et al. 2015). Because Fuzi is extensively used as a potent herb in China, A. carmichaelii is widely cultivated in Jiangyou, Sichuan Province, China. In April 2016, a new leaf spot disease was observed in a Chinese herb planting base of A. carmichaelii in Jiangyou (31.72847° N, 104.68756° W). Thirty field-grown plants were surveyed, and 7% of the total number of leaves of 30 plants had lesions. Gray mycelium and conidia were visible on both leaf surfaces with gray spots. Meanwhile, the lesions occurred in most cases at the tip and the margin of the leaves. Early symptoms showed small, irregular, black spots on the leaves. Subsequently, the spots became larger, sometimes circular, sunken necrotic lesions with gray mycelium and conidia in their center, often rapidly spreading to all parts of the plant under wet, humid conditions. However, under dry and higher temperatures conditions, the disease developed slowly or even became quiescent, and the lesions showed tan centers. For isolation, diseased leaves collected from the planting base were surface-disinfested in 5% NaOCl solution for 3 min, 75% ethanol solution for 30 s, rinsed thrice in sterilized distilled water, air dried, plated on potato dextrose agar (PDA), and incubated at 20°C for 4 days in the dark. Six fungal strains were isolated from these symptomatic leaves. For pathogenicity tests, 10 healthy and consistent leaves from the field were inoculated by a 10-µl droplet of conidia suspension (2 × 106 conidia/ml) from the isolate SY1 on moist paper towels in an enamelware tray. Ten leaves were inoculated with 10 µl of sterile distilled water as controls. Trays were covered individually with transparent plastic film for 4 days after inoculation to maintain high relative humidity and were placed in a greenhouse at 18 to 22°C. Foliar lesions similar to those observed in the field developed on leaves after 3 days inoculation, and after 4 days, 100% of the leaves were severely infected; control plants remained healthy. Pathogenicity tests were repeated three times. The same pathogen was consistently reisolated from the symptomatic tissues. Mycelia were initially hyaline and white, becoming dark gray after 96 h. The conidia produced on PDA were one-celled, ellipsoid or ovoid, 7.1 to 13.4 × 5.2 to 8.6 μm (avg. 10.3 × 6.6 µm). Microsclerotia were round, spherical, or irregular in shape, and 1.1 to 7.1 × 1.0 to 4.8 mm. These morphological characteristics were consistent with those of Botrytis cinerea (Zhang 2006), anamorph of Botryotinia fuckeliana. Teleomorph was not observed. Strain SY1 was selected as a representative for molecular identification. The ITS region of rDNA was amplified with primers ITS1/ITS4 and sequenced. BLAST analysis of the 526-bp segment (GenBank KX229751) showed 100% identity with the sequence of B. fuckeliana (teleomorph of B. cinerea). To further identify the species of B. cinerea, three nuclear protein-coding genes (G3PDH, HSP60, and RPB2) (Staats et al. 2005) were sequenced and the sequences (KX229752, KX229753, and KX229754, respectively) all showed 100% identity with those of B. cinerea. B. cinerea was reported on A. barbatum (Egorova 2007) in Russia, but not on A. carmichaelii. To our knowledge, this is the first report of B. cinerea causing gray mold on A. carmichaelii in China. Although B. cinerea does not usually kill Fuzi plants, it often heavily infects leaves and young shoots. Therefore, this disease could have a significant impact on the establishment and productivity of this crop in the field, especially under cool, wet growing conditions. © The American Phytopathological Society.

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