Physoderma maydis (brown spot of corn)

Lesions first appear as very small, oblong to round yellowish spots on the leafblade, leaf sheath, stalk and, occasionally, the outer ear husks and tassels ofmaize. Lesions may occur in bands across the leaf blade. The spots seldombecome greater than 1 mm in diameter except where two or more of them coalesce,and they may become so numerous as to give the entire leaf blade a rustyappearance (Tisdale, 1919). Infected tissues within the lesion turnchocolate-brown to reddish-brown and lesions coalesce to form large, irregular,angular blotches. Cells of infected tissues disintegrate and expose dustypustules containing large numbers of golden-brown to dark-brown sporangia. Theentire leaf sheath may become brown because of the coalescence of large numbersof lesions. Where infections are this numerous, the entire leaf is often killedbefore the plant becomes mature (Tisdale, 1919).On the stalks, water-soaked lesions may be seen beneath the leaf sheath.Lesions may coalesce to form brown blotches, and later, small pockets of brownsporangia form in the stalks. Stalks may be completely girdled at the nodes andthey are easily broken by the wind following invasion of the tissue by thefungus (Tisdale, 1919).Brown spots appeared on maize leaves when injured roots were inoculated with asporangial suspension of Physoderma maydis. Symptoms also appeared on theleaves when injured collar regions at the base of the stem just above the soillevel were inoculated (Lal and Chakravarti, 1977a).

P. maydis is an important disease in areas of abundant rain and hightemperatures. Yield losses of 20% have been reported in India (Lal andChakravarti, 1976). It is normally a minor problem in the USA. Losses of 6-10%were reported in North Carolina in 1919 (Tisdale, 1919), and 1.9% inMississippi in 1957 (Broyles, 1959). In 1971, a severe outbreak occurred inwhite maize in Illinois, with 80% lodging in some fields (Burns and Shurtleff,1973).