The first finding of Pythium root rot and leaf blight of elephant foot yam (Amorphophallus paeonifolius) in India

S. Guha Roy^1* and C.X. Hong²

¹ Department of Botany, Ramananda College, College Road, Lalbandh, Bishnupur, Bankura, WB 722122, India
² Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University, Hampton Roads Agricultural Research and Extension Center, 1444 Diamond Springs Road, Virginia Beach, VA 23455, USA

*s_guharoy@yahoo.com

Accepted for publication 21/06/07

Elephant foot yam Amorphophallus paeonifolius, formerly known as Amorphophallus campanulatus, produces an edible corm and is widely cultivated from West Bengal to Tamil Nadu, India. It is an example of a crop species that is indigenous to this region and has been included in the National Germplasm Evaluation Programme for tuber crop improvement. This important crop has recently suffered from a root rot and leaf blight disease.

Symptomatic plants ranged from chlorotic and stunted to completely blighted as the disease progressed.  Necrotic root symptoms began at the tip, but progressed quickly eventually killing the whole root. The cortex of severely affected roots could be easily sloughed off, leaving only parts of the vascular system intact. Samples of symptomatic plants from production fields and an experimental farm (All India Coordinated Research Project on Tuber Crops in Nadia district, West Bengal) were collected. The pathogen was isolated by plating symptomatic tissues on amended V8 agar (Guha Roy et al, 2006). Resultant isolates were identified using morphological characters, DNA fingerprinting and sequencing.

Figure 1: Pythium Root rot and leaf blight of elephant yam,  a) Field showing symptoms in various stages of disease progression, b) Single plant showing severely blighted symptoms, c) severely affected corm with rot symptoms

Sporangia were ovoid to globose, papillate, caducous and non-proliferating (41.46 µm ± 2.9 x 37.64 µm ± 2.0). Isolates were homothallic. Oogonia were spherical, smooth walled with elongate diclinous antheridia and aplerotic oospores (39.16 µm ±2.26 diameter). Hyphal swellings were absent.  Based on the above morphological features and ITS sequencing (GenBank accession No. EF455802), the organism was identified as Pythium helicoides. Its SSCP (Single Stranded Conformational Polymorphisms) pattern was also typical of P. helicoides (Kong et al., 2004). Pathogenicity was confirmed by wound-inoculating stem bases of 3-month old healthy plants of A. campanulatus with a 9-mm cork borer and placing 7-mm mycelial discs of 5-day old P. helicoides test cultures in the holes. Plants were maintained at approximately 30 ± 1°C and assessed 15 days post inoculation.  P. helicoides was successfully re-isolated, thus completing Koch’s postulates. Control plants inoculated with agar alone did not develop symptoms.

This is the first report of P. helicoides affecting A. campanulatus in India and worldwide. One isolate was deposited in the World Phytophthora Collection and Virginia Polytechnic Institute and State University, USA, under accession numbers P10973 and 33B2, respectively.

Acknowledgements

Dr. J Tarafdar, Scientist In Charge, All India Coordinated Research Project on Tuber Crops, BCKV, Kalyani, India for access to experimental farm.

References

Guha Roy S, Bhattacharyya S, Mukherjee SK, Mondal N, Khatua DC, 2006. Phytophthora melonis associated with fruit and vine rot disease of pointed gourd in India as revealed by RFLP and sequencing of ITS region. Journal of Phytopathology 154, 612-615

Kong P, Richardson PA, Moorman GW, Hong CX, 2004. Single-strand conformational polymorphism analysis of the ribosomal internal transcribed spacer 1 for rapid species identification within the genus Pythium. FEMS Microbiology Letters 240, 229-236.