First Report of Leaf Spot of Houttuynia cordata Caused by Alternaria alternata in China

Abstract

Houttuynia cordata is a perennial herbaceous plant (family Saururaceae) that is native to southern China, Japan, Korea, and Southeast Asia where it grows well in moist to wet soils. It is commonly used as a Chinese herbal medicine and as a vegetable. In North America and Europe it is also used as an ornamental. From September 2007 to November 2009, symptoms of leaf spot were found on H. cordata leaves in Dangyang County, Hubei, China, with the crop area affected estimated to be over 600 ha per year. Rhizome yield was reduced by 20% on average, with up to 70% yield losses in some fields during the autumn growing season. Lesions were initially small, brown, and oval or circular that developed into dark spots and sometimes formed target spots with white centers. These spots enlarged and overlapped, extending until the leaves withered entirely usually within 2 months. A fungus was consistently recovered from symptomatic leaf samples collected in October 2008 or 2009 with an average 90% isolation rate from ~60 leaf pieces that were surface sterilized with 0.1% mercuric chloride solution. Three isolates, HCDY-2, HCDY-3, and HCDY-4, were used to further evaluate characteristics of the pathogen. On potato dextrose agar, all cultures initially developed white colonies and the centers turned gray or brown after 4 days of incubation. Conidiophores were single or fasciculate, straight or knee curved, gray-brown with regular septa, and 42 to 61 × 4 to 5 μm. Conidia were obclavate or ovate, brown, and 26 to 38 × 12 to 20 μm with three to five transverse and one to three longitudinal or oblique septa. The tops of some conidia developed into secondary conidiophores, which were cylindrical, beige, and 5 to 17 × 3 to 5 μm. The pathogen was identified as Alternaria alternata based on descriptions in Simmons (3). Genomic DNA of HCDY-2 was extracted, and the rDNA-internal transcribed spacer sequence showed 99.6% identity to A. alternata (GenBank No. AY513941). Pathogenicity tests were performed with the three isolates by spraying conidial suspensions (1 × 106 conidia/ml) containing 0.1% Tween 20 onto upper and lower surfaces of leaves of 40-day-old 15-cm high plants. There were 20 leaves from five replicate plants for each isolate. Control plants were treated with sterilized water containing 0.1% Tween 20 only. All plants were incubated with a 16-h photoperiod at 25°C and 90% relative humidity in an artificial climate chamber. Five days after inoculation, typical brown spots were observed on all inoculated leaves but no symptoms were seen on water-treated control plants. Koch's postulates were fulfilled by reisolation of A. alternata from diseased leaves. The pathogenicity tests were carried out twice. A survey of the literature revealed only a few fungal diseases associated with H. cordata (1,2,4), including Phyllosticta houttuyniae, Pseudocercospora houttuyniae, Rhizoctonia solani, and Sclerotium rolfsii. Although A. alternata is a cosmopolitan plant pathogen, it has not been reported on any species in the four genera in Saururaceae (Anemopsis, Gymnotheca, Houttuynia, and Saururus) (3). To our knowledge, this is the first report of A. alternata infecting H. cordata worldwide. References: (1) Y. L. Guo and W. X. Zhao. Acta Mycol. Sin. 8:118, 1989. (2) K. Sawada. Spec. Publ. Taiwan Univ. 8:138, 1959. (3) E. G. Simmons. Alternaria: An Identification Manual. The American Phytopathological Society, St. Paul, MN, 2007. (4) Y. Wu et al. J. Changjiang Vegetables (In Chinese) 2:19, 2007.

Flax black spot caused by Alternaria alternata, a new disease afflicting leaves and the exocarps of flax in China

“…The leaf spot disease was also reported on Hydrangea macrophylla in Italy and Rumex dentatus in Pakistan with occurrence rates over 70% (Garibaldi et al, 2007; Siddiqui et al, 2009). And there have also been a report of this pathogen causing the blackspot disease on Houttuynia cordata in China (Zheng et al, 2011). At present, report on flax black spot in China is rare.…”

Management of anthracnose and blight diseases of Houttuynia cordata Thunb. with fungicides

“…But a few information is available regarding the fungal diseases of the plant home and abroad (Azad andShamsi 2011, Zheng et al 2011). Zheng et al (2011) also reported that symptoms appeared on leaves of H. cordata from September 2007 to November 2009 in Dangyang County, Hubei, China. He also reported the crop area affected estimated to be over 600 ha per year.…”

Effects of botanicals against anthracnose and blight diseases of Houttuynia cordata Thunb

“…The isolated 7 fungi namely Alterneria alternata, Aspergillus fumigatus, Aspergillus niger, Colletotrichum gloeosporioides, Curvularia lunata, Pestaliopsis guepiniand, Rhizopus stolonifer were tested for their pathogenic potentiality. The results revealed that A. alternata and C. gloeosporioides produced symptoms on H. cordata Zheng et al (2011). first reported leaf spot of H. cordata caused by A. alternata from China.…”

“…But little information is available regarding the fungal diseases of the plant in home and abroad (Azad andShamsi 2011and Zheng et al 2011).Previously it was reported that symptoms appeared on leaves of H. cordatafrom September 2007 to November 2009 in Dangyang County, Hubei, China and the crop area affected estimated to be over 600 ha per year. Rhizome yield was reduced by 20% on average, with up to 70% yield losses in some fields during the autumn growing season (Zheng et al 2011).So far there is no report available regarding the control of the diseases of H. cordata.Present research was undertaken to find out a suitable ecofriendly management of the diseases of this important herbal medicinal plant.…”