Stemphylium Leaf Blight: A Re-Emerging Threat to Onion Production in Eastern North America

Abstract

Stemphylium leaf blight (SLB), caused by Stemphylium vesicarium, is a foliar disease of onion worldwide, and has recently become an important disease in the northeastern United States and Ontario, Canada. The symptoms begin as small, tan to brown lesions on the leaves that can progress to defoliate plants. Crop loss occurs through reduced photosynthetic area, resulting in smaller, lower-quality bulbs. Leaf necrosis caused by SLB also can compromise bulb storage, as green leaves are required for the uptake of sprout inhibitors applied prior to harvest. The pathogen can overwinter on infested onion residue and infected volunteer plants. Asymptomatic weedy hosts near onion fields may also be a source of inoculum. Production of ascospores of the teleomorph (Pleospora allii) peaks in early spring in northeastern North America, often before the crop is planted, and declines rapidly as daily mean air temperatures rise. Conidia usually are present throughout the growing season. Application of fungicides is a standard practice for management of the complex of fungi that can cause foliar diseases of onion in this region. Recent assessments have shown that populations of S. vesicarium in New York and Ontario are resistant to at least three single-site mode-of-action fungicides. Three disease prediction systems have been developed and evaluated that may enable growers to reduce the frequency and/or number of fungicide applications, but the loss of efficacious fungicides due to resistance development within S. vesicarium populations threatens sustainability. The lack of commercially acceptable onion cultivars with sufficient resistance to reduce the number of fungicides for SLB also limits the ability to manage SLB effectively. Integrated disease management strategies for SLB are essential to maintain profitable, sustainable onion production across eastern North America.

Detection and Molecular Diagnosis of Stemphylium vesicarium Isolated from Wheat Spikes

“…The causal fungus was isolated and identified morphologically as Stemphylium vesicarium. Stemphylium vesicarium causes onion blight and reduces onion production (Hay et al, 2021). The fungus was stored in slants for further using in the next season.…”

Screening of short-day onions for resistance to Stemphylium leaf blight in the seed-to-bulb stage (stage I) and bulb-to-seed stage (stage II)

“…Stemphylium leaf blight has emerged as a serious constraint for onion production across major onion-growing areas throughout the world ( Hay et al., 2021 ). The disease not only poses a significant threat to winter/ rabi bulb crop but also has a negative impact on the onion seed yield too.…”

“…This pathogen also infects other economically important crops of the Amaryllidaceae family such as garlic ( Allium sativum L.) and leek ( Allium ampeloprasum L.). In particular, Stemphylium vesicarium is a hemibiotrophic fungal pathogen with a broad range of host crop species such as vegetable, field, ornamental, and tree fruit crops ( Hay et al., 2021 ). SLB has emerged as a major bottleneck for achieving the full genetic potential of both bulb and seed crops ( Dangi et al., 2019 ).…”

“…Currently, not a single commercial onion variety resistant to SLB disease is available in the market worldwide. In previous studies, it has been found that with different degrees of susceptibility, almost all the commercial varieties succumb to S. vesicarium infection ( Foster et al., 2019 ; Dangi et al., 2019 ; Hay et al., 2021 ). Several workers have reported a moderate level of resistance in their studies against Stemphylium leaf blight.…”

“…Consequently, bulbs remain small sized and underdeveloped, and upon maturity, tops of bulbs may not lodge which later undergo decay by soil microbes (Raghavendra Rao and Pavgi, 1975). In severe conditions, SLB can also result in premature mortality of plants (Hoepting, 2017). Infection on onion leaves can occur at wide ranges of temperature from 10°C to 26°C (Basallote- Ureba et al, 1999).…”