Fine fescues (Festuca spp.) are cool-season grasses used in low-maintenance turf areas. Mesotrione is a PRE and early-POST herbicide used during establishment of most cool-season turfgrasses, excluding fine fescues. Currently, efforts are being made to breed for increased tolerance to mesotrione in fine fescues to enhance weed control during establishment. This study was conducted to evaluate the association of foliar and root uptake of [14C]mesotrione with the tolerance of three lines each of Chewings fescue [Festuca rubra ssp. commutata Gaudin; syn. F. rubra ssp. fallax (Thuill.) Nyman], hard fescue [Festuca trachyphylla (Hack.) Hack.], and strong creeping red fescue (Festuca rubra L. ssp. rubra) lines. From a rate-titration experiment, the hierarchical rank of species for mesotrione tolerance from highest to lowest was: hard > Chewings > strong creeping red fescue. The hierarchical rank of species for foliar uptake from highest to lowest was: Chewings > strong creeping red > hard fescue. Translocation of foliar-absorbed 14C was not associated with differential tolerance levels of the three species. Root absorption was comparable among species, but differences between lines were detected within the species. The most susceptible lines of Chewings and strong creeping red fescue exhibited greater root uptake than lines with greater tolerance. Hard fescue translocated the least amount of root-absorbed radioactivity to shoots, while Chewings and strong creeping red fescues were comparable.
An herbicide‐resistant weed control system that utilizes naturally occurring mutations to acetyl‐coenzyme A carboxylase (ACCase)‐inhibiting herbicides could provide herbicide selectivity and improve control of grassy weeds in turf. Knowledge regarding the presence of these mutations in grasses is needed to guide development of this type of system. This research subjected 24 species of warm‐season, cool‐season, and grassy weed species to rates of 0, 400, and 1200 g a.i. ha−1 of fenoxaprop herbicide and surveyed these species for the presence of site‐of‐action mutations in ACCase at amino acid (aa) positions 1781, 1999, 2027, 2041, 2076, 2088, and 2096. Nine species including Agrostis capillaris L., Festuca ovina L., Festuca rubra L., Lolium multiflorum Lam., Lolium perenne L., Paspalum dilatatum Poir., Poa annua L., Zoysia japonica Steud., and Z. matrella [L.] Merr. were tolerant to fenoxaprop. Site of action point mutations conferring resistance to ACCase herbicides were found at aa position 1781 in only three of 24 species surveyed (Festuca ovina, Festuca rubra, and Poa annua). The information obtained from this study provide guidance for the development of ACCase resistant weed control systems for turfgrass.
Creeping bentgrass (Agrostis stolonifera L.) is a fine‐textured, cold‐hardy turfgrass used by the golf industry in the transition zone and farther north. Grassy weeds are a recurrent problem for seed producers and golf course managers. Herbicide‐resistant creeping bentgrass would provide the seed producer and golf course manager with an additional tool to control grassy weeds. In the present study, in vitro selection was used to obtain mutants of creeping bentgrass via somaclonal variation that were resistant to the acetyl coenzyme A carboxylase (ACCase) inhibitor, sethoxydim {2‐[1‐(ethoxyimino] butyl)‐5‐[2‐(ethylthio)propyl]‐3‐hydroxy‐2‐cyclohexen‐1‐one}. Selection was imposed on creeping bentgrass calli (total of 13,725) by growing them on induction medium containing 10 µM sethoxydim. Four independent sethoxydim‐resistant calli were identified and subsequently sequenced to confirm the presence of an A to C mutation in the first position of the 1781 amino acid codon causing an isoleucine to leucine substitution. Whole plant dose response experiments showed the sethoxydim‐resistant event, SR1, was resistant to sethoxydim at rates of >3200 g a.i. ha–1. SR1 also showed cross resistance to the ACCase‐inhibitor herbicide, fenoxaprop at rates of > 800 g a.i. ha–1.
Contamination of newly planted bermudagrass (Cynodon spp.) varieties by undesirable o -type bermudagrass genotypes is an ever increasing concern for turf managers because selective control options are limited. In 2009, a sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} tolerant bermudagrass genotype (93-175) was identi ed during herbicide screening at the University of Georgia in Ti on. e objective of this research was to assess the tolerance of 93-175 to three Acetyl-CoA carboxylase (ACCase) herbicides in comparison to the susceptible genotypes Tifway and common bermudagrass. Greenhouse and eld trials were performed between August 2011 and April 2013. Factors in the eld experiment included ACCase herbicides, application rates, bermudagrass genotypes, and locations. Turfgrass injury ratings taken 42 days a er treatment (DAT) and during greenup the following spring supported initial preliminary ndings. At the 1x rate of sethoxydim (280 g a.i. ha -1 ), 93-175 displayed 50 to 87% less injury in comparison to the susceptible genotypes. In the spring of 2013, 93-175 plots treated with a 1x rate of sethoxydim reached 100% recovery during the same time period as non-treated controls, while common and Tifway had only recovered to 48 and 60%, respectively. e tolerance mechanism of 93-175 to sethoxydim did not confer an appreciable reduction of clethodim {(E,E)-(6)-2- [1-[[(3-chloro-2-propenyl)oxy]imino]propyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} or uazifop {(6)-2-[4-[[5-(tri uoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} herbicide treatment e ects. 93-175 will continue to be studied to determine transferability of herbicide tolerance to progeny and the mechanism of the observed tolerance.
Anthracnose, caused by the fungal pathogen Colletotrichum cereale Manns sensu lato Crouch, Clarke & Hillman, can be a damaging disease on many cool-season turfgrasses; however, it has not been reported as an aggressive pathogen on fine fescue species (Festuca spp.). Symptoms and signs associated with anthracnose disease were observed in fine fescues on the Rutgers University Plant Science Research and Extension Farm in Adelphia, NJ, in Jun 2014. The objectives of this study were to identify the causal agent, determine if the isolate of C. cereale (FF1A) obtained from symptomatic Chewings fescue (Festuca rubra L. ssp. commutata Gaudin) plants was pathogenic to Chewings fescue and hard fescue (F. brevipila Tracey) turfs, and whether cultivars and accessions collected from Europe varied in disease susceptibility. Pathogenicity of this fine fescue isolate was evaluated using four Chewings fescue and four hard fescue cultivars or accessions in a growth chamber. Disease symptoms were first observed at 5 days post-inoculation, and evaluations continued to 17 days post-inoculation. Infection was confirmed by morphological evaluations, re-isolation from symptomatic tissues, and real-time polymerase chain reaction (PCR). Three noncommercial accessions (two Chewings fescues and one hard fescue) were very susceptible to the fine fescue C. cereale FF1A isolate, whereas ‘Sword’ and ‘Beacon’ hard fescues exhibited low susceptibility. In addition, an isolate of C. cereale (HF217CS) from annual bluegrass [Poa annua L. f. reptans (Hausskn) T. Koyama] was included, and our data demonstrated that this isolate was also able to infect Chewings fescue and hard fescue. This study confirmed that C. cereale can be a damaging pathogen of fine fescues, and that breeding for resistance to anthracnose should be considered when developing new cultivars.
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