H. Brent Pemberton

Landscape rose response to low moisture levels and a hydrophilic gel

Abstract Containerized plants of five low-maintenance rose (Rosa hybrida L.) cultivars were irrigated at intervals which limited moisture availability for plant growth and development. The cultivars were grown both in a medium amended with a hydrophilic gel and in a control medium. Of the five cultivars, ‘Pink Meidiland’ had the highest leaf water potential (ψL) and lowest transpiration (E), while ‘Ferdy’ maintained the highest E. The smaller leaf surface area of ‘Pink Meidiland’ and larger root to shoot ( R S ) ratio and lower leaf area ratio (LAR) of ‘Ferdy’ contributed to a more favorable water status despite limited moisture availability. When hydrophilic gel was utilized as a medium amendment, ψL was generally higher. Gel had little effect on plant biomass and tended to decrease tissue nutrient content.

What is Rose Rosette Disease

Rose rosette disease (RRD) is incited by a negative-sense RNA virus (genus Emaravirus), which is vectored by a wind-transported eriophyid mite (Phyllocoptes fructiphilus). Symptoms include witches broom/rosette-type growth, excessive prickles (thorns), discolored and distorted growth, and, unlike most other rose diseases, usually results in plant death. RRD is endemic to North America and was first described inManitoba, Wyoming, and California in the 1940s. It has spread east with the aid of a naturalized rose species host and has become epidemic from the Great Plains to the East Coast of North America on garden roses in home and commercial landscapes where losses have been high. The disease was suggested to be incited by a virus from the beginning, but only recently has this been confirmed and the virus identified. The presence of the vector mite on roses has been associated with RRD since the first symptoms were described. However, more recently, the mite was demonstrated to be the vector of the disease and confirmed to transmit the virus itself. As a result of the RRD epidemic in North America and its effects on the national production and consumer markets for roses, a research team comprising five major universities (Texas, Florida, Tennessee, Oklahoma, and Delaware), a dozen growers and nurseries (all regions), six rose breeding programs (California, Wisconsin, Texas, and Pennsylvania), the major rose testing programs (Earth-Kind andAGRS), themajor rose organization (American Rose Society), and themajor trade organization AmericanHort has formed. This research project has been funded by the Specialty Crops Research Initiative through the U.S. Department of Agriculture (USDA) with the short-term objective of improving and disseminating best management practices (BMPs) and the long-term goal of identifying additional sources of resistance and developing the genetic tools to quickly transfer resistance into the elite commercial rose germplasm. Rose rosette disease is incited by a negative-sense RNA virus (genus Emaravirus), which is vectored by a wind-dispersed eriophyid mite (P. fructiphilus) (Di Bello et al., 2015a; Laney et al., 2011). Symptoms on roses include witches broom/rosette type growth, excessive thorniness, and discolored and distorted growth. Unlike most other rose diseases, RRD usually results in plant death (Olson et al., 2015; Windham et al., 2014). Since being identified in the western United States and Canada, it has spread east with the aid of Rosa multiflora, a naturalized rose species host and has become widespread from the Great Plains to the East Coast of North America (Amrine, 2002). This epidemic has spread to garden roses in home and commercial landscapes where losses have been high. The popularity of landscape roses in gardens has increased greatly in recent years, resulting in widespread use of this type of rose in both home and commercial landscapes (Pemberton and Karlik, 2015). This and the occurrence of the disease in poorly managed landscapes where plants are not scouted and rogued have no doubt contributed to the spread of this deadly disease (Olson et al., 2015; Windham et al., 2014). The degree of plant loss threatens the use of garden roses by consumers and the rose production industry itself. RRD is endemic to North America and was first described in Manitoba, Wyoming, and California in the 1940s. In 1940, Conners (1941) observed a ‘‘Witches’ Broom (?virus)’’ symptom with a greatly increased number of spines affecting canes of an unnamed species of rose in Morden, Manitoba. Thomas and Scott (1953) reported receiving diseased specimens of Rosa rubrifolia grown as an ornamental from Lander, WY, in 1941. A specimen from near the same location, but on an unidentified native rose was received in 1942. Also in 1942, the same authors reported a specimen collection with similar symptoms from ‘‘a native rose, possibly Rosa pisocarpa, near Carrville in a mountainous area of Trinity County, CA.’’ Symptoms included witches broom type growth, an indefinite chlorotic pattern in leaves, misshapen leaflets and flowers, and an increase in thorniness. They believed both of these collections to be representative of the same disease, which they referred to as rosette of rose. By the late 1960s, RRD symptoms were found in California on the native rose Rosa woodsii var. ultramontana (Wagnon and Nichols, 1966; Wagnon and Nichols, 1970). Symptoms similar to those reported by Thomas and Scott (1953) were recognized at the University of Nebraska North Platte Experiment Station in 1957 by Viehmeyer (1961). By 1959, a 4to 5-acre block of rose breeding stock at the station was heavily infected (Allington et al., 1968). In the same area, Viehmeyer (1961) indicated that the disease had been found in an area about 200 miles long and 50 miles wide. The same author also described the destruction of several miles of infected R. multiflora hedge in this particular area along with other centers of infestation. In addition to the symptoms described previously, Allington et al. (1968) Received for publication 2 Oct. 2017. Accepted for publication 28 Nov. 2017. This paper is part of the workshop entitled, The Challenges of Rose Rosette Disease (RRD): An Update of the Combating RRD SCRI Project, presented on 9 Aug. 2016, during the ASHS Annual conference, Atlanta, GA. This work was partially funded by the Robert E. Basye Endowment in Rose Genetics, the American Rose Society Research Endowment, and the USDA’s National Institute of Food and Agriculture (NIFA) Specialty Crop Research Initiative project ‘‘Combating Rose Rosette Disease: Short Term and Long Term Approaches’’ (2014-51181-22644/ SCRI). Corresponding author. E-mail: b-pemberton@ tamu.edu. This is an open access article distributed under the CC BY-NC-ND license (http://creativecommons. org/licenses/by-nc-nd/4.0/). 592 HORTSCIENCE VOL. 53(5) MAY 2018 noted the red leaf coloration in R. multiflora and a thickening of new, infected stems in most of the cultivars or species with which they worked. In 1976, RRD was reported in Kansas (Crowe, 1983) and reports increased in the late 1970s in eastern Kansas and western Missouri. Symptoms were noted on rose hybrids in urban areas and on rose hybrids and R. multiflora hedges in rural areas. By 1982, symptoms were reported on cultivated hybrid roses in eastern Oklahoma (Crowe, 1983) and on both cultivated rose hybrids and R. multiflora hedges in northwestern Arkansas (Gergerich and Kim, 1983). Thefirst report ofRRDeast of theMississippi River was found by Hindal et al. (1988) who described infestations in naturalized stands of R. multiflora in Illinois (1985), Kentucky (1985), and Indiana (1986). In 1990, the first report came from Texas where it was found in production fields in east Texas where R. multiflora was used as a rootstock for garden rose production (Ong et al., 2015; Philley, 1995). By 1994, RRD distribution was as far east as Tennessee, Ohio, Pennsylvania, and West Virginia (Amrine, 2002) with reports mainly concerning infections in R. multiflora. In 1996, it was found in Maryland on R. multiflora (Tipping and Sindermann, 2000). In recent years, RRD has spread into garden rose plantings via the mite vector across the Midwest and Eastern United States, resulting in huge losses. In addition, it was found on a hybrid garden rose in a nursery in Florida in 2013 (Babu et al., 2014). Abundantly apparent is the fact that the spread of RRD from western North America to the east has occurred through naturalized stands of R. multiflora. The history and status of the infestation of this introduced plant species along with the ecological damage it has caused have been well reviewed (Amrine, 2002; Amrine and Stasny, 1993). Rosa multiflora is native to eastern China, Japan, and Korea and was introduced into North America in the 1800s for use as a rootstock, and also for wildlife, erosion control, ‘‘living fences,’’ and informal hedges (Amrine, 2002; Hindal et al., 1988; Hong et al., 2012). It soon spread from the original plantings and is now listed as a noxious weed in at least 10 states (Amrine and Stasny, 1993). The use of RRD as a biological control for R. multiflora has been proposed and studied (Amrine, 2002; Amrine and Stasny, 1993; Epstein and Hill, 1999). However, this work has been opposed Table 1. Investigators and key collaborators working on the Specialty Crop Initiative Project Combating Rose Rosette: Short Term and Long Term Approaches. Name Specialty Responsibility Location David H. Byrne, Project Director Rose breeding and genetics Rose breeding and genetics Department of Horticultural Sciences, Texas A&M University, College Station, TX Mark Windham Plant pathology Screening for resistance, BMP Entomology and Plant Pathology Department, University of Tennessee, Knoxville, TN Brent Pemberton Plant physiology, horticulturist Outreach, rose evaluation trials Texas A&M AgriLife Research and Extension Center, Overton, TX Frank Hale Entomologist BMP Soil, Plant, and Pest Center, The University of Tennessee, Nashville, TN Ronald Ochoa Entomologist Mite–plant interactions Systematic Entomology Laboratory, USDA/ ARS, Beltsville, MD Mathews Paret Plant pathologist Diagnostic techniques North Florida Research and Education Center, Quincy, FL Francisco Ochoa Corona Plant pathologist Diagnostic techniques Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK John Hammond Plant pathologist Diagnostic techniques Floral and Nursery Plants Research Unit, USDA/ARS, Beltsville, MD Ramon Jordan Plant pathologist Diagnostic techniques Floral and Nursery Plants Research Unit, USDA/ARS, Beltsville, MD Patricia Klein Molecular biologist Molecular genetics, marker technology Department of Horticultural Sciences, Texas A&M University, College Station, TX Tom Evans Plant pathology, genetics Screening for resistance Department of Plant and Soil Sciences, University of Delaware, Newark, DE Je

