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Characterisation and management of Fusarium wilt of watermelon
Fusarium wilt is one of the most severe diseases in watermelon and is caused by a fungus called Fusarium oxysporum f. sp. niveum (Fon). This strain is only pathogenic on watermelons and can be divided into four races (0, 1, 2 and 3). The disease is one of the major yield limiting factors in production, worldwide. Fon was first detected in the Northern Territory (NT) in May 2011. The disease affected three different varieties of watermelon seedlings and plants from six different locations. To date, two of the races have been detected in Australia. However there is limited published information about the Australian Fon races. It is unclear what race the NT Fon strain is, whether it is a new race and its level of aggressiveness.
The objectives of the projects are to:
- identify the NT Fusarium oxysporum f. sp. niveum race(s) and compare with other Fon races (Australian and international)
- screen rootstocks and grafted watermelons for resistance to Fusarium oxysporum f. sp. niveum [all races]
- implement extension strategies to raise awareness of Fusarium wilt of watermelon, deliver outcomes to industry and propose management strategies.
The project outcomes include:
- obtaining a better understanding of the pathogen's biology by project completion
- determining the NT Fon race(s) and its relatedness to Australian and overseas Fon races by project completion. These findings would assist commercial breeding programs
- by the end of 2015, seedling nurseries and growers are using an integrated strategy for management of Fon that allows them to sustainably produce watermelons on their current infected farms, as a result of the extension activities from this project.
The following is an information update for the project.
Race differential trials in the NT have so far had mixed results. Trials on two varieties of watermelon, 'Kalahari' and 'SP-4' have suggested that two Fon NT isolates are of race 2. The most recent trial however, conducted again on the 'SP-4' variety, has suggested that the NT isolates may actually be of race 3. To date, race 3 has not been reported as present in Australia. This trial will be repeated, and highlights the importance of conducting race differential trials on several varieties of watermelon before race can be determined conclusively
Multiplication of 'Charleston grey' and 'Calhoun grey' seeds, which are traditionally used for Fon race differentials, has been completed and will be used for trials to determine which race is present in the NT and NSW.
Samples from melon growing regions in the NT, NSW, QLD and WA have been taken by University of Sydney post graduate student, Victor Puno. Preliminary race differential trials have found that four isolates from QLD are race 2. Isolates from the NT, NSW and WA have been determined as being either race 2 or 3, with ongoing trials being conducted to differentiate them.
Glasshouse and field trials to determine the effects of temperature on the susceptibility of plants to Fon are currently being conducted in 2014, after being disrupted in 2013 due to resource reallocation during the banana freckle outbreak. These trials will again be repeated in 2015 to assess the reliability of results.
Molecular studies on Fon isolates aim to develop a relatively quick and reliable molecular test for race identification. Thus far, studies have been made difficult due to the restrictions on importing live Fusarium cultures into Australia and the lack of quarantine facilities for working with them. Instead DNA from two isolates of each Fon race are to be imported from the US for future inclusion in comparative molecular studies of Fon isolates.
Molecular characterisation of Fon isolates has commenced by searching for pathogenicity genes. Genome sequencing has been conducted on two NT isolates, and the presence of pathogenic genes has been found. One isolate appears it may be slightly more virulent than the other, but this is yet to be verified.
This project is financially supported by the Northern Territory Department of Primary Industry and Fisheries, Horticulture Australia Limited, Monsanto Australia and Rijk Zwaan Australia.
Images from Tran-Nguyen et al 2012. Outbreak of Fusarium wilt in seedless watermelon seedlings in the Northern Territory, Australia. Australasian Plant Disease Notes. DOI 10.1007/s13314-012-0053-y
Contact the Plant Pathology unit for more information.
Last updated: 18 April 2016