ASHS 2024 Conference

Silver saw palmetto is a native palm of the southeast coast of the United States that is of high ornamental value for native landscapes and commercial potential production due to its fruit’s phytotherapeutic properties. The main propagation method for this palm is seed-based germination, which has very slow and low germination rates. This study assessed imbibition rates, germination in different temperatures that simulated Florida seasons, and pre-sowing treatments. Diaspores were exposed to seeds within the endocarp, intact seeds, scarified seeds, and seeds with their operculum removed. The maximum fresh weight of saw palmetto seeds after imbibition was observed at 11 days. Significant differences in imbibition rates and final weight were noted for seeds with an endocarp, with lower fresh mass, and scarified seeds, which showed the highest rates. Summer temperatures consistently yielded the highest final germination percentage and uniformity for seeds with or without an endocarp on constant summer temperatures or move-along experiments throughout Florida seasons. Pre-sowing treatments, such as the removal of the operculum, proved to be highly efficient in promoting the highest germination percentages and rates, while seeds with an endocarp demonstrated lower and uneven germination. The application of hormones, particularly GA3 at 10,000 ppm, also showed promise in improving germination rates.

Blueberry (Vaccinium sect. Cyanococcus Rydb.), lingonberry (V. vitis-idaea L.) and huckleberry (V. membranaceum; also called black huckleberry or black blueberry) are three important Vaccinium small fruit crops native to the North. They are valuable resources for bioactive components that play important roles in anti-oxidant, anti-tumor, anti-ulcer, and anti-inflammatory activities. They can be propagated to produce true-to-type plants either conventionally or by micropropagation. Propagation in vitro is now well accepted worldwide for commercial production of Vaccinium crops. Proficient plant propagation technique using shoot organogenesis and somatic embryogenesis was successfully established in blueberry and lingonberry. Shoot regeneration and proliferation in in-vitro conditions using various liquid bioreactors have successfully been achieved in various Vaccinium species. One of the major concerns in commercial production is the occurrence of variation in micropropagated plants. This presentation describes the in-depth progress of genetic and epigenetic variations in different Vaccinium species during micropropagation. It addresses different molecular techniques used to monitor true-to-type and epigenetics along with application of epigenetic variation in micropropagated Vaccinium berry crops. Keywords: blueberry, bioreactor micropropagation, DNA-methylation, huckleberry, molecular markers, lingonberry, somaclonal variation

A large group of horticulture species are propagated vegetatively through shoot-tip cuttings harvested from stock plants and planted to form adventitious roots. Adventitious root development (ARD) leads to establishing a carbohydrate sink in the region of root regeneration, which is highly dependent on energy and carbon skeletons. We hypothesized that enhancing the source-to-sink relationship during ARD can lead to an efficient carbon allocation to growth, resulting in a well-rooted cutting. Thus, the research aimed to determine if the application time of a Cytokinin B-Mo-based product during the ARD of unrooted cuttings would impact the source-to-sink relationship and, hence, affect plug growth and quality. The product was applied at four application times plus a negative control as follows: T1: plants without product (control), T2: sticking stage (starting 24 h after the sticking); T3: callus formation stage; T4: root development stage; and T5: toning stage. The experiment was a complete randomized design with five treatments and 60 repetitions for treatment (n=60) in two experimental runs (n=120). The root and shoot length, the number of leaves, the leaf chlorophyll content, the root and shoot dry matter, and the root-to-shoot ratio were measured. Results indicate that applying the product at T2 in ARD's dedifferentiation and induction phase leads to the shortest root and shoot length, the lowest dry matter accumulation, and some phytotoxicity effects. For T3 in ARD's initiation phase, the application results in greater root, total dry matter, and total soluble sugar contents than the control. For T4 in ARD's expression phase, the application results in greater growth, total dry matter, and sucrose and starch contents than control and other treatments. Applying the product in T5 when the roots had grown and reached all the edges of the growing media did not have any benefit compared to the control. Our results suggest that the exogenous application of a product to strengthen the source-to-sink relationship during adventitious root development can potentially enhance the non-structural carbohydrate contents when applied at the root formation phase (T4), which correlates positively with the increase in the length and dry matter of the roots, generating a well-toned rooted cutting.

