Peanut breeders are constantly in search of new sources of genes that confer tolerance or resistance to biotic and abiotic stresses to improve the production and quality. The objective of this study was to evaluate peanut lines generated from interspecific crosses for amounts of wild species introgression, including genes for resistance to peanut root-knot nematodes, tomato spotted wilt virus and leaf spot diseases. Nine diploid Arachis species were crossed with peanut breeding lines and 130 different interspecific hybrid lines were developed. These lines were evaluated for the amount of introgression using RFLP analyses, plant morphology, and disease resistant phenotypes. Based on RFLPs, 41 lines showed measurable introgression and 12 hexaploid-derived lines were polymorphic for at least four probes. Greenhouse and field evaluations indicated that resistance was not present in the lines tested for tomato spotted wilt virus, early leaf spot, or Cylindrocladium black rot. However, resistance approaching that of the wild species was found for the peanut root-knot nematode ( Meloidogyne arenaria ) among lines derived from crosses with Arachis diogoi, A. correntina, A. batizocoi , and A. cardenasii. Introgression lines were resistant (disease ratings of 1.5 to 4.5 and lesion numbers 8 to 63) compared to Southern Runner (ratings of 5.5 to 6 and lesion numbers of nearly 500) for late leaf spot ( Cercosporidium personation ) in field evaluations performed in Gainesville, FL over 2 yr. The greatest resistance was found among lines from crosses with A. batizocoi, A. duranensis, A. stenosperma, A. magma , and A. diogoi. Results indicate that it should be possible to identify molecular markers to tag resistance genes for use in conventional breeding programs and stack these genes in highly productive peanut cultivars.

Tomato spotted wilt virus (TSWV) is among the greatest yield-reducing viruses affecting peanut ( Arachis hypogae a L.). The best known method of control of TSWV is through the use of resistant cultivars. Unfortunately, only a few peanut genotypes with moderate levels of resistance are known. The objectives of this study were to identify additional sources of resistance to TSWV and to determine whether plant descriptor information is associated with reaction to TSWV in the field. Peanut plant introductions from a core collection were evaluated for resistance to TSWV in field trials from 1991 to 1993. Great variability was found among PIs for reaction to natural TSWV epidemics at Attapulgus, GA. Accessions which exhibited potential resistance in 1991 or 1992 were reevaluated in subsequent years. Disease pressure was high in 1993 and 27 accessions exhibited significantly greater resistance than Florunner, and one (PI 262049) had lower disease incidence than Southern Runner. Only minor relationships existed between TSWV incidence and plant descriptor traits (growth habit and maturity) using the stepwise multiple regression procedure. Peanut accessions with resistance to TSWV were found among all maturity levels and growth habits. These accessions provide additional parents and may provide additional genes for resistance that may be useful in developing resistant cultivars.

Peanut ( Arachis hypogaea L.) is susceptible to aflatoxin contamination when pods are developing under drought conditions in the field. The development of cultivars which resist preharvest aflatoxin contamination would be advantageous, but has been limited by the lack of genes for resistance. Several genotypes have been suggested as potential sources of resistance. Conflicting results have been reported on how useful this resistance may be, and some of these sources have never been specifically examined for resistance to preharvest aflatoxin contamination. The objective of this study was to evaluate aflatoxin contamination under drought stressed conditions in potentially resistant peanut genotypes. Twelve peanut genotypes were planted in a randomized complete-block design in field plots in Yuma, AZ in 1991 and 1992. Ten of these genotypes were also planted in a randomized complete-block design in field plots in Tifton, GA in 1992. All plots were inoculated with Aspergillus inoculum and were subjected to 40 to 50 d of drought stress immediately prior to harvest. After harvest, aflatoxin contamination (ppb) of seed was measured. None of the genotypes included in this study were more resistant (P≤0.05) to preharvest aflatoxin contamination than Florunner. The results of this study indicate that it would be desirable to identify higher levels of resistance to preharvest aflatoxin contamination in peanut.

Late leafspot, caused by Cercosporidium personatum , is prevalent in the southeastern United States and causes extensive defoliation and peanut yield losses if fungicides are not applied. Some sources of resistance to late leafspot have already been identified in the United States peanut germplasm collection. In screening 500 peanut plant introductions from the Southern Regional Plant Introduction Station, Experiment, Georgia, 33 genotypes with partial resistance to C. personatum were identified. These lines were evaluated for leafspot resistance and yield without fungicide protection from 1989 through 1991. Although PI 215695, PI 215696 and PI 215724 were significantly more resistant than all other genotypes over the three years, pod yields were low. During years of high disease severity, resistant selections PI 203396 and PI 162529 had the highest yields. Significant positive correlation occurred between late leafspot ratings and shelling percentage (r = 0.43 and 0.47) in 1990 and 1991. Evaluation of the main-stems of plants during the growing season revealed that the three most resistant genotypes had significantly less defoliation than Southern Runner, the only cultivar grown with resistance to late leafspot. There are important genes for resistance present in the United States peanut germplasm collection and there is a need for evaluation of the entire collection for useful resistance to leafspot and other pests.

