Soum Sanogo

Germplasm evaluation and transfer of Verticillium wilt resistance from Pima ( Gossypium barbadense ) to Upland cotton ( G. hirsutum )

Verticillium wilt (VW, Verticillium dahliae) is a worldwide destructive soil-borne fungal disease and employment of VW resistant cultivars is the most economic and efficient method in sustainable cotton production. However, information concerning VW resistance in current commercial cotton cultivars and transfer of VW resistance from Pima (Gossypium barbadense) to Upland (Gossypium hirsutum) cotton is lacking. The objective of the current study was to report findings in evaluating commercial cotton cultivars and germplasm lines for VW resistance in field and greenhouse (GH) experiments conducted in 2003, 2006, and 2007. In the study, 267 cultivars and germplasm lines were screened in the GH, while 357 genotypes were screened in the field. The results indicated that (1) VW significantly reduced cotton yield, lint percentage, 50% span length and micronaire, but not 2.5% span length and fiber strength, when healthy and diseased plants in 23 cultivars were compared; (2) some commercial cotton cultivars developed by major cotton seed companies in the US displayed good VW resistance; (3) many Acala cotton cultivars released in the past also had good VW resistance, but not all Acala cotton germplasm are resistant; (4) Pima cotton possessed higher levels of VW resistance than Upland cotton, but the performance was reversed when the root system was wounded after inoculation; (5) VW resistance in some conventional cultivars was transferred into their transgenic version through backcrossing; and (6) some advanced backcross inbred lines developed from a cross between Upland and Pima cotton showed good VW resistance. The successful development of VW resistant transgenic cultivars and transfer of VW resistance from Pima to Upland cotton implies that VW resistance is associated with a few genes if not a major one.

Quantitative trait locus analysis of Verticillium wilt resistance in an introgressed recombinant inbred population of Upland cotton

Verticillium wilt (VW) of Upland cotton (Gossypium hirsutum L.) is caused by the soil-borne fungal pathogen Verticillium dahlia Kleb. The availability of VW-resistant cultivars is vital for control of this economically important disease, but there is a paucity of Upland cotton breeding lines and cultivars with a high level of resistance to VW. In general, G. barbadense L. (source of Pima cotton) is more VW-resistant than Upland cotton. However, the transfer of VW resistance from G. barbadense to Upland cotton is challenging because of hybrid breakdown in the F2 and successive generations of interspecific populations. We conducted two replicated greenhouse studies (tests 1 and 2) to assess the heritability of VW resistance to a defoliating V. dahliae isolate and identify genetic markers associated with VW resistance in an Upland cotton recombinant inbred mapping population that has stable introgression from Pima cotton. Disease ratings at the seedling stage on several different days after the first inoculation (DAI) in test 1, as well as the percentages of infected and defoliated leaves at 2 DAI in test 2, were found to be low to moderately heritable, indicating the importance of a replicated progeny test in selection for VW resistance. With a newly constructed linkage map consisting of 882 simple sequence repeat, single nucleotide polymorphism, and resistance gene analog–amplified fragment length polymorphism marker loci, we identified a total of 21 quantitative trait loci (QTLs) on 11 chromosomes and two linkage groups associated with VW resistance at several different DAIs in greenhouse tests 1 and 2. The markers associated with the VW resistance QTLs will facilitate fine mapping and cloning of VW resistance genes and genomics-assisted breeding for VW-resistant cultivars.

Integrated management of Phytophthora capsici on solanaceous and cucurbitaceous crops: current status, gaps in knowledge and research needs

Abstract Phytophthora capsici is an oomycete pathogen of vegetable crops worldwide, causing crop losses exceeding 50% and possibly resulting in crop failure. Extensive research has been conducted on various facets of this pathogen since it was first described in 1922. Information from past research efforts has enhanced the understanding of the biology and management of P. capsici. However, this pathogen remains a continuous challenge to vegetable production. This mini-review succinctly provides (i) an appraisal of the current state of management approaches and outlines a framework for designing an integrated management system for P. capsici; and (ii) identifies knowledge gaps and delineates new research perspectives for control of this pathogen.

