Lv R, Zheng L, Zhu Z,Pan L, Huang J, Hsiang T. 2011. First report of stem blight of Eleocharis dulcis caused by Phoma bellidis in China. Plant Disease. Journal Website Reprint
Eleocharis dulcis is a perennial
herbaceous plant in the family Cyperaceae that is native to China and India, where it grows well in moist
to wet soils. Corms from the plant are 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 over 1300 ha per year. Corm yield was reduced by 20% on
average with up to 60% yield losses in some fields. Lesions were initially
small, red-brown, and oval or
circular, and these enlarged to produce apical necrosis, extending until the stems
withered usually within two
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 (PDA). 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 slight salmon color in 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 x 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. 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
(1x106 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 re-isolation of P.
bellidis from diseased stems. The
pathogenicity tests were repeated twice more with the same results. Phoma
bellidis has only been reported previously on
Bellis spp. from England, Denmark, Italy,
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.
(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.