Doctor of Philosophy / Department of Horticulture and Natural Resources / Jack Fry / Megan Kennelly / Zoysiagrasses (Zoysia spp.) use C4 metabolism and are more drought resistant than C3 grasses. However, the long dormancy period between autumn and spring limits the use of zoysiagrass by homeowners and professional turfgrass managers. In addition, large patch has become the primary pest on zoysiagrass, and improved cultivars with good cold hardiness and large patch resistance are needed in the transition zone. Tall fescue (Schedonorus arundinaceus Schreb), a C3 grass, is used frequently in Kansas due to its heat and drought tolerance compared to some other C3 grasses. However, brown patch (Rhizoctonia solani) is the main disease limiting its growth in summer. Alternatively, mixing zoysiagrass with tall fescue may help reduce brown patch incidence. The objective of these projects were to: (1) evaluate methods for establishing a perennial mixture of seeded zoysiagrass and tall fescue; (2) determine whether a zoysiagrass/ tall fescue polystand is less susceptible to brown patch and results in improved summer quality compared to a tall fescue monostand; and (3) evaluate experimental zoysiagrass genotypes to identify one or more potential new cultivars which have high quality and tolerance to cold and large patch. I found that polystands of zoysiagrass and tall fescue were most successfully established by seeding zoysiagrass at 49 kg ha-1 in June and tall fescue at 392 kg ha-1 in September into the established zoysiagrass sward. Polystand establishment was also superior at a 1.9 cm mowing height than a 5.1 cm mowing height. The resulting mixture resulted in improved turf color in late fall and early spring compared to a zoysiagrass monostand. In addition, using a zoysiagrass-tall fescue polystand reduced brown patch by up to 21% compared to a tall fescue monostand. In the zoysiagrass breeding project, I identified ten progeny out of sixty evaluated that had better tolerance to large patch (up to 40 % less plot area affected) and better quality compared to Meyer zoysiagrass, which is the standard cultivar used in the transition zone.

Brown patch, caused by <i>Rhizoctonia solani</i> Kuhn, is an important disease on tall fescue (TF, <i>Festuca arundinacea</i> Schreb, synonym <i>Schedonorus phoenix</i> (Scop.) Holub). <i>Rhizoctonia zeae</i> Voorhees, a related pathogen, causes similar symptoms. Confusion over which <i>Rhizoctonia</i> species is causing symptoms and subjective visual evaluations of disease severity may contribute to variability in observed BP resistance of TF cultivars at multiple locations. The objectives of this study were to develop an objective digital image analysis (DIA) method for evaluating disease and to use DIA to screen tall fescue plant introductions (PIs) for resistance to <i>R. solani</i> and <i>R. zeae</i>. There was a strong correlation (r² = 0.97) between actual disease severity, measured by applying lesioned tissue of a known area to healthy leaves, and DIA calculated disease severity using scanned images of individual leaves (DIA-IL). The accuracy and precision of visual evaluations and DIA evaluations of entire plants (DIA-WP) were evaluated using DIA-IL as a standard of accuracy. Accuracy of DIA-WP was not significantly different from visual evaluation accuracy. Precision was significantly higher for DIA-WP. Evaluation of PIs and putatively BP resistant TF cultivars for resistance to <i>R. solani</i> and <i>R. zeae</i> using DIA-WP identified clones within each PI that ranked high for resistance to <i>R. solani</i> or <i>R. zeae</i>. No clones were identified with high resistance to both <i>R. solani</i> and <i>R. zeae</i>. Improved precision of DIA evaluation methods and inclusion of <i>R. zeae</i> in BP resistance breeding may decrease variability of TF cultivar performance across locations. / Master of Science

Tall fescue (Festuca arundinacea Schreb.) has great utility as a low maintenance turfgrass in the northern and transition zone regions of the United States. However, it is difficult to successfully maintain tall fescue of high quality over consecutive summers because of its susceptibility to the fungal pathogen Rhizoctonia solani, which causes the disease brown patch. Not only is brown patch aesthetically unpleasing in a stand of tall fescue but it can also thin out the turf and allow for the encroachment of undesirable weedy species. Cultivar selection, cultural practices, mixing turf species and timing of pesticide applications all can impact the epidemiology of brown patch in tall fescue. Research was conducted in tall fescue to quantify chitinase activity in different cultivars, elucidate the impact of mowing height and nitrogen fertility on brown patch and bermudagrass (Cynodon dactylon L.) encroachment, to evaluate seeding mixtures of tall fescue with hybrid bluegrass (Poa pratensis x Poa arachnifera) on diseases and weeds as well as measuring the impact of the herbicide bispyribac-sodium on brown patch. Chitinase activity was greater in the tall fescue cultivar that was less susceptible to brown patch. In the mowing-fertility studies, cutting tall fescue at 10 cm generally reduced brown patch and bermudagrass encroachment compared to 6 cm. Mixing hybrid bluegrass with tall fescue reduced disease and weed species infestations compared to tall fescue alone. Applying bispyribac-sodium earlier in April resulted in less brown patch and better weed control compared to application in May. Based on this research brown patch severity and subsequent weed species infestations can be reduced by selecting a tall fescue cultivar with a high basal level of chitinase, mowing it at 10 cm and mixing it with a hybrid bluegrass cultivar. / Ph. D.

