![]() ![]() In addition, oxygen rich and acidic soils have also been found to favor growth of the pathogen. This makes the disease an important issue in regions such as the Southern United States of America, especially for solanaceous crops. Environment Īthelia rolfsii typically prefers warm, humid climates (whence the name of the disease, Southern Blight) which is required for optimal growth (i.e. Infection caused by Southern Blight is not considered systemic. Susceptible plants exhibit stem lesions near the soil line, and thus often wilt and eventually die. Sclerotia formation occurs when conditions are especially warm and humid, primarily in the summer months in the United States of America. After gaining entry, the pathogen uses the plant tissues to produce mycelium (often forming mycelial mats), as well as additional sclerotia. These compounds effectively kill plant tissue and allow the fungus to enter other areas of the plant. The fungus attacks the host crown and stem tissues at the soil line by producing a number of compounds such as oxalic acid, in addition to enzymes that are pectinolytic and cellulolytic. The pathogen has a very large host range, affecting over 500 plant species (including tomato, onion, snapbean and pea) in the United States of America. The sclerotia is a survival structure composed of a hard rind and cortex containing hyphae and is typically considered the primary inoculum. It causes the disease Southern Blight and typically overwinters as sclerotia. The soil-borne fungal pathogen Athelia rolfsii is a basidiomycete that typically exists only as mycelium and sclerotia (anamorph: Sclerotium rolfsii, or asexual state). It can also be called mustard seed fungus. It mostly occurs in warm soils (above 15 ☌) and can be a serious pest of vegetables in tropical and subtropical regions (including Florida, where it was first recognized), causing "southern blight". It has an almost indiscriminate host range, but its capacity to form sclerotia (propagules that remain in the soil) means that it particularly attacks seasonal crops. Īthelia rolfsii occurs in soil as a saprotroph, but can also attack living plants. Small, brownish sclerotia (hyphal propagules) are also formed, arising from the hyphae. Basidia are club-shaped, bearing four smooth, ellipsoid basidiospores, measuring 4–7 by 3–5 μm. Microscopically, they consist of ribbon-like hyphae with clamp connections. The fungus produces effused basidiocarps (fruit bodies) that are smooth and white. With a move to a more natural classification of fungi, Corticium rolfsii was transferred to Athelia in 1978. In 1932, Mario Curzi discovered that the teleomorph (spore-bearing state) was a corticioid fungus and accordingly placed the species in the form genus Corticium. It is, however, not a species of Sclerotium in the strict sense. He placed the species in the old form genus Sclerotium, naming it Sclerotium rolfsii. The specimens sent to Saccardo were sterile, consisting of hyphae and sclerotia. ![]() The species was first described in 1911 by Italian mycologist Pier Andrea Saccardo, based on specimens sent to him by Peter Henry Rolfs who considered the unnamed fungus to be the cause of tomato blight in Florida.
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