Infections of INSV on Spinach and Celery

Impatiens necrotic spot virus (INSV) is a tospovirus spreading primarily by an insect vector, the western flower thrip. INSV is similar to other tospoviruses, including Tomato spotted wilt virus (TSWV), Groundnut ring spot virus (GRSV), and Tomato chlorotic spot virus (TCSV). They can cause economic losses in lettuce crops. Virus diseases were usually minor concern for coastal California lettuce production. However, after INSV was first reported on lettuce in Salinas Valley in 2006 (1), outbreaks of INSV have continued to occur. In 2020, INSV caused significant crop loss on lettuce with $50 million to $100 million in losses. INSV continues to be a serious problem in Salinas Valley in recent years.

INSV has wide host range including weeds, ornamentals and crop plants, such as spinach, pepper, tomato, potato, and peanut. Concerning the impacts of INSV on the other crops commonly grown in Salinas Valley, some PCAs reach out to us on the symptoms of INSV on spinach and celery. INSV on spinach was first reported in Salinas Valley in 2008 (2) and symptoms of INSV on spinach was documented in previous blog post in 2015 (3). Thrip feeding may cause damage on celery appearing as raised ridges (4), but INSV symptoms on celery were unknown to our knowledge.

In a recent survey of fields close to heavily infested lettuce fields, we examined mature spinach and celery fields for symptoms of INSV. The following are photos of INSV symptoms seen on both crops that were confirmed by Agdia Immunostrips.

1. INSV on spinach. Symptoms of INSV on spinach include interveinal yellowing, thickening and deformity of the infected leaves. Infected leaves are dwarfed and crinkled (Fig. 1 and 2). Symptoms can be seen on both young and old leaves. So far INSV on spinach has only been seen on older plantings and its incidence is low.
   

   Fig. 1. Impatiens necrotic spot virus of spinach causing interveinal yellowing

   

   Fig. 2. Impatiens necrotic spot virus of spinach. Arrow indicates deformity of younger leaves

2. INSV on celery. Symptoms of INSV on celery include sunken gray, brown elongated lesions on petioles (Fig. 3). The lesions can appear on both inner and outer surfaces of the petiole, at lower or upper portion of the petiole (Fig. 4), but they mostly appear on older petioles (Fig. 5). Given that the lesions we have observed to date have occurred on older petioles which are easily stripped during harvest, we have not heard of any economic loss of INSV in Salinas Valley celery.

Fig. 3. Brown lesions on a celery petiole caused by INSV

Fig. 4. INSV on celery. Arrows indicate the lesion on older petioles

Fig. 5. Lesion caused by INSV at inner (A) or outer (B) surface of a petiole.

Reference

1. Koike, S. T., Y.-W. Kuo, M. R. Rojas, and R. L. Gilbertson. 2008. First report of Impatiens necrotic spot virus infecting lettuce in California. Plant Dis. 92: 1248.
2. Liu, H.-Y., J. L. Sears, and B. Mou. 2009. Spinach (Spinacia oleracea) is a new natural host of Impatiens necrotic spot virus in California. Plant Dis. 93: 673.
3. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=17521
4. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=17559

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