First report of Embellisia allii causing skin blotch or bulb canker of onion from India

Onion (Allium sativum) is an important bulb crop grown in India used as a vegetable and spice. Diseases are a major factor limiting production, attacking the crop at its vegetative stage and during storage, causing 20-30% losses in storage (Gupta & Srivastava, 1992). In 2008, onion bulbs were collected in a few commercial fields in Karnal, India, that exhibited skin blotch and canker symptoms. The initial symptom of the disease was greyish spots on the outer scales of the bulb, later becoming enlarged and covering the entire bulb with a dark, blackish colour (Fig 1). The fungus was isolated on potato dextrose agar (PDA), purified by using single conidia, and deposited in the culture collection at CABI, U.K. (IMI 397280).

The pathogen was identified as Embellisia allii (Campan.) E.G. Simmons based on morphological characteristics (Ellis, 1976). Colonies on PDA were effuse, grey to brown to black, with diameters averaging 30 mm after five days at 22 ^OC. Microscopic observations revealed chlamydospores (Fig 2A), dark brown to black, forming abundantly on the host, variable in shape and size, up to 100-120 µm long and 3-5 µm wide. Conidia (Fig 2B) were generally smooth, obovoid or ellipsoidal, rounded at the ends, 20-50 x 7-10 µm, mid- to dark-brown to black, with generally two to five (maximum six) thick, very dark transverse septa, and occasionally one or two oblique or longitudinal septa.Short secondary conidiophores occasionally formed bearing several conidia (Fig 2C).

Pathogenicity was confirmed by inoculating two-month-old onion bulbs with mycelium grown on PDA after the outer skin had been bruised by pinching, and then incubated at 22 ^OC. Inoculated bulbs developed symptoms 5-6 days after inoculation that were similar to those observed in storage. The fungus was re-isolated from infected parts. To date, this fungus has been reported from many different countries, including India (Srivastava et al., 2005) but only on garlic. However, to the authors’ knowledge, this is the first record of E.allii on onion.