Kevin E. Kenworthy

Comparison of Water Displacement and WinRHIZO Software for Plant Root Parameter Assessment

Water-displacement and WinRHIZO root-scanning methods were compared for efficacy of root damage assessment. Results from both methods were similar and a highly significant relationship was found between the two methods in trial one (r2 = 0.9968, P < 0.0001) and trial two (r2 = 0.9988, P < 0.0001). Both protocols provide consistent root volume measurements; however, water displacement is preferred as an economical method if a quick evaluation of a large amount of roots is essential. For a more detailed root morphological and architectural analysis, WinRHIZO root scanning provides additional information about several root parameters that cannot be measured by simple water displacement.

Tetraploid bahiagrass hybrids: breeding technique, genetic variability and proportion of heterotic hybrids

Manipulating apomixis for fixing tetraploid bahiagrass (Paspalum notatum Flüggé) hybrids exhibiting superior agronomic characteristics would be a valuable tool for the genetic improvement of this species. The objectives were to create a second generation of hybrids by crossing sexual first-generation tetraploid hybrids (FGTH) and unrelated apomictic FGTH or ecotypes, determine the segregation for mode of reproduction, and estimate the resulting genetic variation and heterosis for several agronomic characteristics. The segregation for mode of reproduction was analyzed using mature embryo sac observations. Field measurements and visual ratings were used to evaluate the growth habit, production of inflorescences, cool-season growth and freeze resistance of hybrids. A ratio of 4.6:1 between sexual and apomictic hybrids was observed. Only 3% of the progeny was classified as highly apomictic. The low proportion of highly apomictic progeny restricts the feasibility of this breeding approach. Large genetic variation was observed among hybrids for growth habit, cool-season growth and freeze resistance. The proportion of hybrids exhibiting heterosis was high for plant height, cool-season growth, and freeze resistance. The tetraploid bahiagrass germplasm contains a large diversity for traits of agronomic importance that can be exploited for the genetic improvement of this species.

Effect of Time and Testing Method in Determining St. Augustinegrass Resistance to Southern Chinch Bugs (Hemiptera: Blissidae)

Abstract St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze, is used as lawn grass throughout the southern United States for its wide adaptation to varying environmental conditions. The southern chinch bug, Blissus insularis Barber, is the plants most damaging insect pest. Host plant resistance of St. Augustinegrass has been determined in numerous studies using various techniques. However, efficacy of these various procedures in determining St. Augustinegrass resistance to southern chinch bug has not been determined. The objective of this study was to determine the effect of time and methodologies in assesing St. Augustinegrass resistance to southern chinch bugs. Four varieties were tested for resistance using 4 methods (bag, jar, box, tube) and 5 time intervals to measure chinch bug mortality. Overall, survival was greater in whole-plant methods (box and tube) than excised stolon methods (bag and jar). The bag test gave the most erratic results of the 4 methods. The effect of time in determining resistance was also evident. In our tests, it was clear that shorter time intervals in measuring mortality may result in not measuring resistance in a variety. In summary, researchers should carefully consider method, time and temperature as important variables in determining St. Augustinegrass resistance to southern chinch bugs.

Nonchemical Methods for Paragrass (Urochloa mutica) Control

Abstract Paragrass is a nonnative category I invasive species in central and south Florida. This perennial grass species outcompetes native vegetation and is capable of rapid spread by vegetative reproduction. Although glyphosate and imazapyr are effective herbicides for paragrass control, the use of herbicides in certain areas may be restricted because of application timing or environmental concerns. Therefore, our objectives were to examine the effect of water depth (saturated vs. flooded) after burning or cutting, and the effect of water depth and duration after simulated roller-chopping, on paragrass regrowth under controlled conditions. In the first study, paragrass plants were cut or burned with a propane burner to 1 cm (0.39 in) above the soil surface. Plants were either watered daily (control), or were subjected to one of two water treatments: water level at the soil surface (saturated) or flooded to a depth of 44 cm. Burned-saturated or burned-flooded plants had 92% less biomass 5 wk after treatment (WAT) than cut-saturated plants. Flooding resulted in plant death regardless of the plant treatment. In the second study, simulated roller-chopping was performed by cutting paragrass stolons into one-, two-, or three-node segments; planting them into flats; and subjecting them to water treatments for 3, 7, 14, 28, and 42 d. Burning, cutting, and roller-chopping could be useful to control paragrass if subsequent flooding is applied. Future research should focus on evaluating the response of these control techniques in natural areas where water depth can be managed. Nomenclature: Paragrass, Urochloa mutica (Forsk.) T. Q. Nguyen. Management Implications: Paragrass is a highly invasive perennial grass species that invades wetland ecosystems of central and south Florida as well as other tropical areas of the world. Invasion of paragrass into such ecosystems typically reduces native species diversity and abundance, and ultimately results in monotypic swards, an unsuitable wildlife habitat. The effect of water depth (saturated vs. flooded) after burning or cutting, and the effect of water depth and duration after simulated roller-chopping on paragrass regrowth were examined under controlled conditions. Burning, cutting, and simulated roller-chopping did not reduce paragrass regrowth without either soil saturation or inundation. In saturated conditions, burning significantly reduced all variables of plant growth compared to cutting. However, both burning and cutting killed paragrass equally when flooded for a period of 5 wk. At least 17 d of flooding or 29 d of saturated conditions were required to reduce paragrass biomass by 90% under our conditions. These results suggest that soil saturation or flooding is required after cultural techniques have been employed. Cutting or burning of paragrass followed by flooding may be an option for natural area managers in areas where herbicides may not be applied due to timing or environmental reasons. Roller-chopping followed by flooding could be an effective option to paragrass control where burning would not possible because of location and timing.

