Genetic and QTL mapping in African bermudagrass.

Cynodon transvaalensis Burtt-Davy is frequently used to cross with C. dactylon Pers. in the creation of F1 hybrid cultivars that are some of the most widely used in the worldwide turf industry. However, molecular resource development in this species is limited. Accordingly, the objectives of this study were to construct a high-density genetic map, and to identify genomic regions associated with establishment rate. In this study, we constructed the first high-density linkage map for African bermudagrass using a genotyping by sequencing approach based on 109 S1 progenies. A total of 1,246 single nucleotide polymorphisms and 32 simple sequence repeat markers were integrated in the linkage map. The total length of nine linkage groups was 882.3 cM, with an average distance of 0.69 cM per interval. Four genomic regions were identified to be associated with sod establishment rate. The results provide important genetic resources towards understanding the genome as well as marker-assisted selection for improving the establishment rate in bermudagrass breeding.

Sequence-based genetic mapping of Cynodon dactylon Pers. reveals new insights into genome evolution in Poaceae.

Bermudagrass (Cynodon dactylon Pers.) is an important warm-season perennial used extensively for turf, forage, soil conservation and remediation worldwide. However, limited genomic information has hindered the application of molecular tools towards understanding genome evolution and in breeding new cultivars. We genotype a first-generation selfed population derived from the tetraploid (4x = 36) 'A12359' using genotyping-by-sequencing. A high-density genetic map of 18 linkage groups (LGs) is constructed with 3,544 markers. Comparative genomic analyses reveal that each of nine homeologous LG pairs of C. dactylon corresponds to one of the first nine chromosomes of Oropetium thomaeum. Two nested paleo-ancestor chromosome fusions (ρ6-ρ9-ρ6, ρ2-ρ10-ρ2) may have resulted in a 12-to-10 chromosome reduction. A segmental dissemination of the paleo-chromosome ρ12 (ρ1-ρ12-ρ1, ρ6-ρ12-ρ6) leads to the 10-to-9 chromosome reduction in C. dactylon genome. The genetic map will assist in an ongoing whole genome sequence assembly and facilitate marker-assisted selection (MAS) in developing new cultivars.

Deficit Irrigation and Fertility Effects on NO3-N Exports from St. Augustinegrass.

Proper management of turfgrass systems is critical for reducing the risk of nutrient loss and protecting urban surface waters. In the southern United States, irrigation can be the most significant management practice regulating the biogeochemical and hydrological cycles of turfgrass systems. A turfgrass runoff research facility was used to assess the effects of deficit irrigation and fertilizer applications on turfgrass canopy cover and nitrate-N (NO-N) exports in runoff from St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] turf over a 2-yr period. Treatments were arranged as a randomized complete block design having eight combinations of irrigation (100, 75, or 50% of estimated turfgrass water requirements) and fertility level (0, 88, and 176 kg N ha yr). Runoff from 31 rainfall events and one irrigation excess event were used to estimate annual and seasonal NO-N exports. The majority of annual NO-N exports occurred during the late winter and spring. Deficit irrigation reduced summer and early autumn runoff volumes. Lower summer and autumn runoff volumes (from deficit irrigation) coincided with reduced NO-N exports from runoff during Year 1. Deficit irrigation combined with fertilizer applications increased runoff [NO-N] in Year 2, suggesting that the previous year's export reduction contributed to higher N accumulation in the system and thus a higher N loss potential. These findings suggest that deficit irrigation can be a tool for reducing seasonal nutrient exports from St. Augustinegrass lawns so long as fertilizer inputs are moderate.

Nitrogen Runoff Losses during Warm-Season Turfgrass Sod Establishment.

Concern exists over the potential loss of nitrogen (N) and phosphorus (P) in runoff from newly established and fertilized lawns. Nutrient losses can be higher from turf when shoot density and surface cover are low and root systems are not fully developed. This study was conducted to evaluate fertilizer source and timing effects on nutrient losses from newly sodded lawns of St. Augustinegrass [ (Walt.) Kuntze]. For each study, 12 33.6-m plots were established on an undisturbed Alfisol having a 3.7% slope. Each plot was equipped with a runoff collection system, instrumentation for runoff flow rate measurement, and automated samplers. A 28-d establishment study was initiated on 8 Aug. 2012 and repeated on 9 Sept. 2012. Treatments included unfertilized plots, fertilized plots receiving 4.88 g N m as urea 6 d after planting, fertilized plots receiving 4.88 g N m as sulfur-coated urea 6 d after planting, and fertilized plots receiving 4.88 g N m as urea 19 d after planting. Runoff events were created by irrigating with 17 mm of water over 27 min. Runoff water samples were collected after every 37.8 L and analyzed for NO-N, NH-N, dissolved organic N (DON), and PO-P. Increases of approximately 2 to 4 mg L NO-N and 8 to 12 mg L PO-P occurred in runoff 1 d after fertilization, which returned to background levels within 7 d. Total fertilizer N lost to runoff was 0.6 to 4.2% of that applied. Delaying fertilizer application until 19 d after planting provided no reduction in nutrient loss compared with a similar application 6 d after planting. Approximately 33% of the N lost in runoff was as DON. This large amount of DON suggests significant N loss from decomposing organic matter may occur during sod establishment.

Design and construction of an urban runoff research facility.

As the urban population increases, so does the area of irrigated urban landscape. Summer water use in urban areas can be 2-3x winter base line water use due to increased demand for landscape irrigation. Improper irrigation practices and large rainfall events can result in runoff from urban landscapes which has potential to carry nutrients and sediments into local streams and lakes where they may contribute to eutrophication. A 1,000 m(2) facility was constructed which consists of 24 individual 33.6 m(2) field plots, each equipped for measuring total runoff volumes with time and collection of runoff subsamples at selected intervals for quantification of chemical constituents in the runoff water from simulated urban landscapes. Runoff volumes from the first and second trials had coefficient of variability (CV) values of 38.2 and 28.7%, respectively. CV values for runoff pH, EC, and Na concentration for both trials were all under 10%. Concentrations of DOC, TDN, DON, PO4₋P, K(+), Mg(2+), and Ca(2+) had CV values less than 50% in both trials. Overall, the results of testing performed after sod installation at the facility indicated good uniformity between plots for runoff volumes and chemical constituents. The large plot size is sufficient to include much of the natural variability and therefore provides better simulation of urban landscape ecosystems.