Michael R. Baring

Identification of QTLs for pod and kernel traits in cultivated peanut by bulked segregant analysis

Bulked segregant analysis was used to identify simple sequence repeat (SSR) markers associated with pod and kernel traits in cultivated peanut, to permit rapid selection of superior quality genotypes in the breeding program. SSR markers linked to pod and kernel traits were identified in two DNA pools (high and low), which were established using selected F 2:6 recombinant individuals resulting from a cultivated cross between a runner (Tamrun OL01) and a Spanish (BSS 56) peanut. To identify quantitative trait loci (QTLs) for pod and kernel-related traits, parents were screened initially with 112 SSR primer pairs. The survey revealed 8.9% polymorphism between parents. Of ten SSR primer pairs distinguishing the parents, five (PM375, PM36, PM45, pPGPseq8D9, and Ah-041) were associated with differences between bulks for seed length, pod length, number of pods per plant, 100-seed weight, maturity, or oil content. Association was confirmed by analysis of segregation among 88 F 2:6 individuals in the RIL population. Phenotypic means associated with markers for three traits differed by more than 40%, indicating the presence of QTLs with major effects for number of pods per plant, plant weight, and pod maturity. The SSR markers can be used for marker assisted selection for quality and yield improvement in peanut. To the best of our knowledge, this is the first report on the identification of SSR markers linked to pod - and kernel- related traits in cultivated peanut.

Advanced Backcross Quantitative Trait Loci (QTL) Analysis of Oil Concentration and Oil Quality Traits in Peanut (Arachis hypogaea L.)

Peanut seed oil is an important commodity worldwide and breeding efforts have been to improve both the quality and quantity of oil produced. Identifying sources of variation and elucidating the genetics of oil concentration and quality in peanut is essential to advancing the development of improved genotypes. The objective of this study was to discover QTLs for oil traits in an advanced backcross population derived from a cross between a wild-species derived amphidiploid, TxAG-6, and a cultivated genotype, Florunner. A BC1F1 population was developed for genetic mapping and an advanced backcross BC3F6 population was phenotyped in three environments and genotyped using SSR markers. Composite interval mapping results identified three genomic regions associated with oil concentration in a combined analysis. Marker PM36, associated with oil concentration and multiple fatty acids in this study, mapped directly to a HD-ZIP transcription factor in diploid Arachis genome sequences. For fatty acid concentrations, results suggested 17 QTLs identified in two or more environments, 15 of which were present across environments. Fourteen genomic regions on 13 linkage groups contained significant QTLs for more than one trait, suggesting that same genes or gene families are responsible for multiple phenotypes. QTLs and the genes identified in this study could be effective tools in marker-assisted breeding targeted at pyramiding seed oil alleles from wild-species while minimizing introgression of non-target chromatin.

Generation means analysis of oil concentration in peanut.

The current interest in biodiesel production has resulted in a concurrent interest in increasing the oil concentration in high-yielding cultivars, which could make peanuts (Arachis hypogaea.) more desirable as a biofuel source. Currently, peanut seed is approximately 450 to 500 g kg−1 oil on a dry weight basis, depending upon location grown, and there is relatively little genetic variation for oil concentration among adapted high-yielding cultivated peanut genotypes. Thus, identifying sources of variation and elucidating the genetics of oil concentration in peanut is essential to advancing the development of high oil genotypes. The objective of this study was to determine the types of gene action governing the inheritance of oil concentration in peanut by generation means analysis. The F1, F2, and backcross generations of two different runner peanut crosses segregating for oil concentration were evaluated in College Station, Texas, in 2010. Significant differences in oil concentration among the generations were detected, and generation means analysis revealed significant additive, dominance, and epistatic effects for oil concentration in both crosses. The broad-sense heritability estimates were 0.85 and 0.78, and narrow-sense heritability estimates were 0.55 and 0.53 for each of the crosses. Our data indicate that transgressive segregants for high oil were observed, and there is sufficient additive variation present to improve the oil concentration of current runner cultivars.

Effects of Fungicides, Time of Application, and Application Method on Control of Sclerotinia Blight in Peanut

Field studies were conducted from 2007 to 2010 to evaluate the response of peanut cultivars to different fungicides, application timings, and methods. Overall, fungicides reduced Sclerotinia blight incidence and increased pod yields when applied to susceptible and partially resistant cultivars. Disease suppression was greater when full fungicide rates were applied preventatively; however, yields between fungicide treated plots were similar. Lower levels of disease and higher yields were achieved with the partially resistant cultivar Tamrun OL07 compared to the susceptible cultivars Flavor Runner 458 and Tamrun OL 02. Despite possessing improved resistance Tamrun OL07 responded to all fungicide applications. While similar levels of disease control were achieved with broadcast or banded applications made during the day or at night, the yield response for the different application methods was inconsistent among years. A negative relationship (slope = −73.8; ; ) was observed between final disease incidence ratings and yield data from studies where a fungicide response was observed. These studies suggest that both boscalid and fluazinam are effective at controlling Sclerotinia blight in peanuts. Alternative management strategies such as nighttime and banded applications could allow for lower fungicide rates to be used; however, additional studies are warranted.

