The phaeosphaeria leaf spot of maize in Brazil: evidences of a new etiological agent?

spot, has been observed causing severe damage in all maizegrowing areas of Brazil since 1982 (Fantin, 1994). The causal organism of this disease was initially described in the USA as Phaeosphaeria maydis (Henn.) Rane, Payak & Renfro (sin. Sphaerulinia maydis Henn.), anamorph Phyllosticta sp. (Rane et al., 1966). Doubts regarding the etiology of this disease have resulted in several attempts to perform Koch ́s postulates in order to identify the real causal agent of this disease in Brazilian conditions (Fantin & Balmer, 1997; Paccola–Meirelles et al., 2001; Amaral et al., 2005). A recent publication by Oliveira et al. (2004, Revista Brasileira de Milho e Sorgo 3:343–356) postulates a species of Sclerophthora as the probable agent of the disease known in Brazil as phaeosphaeria leaf spot of maize. The quality of the information concerning a disease of such importance has to be examined very carefully, as misleading information can cause confusion and also delay progress in key research areas for the development of successful strategies to manage this disease. Thus, as plant pathologist working on maize diseases over the last twenty years, we thought it our duty to draw the scientific community’s attention to some points concerning the results described by Oliveira et al. (2004) which could invalidate the whole concept of a new etiological agent for this disease, as postulated by those authors. In this regard, the above mentioned paper shows a set of photographs whose interpretation provokes heavy doubts. Critical points regarding the illustrated structures are discussed in this letter. Figure 1 on page 346 of the paper shows typical symptoms of the phaeosphaeria leaf spot of maize. Lesions are round or oval, varying in diameter from 0.3 to 1.0 cm. Lesions may also coalesce and become irregular shaped (Fernandes & Oliveira, 1997; Parentoni et al., 1994). These symptoms are clearly different from typical symptoms caused by the two known species of the genus Sclerophthora causing downy mildew on maize. Sclerophthora macrospora (Sacc.) Thirum., C.G. Shaw & Naras. causes an excessive tillering, rolling, twisting of the upper leaves, and a partial or complete proliferation of the tassel, which continues until tassel resembles a mass of leafy structures. These modified leaves, like inflorescences, are described as “crazy top” (Shurtleff, 1986). Typical symptoms of the brown stripe downy mildew, caused by Sclerophthora rayssiae R.G. Kenneth, Koltin & I. Wahl are characterized by the development of narrow chlorotic or yellowish stripes, 3-7 mm wide, with well defined margins and delimited by the veins. The stripes later become reddish to purple. Lateral development of lesions causes severe stripping and blotching (Shurtleff, 1986). Symptoms described in Figure 1 are also completely different from the symptoms of maize CARTA AO EDITOR / LETTER TO THE EDITOR