First Report of Stem Blight of Eleocharis dulcis Caused by Phoma bellidis in China

Abstract

Eleocharis dulcis is a perennial herbaceous plant in the family Cyperaceae, which is native to China and India where it grows well in moist-to-wet soils. It is commonly used as a fruit or a vegetable. From August 2009 to December 2010, symptoms were observed on E. dulcis stems in Tuanfeng County, Hubei, China, with the crop area affected estimated to be more than 1,300 ha per year. Corm yield was reduced by 20% on average with as much as 60% yield losses in some fields. Lesions were initially small, red-brown, and oval or circular that enlarged to produce apical necrosis and extending until the stems withered, usually within 2 months. To obtain isolates, diseased tissue was disinfested for 1 min in 0.1% mercuric chloride solution, rinsed with sterilized water, and plated on potato dextrose agar. Isolates with similar morphological characteristics were consistently recovered. Three isolates, CTF-3, CTF-10, and CTF-11, were used to further evaluate characteristics of the pathogen. After 7 days, white colonies were 76 to 80 mm across on oatmeal agar (OA) with sparse aerial hyphae and a slight salmon color in the conidial masses. Pycnidia produced on OA were globose to subglobose, usually with one slightly ostiolar papilla, olivaceous to olivaceous black, and 93 to 245 μm in diameter. Conidia were hyaline, unicellular, ellipsoidal, mostly with two polar guttules, and 3.6 to 6.2 × 2.0 to 3.3 μm. Chlamydospores were absent. Growth of the isolates on malt extract agar (MEA) was slower than on OA, and the colony diameters at 7 days were 60 to 65 mm. The reactions with 1M NaOH were both positive on OA and MEA where the cultures initially changed to yellow green and gradually turned to red. The pathogen was identified as Phoma bellidis Neerg. based on descriptions in Boerema et al. (2). Pathogenicity tests were performed with the three isolates in the laboratory by spraying conidial suspensions (1 × 106 conidia/ml) containing 0.1% Tween 20 until runoff (30 ml per plant) onto stem surfaces of 50-day-old, 60 cm tall plants. For each isolate, there were 50 stems from five replicate plants that had multiple stems per plant. Control plants were treated with sterilized water containing 0.1% Tween 20 only. Plants were incubated with a 16-h photoperiod at 28°C and 90% relative humidity in an artificial climate chamber. Five days after inoculation, typical red-brown spots were observed on all inoculated stems but no symptoms were seen on water-treated control plants. Koch's postulates were fulfilled by reisolation of P. bellidis from diseased stems. The pathogenicity tests were repeated twice more with the same results. P. bellidis has only been reported previously on Bellis spp. from England, Denmark, Italy, the Netherlands, and Switzerland (1,2). Furthermore, there are only a few fungal diseases known to be associated with E. dulcis, and none so far that involve species of Phoma (3,4). To our knowledge, this is the first report of P. bellidis infecting E. dulcis worldwide. References: (1) M. M. Aveskamp et al. Stud. Mycol. 65:27, 2010. (2) G. H. Boerema et al. Phoma Identification Manual: Differentiation of Specific and Infra-Specific Taxa in Culture. CABI Publishing, Wallingford, UK, 2004. (3) P. L. Lentz. Am. Midl. Nat. 67:184, 1962. (4) L. Pan et al. J. Changjiang Vegetables (in Chinese) 14:10, 2010.

First Report of Leaf Spot Disease in Angelica dahurica Caused by Phoma bellidis in China

“…The characteristics were all similar in terms of morphology and culture, except that the pycnidia of P. bellidis on A. dahurica were smaller (91–160 μ m in diameter) than those on E. dulcis (93–245 μ m in diameter) (Lv et al. ), although these measurements still fit in this size range. For further verification, analysis of the ITS and TUB regions of rDNA provided a more reliable approach for the identification of the isolates, which formed a unique and well‐supported clade in the combined tree.…”

“…) and on E. dulcis in China (Lv et al. ). During the identification of the causal agent, the isolates of P. bellidis on E. dulcis were compared with the isolate from A. dahurica .…”

“…Among the isolates obtained, isolate SAUCC 1308 was selected as the representative fungus for further studies. The morphological characteristics of the isolate were examined, photographed and measured with Nikon Eclipse 80i microscope, including shape and size of conidia and pycnidia as previously described Lv et al 2011).…”

“…The fungal mycelial plugs (5 mm diameter) collected from the growing edge of a 14-day-old culture were incubated at 25°C in the dark on PDA, oatmeal agar (OA) (Den Bree€ yen et al 2006) and malt extract agar (MEA) (malt extract 30 g and agar 15 g/l distilled water, pH 5.6 AE 0.2). The cultures after 7 and 14 days were assessed in terms of the growth rate of mycelia, colony morphology and conidial morphology (Aveskamp et al 2010;Lv et al 2011). Images of the colonies of the isolate were captured using a camera.…”

“…Based on cultural and morphological characteristics, the isolate from A. dahurica matched the description of Phoma bellidis Neerg. (Lv et al 2011;De Gruyter et al 1993). The morphological identification was further confirmed by ITS and TUB sequence analyses.…”