Symptoms and losses caused by onion yellow dwarf virus and iris yellow spot virus diseases of onion crop in Northern India.

摘要

Production of bulb and seed crop of onion ( Allium cepa L.) is hampered by onion yellow dwarf virus (OYDV) and iris yellow spot virus (IYSV) with incidence of 83.2% and 89.9% in bulb crop and 90.6% and 88.2% in seed crop, respectively in the popularly grown cv. Hisar-2. Four symptoms-based variants of OYDV designated as grade A, B, C and D produced varied types of symptoms in onion crop incurring heavy losses in bulb and seed production. IYSV caused tiny hay coloured spots of different shapes and sizes on leaves and escapes which later coalesced leading to drying and lodging of scapes. The plant height, bulb weight and bulb size were reduced due to both viral diseases in bulb crop. The plant height and yield parameters viz., weight of umbel, number, seed weight in umbel and seed yield of plant were greatly reduced by the infection of OYDV grade A in seed crop. However, the seed quality parameters viz., test weight, germination and seed vigour index were highly affected due to infection of IYSV, because there was drying and lodging of seed crop before seed maturation.