Cordana leaf spot

Cordana leaf spot is a disease of banana that, even though it is common worlwide, has generally little impact on production. It is caused by two Neocordana fungi that are often found as secondary invaders of leaf lesions caused by other fungi.

Causal agents

Two Neocordana species are responsible for Cordana leaf spot symptoms: Neocordana musae1 , formerly Cordana musea2 and originally described as Scoletrichum musae3 ; and Neocordana johnstonii1 , formerly Cordana johnstonii4 , which causes a disease very similar in appearance.

Distribution

Cordana leaf spot caused by N. musae is found in banana plantations all over the tropics.

Cordana leaf spot caused by N. johnstonii was reported in Australia (Queensland, New South Wales, Norfolk Island, Lord Howe Island), Indonesia (Papua province), Malaysia (Cameron Highlands), Philippines and Tonga.

The observations from Australia indicate that N. johnstonii is better adapted to cooler climates. The species was found in herbarium samples of Cordana leaf spot collected in New South Wales starting in the 1930s, as well as on Lord Howe Island off the coast of New South Wales, and Norfolk Island (between Australia and New Zealand), whereas N. musae was found to be the cause of most Cordana leaf spot in Queensland and was also identified in the Northern Territory. The distribution of the two species overlaps in the southern part of Queensland, close to the border with New South Wales5 .

Symptoms

The most characteristic symptoms of the disease are on the leaf. They are large, pale brown, oval to fusiform necrotic lesions with pale grey  concentric ring patterns, with a dark brown border surrounded by a bright yellow halo separating the lesion from the healthy leaf tissue6 . Often, lesions coalesce into large necrotic patches. The leaves ultimately turn brown and  dry out.

The leaf spots caused by N. musae are larger and oval to elliptical in shape, while those caused by N. johnstonii are generally smaller and become more fusiform with age5 .

Invasion often occurs at leaf margin in plants weakened by senescence, adverse environmental conditions, nutritional deficiencies, wounds or infections cused by other pathogens. Symptoms are often seen around lesions caused by other pathogens. When the infection is associated with other diseases, e.g. with black leaf streak, the lesions are enlarged and become necrotic. This occurs especially under humid conditions.

References