Plasmopara australis newly recorded from Brazil on the new host Luffa cylindrica

Luffa cylindrica, known as smooth loofah, sponge gourd, dish-cloth gourd and vegetable sponge (local name: bucha), is a member of the Cucurbitaceae that is native to tropical Asia, possibly India. It was an important crop before the Second World War because of its use as a biological filter. In Brazil, loofah is a subsistence crop for small farmers. A downy mildew, caused by Pseudoperonospora cubensis, is one of the most important diseases for this crop (Purseglove, 1968), but although this fungus is a common cucurbit pathogen worldwide and also in Brazil, it has never been recorded on loofah in Brazil (Mendes et al., 1998).

In May of 2005 plants of L. cylindrica were found showing moderate downy mildew symptoms in a small spontaneous population in the locality of Viçosa, state of Minas Gerais, Brazil. The lesions were amphigenous, initiating as slight discolorations of the tissues, become yellowish to necrotic, mostly vein-limited, with a clear water-soaked margin and a white, lanose to felt-like mass of fungal structures abaxially.(Fig. 1-6). A sample was deposited in the local herbarium (VIC 28797).

The fungus had the following morphology, as observed under the light microscope: Sporangiophores up to 460 µm long, aseptate, hialine, cylindrical, straight, with a slightly swollen base 10-18 µm, branches mostly at right angles and with truncated tips, sporangia deciduous, predominately oblong, 13-22 x 9-13 µm, l/w ratio (1.18-)1.36-1.90(-2.20), slightly papilate, sometimes with a small pedicel 1-2 µm long; sexual stage not found (Fig. 7-8). Morphology of this fungus places it unequivocally in the genus Plasmopara. Only two Plasmopara species are known on Cucurbitaceae: Plasmopara australis and Plasmopara orientalis. None of these were ever reported on L. cylindrica (Farr et al., No Date). P. australis is considered restricted to Argentina and N. America, while P. orientalis was recorded from far eastern Russia, China and Japan (Constantinescu, 2002). The combination of characters presented by the fungus on loofah matches well within the concept adopted by the former author for P. australis. This is, therefore, the first record of this fungus for Brazil and the first record of this fungus on L. cylindrica worldwide.