Symptoms - False Smut-paddy

The disease occurs in the field at the hard dough to mature stage of the crop. The fungus transforms individual grains of the panicle into greenish spore balls that have a velvety appearance. The spore balls are small at first and visible in between glumes, growing gradually to reach 1 cm or more in diameter and enclosing the floral parts. They are covered with a membrane that bursts as a result of further growth. The color of the balls become orange and later yellowish green, or greenish black. At this stage, the surface of the ball cracks. The outermost layer of the ball is green and consists of mature spores together with the remaining fragments of mycelium.

The outer soporiferous region is three-layered. The outermost layer is greenish black with powdery spores; the middle layer, orange; and the innermost layer , yellowish.

Infections are of two types. One type takes place at the very early flowering stage when the ovary is destroyed while the style, stigmas, and anther lobes are buried in the spore mass. The second type occurs on the mature grain when spores accumulate on glumes, absorb moisture, swell, and force the lemma and palea to come apart. The fungus finally contacts the endosperm; ultimately the whole grain is replaced and enveloped by the fungus.

Chlamydospore

a thick- or double-walled asexual spore formed directly from a vegetative hyphal cell that functions for overwintering or as a resting stage.

formed on the spore balls are born laterally on minute sterigmata on radial hyphae, and are spherical to elliptical, warty, olivaceous, 3-5 x 4-6 µm. Younger spores are smaller, paler, and almost smooth.

Chlamydospores germinate in culture by germ tubes that become septate and form conidiophores bearing conidia at the tapering apex. These conidia are ovoid and very minute.

Some of the green spore balls develop one to four sclerotia in the center. These sclerotia overwinter in the field and produce stalked stromata the following summer or autumn. The stromata form a swelling at the tip of the stalk, are more or less globose, and contain perithecia around the periphery. Each flask-shaped perithecium contains about 300 asci. The asci are cylindrical with a hemispherical apical appendage, 180-220 x 4µm, and 8-spored. Ascospores are hyaline, filiform, unicellular, and 120-180 x 0.5-1µm.

In temperate regions, the fungus survives the winter by means of sclerotia as well as chlamydospores. It is believed that the primary infections are initiated mainly by the ascospores produced from the sclerotia. Chlamydospores play an important role in secondary infection, which is a major part of the disease cycle.

Studies in India and China showed that there are varieties/ lines/accessions that are resistant to false smut. Spraying with

• jinggamycin + Bordeaux mixture or chlorothalonil + metalaxyl combinations
• triadimefon, or
• carbendazim

at late booting to heading stage gave good control of false smut.