The production of cultivated peanut, an important agronomic crop throughout the United States and the world, is consistently threatened by various diseases and pests. Sclerotinia minor Jagger (S. minor), the causal agent of Sclerotinia blight, is a major threat to peanut production in the Southwestern US, Virginia and North Carolina. Although information on the variability of morphological traits associated with Sclerotinia blight resistance is plentiful, no molecular markers associated with resistance have been reported. The identiWcation of markers would greatly assist peanut geneticists in selecting genotypes to be used in breeding programs. The main objective of this work was to use simple sequence repeat (SSR) primers previously reported for peanut to identify a molecular marker associated with resistance to S. minor. Out of 16 primer pairs used to examine peanut genomic DNA from 39 diVerent genotypes, one pair produced bands at approximately 145 and 100 bp, consistent with either S. minor resistance or susceptibility, respectively. Cloning and sequencing of these bands revealed the region is well conserved among all genotypes tested with the exception of the length of the SSR region, which varies with disease resistance levels. This is the Wrst report of a molecular marker associated with resistance to Sclerotinia blight in peanut. The identiWcation of this marker and development of a PCR-based screening method will prove to be extremely useful to peanut breeders in screening germplasm collections and segregating populations as well as in pyramiding S. minor resistance with other desirable traits into superior peanut lines. Abbreviations ABLAdvanced breeding line AFLP AmpliWed fragment length polymorphism QTL Quantitative trait loci RAPD Random ampliWed polymorphic DNA RFLP Restriction fragment length polymorphism SCAR Sequence characterized ampliWed region SSR Simple sequence repeat Cultivated peanut (Arachis hypogaea L.) is a selfpollinated allotetraploid (2n = 4x = 40), which is
Bermudagrass (Cynodon sp.) is an important warm‐season forage grass for the South and may have value as a bioenergy feedstock. The objective of this study was to measure the genetic relatedness among entries of the Cynodon clonal forage bermudagrass core collection and seven commercial forage cultivars using plant phenotype and molecular marker data from amplified fragment length polymorphisms. The collection was assessed for 22 phenotypic traits, including forage quality, plant architecture, growth habit, and ploidy level. Phenotypic variability was preserved in the forage bermudagrass core collection constructed based on 21 phenotypic traits and ploidy levels. The majority of molecular marker polymorphism observed was within phenotypic clusters (89.6%) and within the five ploidy levels (94%), and STRUCTURE analysis indicated significant admixture. Overall, the combined genetic and phenotypic variability found within the bermudagrass core collection will aid in selection of parental crosses for mapping and potential quantitative trait loci discovery and to identify parental lines that may yield greater genetic gain in breeding for important traits.
Rhizoma peanut (Arachis glabrata Benth.) has potential to provide high quality forage during summer months; however, establishment of the stand is slow and cold tolerance is limited. During the three growing seasons from 2006 to 2010, a randomized complete block design experiment was initiated at four locations, near Tifton, GA (2006, 2007, and 2008), Gene Autry, OK (2006), Burneyville, OK (2007 and 2008), and Vashti, TX (2007 and 2008), evaluating 16 rhizoma peanut genotypes for better establishment characteristics and cold tolerance. At the end of the establishment year, genotype A6 (PI 210555) had the greatest coverage (74%), followed by genotypes A156 and A160 (51 and 56%, respectively), while genotypes A10 and A42 had the least coverage (9 and 13%, respectively). The remaining genotypes were intermediate and generally did not differ from the released cultivars Florigraze, Arbrook, and Latitude 34, which had 25, 25, and 30% coverage, respectively. In the second season after establishment, genotypes Latitude 34 and A160 produced the greatest yields (1000 and 1360 kg ha−1, respectively). In the third season after establishment, Latitude 34 (3630 kg ha−1) outyielded all genotypes except A156 and A160 (2610 and 2260 kg ha−1, respectively). Therefore genotypes A160 and Latitude 34 consistently had the greatest coverage and production and may have greater cold tolerance. However, in the final year (2010), there were no genotypes that survived the winter.
Sclerotinia blight, caused by Sclerotinia minor Jagger, has become one of the major limiting factors in peanut (Arachis hypogaea L.) production. The objectives of this research were to evaluate the effects of plant spacing on disease incidence and severity of Sclerotinia blight in peanut research plots, to measure the level of apparent resistance at different seeding rates, and to determine which methods would produce clearest selection criteria in space-planted breeding plots. Four peanut cultivars, Tamspan 90, Southwest Runner, Okrun, and Flavor Runner 458, were evaluated in field plots at four plant spacings (6, 15, 30, and 46 cm) in 2003 and 2004. Increased plant spacing improved sensitivity of disease incidence based determination of cultivar resistance but did not increase mean incidence significantly. Disease severity reached the highest level at the widest plant spacing. Final disease incidence provided excellent differentiation of genotypes with different levels of resistance and required the least amount of labor as compared with other methods of disease assessment.A.L. Maas, USDA-ARS, Coastal Plain Exp. Sta.,
Rhizoma peanut (Arachis glabrata Benth.) is a forage crop with increasing acreage (>10,500 ha) in the coastal plain region of the United States. Peanut mottle virus (PeMoV), a member of the family Potyviridae, is transmitted nonpersistently by aphids and seed-transmitted in A. hypogaea. Important hosts of the virus include peanut, soybean, and pea. During January of 2006 in Tifton, GA, immature rhizoma peanut plants identifier A176 with a lost PI number and PI 243334 exhibiting chlorotic ringspots were tested for viruses (potyviruses, Tomato spotted wilt virus [TSWV] and Cucumber mosaic virus [CMV]) frequently found in crops in the southeastern United States. All symptomatic plants tested were positive in the general potyvirus screen by indirect ELISA (Agdia, Inc., Elkhart, IN) and negative for TSWV and CMV. Leaves from two symptomatic plants of A176 and several asymptomatic genotypes were blotted onto FTA cards (Whatman Inc., Maidstone, UK) to bind viral RNA for preservation and processed according to the manufacturer's protocol. To determine the specific potyvirus identity, punch-outs from the FTA cards were used for reverse transcription (RT)-PCR (3) to test for PeMoV and Peanut stripe virus (PStV), both of which are found in A. hypogaea in Georgia. The forward primer (5′-GCTGTGAATTGTTGTTGAGAA-3′) and the reverse primer (5′-ACAATGATGAAGTTCGTTAC-3′) were specific for PeMoV and the forward primer (5′-GCACACACTTCTTGGC ATGG-3′) and reverse primer (5′-GCATGCCCTCGCCATTGCAA-3′) were specific for PStV (2). The primers are specific to the respective viral coat protein genes. Amplicons of the expected size (327 bp) were produced from symptomatic A176 and PI 243334 samples but not from the asymptomatic genotypes. The resulting PCR product was sequenced and a BLAST search in GenBank confirmed PeMoV (98 to 99% nt identity with Accession Nos. X73422 and AF023848). This finding is of significance because rhizoma peanuts are typically propagated by cuttings. Therefore, maintaining virus-free stock is critical. Although, PeMoV has been found in A. pintoi in Colombia (1), to our knowledge, this is the first report of PeMoV in rhizoma peanut (A. glabrata) peanut anywhere in the world. References: (1) A. A. Brandt et al. Plant Viruses Online: Descriptions and Lists from the VIDE Database, 2007. (2) R. G. Dietzgen et al. Plant Dis. 85:989, 2001. (3) R. D. Gitaitis et al. Phytopathology (Abstr.) 95(Suppl):S35, 2005.
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