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Cohen R.,Newe Yaar Research Center | Pivonia S.,Arava Research and Development | Crosby K.M.,Texas A&M University | Martyn R.D.,Purdue University
Horticultural Reviews

Monosporascus root rot and vine decline (sudden wilt), caused by the soilborne fungus Monosporascus cannonballus, has become one of the most important diseases of melon and watermelon worldwide. The fungus infects the roots early in the growing season, causing severe necrosis and ultimately resulting in a sudden and severe collapse of the vines late in the season. Melon (Cucumis melo) and watermelon (Citrullus lanatus) are the most severely affected, but all cucurbits tested to date can be infected; severe disease, however, is rarely observed except on melon and watermelon. The extensive root systems of the Cucurbita spp. and Lagenaria spp. offer some tolerance to the disease, which makes them suitable to serve as rootstocks. Fruit load, heat, drought, and other stresses may exacerbate disease symptoms and cause a collapse of the vines. Monosporascus cannonballus is somewhat unique as an ascomycete as it produces only one large ascospore per ascus, while two other species in the genus produce more than one. All species of the genus are pseudothermophiles, growing optimally at 25o-30oC, and are presumably native to hot, semiarid climates. Monosporascus spp. have been isolated from roots of numerous plant species, including dicots and monocots, although disease symptoms in plants other than cucurbits are rare. Monosporascus was described as a new genus and species in 1974, but pathogenicity to cucurbits was not established until 1983. Disease development in the field requires warm soil temperatures above 25oC. Ascospores are the overseasoning propagule and germinate in the presence of host root exudates and soil microflora. Initial infection occurs in the fine feeder roots, causing severe necrosis. The stimulation of tyloses in the xylem tissue leads to reduced water uptake and translocation, causing the vines to wilt suddenly. Management of sudden wilt has relied predominantly on preplant soil fumigation with methyl bromide. While effective, this method is not sustainable, given the phase-out of methyl bromide. Sanitation techniques that remove infected roots from the soil immediately after harvest can reduce the inoculum buildup in the soil and disease the following cycle but could be cost prohibitive in some production areas. Timely application of fungicides through the drip irrigation system during the growing season offers a cost-effective alternative to fumigation. Grafting melon or watermelon onto tolerant Cucurbita spp. rootstocks is gaining acceptance; however, there may fruit quality issues in some instances. The development of host plant resistance utilizing exotic C. melo germplasm has been pursued with promising results, but it is a slow process and has focused on just a few commercial melon types. An integrated strategy continues to evolve for control of sudden wilt and includes enhancing plant root system development, timely fungicide application, irrigation and soil management practices, and adoption of improved rootstocks and resistant melon lines. © 2012 Wiley-Blackwell. Published 2012 by John Wiley and Sons, Inc. Source

Weintraub P.G.,Gilat Research Center | Pivonia S.,Arava Research and Development | Steinberg S.,Sde Eliyahu Ltd
Crop Protection

Frankliniella occidentalis (Pergande) is a primary pest of greenhouse crops worldwide, in organic and integrated pest management control practices, Orius spp. are frequently released for thrips control. However, Orius spp. are relatively expensive to produce. More cost-efficient rearing systems and reduced release rate might reduce the expense. In these trials, we released Orius laevigatus (Fieber) at different rates with or without simultaneous release the predatory mite Amblyseius swirskii Athias-Henriot, another known thrips predator, which is less expensive to rear. There was no significant difference in the number of O. laevigatus recovered in which either 2 or 6 individuals were released per square meter, and there was no difference in thrips control among any of the release strategies using O. laevigatus, suggesting that a reduced release rate can maintain effective thrips control. There was no significant difference in the quality or quantity of the pepper yield between treatments in which either 2 or 6 Orius/m2 or Orius plus A. swirskii were released. © 2011 Elsevier Ltd. Source

Lugassi-Ben-Hamo M.,Ben - Gurion University of the Negev | Kitron M.,Arava Research and Development | Bustan A.,Ben - Gurion University of the Negev | Zaccai M.,Ben - Gurion University of the Negev
Scientia Horticulturae

