ABSTRACT Peanut rust, caused by Puccinia arachidis Speg., is a foliar disease that plagues peanut production along with early and late leaf spots, Passalora arachidicola (Hori) U. Braun and Nothopassalora personata (Berk. & M.A. Curtis) U. Braun, C. Nakash, Videira & Crous, respectively. Rust can cause up to 80% yield losses without control and is widespread in tropical countries but is also a sporadic problem in the United States. An integrative plant management strategy with rust resistant peanut cultivars is needed to decrease dependence on costly fungicides and increase yields for farmers who cannot afford or do not have access to fungicides. Only moderate levels of rust resistance have been identified in cultivated peanut germplasm, but fortunately, high resistance to rust has been identified in wild Arachis species that can be introgressed into peanut cultivars. In this study, 16 diploid, wild Arachis species, five diploid, interspecific hybrids, 11 unique, allotetraploid interspecific hybrids, and two cultivated peanut controls were tested for resistance to rust. Resistance was evaluated in vitro by incubation time, susceptibility index (calculated based on the number of lesions of different diameters)/ leaf area, total number of lesions/ leaf area, and total number of sporulating lesions/ leaf area. All wild Arachis species tested were very highly resistant to rust, except for A. ipaënsis , the B-genome progenitor of cultivated peanut. Additionally, all interspecific hybrids and synthetic allotetraploids not produced with A. ipaënsis as a parent did not show symptoms for rust. Any of these nine synthetic allotetraploids, BatCor , BatDur 1, BatDur 2, BatSten 1, GregSten , MagCard , MagDio , MagDur , and ValSten 1 are recommended for progression to QTL mapping of rust resistance. These resistance QTLs can be pyramided into peanut cultivars to protect yields in the United States and to increase yields in tropical, developing countries for farmers that cannot afford, or do not have access to, costly fungicides.

ABSTRACT Wild, diploid Arachis species are a great source of biotic and abiotic stress resistances and tolerances for peanut breeding programs; however, these species also have undesirable characteristics such as small seed size, low yield, and weak peg strength. Peg strength has been shown to have a positive, linear relationship with yield in cultivated peanut. Therefore, the weak peg strength of wild Arachis species could be detrimental to yield and needs to be selected against when introgressing useful alleles from wild species into elite germplasm. To enable breeders to effectively utilize these wild species, we sought to characterize peg strength and anatomical characteristics correlated with peg strength in seven diploid Arachis species, as well as four allotetraploids, six (cultivated peanut lines x allotetraploid) F 1 hybrids, and two cultivated peanut breeding lines. For each genotype, five mature pegs were tested for peg strength and cross-sections for three of the five pegs were subsequently taken and analyzed for peg anatomical characteristics including total peg cross-section area, mean bundle cap area, total bundle cap area, bundle cap as a percentage of peg area, bundle cap number, mean distance between bundle caps, total distance between bundle caps, and tannin cell count. Genotype was a significant indicator for peg strength and all the anatomical characterization parameters (P < 0.05). Peg strength was positively and highly correlated with peg area, mean bundle cap area, total bundle cap area, and bundle cap number. Peg strength comparable to that of peanut breeding lines was recovered in the F 1 hybrids. Because weak peg strength in the wild species appears to be recessive, strong pegs can likely be easily selected during the process of introgression.

ABSTRACT Fall armyworm (FAW) is an economically devastating, invasive pest in Sub-Saharan Africa and can be a major pest in the Americas. This pest feeds on more than 80 plant species, including peanut, and threatens the food security of millions of people who rely on these crops in Sub-Saharan Africa. An integrated pest management strategy, including resistant crop cultivars, is needed to control FAW, since populations have been reported to develop insecticide resistance. Genetic sources of host resistance to FAW are limited in cultivated peanut; however, strong resistance to FAW was reported previously in peanut wild relatives. In this in vitro study, we tested diploid peanut relatives including A. ipaensis KG37006 ( Ipa ), A. duranensis 30060 ( Dur ), A. correntina 9530 ( Cor 9530), and A. correntina 9548 ( Cor 9548); allotetraploids including IpaCor 9530 4x , IpaDur 4x ; F 2 hybrids [ A. hypogaea 13-1014 x IpaCor 9530 4x ]; and cultivated peanut lines A. hypogaea ‘13-1014′ and ‘Georgia Green' for FAW resistance to identify valuable materials in our breeding program. FAW development was measured by survival, larval weight, larval stage duration, pupation, pupal stage duration, moth emergence relative to pupation, and moth sex. All allotetraploids showed promise as donors for FAW resistance. This FAW resistance was derived primarily from A. ipaensis , but A. duranensis was also identified as a source of resistance, though more moderate. A high level of heterogeneity was found in A. correntina 9530, which likely contributed to the variable performance of this species in the bioassay. Producing hybrids and allotetraploids with wild Arachis species does not guarantee that each derived line from these crosses will be resistant, and since these lines are segregating, selection for resistance is still needed.

