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Margaret T. Mmbaga, Lucas M. Mackasmiel and Frank A. Mrema

Macrophomina phaseolina is a nonspecialized soil-borne pathogen that can become a problem by causing root rot, charcoal rot, collar rot, damping-off, wilt, leaf blight, and stem blight in both agricultural and natural or landscape environments

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J.O. Kuti, G.V. Latigo and J.O. Bradford

Soil-borne pathogens such as Macrophomina phaseolina (the causative agent of charcoal rot) and Phymatotrichum omnivorum (the causative agent of cotton root rot) contribute to mortality of transplanted guayule (Parthenium argentatum, Gray) seedlings in southern Texas. In order to select guayule genotypes for resistance to these pathogens, it would be useful to develop reliable greenhouse inoculation procedures for screening guayule seedlings. Twelve-week-old guayule seedlings (`11591', a USDA standard breeding line) were inoculated using two inoculation methods (soil-drenching and root-dipping) in two soil media (field soil and commercial soil mix). Plants were rated for disease severity 2 to 5 months after inoculation and pathogens were re-isolated from diseased plants to establish Koch postulates. The soil drenching technique, using field soil, caused rapid development of disease symptoms that were consistent with re-isolation frequencies of pathogens from the diseased plant tissues.

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Amnon Koren* and Menahem Edelstein

Grafting technology for vegetable transplants was introduced to Israel eight years ago by Hishtil Nurseries, Inc. The main goal of grafting was to find a substitute for methyl bromide, the elimination of which was pending. The use of grafted watermelon transplants soon followed. Presently, more than 40% of watermelon transplants are grafted. The chief reason for the success of grafted transplants is their tolerance to soil-borne pathogens, including Fusarium, Monosporascus, and Macrophomina. Yields of grafted transplants are often much higher, and it has been shown possible to grow watermelons with saline water (4.5). A limitation of grafted transplants is that presently, we do not have a good solution for nematodes. A drawback is that in order to get good watermelon taste and flavour, the grower needs the experience to adjust agrotechniques, especially determining the best harvest date. Grafted tomato transplants were also introduced early on. Grafted tomato transplants can have excellent resistance to fusarium crown rot, corky root, and other soil-borne pathogens. Some rootstocks have been observed to tolerate water salinity of 8 ec and still produce commercially acceptable yields. Limitations to the use of grafted tomato transplants are the lack of compatibility of some of the cultivars with the rootstocks and the breakdown of nematode resistance at high soil temperatures. Melons, eggplants, and cucumbers are grafted under some conditions.

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Roni Cohen*, Yosef Burger and Menahem Edelstein

The use of grafted vegetables as one of the alternatives to soil disinfestation with methyl bromide is increasing in Israel. Watermelon (Citrullus lanatus) and melon (Cucumis melo) plants are grafted mainly onto Cucurbita rootstocks for lessening losses due to soil-borne pathogens. The contribution of the rootstock to the grafted plant's resistance depends on the nature of the disease. In general, damage caused by non-specific root-rot pathogens such as Rhizoctonia solani, Macrophomina phaseolina, Monosporascus cannonballus, and Pythium spp. are effectively reduced by using Cucurbita rootstocks. However, these rootstocks provide only partial protection from vascular diseases such as fusarium wilt, in which case better protection can be achieved by grafting susceptible melons onto monogenic fusarium-resistant melon rootstocks. The performance of the grafted plants depends not only on the rootstock but also on the scion response to pathogens and on the effect of the environment on disease development. The response of grafted and non-grafted melons of different cultivars to sudden wilt disease caused by the fungus Monosporascus cannonballus was evaluated in field trials conducted in the fall and spring growing seasons. Significant differences in disease incidence were found among cultivars, between grafted and non-grafted plants, and between seasons. Grafting reduced plant mortality in the spring and fall experiments but prevention of yield losses was more effective in the spring. More emphasis should be given to finding suitable rootstocks and adjusting agrotechniques for successful commercial cultivation of grafted melons in the fall.

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Margaret T. Mmbaga, Lucas A. Mackasmiel and Frank A. Mrema

Macrophomina phaseolina is a well-documented soilborne pathogenic fungus that causes root rot or charcoal rot, collar rot, and damping-off diseases in diverse plants. More than 500 plant species across ≈100 genera that include food crops

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Christopher A. Clark, Washington L. da Silva, Ramón A. Arancibia, Jeff L. Main, Jonathan R. Schultheis, Zvezdana Pesic van-Esbroeck, Chen Jiang and Joy Smith

progressing from either the proximal or the distal end of the root or both and a more restricted tip rot that appears in storage near the proximal end of the root ( Arancibia et al., 2013 ; Clark et al., 2013a ). Various fungi have been isolated from each

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Ramón A. Arancibia, Jeffrey L. Main and Christopher A. Clark

necessary to develop proper management strategies. Tip rot is manifested at or close to the proximal end of the storage root as a small sunken and irregular lesion delimited by a sharp border ( Fig. 1 ). The lesion is usually shallow and progresses onto

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Vance M. Whitaker, Craig K. Chandler, Natalia Peres, M. Cecilia do Nascimento Nunes, Anne Plotto and Charles A. Sims

‘Florida127’ was similar to that of ‘Florida Radiance’ with two exceptions. The incidence of anthracnose fruit rot (causal agent Colletotrichum acutatum ) and botrytis fruit rot (causal agent Botrytis cinerea ) and mortality due to phytophthora root rot

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Jacqueline Joshua and Margaret T. Mmbaga

et al., 2016 ), and were effective against Macrophomina root rot disease ( Mmbaga et al., 2018b ). The objectives of this study were 1) to identify soilborne pathogens from snap bean roots and rhizosphere soil where fungicides are not used in

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Vance M. Whitaker, Natalia A. Peres, Luis F. Osorio, Zhen Fan, M. Cecilia do Nascimento Nunes, Anne Plotto and Charles A. Sims

acutatum species complex), charcoal rot (caused by Macrophomina phaseolina ), Phytophthora crown rot (caused by Phytophthora cactorum ), and Colletotrichum crown rot (caused by Colletotrichum gloeosporioides species complex) were described in Seijo et