September 21, 2005
From: British Society for Plant Pathology, New Disease Reports, Vol. 12 [edited] <http://www.bspp.org.uk/ndr/jan2006/2005-68.asp>

Plasmopara australis newly recorded from Brazil on the new host Luffa cylindrica
DJ Soares, DF Parreira, RW Barreto, Departamento de Fitopatologia, Universidade Federal de Vicosa, Vicosa, Minas Gerais, Brazil, 36571-000. Accepted for publication 08/08/05.

_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, but although this fungus is a common cucurbit pathogen worldwide and also in Brazil, it has never been recorded on loofah in Brazil.

In May of 2005 plants of _L. cylindrica_ were found showing moderate downy mildew symptoms in a small spontaneous population in the locality of Vicosa, 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. A sample was deposited in the local herbarium (VIC 28797).

The fungus had the following morphology, as observed by light microscopy: sporangiophores up to 460 micrometers long, aseptate, hyaline, cylindrical, straight, with a slightly swollen base 10-18 micrometers, branches mostly at right angles and with truncated tips, sporangia deciduous, predominately oblong, 13-22 x 9-13 micrometers, l/w ratio (1.18-)1.36-1.90 (-2.20), slightly papilate, sometimes with a small pedicel 1-2 micrometers long; sexual stage not found. Morphology of this fungus places it unequivocally in the genus _Plasmopara_. Only 2 _Plasmopara_ species are known on _Cucurbitaceae_: _Plasmopara australis_ and _P. orientalis_.

Neither of these were ever reported on _L. cylindrica_. P. australis is considered restricted to Argentina and North America, while P. orientalis was recorded from far eastern Russia, China, and Japan. 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 1st record of this fungus for Brazil and the first record of this fungus on _L. cylindrica_ worldwide.

References:
Constantinescu O. Plasmopara orientalis sp. nov. (Chromista, Peronosporales). Sydowia 2002; 54: 129-36.
Farr DF, Rossman AY, Palm ME, McCray EB. Fungal Databases, Systematic Botany & Mycology Laboratory, ARS, USDA. Retrieved June 24, 2005, from <http://nt.ars-grin.gov/fungaldatabases/>
Mendes MAS, Silva VL, Dianese JC, Ferreira MASV, Santos CEN, Neto EG, et al. Fungos em Plantas no Brasil. Brasília, Brazil: EMBRAPA-SPI, 1998.
Purseglove JW. Tropical Crops - Dicotyledons. England: Longman Group Ltd, 1968.

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[This report records the presence of _P. australis_ in Brazil for the first time. Based on the information at hand, it is difficult to assess the effect of the pathogen on the host. There is not much information about downy mildew disease on this particular crop.

The link to the original piece contains all of the text and graphics and is located at the top of the list of links.
Link: <http://cuke.hort.ncsu.edu/cucurbit/cuke/dshndbk/dm.html> - Mod.DH]