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

Fungal diseases of peanut are responsible for increased production costs and yield losses of up to 50% for peanut producers in the U.S. Few cultivars with disease resistance have been developed through traditional breeding practices. There is an urgent need for developing cultivated peanut (Arachis hypogaea L.) cultivars that are resistant to the broad spectrum of fungal pathogens that pose a recurring threat to peanut health. Hydrolases such as chitinase and β-1-3-glucanase are known to degrade the cell walls of many fungi that attack plants, making them likely candidates for over-expression through genetic engineering to produce disease-resistant crops. Somatic embryos of the peanut cultivar Okrun were transformed with a chitinase gene from rice, and/or a β-1-3-glucanase from alfalfa via microprojectile bombardment. Regenerated Okrun lines were tested for the presence of the transgenes by polymerase chain reaction (PCR) and Southern blot and for transgene expression by colorimetric assays. Transgenic lines exhibited hydrolase activities 0-37% above levels observed in nontransformed Okrun plants.

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In 2001, entries from the peanut core collection, a subset of the USDA peanut germplasm collection, were planted in non-replicated plots in a field with a history of Sclerotinia blight caused by Sclerotinia minor. Variability existed among entries for reaction to Sclerotinia blight. Of the 744 entries evaluated, 11% had no disease, nearly 30% had ,10% disease incidence, and only 21% had 50% disease incidence or more. Most of the resistant entries had an upright growth habit and were in early and mid-maturity groups. Many of the early maturing entries were susceptible to the foliar disease pepper spot which occurred throughout the study. Entries were selected for further evaluation in replicated plots based on a nil to low (,10% 208, 128, 804, 582, and 273 combined resistance to Sclerotinia blight, pepper spot, and web blotch with less than erect growth habits. Entry 103 had good Sclerotinia blight resistance and yield, but an upright growth habit. Entry 92 had an upright growth habit and low yield, but good Sclerotinia blight resistance. Entries 92 and 103 had upright growth habits but were among the best entries for resistant to pepper spot and web blotch. Entries 426, 184, and 562 were upright and susceptible to pepper spot, but had resistance to web blotch and the best resistance to Sclerotinia blight. These entries appear to be useful sources of resistance to Sclerotinia blight for breeding programs and for increasing the probability of finding additional sources of resistance in clusters of germplasm identified within the entire USDA collection.