Location: Floral and Nursery Plants Research2012 Annual Report
1a. Objectives (from AD-416):
This study will include three objectives. First, we will evaluate 46 Spiraea accessions using over 30 descriptor traits used in GRIN by the WLPCGC in two distinct physiographic locations within the state of Georgia (Athens and Savannah). This information will be provided to GRIN for inclusion in the GRIN database. Second, we will measure the overall landscape quality of each accession with an emphasis on heat tolerance and plant form in each of the two aforementioned physiographic regions. Third, we will measure the invasive potential of these accessions by conducting seed viability and germination tests on each accession.
1b. Approach (from AD-416):
Experimental design for this study will be a randomized complete block design with three replications. We will use the expected mean squares from the analysis of variance to calculate broad sense heritabilities, which will distinguish proportions of genetic and environmental variance for each trait. Each replication will consist of one individual per taxa. Plant material will be acquired from Chicago Botanic Garden, the official NAPCC Spiraea collections repository. Cuttings of accessions will be taken in the fall of 2007 and rooted in greenhouses using the protocol of Dirr and Heuser (2006). Plants will be transferred to in-ground beds in the spring of 2008 at two locations: Athens, GA (USDA Zone 7b) and Savannah, GA (USDA Zone 8b). Planting beds will be arranged in linear-rows with individuals planted on 5’ staggered centers. Drip-irrigation will be applied as needed the first growing season while plants are becoming established and subsequently removed for the remainder of the study unless severe drought warrants irrigation. Measurement of the aforementioned USDA-ARS woody landscape plant descriptor traits and mortality will begin April 1, 2009, and conclude on November 15, 2010. Disease and insect measurements will include pathogen/pest ID and percent of plant affected. Attractiveness, floral impact, persistence of foliage, plant vigor, and summer drought/heat tolerance will be measured on a 1-10 scale with one being the least and 10 being the highest. Color measurements will all be performed using the Royal Horticultural Society Colour Chart. All size measurements will be taken in centimeters. Number of fruit produced per umbel will be taken from an average of five randomly selected umbels per individual. All date measurements will be reported on a 1-365 scale beginning with January 1 and ending with December 31. Invasive potential will be measured by calculating the percentage of viable seed and germination percentage of 100 seed per individual using two techniques: 1) Tetrazolium tesing in 0.1% solution of 2,3,5-triphenyltetrazolium chloride (Miller, 2004). 2) Germination test on moist filter paper. Additionally, we will qualitatively measure seed production of each genotype by assessing the mean number of seed produced per umbel using five umbels per plant. We will also calculate the mean number of umbels for each genotype. By multiplying the mean number of seed produced per umbel with the mean number of umbels per genotype, we will ascertain a overall value for seed production of each genotype in the study.
3. Progress Report:
Spiraea accessions were obtained from Chicago Botanic Garden (CBG) as part of the North American Plant Collection Consortium (NAPCC) and from various sources and collection trips. There are currently 32 of the original 36 Spiraea accessions, planted in 2009, in the University of Georgia collection, with four accessions not surviving the 2009-10 winter. We were unable to obtain six accessions listed on the grant due to discrepancies between labeling and phenotypic traits at CBG and nurseries. Data collected includes the following: disease and insect incidence and severity under natural growing conditions; visual attractiveness of whole plant measured at varying intervals throughout growing season; color of immature and mature foliage; flower diameter, overall floral impact and umbel size; flower color; number of fruit produced per umbel; growth habit; inflorescence size; invasive potential based on mature seed viability and germination percentage; leaf size and shape; persistence of leaves in drought conditions and during winter months; plant size and shape; immature, mature, and winter stem color; plant vigor in landscape setting; date of fall leaf drop, emergence from winter dormancy, first and peak anthesis, and seed ripening; and, summer drought and heat tolerance. Data collection began in summer 2009 and continues with a completion date of fall 2012. Thus far, all accessions have exhibited minimal disease incidence or pressure. Insect pressure on Spiraea species and cultivars in the trial has been limited to minor aphid pressure on new foliage and within flower umbels. Leaf emergence, plant size, persistence of leaves in drought conditions and mortality data continue to be collected. Leaf color, growth habit, plant vigor, date of first anthesis, flower size, flower color, plant attractiveness, stem color, floral impact, plant vigor, and mortality data continue to be collected. Seed viability and germination data were collected in fall 2010 and will be again in fall 2012.