ABSTRACT The peanut CSSL population represents one of the ways that interspecific hybridization has been used to introduce genetic variation into cultivated peanut. The lines were developed by crossing Fleur 11, a farmer preferred spanish cultivar from West Africa with a synthetic allotetraploid. The latter was developed by crossing A. duranensis to A. ipaensis and tetraploidizing the resultant hybrid. Subsequent selection with genetic markers resulted in a population comprising lines with small chromosome segments from the wild in a cultivated peanut background. The objective of this study was to characterize the protein, total oil, fatty acid and sugar profiles of the population. The results indicated that the values of Fleur 11 for all the traits analyzed were within the normal range expected in peanut. Since the population had a uniform genetic background derived from Fleur 11, the profiles for a majority of the lines were comparable to Fleur 11. However, three lines (CSSL 84, CSSL 100 and CSSL 111) were found to have elevated oleic acid and reduced linoleic and palmitic acid relative to Fleur 11. The oleic to linoleic acid ratios (O/L) for these lines were 118, 104 and 97% greater than that of Fleur 11, respectively. While the increased values are still considered to be within the normal oleic acid range, the effect of introgressions on these lines represent the possibility of discovering new sources of high O/L polymorphisms. Such polymorphisms have the potential for use in further improving peanut oil quality.

ABSTRACT In peanut ( Arachis hypogaea L.), most agronomically important traits such as yield, disease resistance, and pod and kernel characteristics are quantitatively inherited. Phenotypic selection of these traits in peanut breeding programs can be augmented by marker-assisted selection. However, reliable associations between unambiguous genetic markers and phenotypic traits have to be established by genetic mapping prior to early generation marker-assisted selection. Previously, a nested association mapping (NAM) population of 16 recombinant inbred line populations (RILs) consisting 4870 lines was established. In order to facilitate effective mapping of such a large genetic resource, the first objective of the current study was to phenotype the parental lines for yield, pod traits, field maturity, germination, plant morphology, salt tolerance and resistance to tomato spotted wilt virus (TSWV) and late leaf spot (LLS). For most measured traits, more than one parental combination demonstrated statistically significant variation which can be further quantified and mapped in the respective RIL populations. The second objective of this study was to genotype the parental lines using the Arachis Axiom SNP arrays to reveal the marker density of the mapping populations. The Version 1 array identified 1,000 to 4,000 SNPs among the population parents and the number of SNPs doubled on the Version 2 array. Further phenotyping and genotyping of the NAM populations will allow the construction of high density genetic maps containing quantitative trait loci.

ABSTRACT For crops with a narrow cultivated genetic base, incorporating beneficial alleles from related species through alien introgression widens the genetic base and provides key resistances to disease and abiotic stresses. Fine mapping of these introgressions can increase the efficiency of marker-assisted selection for breeding programs. To facilitate high resolution fine mapping of alien introgressions, we developed an automated pipeline, IntroMap. This pipeline was developed with accessibility and utility in mind, and does not present novel mapping algorithms. Using five diploid wild Arachis species, we identified diagnostic SNP sets for introgression mapping in Arachis hypogaea, cultivated peanut. IntroMap has applicability in all crops where alien introgression is used to bring in beneficial alleles from related species, so the pipeline includes an option to generate new diagnostic SNPs from any species/accession of interest for use in the pipeline. These user generated resources will be included for distribution with IntroMap to increase the SNP resources for all users. We demonstrate the efficacy of IntroMap by fine mapping three alien introgressions in an elite peanut breeding line with superior disease resistance. IntroMap works well even at low coverage, recovering at 2x coverage almost 50% of the diagnostic SNPs found at 10x coverage. The true benefit of IntroMap is the availability and generation of shared public resources, specifically for Arachis spp. IntroMap is freely distributed at https://sourceforge.net/projects/intromap/ .

ABSTRACT Strong host resistance to root-knot nematode (RKN; Meloidogyne arenaria ) introgressed from a wild diploid species to cultivated peanut was previously shown to be located on a large chromosomal region of linkage group A09. Little to no recombination in mapping populations has hindered fine mapping of the resistance genes. In order to further delineate the introgressed region, additional polymorphic markers were added to the linkage group A09 using a recombinant inbred line population developed from Gregory x Tifguard in which Gregory is the susceptible parent and Tifguard is the resistant parent harboring the alien introgression. Map distance within the introgressed region based on this population increased to 8 cM compared with zero recombination in an earlier generation. Lines with rare recombination within this introgressed region were phenotyped and it was demonstrated that one portion of the introgressed region confers moderate resistance while a smaller, distal portion confers strong resistance to RKN. Molecular markers associated with the introgressed region conferring strong resistance can be deployed in peanut breeding programs to improve selection for RKN resistance.