Generation Means Analysis of Fatty Acid Composition in Peanut

Optimizing the chemical composition of peanut (Arachis hypogaea L.) oil is essential for the production of biodiesel. Specifically, increasing the ratio of oleic to linoleic acid (O/L) in peanut oil and reducing the long chain saturated fatty acid concentration (which includes arachidic, behenic, and lignoceric acids) produces high-quality, stable methyl esters for biodiesel. Therefore, elucidating the inheritance of these factors and their relationships in peanut populations segregating for high oil is critical. The F1, F2, and backcross generations derived from two crosses, both involving a high oil concentration, low O/L runner breeding line (31-08-05-02) and two high O/L, normal oil concentration, adapted runner genotypes (Tamrun OL01 and Tamrun OL07), were evaluated in College Station, Texas, in 2010. The results from generation means analysis confirm that the high-oleic trait is under simple genetic control and can be manipulated through breeding and selection. Most fatty acids were controlled primarily by additive gene action, which is highly selectable. Dominance effects also played an important part in the inheritance of most fatty acids. Additive × dominance interaction was significant in the inheritance of stearic and arachidic acids in the cross involving Tamrun OL07. Oil concentration was also negatively correlated with oleic acid concentration in the F2 generations of both crosses and positively correlated with arachidic acid in most of the segregating generations evaluated. Therefore, developing a peanut genotype high in oil and oleic acid concentration that has reduced long chain saturates will require the evaluation of large numbers of segregating progeny.

Diallel Anaysis of Oil Production Components in Peanut (Arachis hypogaea L.)

Peanut (Arachis hypogaea L.) has the potential to become a major source of biodiesel, but for market viability, peanut oil yields must increase. Oil yield in peanut is influenced by many different components, including oil concentration, seed mass, and mean oil produced per seed. All of these traits can potentially be improved through selection as long as there is sufficient genetic variation. To assess the variation for these traits, a diallel mating design was used to estimate general combining ability, specific combining ability, and heritability. General combining ability estimates were significant for oil concentration, weight of 50 sound mature kernels (50 SMK), and mean milligrams oil produced per SMK (OPS). Specific combining ability was significant for oil concentration. Reciprocal effects were detected for OPS. Narrow-sense heritability estimates were very high for oil concentration and 50 SMK and low for OPS. The low OPS heritability estimate was caused by the negative correlation between oil concentration and seed size. Consequently, oil concentration and seed mass alone can be improved through early generation selection, but large segregating populations from high oil crosses will be needed to identify progeny with elevated oil concentrations that maintain acceptable seed sizes.

Mapping QTLs for Leafspot Resistance in Peanut Using SNP-Based Next-Generation Sequencing Markers

Leafspot is one of the major diseases of peanut (Arachis hypogaea L.) that can cause more than 50% yield loss. The objective of this study was to identify and map quantitative trait loci (QTLs) for resistance to leafspot disease. An F2:6 recombinant inbred line (RIL) population, derived from a released cultivar Tamrun OL07 and a highly tolerant breeding line Tx964117, were used as a mapping population. A total of 90 RILs were planted for disease phenotyping in Yoakum, Texas in 2010 and 2012. A genetic map spanning the 20 linkage groups was developed using 1,211 SNP markers based on double digest restriction-site associated DNA sequencing (ddRAD-seq). A total of six quantitative trait loci (QTLs) were identified, with LOD score values of 3.2-5.0 and phenotypic variance explained ranging from 11%-24%. Major QTLs identified in this study may be used as potential targets for peanut improvement to leafspot disease through molecular breeding.

Variability of Total Oil Content in Peanut Across the State of Texas

The state of Texas has three major regions with a history of peanut production: South Texas, Central Texas, and West Texas. The Texas A&M AgriLife peanut breeding program conducts replicated advanced yield trials at multiple locations within each of these regions annually. This study was initiated using entries from these same advanced line tests to determine if there were inter-regional and/or intra-regional differences in total oil content. The study was comprised of five cultivars used as checks in our yield tests and five advanced breeding lines. Three replications of each entry were tested for two South Texas, two West Texas, and two Central Texas locations. All of the samples were tested using nuclear magnetic resonance (NMR), which is a non-destructive test to determine the total oil content. A significant genotype by environment interaction was observed in both years of the study. Significant genotype differences were observed in all locations except the Stephenville location, which was inoculated with Sclerotinia minor in 2008. Maturity was significantly correlated with oil content across all locations for 2009 data.

Comparison of three peanut cultivars under varying field conditions.

Abstract Cultivar selection is one of the most economically important decisions made by peanut producers. The development of genotypes capable of maintaining yield and quality under a wide range of conditions is important so that profitability can be maximized. Issues such as declining irrigation capacity and diseases limit production in parts of Texas. Efforts of the Texas AgriLIFE Peanut Breeding Program are to develop genotypes with improved yield potential, total sound mature kernels (TSMK), and disease resistance. Cultivar trials were conducted in 2009, 2010, and 2011 to evaluate the performance of the cultivar Tamrun OL11, formerly breeding line TX-55308. Trials were established in several different production areas under various field conditions and included the commercial standards Flavor Runner 458 and Tamrun OL07. Yields were similar for Flavor Runner 458 and Tamrun OL07 at 4538 and 4534 kg ha-1, respectively; whereas, Tamrun OL11 averaged 4845 kg ha-1. TSMK+SS for Tamrun OL11 were 1.3 and 2.4% ...