The narrow genetic base of the US soybean (Glycine max [L.] Merr.) crop makes it vulnerable to emerging abiotic and biotic stress challenges, and limits resiliency of the soybean crop to meet changes in consumer demand for improved seed composition and agronomic performance. The United States Department of Agriculture Glycine soja (Siebold & Zucc.) germplasm collection provides a valuable genetic resource to meet these challenges. Glycine soja is more genetically diverse than domesticated soybean. Even though wild soybean hybridizes freely with G. max, breeding efforts with wild soybean have not been widely employed because the interspecific progeny inherits undesirable traits from the wild parent. Particularly, these progenies inherit a vine-like architecture that prevents machine harvest. We assessed the potential for improving recovery of agronomically valuable progeny from interspecific crosses in three experiments using 11 interspecific populations. We found that optimal choice of either parent could triple the frequency of recovery of desirable progeny. Selection for large F-3 seed size was positively correlated with upright growth habit/plant architecture in five of 11 populations and could triple the recovery of desirable plants. Marker analysis of parents and progeny indicated selection for larger seed size caused minimal selection against the genome of the wild parent. Most genetic markers specific to a wild parent could be recovered in the aggregate of 8-10 upright interspecific progenies, identified via post selection marker analysis. We concluded that choice of parent and selection for larger seed can maximize recovery of the wild genome in machine harvestable progenies.

Kernel shape and beta-glucan content are important attributes for oat (Avena sativa L.) millers. The identification of genomic regions controlling these traits, as well as their effect on phenotype, will enable rapid gain from selection. The objectives of this study were (a) to identify the genomic regions associated with kernel shape in an oat panel adapted to subtropical environments and (b) to clarify the relationship between kernel shape and beta-glucan content in oat. An elite oat panel comprising 406 inbred lines was assessed in Londrina and Eldorado do Sul, Southern Brazil. Genome-wide association analyses were performed for each environment separately and also in a multi-environment analysis. Phenotypic and genetic correlation coefficients were estimated between kernel shape traits and beta-glucan content. Genomic regions influencing kernel length were identified on Mrg06, Mrg21, and Mrg24. Kernel width and kernel thickness were genetically correlated and shared a quantitative trait locus, located on Mrg13 of the oat consensus map. Phenotypic and genetic correlations were found between kernel shape traits and beta-glucan content, indicating a negative relationship between kernel width or kernel thickness and beta-glucan content. Oat breeding programs that aim to maintain minimum levels of beta-glucan for nutrition and minimum kernel widths for milling will need to screen for both traits; otherwise, indirect selection will lead to unfavorable results. However, the negative correlation was not too strong (-0.4), suggesting that improvement for both traits can be made simultaneously.

USDA‐Max × Soja Core Set‐1 (USDA‐MxS‐CS1‐1 to USDA‐MxS‐CS1‐17 [Reg. No. GP‐417 to GP‐433, PI 689053 to PI 689069]) is a group of 17 interspecific breeding lines developed from the hybridization of lodging‐resistant soybean cultivar N7103 [Glycine max (L.) Merr.] with wild soybean plant introduction PI 366122 [G. soja Siebold & Zucc.]. These materials were released by the USDA‐ARS and the North Carolina Agricultural Research Service (March 2017) to expand the North American soybean breeding pool. The full‐sib breeding lines are 50% wild soybean by pedigree and developed through bulk breeding and pedigree selection. Marker analysis of 2455 well‐distributed polymorphic single‐nucleotide polymorphism loci revealed that individual breeding lines ranged from 21 to 40% alleles derived from wild soybean. Collectively, most of the wild soybean genome was transferred to the core set in that 5, 10, and 17 breeding lines captured 83, 98, and 99% of G. soja–derived polymorphic alleles. Physical linkage maps suggested that extensive recombination occurred between the G. max and G. soja genomes. The 17 breeding lines are well adapted to the southeastern United States, exhibited seed yield ranging from 75 to 97% of the domesticated parent, and are group VI or VII maturity. Some breeding lines displayed increased seed protein, oil, or methionine content, and all exhibited increased seed size as compared to the domesticated parent. The novel genetic diversity, positive agronomic performance, and improved seed composition of these lines suggest that they are valuable genetic resources for US soybean breeding.

Soybean [Glycine max (L.) Merr.] genetic diversity is limited because domesticated soybean has undergone multiple genetic bottlenecks. Its progenitor, the wild soybean [Glycine soja Siebold & Zucc], has not undergone the same intense selection and is much more genetically diverse than domesticated soybean. However, the agronomic importance of diversity in wild soybean is unclear, and its weedy nature makes assessment difficult. To address this issue, we chose for study a highly selected, adapted F4-derived progeny of wild soybean, NMS4-44-329. This breeding line is derived from the hybridization between G. max cultivar N7103 and G. soja PI 366122. Agronomic comparisons were made among N7103, NMS4-44-329 and their F1 and F2 progeny in replicated yield trials at two North Carolina locations. Significant F1 mid-parent heterosis was observed at each location for seed yield (189 and 223 kgha-1, P<0.05 and P<0.10, respectively), seed protein content (1.1g/100g, P<0.01) and protein production per hectare (101 and 100 kgha-1, P<0.01 and P<0.06, respectively). Increased yield, seed protein content and protein production per hectare in the hybrids suggested that wild soybean has the potential to improve agronomic traits in applied breeding. Comparisons of differentially-expressed genes in the hybrid vs. parents identified genes associated with N metabolism. Non-additive changes in gene expression in the hybrids relative to the parents could reasonably explain the improved protein levels in the F1 hybrids. Changes in gene expression were influenced by environmental effects; however, allele specific bias in the hybrids were well correlated between environments. We propose that changes in gene expression, both additive and non-additive, and changes in allele specific expression bias may explain agronomic traits, and be valuable tools for plant breeders in the assessment of breeding populations.

