DISEASE AND PEST RESISTANCE
Disease pressure results in reduced income to growers through yield losses and from the cost of chemical treatments. Development of resistant varieties is an important means of increasing grower profitability.
Nematodes. Root-knot nematodes (Meloidogyne arenaria Neal (Chitwood) affect peanuts in many states, and some fields in Central Texas have been abandoned for peanut production because of the severity of infection. No significant resistance exists in the cultivated peanut A. hypogaea; however, resistance was transferred from wild species through an interspecific cross (Florunner × [A. batizocoi K9484 × (A. cardenasii GKP10017 × A. diogoi GKP10602)]4x) by Dr. Charles Simpson. The world’s first resistant variety, Coan, derived from this cross has been released by Texas A&M (Simpson and Starr, 2001). A second high-yielding nematode-resistant variety is currently close to release. Release is being accelerated by the use of molecular markers to select for true-breeding lines.
Leafspot. Early leafspot [ELS] (Cercospora arachidicola) and late leafspot (Cercosporidium personatum) cause serious losses worldwide and in South Texas where high temperature and humidity are present. Resistance is quantitative, and only low- to moderate levels of resistance are present in the cultivated peanut species. There are high levels of resistance to leafspot in several wild species, including A. cardenasii and A. diogoi. BC3F1 progeny from the TxAG-6 introgression program have demonstrated an 85% reduction in early leafspot disease incidence (J. Starr, unpublished results). Jointly with the University of Georgia, we are currently in the process of identifying quantitative trait loci (QTLs) for ELS resistance in the BC3 generation. This cross has the potential for developing highly-resistant varieties, assisted by use of molecular markers.
Nematode resistance. We will develop runner and Spanish varieties with resistance to nematodes having high oleic acid content and, for West Texas, early maturity. This is being done in collaboration with Drs. James L. Starr and Charles E. Simpson .
Leafspot Resistance. Our goal is to develop high-yielding, leafspot-resistant varieties with acceptable yield. We will also develop molecular markers to use for selecting different resistance mechanisms and against introgressed genes for low yield and other undesirable traits. We will also develop a series of near-isogenic lines from the wild species material, making these genes available to the general peanut community.
Nematode resistance. We are currently making crosses among parents having nematode resistance, high O/L, and/or early maturity. Conventional screening and molecular markers will be used for selection.
Leafspot resistance We are growing introgression populations at Yoakum, TX. We will take disease ratings, and use DNA markers to estimate the number of leafspot resistance genes present.