During acclimation of unrooted cuttings (URC) under mist irrigation, the moisture status of URC is greatly affected by environmental conditions such as high photosynthetic photon flux density (PPFD) and vapor pressure deficit (VPD), both of which can cause rapid dehydration. The objective of this study was to characterize the effects of PPFD and VPD on indoor acclimation of Chrysanthemum ‘Olympia White’ URC. Cuttings were stuck in a peat-perlite substrate in propagation trays, placed under sole-source lighting in chambers where ultrasonic fog was used to automatically control relative humidity (RH). Mist irrigation was applied every 20 to 30 min for 3 h. Over 12 h, URC were exposed to 0, 35, 70, 80, 105, 140, or 210 µmol·m–2·s–1 PPFD and 70, 80, 90, or 100% RH setpoints, resulting in air VPD levels ranging from 0.02 to 0.59 kPa. In the chambers, there was a high level of environmental control, and PPFD did not affect air VPD (P = 0.712), which were therefore considered as independent climatic factors. Leaf temperature minus air temperature was considered an indicator of plant energy balance, where a warmer leaf than air temperature is a driver of evapotranspiration. Plant leaf temperature became cooler than the air temperature as air VPD increased (P = 0.024), likely caused by evaporative cooling of leaves. In contrast, increasing PPFD increased leaf temperature relative to air temperature, likely through radiant heating. Leaf VPD was positively correlated with air VPD (adjusted-R2 = 0.88) but was also affected by the interaction of PPFD and air VPD (P < 0.05). Two hours after misting was terminated (5 h total), some plants showed clear wilting especially under low RH. At 5 h, stomatal conductance and evapotranspiration of URC was increased by PPFD and decreased by air VPD (P < 0.01), although there was an interaction between PPFD and air VPD for stomatal conductance (P < 0.005). Further results highlighting responses to RWC, water uptake, and water loss will be presented.

Prairie willow (Salix humilis) is a naturally compact and adaptable shrub willow native to the eastern United States. This taxon has potential for use in managed landscapes because of its desirable habit, attractive flowers and foliage, and its purported tolerance to fluctuations in soil moisture. This adaptability could be advantageous for urban green infrastructure applications. However, unlike most willows, S. humilis is thought to exhibit recalcitrance to standard asexual propagation techniques. This recalcitrance is exacerbated by observed susceptibility to fungal infections that cause cutting mortality during propagation. Because juvenility can improve the rooting of propagules, we questioned whether stock plant rejuvenation (coppicing) and propagule treatment with fungicide would influence rooting and survival of S. humilis dormant hardwood cuttings. In February 2024, 300 full-length dormant stems were harvested at the USDA Plant Introduction Station in Ames, Iowa from stock plants that were either coppiced or not coppiced the previous year. Uniformly-sized basal cuttings were acquired by removing the proximal 23 cm of each stem. Experimental trials (N=300; n=75) evaluating the full factorial of stock plant status [non-coppiced (-coppice) or coppiced ( coppice)] and fungicide application [non-treated (-fungicide) or treated ( fungicide) by submerging propagules in T-Bird with 46.2% Thiophanate-methyl for 15 minutes] were conducted in a cool greenhouse at the University of Minnesota Horticultural Research Center in Chaska, MN. All cuttings were treated with 0.8% indole-3-butyric acid via Hormodin-3 Talc powder and stuck in 50 cell trays (5 × 5 × 12.5 cm cells) with a 1:1 perlite:bark-based media and placed on heat mats (22ºC) using a completely randomized design. Total number of propagules rooted, length of the longest three roots, and number of roots were recorded. Propagules were ranked on their overall rooting performance using a Likert Scale. Rooting percentage was 77%, 56%, 87%, and 69% for coppice/ fungicide, coppice/-fungicide, -coppice/ fungicide, and -coppice/-fungicide, respectively. Compared to the non-coppiced propagules, mean count of roots decreased by 41% for coppiced propagules, across fungicide applications. Compared to propagules not treated with fungicide, mean count of roots increased by 19% for propagules treated with fungicide, across coppice treatments. Future research will evaluate different types of cuttings to generate a complete vegetative propagation protocol for Salix humilis. This work supports the introduction of this versatile plant into commercial production, thereby augmenting the ornamental plant palette for challenging urban landscapes.