A Search for the Phylogenetic Relationship of the Ascomycete Rhizoctonia leguminicola Using Genetic Analysis

Rhizoctonia leguminicola, which causes fungal blackpatch disease of legumes and other plants, produces slaframine and swainsonine that are largely responsible for causing salivation, lacrimation, frequent urination, and diarrhea in grazing animals including cattle, sheep, and horses. The original identification of R. leguminicola was based only on morphological characters of the fungal mycelia in cultures because of the lack of fungal genetic markers. Recent investigations suggested that R. leguminicola does not belong to genus Rhizoctonia and is instead a member of the ascomycetes, necessitating an accurate reclassification. The objective of this study was to use both genetic and morphological characters of R. leguminicola to find taxonomic placement of this pathogen within ascomycetes. Internal transcribed spacer region (ITS) and glyceraldehyde-3-phosphate dehydrogenase (gpd) encoding gene were amplified from R. leguminicola isolates by PCR using universal primers and sequencing. Rhizoctonia leguminicola ITS and gpd sequences were aligned with other fungal sequences of close relatives, and phylogenetic trees were constructed using neighbor-joining and parsimony analyses. Rhizoctonia leguminicola isolates were clustered within a clade that contains several genera of ascomycetes belonging to the class dothideomycetes. We suggest that the fungus is misidentified in the genus Rhizoctonia and propose its reclassification in a new genus within the phylum Ascomycota.

Resistance sources, resistance screening techniques and disease management for Fusarium wilt in cotton

Fusarium wilt (FW), caused by the fungal pathogen Fusarium oxysporum f. sp. vasinfectum (FOV), is a significant economic constraint to cotton production worldwide. The pathogen has a wide geographical distribution, and its biological characteristics have enabled its establishment of eight races in several agro-ecosystems spanning from regions with high precipitation to semi-arid and arid irrigated zones. Management of Fusarium wilt is challenging because of the ability of FOV to persist in production systems through formation of long-lived chlamydospores and through its parasitic and pathogenic associations with cotton and other rotational cops and weeds. The interaction of FOV with nematodes constitutes additional constraints to the management of the disease. Breeding and utilizing FW-resistant cultivars has proven to be the most cost-effective control method. Numerous approaches and methods have been used in screening cotton for resistance to FW. This review provides a background on accumulated knowledge over the past two decades on sources of FW resistance and methods of screening for resistance including inoculation and evaluation protocols in cotton. The review also provides an overview of the biology and management of FOV.

Microorganisms Associated with Valencia Peanut Affected by Pod Rot in New Mexico

Abstract Pod rot of peanut is a disease that occurs worldwide. Soilborne pathogens typically causing pod rot include Rhizoctonia solani, Sclerotium rolfsii, and Pythium spp. Although pod rot is known to occur in New Mexico, no etiological study has been conducted on this disease. In 2005 and 2006, 14 Valencia peanut fields were surveyed in eastern New Mexico where the majority of Valencia peanut is produced. The primary focus of the study was to isolate and identify microorganisms associated with pod rot. The secondary focus of the study was to characterize microorganisms from roots and stems from the same plants selected for pod rot assessment. Peanut plants were collected and processed for isolation of microorganisms by plating seeds, pieces of hull, root, and stem on acidified potato dextrose agar. In both years, the average incidence of pods with hull discoloration or pod rot symptoms varied from 55–60 to over 90%, and disease severity ranged from 5 to over 90% across all fields surveyed. A diverse gr...

Evaluation of commercial Upland (Gossypium hirsutum) and Pima (G. barbadense) cotton cultivars, advanced breeding lines and glandless cotton for resistance to Alternaria leaf spot (Alternaria alternata) under field conditions

