USING EXOGENOUS HORMONE APPLICATION TO SUPPRESS AXILLARY SHOOT DEVELOPMENT IN TOBACCO

The variability in the number of basal axillary shoots (ground suckers) among all tobacco (Nicotiana tabacum L.) varieties, has increased since the hydroponic transplant production system became the standard. The larger root ball of hydroponically produced transplants compared to traditionally produced transplants potentially generates a difference in the ratio of auxin (inhibits axillary shoot formation) to cytokinin (promotes lateral branching), that induces basal axillary shoot development. Starting in 2014, studies were conducted to investigate whether the addition of synthetic auxins or cytokinins to hydroponic transplant production could prevent ground sucker formation. Different tobacco cultivars, with high or low ground sucker potential, were evaluated in extensive dilution trials using the synthetic auxin 1-Naphthalene acetic acid (NAA) or cytokinin 6-Benzylaminopurine (BA). Initial results indicated that a 2nM concentration of NAA significantly reduced axillary shoots in the known ground sucker producer, compared to the control. From these results, NAA and BA was added to the hydroponic transplant solution at concentrations in the range of 2-50 nM for the 2015 field trials; however, these studies failed to confirm the preliminary greenhouse findings. Nonetheless, it was clear from the 2015 field results that the varieties used are genetically different from one another in ground sucker potential. Following the 2015 field study, an additional greenhouse experiment using higher concentrations of NAA showed that a 1µM NAA hydroponic solution reduced ground sucker number. From this, a second set of field studies were conducted in 2016 using the higher rates of NAA. Burley variety TN86 and dark variety KTD6 (known ground sucker producers) were used in the 2016 studies. Five hormone treatments (NAA 500-5000 nM and an untreated control) and five tray (128, 200, 242, 288, and 338 cells per tray) were evaluated. Tray size was added to determine if increasing transplant root ball size was correlated with an increase in ground suckers. Although statistically significant differences were found among treatments applied to both TN86 and KTD6, there was no treatment that consistently reduced ground sucker numbers. No notable trend in ground sucker number indicates that an increase in the root ball size of tobacco transplants produced in the float bed system compared to traditionally produced transplants is not the sole cause of increased ground sucker number. In conclusion, from the results of the entire study, it is apparent that an exogenous auxin application (within the conditions used in this study) will not consistently or predictably suppress ground sucker development in tobacco; perhaps the only consistency in the data is how inconsistent ground sucker formation is from environment to environment, and variety to variety

Optical Sorter-Based Selection Effectively Identifies Soft Red Winter Wheat Breeding Lines with \u3cem\u3eFhb1\u3c/em\u3e and Enhances FHB Resistance in Lines with and without \u3cem\u3eFhb1\u3c/em\u3e

Previous results from our lab have shown that using an optical sorter to identify Fusarium head blight (FHB) resistant breeding lines was effective at reducing the toxin deoxynivalenol (DON) and FHB-associated kernel damage. In this paper we quantified the proportion of desirable genotypes at FHB resistance QTL in lines from three selection cycles of optical sorting. Breeding lines were genotyped at loci on chromosomes 3BS, 2DL, and 5A using the following DNA markers: TaHRC, CFD233, and GWM304. TaHRC is a KASP marker for Fhb1, a major FHB resistance QTL on chromosome 3BS. CFD233 is an SSR marker for Qfhs.nau-2DL on chromosome 2DL. GWM304 is an SSR marker for Qfhs.ifa-5A on chromosome 5A. Sorter selection was effective at identifying lines that had the resistant genotype at TaHRC; in other words, the sorter was able to identify lines with resistance alleles at Fhb1. The sorter was less effective at selecting for the resistant genotype at CFD233 and GWM304. However, the proportion of lines with resistant genotypes at GWM304 did increase with additional sorter selection, just not to the degree that was observed for the Fhb1-associated marker. The proportion of lines with resistant alleles at CFD233 did not show a consistent trend. In addition to increasing the proportion of lines with Fhb1 and Qfhs.ifa-5A each selection cycle, optical sorter-based mass selection enhanced FHB resistance in different marker genotype combinations evaluated in this study. For example, there were net reductions in DON and kernel damage after two cycles of sorter selection in 15X110601S07002, a line with Fhb1, with Qfhs.nau-2DL, and with Qfhs.ifa-5A; final C3 DON levels were 63% of the resistant check (KY02C-3005-25). Kernel damage was also reduced in 15X110601A08221 a line without Fhb1, without Qfhs.nau-2DL, and without Qfhs.ifa-5A. Our findings suggest the increased resistance observed in different marker genotype combinations was conferred by QTL other than Fhb1, QFhs.nau-2DL, and Qfhs.ifa-5, and validate our previous results that the optical sorter is effective at selecting FHB-resistant breeding material

Mass Selection for Reduced Deoxynivalenol Concentration Using an Optical Sorter in SRW Wheat

Fusarium head blight (FHB) of wheat (Triticum aestivum L.) results in discolored Fusarium damaged kernels (FDK) contaminated with deoxynivalenol (DON). DON accumulation, a primary measure of FHB resistance, can be used as a basis for selection, but testing each genotype in several genetically variable populations is expensive and time-consuming. Therefore, FHB resistance breeding decisions are routinely based on in-field phenotypic evaluation. However, using an optical sorter as an alternative to in-field evaluation, mass selection (MS) for FHB resistance can be quickly performed post-harvest. The objective of this study was to utilize an optical seed sorter to select breeding lines with enhanced FHB resistance (lower DON and FDK values). Three hundred F4 derived breeding lines were grown in an inoculated disease nursery over several years in Lexington, KY. Grain from each breeding line was sorted using an optical seed sorter calibrated to reject scabby (discolored) seed. The accepted (non-scabby) seed was used to plant subsequent generations. DON and kernel damage traits were lowered each cycle of line selection with the optical sorter. Our findings suggest that optically sorting grain may be an effective breeding strategy for lowering DON accumulation and limiting kernel damage associated with FHB