Carex wahuensis subsp. wahuensis is an endemic Hawaiian species extensively used as a ground cover in landscaping and restoration. In recent years, a variegated form was identified and is now starting to be utilized in a handful of landscaping projects. While the green wild-type has been primarily propagated through seeds, protocols for single plant divisions are lacking and limits the commercialization and availability of the variegated form. In this study, we investigated the effect of indole-3-butyric acid (IBA) application as well as the presence or absence of roots and inflorescences on propagating single plant divisions of variegated C. wahuensis subsp. wahuensis. Container grown clumps were divided into single plantlets, with or without flowers and with or without roots (trimmed 7.6 to 10.2 cm length). For the first experiment, plantlets without flowers but with pre-existing roots were treated with or without 3000 ppm IBA and planted in 1:1 perlite and vermiculite. For the second experiment, plants with roots but with or without flowers, and plants without roots and flowers were also planted in 1:1 perlite and vermiculite. Both experiments were located on a mist bench, which activated every 2 minutes for 12 seconds, and both were allowed to root for up to 135 days. Root length and rooting index was recorded for the first experiment at 45 and 90 days after planting while rooting index was recorded for the second experiment at 45, 90 and 135 days after planting. Application of IBA did not improve root length and rooting index of plantlets. However, there was an observed difference in root length and rooting index between experimental runs. In the second experiment, plants with roots and no flowers exhibited the highest rooting index (3.3 = light rooting) followed by plants with no flowers and no roots (2.9 = alive but no roots to light rooting). Plants with flowers and roots exhibited the lowest rooting index (1.7 = mostly dead). Results of the study indicate that vegetative single plantlets of variegated Carex wahuensis subsp. wahuensis can be successfully rooted within 135 days after planting under mist.

Osmanthus is a genus of ornamental plants with valuable qualities such as pest resistance, evergreen foliage, and aromatic flowers. However, different species respond differently to growth hormones for propagation. This study aimed to evaluate the types and rates of plant growth hormones on different species of Osmanthus propagation. Six distinct Osmanthus species (Osmanthus heterophyllus ‘Kaori Hime’, Osmanthus armatus ‘Jim Porter’, Osmanthus x fortunei ‘Patty's Secret’, Osmanthus heterophyllus ‘Rotundifolius’, Osmanthus delavayi, and Osmanthus x fortunei ‘Fruitlandii’) were treated with Indole-3-butyric acid (IBA) powder, 500 mg/L and 2000 mg/L of Potassium Indole-3-butyric acid (K-IBA), 10% Kelpak (seaweed extract), and water dip (the control). The cuttings’ survival rates, rooting rates, callus rate and area, and root length were recorded. The results showed the O. heterophyllus ‘Kaori Hime’ exhibited the best survival and rooting rates, while the O. heterophyllus ‘Rotundifolius’ had the lowest survival rate, the O. armatus ‘Jim Porter’ had the highest callus quantity. Plants treated with IBA powder had significantly larger callus area than those seaweed treatments. In conclusion, O. x fortunei 'Fruitlandii' and O. heterophyllus 'Kaori Hime' exhibit superior performance in all six measurements compared to other plant species and are highly recommended. Conversely, O. delavayi and O. heterophyllus 'Rotundifolius' have displayed considerably weaker performance and are not recommended. Further research is necessary to determine the effectiveness of other propagation methods and treatments for Osmanthus.