First Report of Southern Blight of Okra (Abelmoschus esculentus) Caused by Sclerotium rolfsii in Côte d'Ivoire

Abstract

Southern blight caused by Sclerotium rolfsii Sacc. was observed on okra (Abelmoschus esculentus) cv. Clemson Spineless in January 2010 during a survey of vegetable fields in Rubbino, Côte d'Ivoire, which is one of the most important areas for vegetable production. Plants exhibited symptoms of a dark brown lesion on the stems near the soil line. Upper roots became light to dark brown, the lower leaves wilted, turned yellow, and a white mat of fungal mycelium developed on the stem lesion. Numerous, white, spherical sclerotia formed on the infected stem and on soil surfaces around the infected plants. Sclerotia (0.5 to 1.2 mm in diameter) later turned tan to dark brown and the entire plant wilted. Eleven fields, with a total of approximately 26 ha surveyed, were affected and disease incidence reached approximately 15% in the fields. Sclerotia were collected and the fungus cultured on acidified potato dextrose agar (PDA) plates. The fungus grew rapidly on PDA and the hyphae at the edge of the colonies were large straight cells with one or more clamp connections at each septum. Secondary and tertiary hyphae were slender and lacked clamp connections. Whitish sclerotia were observed on the mycelial mats 5 to 7 days after incubation, which later turned tan to brown when mature. The fungus was identified as S. rolfsii based on the characteristics of mycelia and sclerotia (1). Sclerotia produced on PDA were used to inoculate okra seedlings under greenhouse conditions at rates of 10, 20, and 30 sclerotia per plant. Sclerotia were placed just under the soil surface around the root of 4-week-old seedlings of okra cv. Clemson Spineless. Symptoms identical to those on field samples developed on all inoculated plants. S. rolfsii was reisolated from diseased plants and the identity was confirmed. S. rolfsii has previously been reported as causing disease in Côte d'Ivoire (2). To our knowledge, this is the first report of southern blight caused by S. rolfsii on okra in this country. Okra is an important vegetable crop in Côte d'Ivoire and therefore the occurrence of southern blight and susceptibility of okra cultivars to this disease needs to be taken into account in okra production. References: (1) Z. K. Punja and A. Damiani. Mycologia 88:694, 1996. (2) R. Resplandy et al. Ann. Epiphyt. 1:1, 1954.

Morphological and Pathogenic Characterization of Sclerotium rolfsii, the Causal Agent of Southern Blight Disease on Common Bean in Uganda

“…Southern blight, which is also termed sclerotium root rot or southern stem rot, was first identified on tomato (Solanum lycopersicum L.) in 1892 (Rolfs 1892) and is now known to occur across most crop types, particularly in warm regions (Aycock 1966;Domsch 1980;Farr et al 1989). For example, the disease has been reported on common bean (Phaseolus vulgaris) in Uganda (Paparu et al 2018), India (Mahadevakumar et al 2015), and Italy (Garibaldi et al 2013); maize (Zea mays) in Pakistan (Yasmin et al 1984); soy bean (Glycine max) in Nigeria (Akem and Dashiell 1991); potato (S. tuberosum) in Italy (Garibaldi et al 2006); okra (Abelmoschus esculentus) in Côte d'Ivoire (Koné et al 2010); and sesame (Sesamum indicum L.) in Mexico (Hernández-Morales et al 2018).…”