Anamorphic Erysiphe australiana causing powdery mildew on Lagerstroemia indica in Brazil

Lagerstroemia indica (pride of India, queen's rose; local name: extremosa) is a small tree in the Lythraceae, native to India, which has become one of the main urban ornamental trees in the southern states of Brazil (Lorenzi et al. 2003). Severe powdery mildew outbreaks have been observed on L. indica trees grown as ornamentals in Viçosa, (State of Minas Gerais, Brazil), beginning in the spring of 2002. The sole fungal disease listed by Mendes et al. (1998) as occurring in Brazil on this host is black mildew caused by Irenopsis lagerstroemiae but Stammer & Tomaz (1991) have also recorded the occurrence of an undetermined species of Oidium on this host. However no description or illustration of this powdery mildew was provided by those authors.

White superficial colonies, with abundant sporulation, developed amphigenously on leaves and also on the non-lignified parts of the stems (Fig. 1). Infected tissues often became distorted and necrotic. Defoliation and death of young shoots often resulted. Hyphae were 2.5-5.0 µm wide, septate, branched, hyaline, smooth, with mycelial appressoria lobed; conidiophores were epiphytic, produced from the external mycelium, unbranched, cylindrical, 37-73 x 6-10 µm, 1-2 septate, hyaline, smooth; foot-cells were cylindrical, straight, 16-32 x 5-10 µm; conidia were produced singly at the apex of the conidiophores, cylindric, doliiform or ellipsoid, 22-44.5 x 11-20 µm l/w ratio 1.4 - 3.2, aseptate, hyaline, smooth (Fig. 2); germ tubes, 1-4 at an end of the spore, were either short and immediately producing multilobed appressoria or moderately long (1-2 x the length of the conidium), ending in a lobed or inconspicuous appressorium (Figs 3 & 4).

The teleomorph was absent but the anamorph morphology is identical to that described for Erysiphe australiana [syn. Uncinuliella australiana], a common powdery mildew species infecting Lagerstroemia spp. worldwide (Braun, 1987) and reported from Argentina and Venezuela. Representative material was deposited in the herbarium (VIC 26568, VIC 26570). This is the first record of this species of powdery mildew attacking L. indica in Brazil.