Improved genetic parameter estimations in zoysiagrass by implementing post hoc blocking

Randomized complete block (RCB) design is the most widely used experimental design in biological sciences. As number of treatments increases, the block size become larger and it looses the capacity to control the variance within block, which is its original purpose. A method known as post hoc blocking could be used in these cases to improve the genetic parameter estimation and thus obtain an unbiased assessment of the performance of a given treatment. In trufgrass breeding, as other breeding program, this is a common challenge. The goal of this study was to test the capacity of different post hoc blocking designs to improve the genetic parameter estimation of zoysiagrass (Zoysia spp.). We evaluated two post hoc blocking designs; row–column (R–C) and incomplete block (IB) designs on five genotype trials located in Florida. The results showed that post hoc R–C design had superior model fitting than both the original RCB and the post hoc IB designs when studied at the single measurement level and at the site level. The narrow-sense heritability (0.24–0.40) and the genotype-by-measurement correlation (0.57–0.99) did not change significantly when R–C was compared to the original RCB design. The ranking of the top performing genotypes changed considerably when comparing RCB to R–C design, but the degree depended on the location analyzed. We conclude that the change in the ranking of the top (potentially select individuals) is coming from the better control of intra-block environmental variation, and this could potentially have a significant impact on the breeding selection process.

Evaluation of Alternative Herbicides for Southern Crabgrass (Digitaria ciliaris) Control in St. Augustinegrass

