Propagation Beds Research Articles

Effect of simulated synthetic auxin herbicide sprayer contamination in sweetpotato propagation beds

AbstractField studies were conducted to determine the effects of synthetic auxin herbicides at simulated exposure rates applied to ‘Covington’ sweetpotato propagation beds on the quality of nonrooted stem cuttings (slips). Treatments included diglycolamine salt of dicamba, 2,4-D choline plus nonionic surfactant (NIS), and 2,4-D choline plus glyphosate at 1/10, 1/33, or 1/66 of a 1X application rate (560 g ae ha−1 dicamba, 1,065 g ae ha−1 2,4-D choline, 1,130 g ae ha−1 glyphosate) applied at 2 or 4 wk after first slip harvest (WASH). Injury to sweetpotato 2 wk after treatment was greatest when herbicides were applied 2 WASH (21%) compared to 4 WASH (16%). More slip injury was caused by 2,4-D choline than by dicamba, and the addition of glyphosate did not increase injury over 2,4-D choline alone. Two weeks after the second application, sweetpotato slips were cut 2 cm above the soil surface and transplanted into production fields. In 2019, sweetpotato ground coverage 8 wk after transplanting was reduced 37% and 26% by the 1/10X rates of dicamba and 2,4-D choline plus NIS, respectively. Though dicamba caused less injury to propagation beds than 2,4-D choline with or without glyphosate, after transplanting, slips treated with 1/10X dicamba did not recover as quickly as those treated with 2,4-D choline. In 2020, sweetpotato ground coverage was 90% or greater for all treatments. Dicamba applied 2 WASH decreased marketable sweetpotato storage root yield by 59% compared to the nontreated check, whereas treatments including 2,4-D choline reduced marketable yield 22% to 29%. All herbicides applied at 4 WASH reduced marketable yield 31% to 36%. The addition of glyphosate to 2,4-D choline did not increase sweetpotato yield. Results indicate that caution should be taken when deciding whether to transplant sweetpotato slips that are suspected to have been exposed to dicamba or 2,4-D choline.

Assessing Growth Parameters from Culm Cuttings of Bambusa vulgaris at the University of Dschang Botanic Garden, West Region of Cameroon: Implications for the Bamboo Resource Base and Rural Livelihoods

Dwindling supplies of bamboo resources and the increase in the demand for bamboo have led to the need for better propagation techniques. This is the only way to ensure the sustainability of the bamboo resource base and improve livelihoods. Thus, this study was carried out to examine the different growth parameters of culm cuttings of Bambusa vulgaris in propagation beds with a substrate consisting of dark soil, manure (compost) and sand in a ratio of 1:1:1. Data on different growth parameters was collected on a daily basis over a three week period and analyzed using appropriate descriptive and inferential statistics. It was found that the different growth parameters (diameter, height, leaves and sheaths) of culm cuttings of B. vulgaris evolved in like manner in three propagation beds. Descriptive statistics for growth parameters of culm cuttings of B. vulgaris showed little or no differences across three shelter/propagation beds (shelter bed 1, shelter bed 2 and shelter bed 3) with 1.4675 ± 1.6172 cm, 93 ± 112 cm, 22 ± 30 leaves, and 4 ± 6 sheaths being the mean diameter, height, number of leaves and number of sheaths for all three propagation beds, respectively. ANOVA test showed no statistically significant variation (p > 0.05) between growth parameters of culm cuttings of B. vulgaris across the three propagation beds, implying that the different growth parameters were relatively similar. Pearson correlation showed the existence of direct and inverse relationships between the different growth parameters of culm cuttings of bamboo. The existence of these direct and inverse relationships could be attributed to the rapid growth rate of bamboo, the substrate used, and the species of bamboo used (B. vulgaris). The study recommends more large-scale propagation projects of this bamboo species in order to ensure the sustainability of the bamboo resource base and improve livelihoods of bamboo dependent rural communities.