In previous research, we discovered a favorable quantitative trait locus (QTL) in cigar tobacco cultivar 'Beinhart 1000' designated as Phn15.1, which provides a high level of partial resistance to the black shank disease caused by Phytophthora nicotianae. A very close genetic association was also found between Phn15.1 and the ability to biosynthesize Z-abienol, a labdanoid diterpene exuded by the trichomes onto above-ground plant parts, and that imparts flavor and aroma characteristics to Oriental and some cigar tobacco types. Because accumulation of Z-abienol is considered to be undesirable for cultivars of other tobacco types, we herein describe a series of experiments to gain insight on whether this close association is due to genetic linkage or pleiotropy. First, in an in vitro bioassay, we observed Z-abienol and related diterpenes to inhibit hyphal growth of P. nicotianae at concentrations between 0.01 and 100 ppm. Secondly, we field-tested transgenic versions of Beinhart 1000 carrying RNAi constructs for down regulating NtCPS2 or NtABS, two genes involved in the biosynthesis of Z-abienol. Thirdly, we also field tested a recombinant inbred line population segregating for a truncation mutation in NtCPS2 leading to an interrupted Z-abienol pathway. We observed no correlation between field resistance to P. nicotianae and the ability to accumulate Z-abienol in either the transgenic materials or the mapping population. Results suggest that, although Z-abienol may affect P. nicotianae when applied at high concentrations in in vitro assays, the compound has little effect on black shank disease development under natural field conditions. Thus, it should be possible to disassociate Phn15.1-mediated black shank resistance identified in cigar tobacco cultivar Beinhart 1000 from the ability to accumulate Z-abienol, an undesirable secondary metabolite for burley and flue-cured tobacco cultivars.

Plant breeders and crop managers would benefit from an increased ability to predict the requirements for onset of anthesis in tobacco (Nicotiana tabacum L.). This study was performed to determine the relationship in the field between heat unit (HU) accumulation and the onset of anthesis in tobacco genotypes varying for the zygosity of an introgressed quantitative trait loci (QTL) designated as Many Leaves (Ml) affecting flowering team and leaf number. Three commercially important cultivars or breeding lines (Speight 168, K326, and NCTG‐61), their nearly isogenic homozygous (MlMl) and heterozygous (Mlml) counterparts, and three BC6F3 null‐segregant (mlml) lines, were evaluated at three locations and over 2 yr. Days to anthesis (DTA) and HU accumulation were determined. In each environment, the MlMl, Mlml, and mlml genotypes were found to be grouped according to the zygosity of the Ml trait, with the mlml genotypes flowering first followed by Mlml and MlMl genotypes, respectively. An exception to this trend was Speight 168 MlMl, which consistently fell within the Mlml grouping for DTA. No consistent relationships were observed between HU and DTA, which was highly variable among environments. Integrated HU (area under the HU curve) during the 28 d after transplanting (DAT) was positively associated (R2 = 0.98; P = 0.0001) with the range of DTA among all genotypes. Integrated HU was a better indicator of the pattern of HU attainment than merely the amount. Early HU exposure seemed important in determining the range in DTA amongst the genotypes examined.

ABSTRACTIncreased cured leaf yield is an important breeding target for flue‐cured tobacco (Nicotiana tabacum L.), but genetic improvement for this trait has slowed in the last thirty years. Yield is positively correlated with days to flowering and leaf number in this species. Use of novel allelic diversity influencing these traits might contribute to further yield improvement. In this study, an introgressed quantitative trait locus (QTL) affecting flowering time and leaf number, designated as Many Leaves (Ml), was backcrossed into three genetic backgrounds of flue‐cured tobacco. Field evaluation of nearly isogenic MlMl lines and Mlml hybrids indicated that the QTL acted in an additive to partially dominant fashion to delay flowering and increase leaf number. This resulted in significant increases in yield and cash return per hectare. As the zygosity of Ml increased, corresponding decreases in percentage total alkaloids and increases in percentage reducing sugars were observed, however. Incorporation of Ml into flue‐cured tobacco breeding programs may be useful for increasing cured leaf yields in certain environments. Concurrent modification of the genetic potential to accumulate alkaloids would be also important under current industry requirements, however.

Methods for rapid inbreeding are desirable for reducing the time required to complete a breeding cycle and to increase genetic gain per year. Constitutive expression of FLOWERING LOCUS T (FT) derived from Arabidopsis has previously been shown to reduce generation time in tobacco (Nicotiana tabacum L.) and other crop plants. Here, we used tobacco as a model system to investigate the utility of a modified single-seed descent (SSD) breeding method where transgenic expression of 35S:FT was used to reduce generation time during inbreeding. The transgene was maintained in hemizygous condition during inbreeding, and null segregants were isolated in the F-4:5 generation to create nontransgenic F-5:6 lines that were produced in nearly half the time that would have been required using conventional SSD. Opportunities for selection among 35S: FT plants during inbreeding were demonstrated by selecting for quantitative levels of resistance to the soil-borne pathogen Phytophthora nicotianae. Populations of selected lines exhibited significantly higher levels of resistance relative to random lines, greater frequencies of highly resistant genotypes, and lower frequencies of highly susceptible genotypes. The system outlined here could lead to more rapid commercialization of improved cultivars in crop species amenable to manipulation of flowering time via transgenic expression of FT-like genes. Strategies to enhance the frequency of favorable alleles in resulting populations can be incorporated into the method.