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

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.

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.