Rhizoctonia blight (sensu lato) is a common and serious disease of many turfgrass species. The most widespread causal agent R. solani consists of several genetically different anastomosis groups (AGs) and subgroups. Though anastomosis or hyphal fusion reactions have been used to group Rhizoctonia species, they are time consuming and sometimes difficult to interpret. Anastomosis reactions are incapable of identifying isolates belonging to different AG subgroups within an AG. This study evaluated molecular techniques in comparison with traditional anastomosis grouping (AG) to identify and group isolates of Rhizoctonia. More than 400 Rhizoctonia isolates were collected from diseased turfgrass leaves from eight geographic areas in Virginia and Maryland. A random sample of 86 isolates was selected and initially characterized by colony morphology, nuclei staining and anastomosis grouping. Molecular identification was performed by analysis of rDNA-ITS region and DNA fingerprinting techniques universally primed PCR (UP-PCR) and amplified fragment length polymorphism (AFLP). The cladistic analysis of ITS sequences and UP-PCR fragments supported seven clusters. Isolates of R. solani AG 1-IB (n=18), AG 2-2IIIB (n=30) and AG 5 (n=1) clustered separately. Waitea circinata var. zeae (n=11), and var. circinata (n=4) grouped separately. A cluster of six isolates (UWC) did not fall into any known Waitea group. Most of the binucleate Rhizoctonia-like fungi (BNR) (n=16) grouped separately. AFLP grouping also largely agreed with the above results. However, UWC isolates clustered into two groups. Molecular analyses corresponded well with traditional anastomosis grouping by clustering isolates within an AG or AG subgroup together. UP-PCR cross-hybridization could distinguish closely related Rhizoctonia isolates to their infraspecies level. Genetically related isolates belonging to the same AG subgroups cross-hybridized strongly, while isolates of different AGs did not cross-hybridize or did so weakly. Sequence-characterized amplified region (SCAR) markers were generated from UP-PCR products to identify isolates of major pathogenic groups AG 1-IB and AG 2-2IIIB. Specific primer pairs successfully distinguished isolates of AG 1-IB and AG 2-2IIIB from isolates of other AGs. Sensitivity of Rhizoctonia species and AGs was tested in vitro to commercial formulations of iprodione, triticonazole and pyraclostrobin. W. circinata isolates were moderately sensitive to iprodione while isolates of R. solani and BNR were extremely sensitive. Isolates of AG 2-2IIIB showed less sensitivity to triticonazole than other Rhizoctonia isolates. W. circinata var. zeae isolates were moderately sensitive to pyraclostrobin while most of the other isolates were extremely sensitive. / Ph. D.

<p> Brown patch (caused by various <em>Rhizoctonia </em>and <em>Rhizoctonia-</em>like species) is one of the major summer diseases of tall fescue [<em>Schedonorus arundinaceus</em> (Schreb.) Dumort., nom. cons.]. Fungicides are available to suppress brown patch; however, there is increasing interest to reduce lawn pesticide inputs. Excessive summer nitrogen (N) applications and extended periods of leaf wetness have been suggested to enhance brown patch. Five projects were conducted from 2020 to 2022 to evaluate individual and various combinations of cultural management practices to improve brown patch management strategies through reducing chemical inputs and promoting environmentally sound integrated pest management (IPM) practices. Brown patch host resistance of 15 tall fescue cultivars was evaluated in a controlled environment study and various morphological characteristics were correlated to brown patch severity. A 45% reduction in brown patch was observed with a resistant cultivar, and cultivars with faster growth rates, wider sheath widths and shorter sheath length correlated with reduced brown patch resistance. A field study evaluated five cultivars fertilized with urea-N from April to July, totaling 73.5 or 245.0 kg N ha^-1. A resistant cultivar had the greatest influence on reducing disease, and N-rate generally did not influence disease severity. Differences in seasonal brown patch was compared in a three-year field study for various natural organic fertilizers. Feather-bone meal and soybean meal-based products decreased disease compared to non-fertilized turf. Chemical suppression of leaf-wetness was studied using different surfactant chemistries applied on a 14 to 21-d application frequency and some chemistries reduced disease. When evaluating the various interactions of cultivar, N rate, and surfactant compared to a granular fungicide, the greatest impact was achieved when planting a resistant cultivar, reducing disease severity by 68%. Additionally, the combination of a resistant cultivar and application of a surfactant had the same seasonal brown patch compared to a susceptible cultivar with fungicide applications during year two of evaluation. In summary, these studies demonstrate significant reductions in brown patch can be achieved when utilizing the aforesaid best management practices which can substantially reduce the need for frequent lawn fungicides.  </p>