Distribution, cultivar susceptibility, and epidemiology of Apium virus Y on celery in coastal California

Authors: KOIKE, STEVEN - University Of California - Cooperative Extension Service; Liu, Hsing Yeh; Sears, John; TIAN, TONGYAN - California Department Of Food And Agriculture; DAUGOVISH, OLEG - University Of California - Cooperative Extension Service; DARA, SURENDRA - University Of California - Cooperative Extension Service

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2011
Publication Date: 5/1/2012
Citation: Koike, S.T., Liu, H., Sears, J.L., Tian, T., Daugovish, O., Dara, S. 2012. Distribution, cultivar susceptibility, and epidemiology of Apium virus Y on celery in coastal California. Plant Disease. 96(5):612-617.

Interpretive Summary: Apium virus Y (ApVY) is a potyvirus that was recently found to cause crop loss to celery (Apium graveolens) in California. Symptoms on leaves vary greatly and consist of general chlorosis, chlorotic or necrotic line patterns, chlorotic blotches and mottling, necrotic lesions, ringspots, and distorted and twisted leaflets. Depending on the cultivar, celery petioles could also exhibit extensive necrotic, sunken, elongated lesions. Severely affected plants were unmarketable. Disease incidence surveys found that a susceptible celery could have as high as 55 to 71 % disease. Because it was noted that the Apiaceae weed poison hemlock (Conium maculatum) was present in almost all areas where ApVY affected celery, a four year survey collected overwintered hemlock from a six coastal county region and tested composite samples for the virus using RT-PCR and ApVY specific primers. These plants were commonly infected with ApVY, ranging from 14 to 87% positive. Seeds collected from these plants were also positive when tested with the same RT-PCR method. However, when ApVY-positive hemlock seeds were germinated and the resulting seedlings tested, all results were negative. The failure of the virus to be transmitted from hemlock seeds to seedlings was further documented by collecting newly germinated hemlock seedlings from the field and testing them with RT-PCR. All such seedlings were negative for ApVY even though large, adjacent, overwintered hemlock tested positive. Two crops of celery seed were produced from ApVY-positive mother plants; celery seed from these infected plants likewise tested positive for ApVY but seedlings grown from the seed lots were negative for the virus. Twenty-one celery and celeriac cultivars were inoculated with ApVY using viruliferous aphids, planted in a replicated field trial, and then grown to maturity. Seven cultivars remained symptomless, tested negative for the virus, and showed signs of possible resistance. The epidemiology of disease caused by ApVY in California evidently involves poison hemlock as a common overwintering host with subsequent vectoring of the virus from hemlock to celery via aphids. The virus is not seed-borne in this weed host or in celery. Growers can control this disease by managing poison hemlock weed populations, controlling aphids, and by planting celery cultivars that are not susceptible to ApVY.

Technical Abstract: Apium virus Y (ApVY) is a potyvirus that was recently found to cause crop loss to celery (Apium graveolens) in California. Symptoms on leaves vary greatly and consist of general chlorosis, chlorotic or necrotic line patterns, chlorotic blotches and mottling, necrotic lesions, ringspots, and distorted and twisted leaflets. Depending on the cultivar, celery petioles could also exhibit extensive necrotic, sunken, elongated lesions. Severely affected plants were unmarketable. Disease incidence surveys found that a susceptible celery (cv. 414) could have as high as 55 (2007) and 71 (2008) percent disease. Because it was noted that the Apiaceae weed poison hemlock (Conium maculatum) was present in almost all areas where ApVY affected celery, a four year survey collected overwintered hemlock from a six coastal county region and tested composite samples for the virus using RT-PCR and ApVY specific primers. These plants were commonly infected with ApVY, ranging from 14 to 87% positive. Seeds collected from these plants were also positive when tested with the same RT-PCR method. However, when ApVY-positive hemlock seeds were germinated and the resulting seedlings tested, all results were negative. The failure of the virus to be transmitted from hemlock seeds to seedlings was further documented by collecting newly germinated hemlock seedlings from the field and testing them with RT-PCR. All such seedlings were negative for ApVY even though large, adjacent, overwintered hemlock tested positive. Two crops of celery seed were produced from ApVY-positive mother plants; celery seed from these infected plants likewise tested positive for ApVY but seedlings grown from the seed lots were negative for the virus. Twenty-one celery and celeriac cultivars were inoculated with ApVY using viruliferous aphids, planted in a replicated field trial, and then grown to maturity. Seven cultivars remained symptomless, tested negative for the virus, and showed signs of possible resistance. The epidemiology of disease caused by ApVY in California evidently involves poison hemlock as a common overwintering host with subsequent vectoring of the virus from hemlock to celery via aphids. The virus is not seedborne in this weed host or in celery. Growers can control this disease by managing poison hemlock weed populations, controlling aphids, and by planting celery cultivars that are not susceptible to ApVY.