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Date: February, 2008
Source: The American Phytopathological Society, Plant Disease 2008; 92(2): 313 [edited]
<http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-92-2-0313C>


[Reference: AM Al-Sa'di, et al: First report of _Pythium splendens_ associated with severe wilt of muskmelon (_Cucumis melo_) in Oman.
Plant Dis 2008; 92(2): 313; DOI: 10.1094/PDIS-92-2-0313C]

Muskmelon (_Cucumis melo_ L.) is one of the most important vegetable crops in Oman. In the fall of 2004, sudden wilt was observed in muskmelon grown in a field at Sultan Qaboos University, Muscat. The disease was characterized by rapid collapse of vines and muskmelon plants at the fruit production to maturation stage, associated with brown to dark brown rotted primary and secondary roots. The disease resulted in death of more than 85 percent of muskmelon plants in that field.

_Pythium_ spp. were consistently isolated from crowns and roots of plants showing wilt symptoms. Further identification of 5 isolates of _Pythium_ produced a nucleotide sequence 806 basepairs long, which was identical among all isolates. Comparison with sequences deposited at the National Center for Biotechnology Information revealed 100 percent nucleotide similarity to a previously published sequence of an isolate of _P. splendens_ from cucumber from Oman, for which identification has also been confirmed by morphological characteristics.

In pathogenicity tests conducted in a greenhouse, _P. splendens_ induced damping-off symptoms on 7-day-old muskmelon seedlings and also reproduced the same wilt symptoms observed in the field when 2-month-old muskmelon plants were inoculated with 3-day-old _P. splendens_ cultures. To our knowledge, this is the 1st report of association of _P. splendens_ with wilt of muskmelon in Oman.

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[Fungal diseases called sudden or severe wilt of melon occur in many areas of the world, particularly in arid and semi-arid areas, and can cause severe yield losses. The term is a generic name for plants that suddenly die at or around fruit filling and is associated with fungal root infection and plant stress occurring at fruit set. Several
soil-borne fungi can be associated with the symptoms, including several species of _Pythium_, which destroy the plant feeder roots and invade larger roots, thus restricting water uptake. The high demand for water during fruit enlargement cannot be met following this invasion, and the vine wilts and plant death follows with immature fruits. The fungi can be spread by soil and infected plant material. Disease management includes cultural practices and use of resistant varieties. Soil fumigation and some fungicide treatments have been found to be of limited use.

_P. splendens_ is found in many areas of the world on a wide range of hosts, including crops such as taro and oilpalm, but has rarely been reported as being associated with sudden wilt of cucurbits. It has, however, been reported as one of the main causal agents of melon wilt in Japan.

Maps of Oman:
<http://meteorites.wustl.edu/oman.jpg> and
<http://healthmap.org/promed?v=20.6,56.1,5>

Pictures of sudden wilt symptoms on melon:
<http://www2.dpi.qld.gov.au/images/8223.jpg>,
<http://www2.dpi.qld.gov.au/images/8222.jpg> and
<http://www2.dpi.qld.gov.au/images/8170.jpg>

Links
General information on sudden wilt diseases of melons:
<http://www2.dpi.qld.gov.au/horticulture/11648.html>
_P. splendens_ causing melon wilt in Japan:
<http://sciencelinks.jp/j-east/article/200702/000020070207A0024751.php> and
<http://www.niast.go.kr/workpds/workpdsDown.asp?idx=3378&tG=1>
Biocontrol of _P. splendens_ on melon:
<http://www.fao.org/agris/search/display.do;jsessionid=790E8046426152BA03116FAE1B4540AA?f=./2004/v3005/IT2004060931.xml;IT2004060931>
Information on _Pythium_ species:
<http://taropest.sci.qut.edu.au/LucidKey/TaroPest/Media/Html/Fungi/Pythium/Pythium3.htm>
_P. splendens_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=278667>. 
- Mod.DHA]