Alternaria leaf spot (ALS, caused by Alternaria spp.) is one of the most common foliar diseases in cotton (Gossypium spp.) that occurs in most cotton-growing regions of the world including the United States. In New Mexico, ALS caused by A. alternata (Nees:Fr.) Keissler is becoming prevalent due to favorable weather conditions in the late cropping season; however, there is limited information on screening cotton for ALS resistance. In this study, a total of 125 Upland cotton (G. hirsutum L.) genotypes were separated into 5 trials each with 32 entries and 3–4 replications, together with one trial including 8 Pima cotton (G. barbadense L.) cultivars and lines with 4 replications in 2016. Three additional field trials each with 32 or 34 genotypes and 4 replications were conducted in 2017. Based on the high disease incidence (99.9% with a range of 90–100% in 2016 and 100% in 2017) and high disease severity index (DSI, 26.7–92.0 with a mean of 62.4 in 2016 and 42.0–89.0 with a mean of 66.7 in 2017) of foliar symptoms in the late growing season in both years, no cotton genotype was immune to ALS (A. alternata) under the natural infection field conditions. The analysis of variance showed that there were significant genotypic variations in six of the nine replicated trials, and the broad-sense heritability estimates for DSI ranged from 0.489 to 0.702 with an average of 0.566. No significant genotypic difference was detected among Pima cotton cultivars and lines in both years. An orthogonal contrast detected no overall significant difference between Upland and Pima cotton in both years, while 15 Upland glandless lines as a group, had a significantly lower DSI than the glanded group with 17 Upland lines in one replicated test. Glandless NuMex COT 15 GLS, NM 13P1117 and NM 12Y1002, and glanded commercial transgenic FM 2484 B2F, PHY 444 WRF and NG 4545 B2XF were consistently resistant to ALS in two or more tests. The results provide useful information for breeding cotton for ALS resistance.

First Report of Fusarium Wilt of Cotton Caused by Fusarium oxysporum f. sp. vasinfectum Race 4 in Texas, U.S.A.

Fusarium wilt of cotton (Gossypium spp.), caused by the soilborne fungus Fusarium oxysporum f. sp. vasinfectum (FOV), is a widespread and economically important disease. FOV is genetically diverse with numerous described races and genotypes (Cianchetta et al. 2015), most of which cause disease only in the presence of plant-pathogenic nematodes; however, FOV race 4 is extremely virulent and can cause severe, early-season damage in the absence of nematodes. Race 4 was first described in India (Armstrong and Armstrong, 1960) and has likely spread to other cotton-producing regions through cotton seed. FOV race 4 was first detected in California in 2001 (Kim at el. 2005), and had not been confirmed elsewhere in the U.S.A. (Cianchetta et al. 2015) until recently. In June of 2016 and 2017, severe Fusarium wilt symptoms, including wilting, root rot and stem discoloration, that were consistent with FOV race 4 were observed on seedlings of Pima cotton (Gossypium barbadense) in the Upper Rio Grande Valley of Texas i...

Factors affecting mycelium pigmentation and pathogenicity of Sclerotinia sclerotiorum on Valencia peanut

Abstract: Sclerotinia sclerotiorum infects a broad range of plant hosts, and is typically identified by the production of white mycelium and black sclerotia on infected plants and culture. Isolates of S. sclerotiorum with darkly-pigmented mycelium have been reported on Valencia peanut in New Mexico and Texas. This study was conducted to determine the relationship between dark pigmentation in mycelium, oxalic acid production, and pathogenicity of S. sclerotiorum on Valencia peanut. A darkly-pigmented (SD) and a mutant, non-pigmented (SW) isolate of S. sclerotiorum were compared for vegetative growth on various growth media under different environmental conditions, and for pathogenicity on peanut. The SD isolate became darker in mycelium pigmentation as temperature increased beyond 20 °C and at pH between 5.0 and 6.0. Pigmentation in the SW isolate remained unaffected. Oxalic acid production did not increase in either SD or SW isolates when grown on media amended with pure oxalic acid or its precursor arabinose. The SD isolate caused peanut plant death and necrotic lesions on leaflets, while the SW isolate did not cause any symptoms. The differential behavior of SD and SW isolates in pathogenicity does not appear to be associated with mycelium pigmentation.

Additional file 1: of Genetic analysis of Verticillium wilt resistance in a backcross inbred line population and a meta-analysis of quantitative trait loci for disease resistance in cotton

Mapping of quantitative trait loci for Verticillium wilt resistance in a backcross inbred line population of (SG 747 × Giza 75) × SG 747 BC 2 F 4 .