ABSTRACT Modern farming is dependent on continual development of improved cultivars and efficient cultural management practice. In addition, dissecting genetic components of heritable traits also relies on the development of large mapping populations. Artificial hybridization is the critical initial step in these processes. Peanut is a self-pollinating crop with a typical yield of less than three seeds per flower; therefore, significant effort is required to produce sufficient hybrid seeds for subsequent trait selection and/or establishment of mapping populations. A study was conducted to evaluate the effect of multiple factors on the success rate of artificial hybridization assessed by transmission of molecular markers unique to the paternal parent. Multiple peanut genotypes were crossed with a breeding line homozygous for both high oleic acid and nematode resistance. The impacts of operator, pollination time, flower integrity, genotype and environment on hybridization were evaluated. Data indicated that operator, pollination time and environment significantly affected the success rate of peanut hybridization. Pods from runner type parental plants that contain hybrid seeds were more likely to contain single seeds than those derived from self-pollination. Hybrid seed loss due to seed rot and peg damage reduced yield. Improving hybridization success rate by increasing humidity, decreasing temperature, personnel training and greenhouse management is recommended.

ABSTRACT Reliable and objective phenotyping of peanut pod and seed traits is important for cultivar selection and genetic mapping of grade components. To develop useful and efficient methods to quantitatively define peanut pod and seed traits, a group of peanut germplasm with high levels of phenotypic variation was included in this study. Digital image analysis was employed to quantify peanut pod volume using projected 2-dimensional pod area as an effective surrogate parameter. Strong correlation between pod volume measured by water displacement and image analysis was established (R 2 = 0.891). Pod volume, pod density and kernel percent were observed to vary significantly among the germplasm lines. To define testa color, hue angle analysis was performed on a subset of germplasm with solid testa color. It was determined that hue angle can sufficiently differentiate genotypic differences based on testa color variation.

ABSTRACT The identification of molecular markers for economically significant traits should greatly improve the speed and efficiency of all peanut ( Arachis hypogaea L.) breeding programs. Development and phenotypic evaluation of recombinant inbred line (RIL) populations of peanut, along with molecular genotyping, will be essential for association of markers with traits. The primary objectives of this research were to develop 16 structured RIL populations that can be used by the peanut research community, and to begin high-resolution phenotyping of these populations. Crosses were made using a 2 by 8 (common by unique) factorial nested association mapping design. Parents were selected to attempt to maximize genetic diversity while meeting practical breeding objectives. First, two modern runner cultivars (Tifrunner and Florida-07) were selected as common parents because runner cultivars account for about 80% of the production in the U.S. Second, the eight unique parents were selected to supply diversity across market classes and botanical varieties and are donors of favorable alleles for enhancing drought tolerance and resistance to most important disease of peanut in the U.S. The eight unique parents are N08082olJCT (a Bailey derived high oleic breeding line), C76-16, NC 3033, SPT 06-06, SSD 6 (PI 576638), OLin, New Mexico Valencia A, and Florunner. The 16 populations were advanced using summer and winter nurseries. Input from multiple disciplines has resulted in a prioritized list of populations and traits that should be examined, and seed increase has begun to provide the community with material for extensive phenotyping. In-depth phenotyping and genotyping of these populations should result in markers that can be deployed by breeding programs for the development of improved cultivars.

A nonheme chloroperoxidase gene ( cpo-p ) from Pseudomonas pyrrocinia , a growth inhibitor of mycotoxin-producing fungi, was introduced into peanut via particle bombardment. The expression of the cpo-p gene is predicted to increase pathogen defense in peanut. Embryogenic peanut tissues were bombarded with gold particles coated with plasmid pRT66 carrying the cpo-p and hygromycin phosphotransferase ( hph ) genes, under the control of a double CaMV 35S and a single CaMV 35S promoter, respectively. Selection for hygromycin-resistant somatic embryos was performed on a liquid medium containing 10–20 mg/L hygromycin 3–4 days after bombardment. The integration and expression of the cpo-p gene was confirmed by Southern, Northern and Western blot analyses. In vitro bioassay using crude protein extracts from transgenic T0, T1, and T4 plants showed inhibition of Aspergillus flavus hyphal growth, which could translate to a reduction in aflatoxin contamination of peanut seed.