Switchgrass and little bluestem cultivars show performance variation across eight states in national grass trials

Landscape plant evaluations were conducted in eight states: Colorado, Minnesota, North Carolina, Ohio, Oregon, Pennsylvania, Texas, and Vermont for 17 switchgrass (Panicum virgatum) and five little bluestem (Schizachyrium scoparium) cultivars. Additional locations in Florida (Fort Lauderdale, Fort Pierce, Quincy, and Wimauma), Nebraska (Lincoln), and Lubbock and San Marcos completed 1 or 2 years of the trials. Plants were established in 2012 and data were collected for 3 years, 2013–15. Sites were asked to compile annual data on plant height, width, flowering time, fall color, pests, foliage color determined by the Royal Horticultural Society’s color chart, plant form, flowering date, floral impact, self-seeding, winter injury, landscape impact, and mortality. Texas A&M Agricultural Research and Extension Center (Overton), Florida (all four locations), and Vermont had the highest mortality rate. Southern Florida locations lost 50% of their plants by the end of 2014. Wide variation was reported for landscape impact, individual cultivar height, and width from different regions of the United States. Three of the 17 switchgrass cultivars, Cloud 9,Northwind, and Thundercloud, had a rating of 4.0 or higher averaged over six or more locations for plant form, floral, and landscape impact. ‘Shenandoah’ and ‘Warrior’ switchgrass had a rating of 4.0 or higher averaged over six or more locations for plant form and landscape impact, but not floral impact. Only one of the five little bluestem cultivars, Blue Heaven rated 4.0 or higher, for plant form and landscape impact when averaged over six or more locations. This range of variability in landscape plant performance demonstrates the importance of local plant evaluations.