Relationships and Utilization of Arachis Germplasm in Peanut Improvement.

Abstract

Cultivated peanut, Arachis hypogaea L., is a tetraploid (2n = 4x = 40) species considered to be of allopolyploid origin. Its closest relatives are the diploid (2n = 2x = 20) annual and perennial species included with it in section Arachis. An understanding of taxonomic relationships among those species may allow for more efficient utilization of alien germplasm in applied peanut improvement. A total of 108 accessions, representing 26 species in section Arachis were genotyped with AFLP markers. Cluster and principal component analyses of the data supported previous taxonomic classifications and genome designations. Based on genetic distances and cluster analysis, "A" genome accessions 30029 (A. helodes), and 36009 (A. simpsonii), and "B" genome accession 30076 (A. ipaensis) were the most closely related to both A. hypogaea suggesting their involvement in the evolution of the tetraploid species.

Accession 10602 of A. diogoi possesses resistance to TSWV. Associating molecular markers with resistance would greatly aid in the transfer of resistance into high performing A. hypogaea backgrounds. In an attempt to find markers associated with TSWV resistance, a genetic linkage map was constructed for an F2 population of A. kuhlmannii x A. diogoi. The map consisted of 102 AFLP markers grouped into 12 linkage groups and spanning 1068.1 cM. The map allowed the evaluation of the Arachis genome for associations between response to TSWV infection and the AFLP markers. Five markers, all located in the same linkage group (LG V) were closely associated (0.0009 < P < 0.0021) with TSWV resistance as well as several other associations believed to be linked with minor genes conferring resistance. These markers will be studied for utilization in peanut breeding with marker-assisted selection.

Development of cultivars with moderate to high levels of field resistance to tomato spotted wilt virus (TSWV) is the most promising means of managing spotted wilt of peanuts. Breeding efficiency can be maximized by choosing parents based on their potential to produce superior progeny. Best Linear Unbiased Prediction (BLUP) is a method for estimating the breeding value of a parent based on its own performance as well as that of its relatives. The method was used in the present study to identify lines with superior ability to transmit TSWV field resistance to their progeny. BLUPs for yield, meat content, crop value, and pod brightness also were calculated. Six different weighting schemes were designed and used for index selection in order to pick lines with superior breeding values for a combination of all traits analyzed. Thirteen lines were selected with at least four of the six weighting schemes suggesting that these lines should be able to transmit to their progenies not only reduced TSWV incidence, but also increased yields and improved quality traits.