First report of taro black rot caused by Ceratocystis fimbriata in China

Q. Huang^1,2, Y.Y. Wang^1,2, Y.Y. Zhao¹, Y.X. Jiao¹, X.F. Li¹, H.R. Chen¹ and Y.Y. Zhu^1,2*

¹ College of Plant Protection, Yunnan Agricultural University, Kunming, 650201, China
² The Center for Agricultural Biodiversity Research and Training of Yunnan Province, Yunnan Agricultural University, Kunming 650201, China

*yppl@public.km.yn.cn

Accepted for publication 24/01/07

Colocasia esculenta is the most widely cultivated species of taro in China, because it does not require a large growing area and is relatively easy to obtain and maintain.  In 2005, a hitherto unseen post-harvest disease of taro, a superficial black rot, was observed at a Chenglong vegetable company storage barn in Chenggong County in Kunming, Yunnan, China (Fig. 1).  A fungus was consistently isolated from rotted corms when diseased tissue was incubated between slices of fresh carrot root (Moller & DeVay, 1968).

Figure 1: Typical of black rot symptom of C. esculenta

The fungus was identified as Ceratocystis fimbriata using morphology and molecular features.  The ITS region of rDNA was sequenced using the procedures of Baker et al. (2003).  Analysis of ITS sequence data (GenBank accessions AM293382-AM293383) showed that the isolates were 97% homologous to those from diseased taro in Brazil (GenBank accessions AY526286-AY526290) by BLAST analysis; and 96% homologous to isolates on Colocasia spp. from Hawaii and to Chinese herbarium material that was over 70-years-old (GenBank accessions AY526304-AY526307).  Hawaiian and Chinese material was considered by Harrington et al. (2005) to represent a previously uncharacterized taxon in the Asian clade of C. fimbriata, while Brazilian isolates fall into the ‘Latin American’ clade.

Figure 2: Surface (left) and internal pseudopetiole (right) symptoms on C. esculenta at one week post-inoculation

Of thirteen isolates derived from single ascospores, five were tested for their ability to cause corm rot.  In laboratory tests, taro corms were inoculated by wounding the corm surface and placing a 0.2 µl aliquot of a spore suspension of the fungus (2.0 x 10⁵ conidia per ml) over the wound; inoculated corms were then stored at 20-26ºC.  All five isolates tested caused black rot symptoms identical to those originally observed; no rot was observed in controls inoculated with water alone.  In greenhouse tests using 3 isolates, inoculation was done using the method of Harrington et al. (2005): a conidial suspension of each isolate was diluted to 2.0 × 10⁵ spores per ml, and 0.2 µl was injected into wounds on nine pseudopetioles on each of three two-month-old plants of C. esculenta.  Control solutions consisted of water applied to a sterile MYEA plate.  As disease progressed, inoculated leaves withered and dried; by 3 weeks, all 9 inoculated leaves had died (Figs 2 & 3), while control plants showed no symptoms.  The fungus was successfully re-isolated from inoculated pseudopetioles.

Figure 3: Dying leaf of C. esculenta at 3 weeks post-inoculation

Although this disease has been reported from Brazil and the United States (Hawaii) and the organism is known from China from one herbarium specimen from 1949 (Thorpe et al. 2005), this is the first report of the disease from China.

Acknowledgements

This work was supported by 973 project of China (No.2006CB100203) and Yunnan Provincial project (No.2003NG08).

References

Baker CJ, Harrington TC, Krauss U, 2003. Genetic variability and host specialization in the Latin American clade of Ceratocystis fimbriata. Phytopathology 93, 1274-1284.

Harrington TC, Thorpe DJ, Marinho VLA, 2005. First report of black rot of Colocasia esculenta caused by Ceratocystis fimbriata in Brazil. Fitopatologia Brasileira 30, 88-89.

Moller WJ, Devay JE, 1968. Carrot as a species-selective medium for Ceratocystis fimbriata. Phytopathology 58, 123-124.

Thorpe DJ, Harrington TC, Uchida DJ, 2005. Pathogenicity, Internal Transcribed Spacer-rDNA Variation, and Human Dispersal of Ceratocystis fimbriata on the Family Araceae. Phytopathology 95, 316-323.

The British Society for Plant Pathology