Abstract Southern crabgrass is a common turfgrass weed throughout the United States, and in Florida a troublesome problem in St. Augustinegrass lawns. Because of herbicide label changes and lack of herbicide tolerance, no POST herbicides are currently registered for homeowner use for crabgrass control in residential and commercial St. Augustinegrass lawns. Alternative weed control methods, including cultural practices and unconventional herbicides, have been investigated to a limited extent for postemergence crabgrass control. In this study, alternative herbicides evaluated included 30% acetic acid, borax, sodium bicarbonate, and Garden Weasel AG Crabgrass Killer (sodium bicarbonate formulation including cinnamon, wheat and corn flour, and cumin). Treatments were applied to southern crabgrass at three growth stages (one to two leaf, three to four leaf, or one to two tiller). In the greenhouse, 30% acetic acid applied twice at 280 L ha−1 and two rates of AG Crabgrass Killer at 976 or 1,465 kg ha−1 provided ≥ 70% control of one to two–leaf southern crabgrass when evaluated 7 d after initial application (DAIA). No treatment provided > 70% control of three to four–leaf or one to two–tiller southern crabgrass or any size crabgrass beyond 7 DAIA. In field trials, no treatment provided acceptable (≥ 70%) southern crabgrass control at any weed stage. Initial turf injury was unacceptable for most rates of 30% acetic acid, sodium bicarbonate, and AG Crabgrass Killer, causing > 20% St. Augustinegrass injury 7 DAIA. By 21 DAIA, turf injury levels had fallen to ≤ 20% for most treatments. Because of high turfgrass injury and little residual control, alternative herbicides tested are not an effective substitute for using preemergence herbicides for southern crabgrass control. If other options are not available, they may have a role as a limited spot treatment in St. Augustinegrass. Nomenclature: Acetic acid; southern crabgrass, Digitaria ciliaris (Retz.) Koel.; St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze. Resumen Digitaria ciliaris es una maleza común en céspedes a lo largo de los Estados Unidos, y en Florida es problemática en el césped para jardín St. Augustine. Debido a cambios en las etiquetas de herbicidas y la ausencia de tolerancia a herbicidas, actualmente no hay herbicidas POST registrados para uso por parte de los dueños de hogares para el control de D. ciliaris, en céspedes St. Augustine en zonas residenciales y comerciales. Métodos de control de malezas alternativos, incluyendo prácticas culturales y herbicidas no convencionales han sido investigados en forma limitada para el control en pos-emergencia de D. ciliaris. En este estudio, se evaluaron herbicidas alternativos incluyendo acetic acid al 30%, borax, sodium bicarbonate, y Garden Weasel AG Crabgrass Killer (formulación de sodium bicarbonate incluyendo harinas de canela, trigo y maíz y cumin). Los tratamientos fueron aplicados a D. ciliaris en tres estadios de crecimiento (una a dos hojas, tres a cuatro hojas, y uno a dos hijuelos). En el invernadero, acetic acid al 30% aplicado dos veces a 280 L ha−1 y dos dosis de AG Crabgrass Killer a 976 ó 1,465 kg ha−1 brindaron ≥ 70% de control de D. ciliaris de una a dos hojas, cuando se evaluó 7 d después de la aplicación inicial (DAIA). Ningún tratamiento brindó > 70% de control en D. ciliaris de tres a cuatro hojas o de uno a dos hijuelos, o en ninguno de los estadios de crecimiento más allá de 7 DAIA. En los experimentos de campo, ningún tratamiento brindó un control aceptable (> 70%) de D. ciliaris en ninguno de los estadios de crecimiento. El daño inicial en el césped fue inaceptable para la mayoría de las dosis de acetic acid al 30%, sodium bicarbonate, y AG Crabgrass Killer, las cuales causaron > 20% de daño en el césped St. Augustine 7 DAIA. A 21 DAIA, el daño en el césped había caído a ≤ 20% en la mayoría de los tratamientos. Debido al alto daño causado al césped y el poco control residual, los herbicidas alternativos evaluados no son un sustituto efectivo para el uso de herbicidas en preemergencia para el control de D. ciliaris. Si no hay otras opciones, estos herbicidas alternativos podrían tiene un rol limitado para el control con aplicaciones dirigidas en el césped St. Augustine.

Zoysiagrass genotype responses to Sphenophorus venatus vestitus (Coleoptera: Curculionidae).

ABSTRACT The hunting billbug, Sphenophorus venatus vestitus Chittenden, is a pest that damages stems, rhizomes, and roots of zoysiagrass through a combination of adult and larval feeding. Management of this pest is difficult because it has multiple, overlapping generations in the southern United States, and symptoms of infestations are often misdiagnosed and inappropriately treated as drought stress or disease. Experiments were conducted in a greenhouse where 18 zoysiagrass cultivars were potted and infested with S. v. vestitus adults to examine the response of zoysiagrass genotypes to S. v. vestitus feeding damage. Results showed that zoysiagrass species and cultivars differed in susceptibility to S. v. vestitus, indicating that variable tolerance may exist in these turfgrasses for improvement through breeding. In general, Zoysia japonica Steudel was more susceptible to S. v. vestitus feeding damage and supported more S. v. vestitus than Zoysia matrella (L.) Merrill. Among the Z. japonica cultivars, ‘Belair’ and ‘Zenith’ had less desirable agronomic traits and incurred greater feeding damage than other cultivars more tolerant to billbug damage. With Z. matrella, ‘Diamond’ and ‘Pristine Flora’ displayed superior agronomic traits and had the least feeding damage and lowest infestations of billbug immatures and were therefore considered the most tolerant or resistant Z. matrella cultivars tested. Results indicate that stem diameter may be an important factor for adult feeding and oviposition site selection, which might explain the different responses between Zoysia spp. to S. v. vestitus damage.

Breeding forages in Florida for resistance to nematodes

Abstract. Forage legumes and grasses provide the basis for the worldwide ruminant animal livestock industry, and most of these forages come from perennial pasture plants. As animal agriculture has intensified, pest pressures on perennial forages often also become more prevalent. Among these pest plant parasitic nematodes, especially root-knot nematodes (RKN) (Meloidogyne spp.) have been shown to be major forage crop pests. In this paper, we summarise research from the University of Florida related to development of methods for screening germplasm for RKN responses, results from germplasm evaluations across a range of forage legume and grass species, and progress from breeding and selection research including studies of the genetic basis of resistance. We then present prospects for continued genetic improvement in RKN resistance using conventional and modern molecular methods.