The effects of shading on lisianthus (Eustoma grandiflorum) floral transition, plant development, flower yield and quality, and content of starch and soluble sugars were assessed in three cultivars, over two consecutive years. Shading nets affording 67% or 88% reduction in light intensity, were fitted at planting in the greenhouse for periods ranging from 3 to 8 weeks. Meristem morphology at floral transition was characterized by apical meristem widening and the appearance of two bract primordia. Floral transition time was affected by cultivars, but in general, longer and heavier shade treatments delayed floral transition; the longest delay (6 weeks) being recorded in Mariachi White under 88% shade for 7 weeks or under a combined shade treatment of 88% for 3 weeks followed by 67% for 5 weeks. Despite interactions between cultivar and shade treatment, consistent trends were discerned: the heaviest and most prolonged shading reduced yield (up to 40%), cut stem length (up to 15%), and number of flower buds/stem (up to 26%), within cultivar. Total carbohydrates levels were very low, and it is questionable whether changes observed in carbohydrate quantity following shade treatments had any effect on plant growth or flower yield. Rather, it appears that lisianthus is very dependent on current photosynthesis, so that even a brief shading interlude could reduce branching and flower quality. It may be concluded that the intensive shading usually applied is detrimental for lisianthus. © 2009 Elsevier B.V. All rights reserved. Source

Edelstein M.,Israel Agricultural Research Organization | Cohen R.,Israel Agricultural Research Organization | Elkabetz M.,Israel Agricultural Research Organization | Pivonia S.,Arava Research and Development | And 3 more authors.

Melon plants grafted on Cucurbita rootstock may suffer from nutritional deficiencies due to reduced absorption and translocation of minerals to the foliage. Melon (Cucumis melo L.) cv. 6023 was grafted onto two interspecific Cucurbita rootstocks (Cucurbita maxima 3 Cucurbita moschata) ‘TZ-148’ and ‘Gad’. Nongrafted melons were used as controls. Two fertilization field experiments were conducted in walk-in tunnels in the northern Arava valley of southern Israel. Two fertigation regimes were used: 1) standard and 2) enriched for magnesium (Mg; 150 mg·LL-1), manganese (Mn; 7.5 mg·LL-1), and zinc (Zn; 0.75 mg·LL-1) to increase the concentrations of the lacking elements. The enriched fertigation significantly increased Mn, Zn, and Mg contents in the leaf tissue. Concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sodium (Na), chloride (Cl), iron (Fe), and boron (B) were unaffected by the enriched fertilizer. There were no deficiency symptoms in grafted plants supplied with the enriched fertilizer. © 2016, American Society for Horticultural Science. All rights reserved. Source

Pivonia S.,Arava Research and Development | Gerstl Z.,Institute of Soil, Water and Environmental Sciences | Maduel A.,Arava Research and Development | Levita R.,Arava Research and Development | Cohen R.,Newe Yaar Research Center
European Journal of Plant Pathology

Sudden wilt (vine decline) of melon caused by Monosporascus cannonballus is a problem in arid and semiarid regions worldwide. Preplanting soil disinfestation with methyl bromide, a common treatment for disease management, has been banned in many countries, raising the need for alternative disease-control measures. Soil fungicide application during the growing season is one possible treatment. Twelve fungicides were evaluated in vitro for M. cannonballus suppression, seven of those were evaluated under field conditions. The fungicides azoxistrobin, prochloraz and pyraclostrobin + boscalid exhibited high and similar efficacies in controlling sudden wilt disease under field conditions. Fludioxonil applied at high rates was also effective but was phytotoxic. Fluazinam, the first fungicide found capable of suppressing sudden wilt and one which has been used in Israel since 2000, was less effective. The results indicate that two applications of a fungicide during the short fall season should be sufficient for effective control of the disease. In the long spring season, at least three applications are needed to protect the melon crop. Melon fruits were examined for fungicide residues and only boscalid residues were found. This fungicide was therefore limited to the first application before fruit set. © 2010 KNPV. Source

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