Recently, the peanut ( Arachis hypogaea L.) industry has expressed a greater need for higher percentages of fancy pods and extra large kernels (ELK), especially for use in large-seeded in-shell products. Genetic control of these traits has been reported to range in complexity from simple inheritance to the inclusion of multiple modifier genes. This study was conducted to determine the general combining ability (GCA) effects of 50 peanut genotypes on pod and seed size. Each genotype was used five times as a female parent and five times as a male parent in a partial diallel crossing program. F 1 hybrids were grown and their pods were harvested for measurements of pod and seed size. The F 2 generation was planted the following year and similar measurements were recorded using the single pod descent procedure. Individual F 2 plants were harvested and pod and seed characteristics measured for segregation information within four crosses. General combining ability effects were not well correlated between generations (r=0.53-0.56) or with the same traits measured on pure-line parents (r=0.32-0.42). PI 298845, PI 314897, PI 325079, Jenkins Jumbo, and Fla 393-8-1-1-1-1-1-2 had consistently large positive GCA effects on pod and seed weight. F 2 segregation patterns indicated that some crosses exhibit predominantly additive gene action while one cross (PI 270818 / PI 269111) showed dominance toward smaller pods. Transgressive segregation occurred for pod and seed size traits in four crosses. Substantial genetic variability for pod and seed size remains in the peanut germplasm collection.

Means of yield and qualitative traits are assessed in multi-location tests in the final stages of breeding line evaluation. Due to large environmental variation and genotype x environment interactions, it is often desirable to compare stability of lines over a range of environments. The objective of this study was to use various stability parameters to try and determine the stability of experimental breeding lines. Using data from regional advanced peanut ( Arachis hypogaea L.) breeding line yield trials conducted over 3 years and four locations in Virginia and North Carolina, the stability of peanut cultivars and breeding lines was compared. Stability variance was found to be highly correlated (0.91–1.00) with covariate adjusted stability variance. In many instances, the stability-variance parameters produced similar results to pairwise regressions and dissimilarity measures when compared with standard cultivars. However, the distance parameters and regressions provided more precise information on relative responses in varying environments of two advanced breeding lines being considered for release. This allowed for direct comparison to cultivars targetted for replacement. NC 18411 had equal mean yields and qualitative traits but better stability than breeding line NC 18423. Regression analysis indicated that NC 18423 performed best in good environments but worse than most other cultivars in poor environments. Means and stability of value per kilogram and value per hectare were highly correlated with percentage of sound mature kernels and yield (0.92–0.99), respectively. A comparison of means and stability parameters was effective in discerning superiority of peanut breeding lines for potential release and use by growers.

Four parental lines with resistance to early leafspot caused by Cercospora arachidicola Hori and four parental lines with resistance to late leafspot caused by Cercosporidium personatum (Berk. & Curt.) Deighton and the F 1 hybrid progeny from crosses between the two groups of parents were evaluated for resistance to both leafspot diseases in the greenhouse using a detached leaf technique. The subsequent F 2 plants of all crosses were evaluated in the field for resistance to early leafspot in order to estimate combining ability effects for components of partial resistance and to identify parents useful in developing lines resistant to both diseases. General combining ability, attributed largely to additive genetic variance, accounted for the largest portion of the variability among the F 1 and F 2 generations for most parameters of resistance to both early and late leafspots. Reciprocal effects and heterosis toward the susceptible parents were also significant for parameters of resistance to the two pathogens. GP-NC 343 and FESR 5-P2-B1 were the best parents for incorporating genes for resistance to both early and late leafspots. Progenies of NC 17090 had a high level of resistance to late leafspot in detached leaf tests and progeny of PI 350680 had reduced defoliation from early leafspot in the field. Broad-sense heritabilities ranged from 0.2 to 0.4 for parameters of resistance to early leafspot estimated from the pooled variances of F 2 plants of all crosses planted in the field. Parameters of resistance evaluated in the greenhouse for F 1 hybrids were compared to parameters evaluated in the field for the F 2 population by rank correlation of entry means. Latent period and sporulation of the fungus on detached leaves of F 1 generation plants correlated (r = −0.46 and 0.54, respectively) with defoliation of F 2 plants in the field.