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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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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

Open access

Jacqueline Joshua and Margaret T. Mmbaga

, Fusarium ( F. solani f. sp. phaseoli and F. oxysporum f . sp. phaseoli ), Phytophthora spp., Sclerotium rolfsii , and Macrophomina phaseolina ( Bost et al., 2013 ). Seed treatments with chemical fungicides have been useful in managing soilborne

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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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Phillip N. Miklas, Valerie Stone, Carlos A. Urrea, and James S. Beaver

A genetic linkage map of 170 RAPD markers mapped across 79 recombinant inbred lines (Dorado and XAN-176) reveal genomic regions that condition multiple disease resistance to fungal (Ashy Stem Blight—Macrophomina phaseolina), viral (bean golden mosaic virus—BGMV), and bacterial (common bacterial blight—Xanthomonas campestris pv. phaseoli) pathogens of common bean (Phaseolus vulgaris). A genomic site on linkage group US-1 had a major effect, explaining 18%, 34%, and 40% of the variation in phenotypic reaction to ashy stem blight, BGMV, and common bacterial blight disease, respectively. Adjacent to this region was a QTL conditioning 23% of the variation in reaction to another fungal pathogen, web blight (Thanatephorus cucumeris). A second genomic site on linkage group US-1 had minor affect on multiple resistance expression to the same fungal (15%), viral (15%), and bacterial (10%) pathogens. It is unknown whether these specific genomic regions represent a series of linked QTL affecting resistance to each disease separately or an individual locus with pleiotropic effect against all three pathogens.

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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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Phillip N. Miklas, Richard Delorme, Valerie Stone, Mark J. Daly, J. Rennie Stavely, James R. Steadman, Mark J. Bassett, and James S. Beaver

Understanding the genomic associations among disease resistance loci will facilitate breeding of multiple disease resistant cultivars. We constructed a genetic linkage map in common bean (Phaseolus vulgaris L.) containing six genes and nine quantitative trait loci (QTL) comprising resistance to one bacterial, three fungal, and two viral pathogens of bean. The mapping population consisted of 79 F5:7 recombinant inbred lines (RILs) derived from a `Dorado'/XAN 176 hybridization. There were 147 randomly amplified polymorphic DNA (RAPD) markers, two sequence characterized amplified region (SCAR) markers, one intersimple sequence repeat (ISSR) marker, two seedcoat color genes R and V, the Asp gene conditioning seed brilliance, and two rust [Uromyces appendiculatus var. appendiculatus (Pers.:Pers) Unger] resistance genes: one conditioning resistance to Races 53 and 54 and the other conditioning resistance to Race 108. These markers mapped across eleven linkage groups, one linked triad, and seven linked pairs for an overall map length of 930 cM (Kosambi). Genes conditioning resistance to anthracnose (Co-2) [Colletotrichum lindemuthianum (Sacc. and Magnus) Lams.-Scrib.], bean rust (Ur-5), and bean common mosaic virus (I and bc-3) (BCMV) did not segregate in this population, but were mapped by inference using linked RAPD and SCAR markers identified in other populations. Nine previously reported quantitative trait loci (QTL) conditioning resistance to a variety of pathogens including common bacterial blight [Xanthomonas campestris pv. phaseoli (Smith) Dye], ashy stem blight [Macrophomina phaseolina (Tassi) Goid.], and bean golden mosaic virus (BGMV), were located across four linkage groups. Linkage among QTL for resistance to ashy stem blight, BGMV, and common bacterial blight on linkage group B7 and ashy stem blight, BGMV, and rust resistance loci on B4 will complicate breeding for combined resistance to all four pathogens in this population.

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Maria T. Ariza, Juan J. Medina, Luis Miranda, José A. Gómez-Mora, Berta De Los Santos, Antonieta de Cal, Elsa Martínez-Ferri, Lucía Cervantes, Rosalía Villalba, and Carmen Soria

’ susceptibility to Verticillium dahliae , Phytophthora cactorum , Podosphaera aphanis , Macrophomina phaseolina , and Colletotrichum acutatum was evaluated such as described in Avilés et al. (2009) , De los Santos et al. (2009) , Redondo et al. (2009

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

(causal agent Phytophthora cactorum ) and charcoal rot (causal agent Macrophomina phaseolina ) were not different from ‘Florida Radiance’ in either season. However, ‘Florida127’ had higher incidence of foliar powdery mildew (causal agent Podospharea

Open access

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