First Report of Phytopythium vexans Causing Root and Crown Rot on Flowering Cherry in Tennessee.

Flowering cherry (Prunus serrulata Lindl. 'Kwanzan') rooted cuttings grown in propagation beds containing 40% coarse sand and 60% ground pine bark in a commercial propagation nursery in Warren County, Tennessee were exhibiting root and crown rot in December 2016. Dark brown to black soft lesions were observed in the roots as well as the crown region of flowering cherry rooted cuttings and those rooted cuttings were non-marketable due to lesions. Disease incidence was approximately 60% of 10,000 plants. Phytophthora ImmunoStrip test (Agdia Inc., Elkhart, IN, USA) was performed and the test result was positive. Diseased plant tissues were surface sterilized with 70% ethanol and washed twice with distilled water. Culturing the affected root and crown parts (1 cm pieces) on V8-PARPH, an oomycete-selective medium consistently yielded whitish radiate mycelial growth pattern with spherical zoospores, filamentous to globose oogoni, elongated, and cylindrical antheridia with constrictions (De Cock et al., 2015) after 7 days of incubation at 25°C in a 12-h fluorescent light and dark cycle, which is the typical morphology of Phytopythium vexans (de Bary) Abad, de Cock, Bala, Robideau, Lodhi & Lévesque. To confirm pathogen identity, total DNA was extracted using the UltraClean Microbial DNA Isolation Kit (MO BIO Laboratories, Inc., Carlsbad, CA, USA) directly from a 3-day old culture of isolate (FBG2017010) on V8 medium. The internal transcribed spacer (ITS) and 28S large subunit of ribosomal RNA, and cytochrome c oxidase subunit I (CoxI) of mitochondrial DNA (mtDNA) genes/ region were amplified by PCR using the primer pairs ITS1/ ITS4 (White et al., 1990), NL1/ NL4 (Baten et al., 2014), and Levup and Fm85mod (Robideau et al., 2011), respectively. The PCR products were sequenced and the sequences (GenBank accession nos. MT533275, MT533451, and MT547980) were compared to the voucher specimens. They were 99.23, 99.60, and 98.92% similar to those of P. vexans isolates in the NCBI database (HQ643400, KR092144, and HQ708996, respectively). To complete Koch's postulates, 'Kwanzan' flowering cherry rooted cuttings grown on propagation substrate (10 cm pot containing 1 kg sterilized 40% coarse sand and 60% ground pine bark) were inoculated with identified pathogen and observations were taken on root rot disease symptoms. Five plants were inoculated with 100 ml of pathogen agar-slurry (1 plate of a 7-day old culture of isolate FBG2017010/1 L of sterilized water), and five control plants were drenched with agar slurry. The plants were maintained in the greenhouse condition (day/night temperature of 26/24°C), and irrigated twice a day for 2 min by overhead irrigation system. After 2 weeks, dark brown to black necrotic root lesions developed on all inoculated cuttings and P. vexans was consistently re-isolated from the inoculated plants. The morphology of the pathogen isolated on the V8-PARPH medium was identical to the original isolate. All control plants remained symptom-free and P. vexans was not isolated from the root tissue. To our knowledge, this is the first report of P. vexans causing root and crown rot in 'Kwanzan' flowering cherry in Tennessee, which can be a potential threat for the nursery crop production. The identification of P. vexans, the causal agent of Phytopythium root and crown rot is important in determination and implementation of effective management strategies.

Effect of Organic Inputs and Solarization for the Suppression of Rhizoctonia solani in Woody Ornamental Plant Production.

Soilborne diseases are the most economically significant problem faced by Southern region nursery producers. The goal of this research was to improve Rhizoctonia root rot disease management through the use of soil solarization alone and in combination with biofumigant cover crops—arugula ‘Astro’ (Eruca vesicaria ssp. sativa), mustard green ‘Amara’ (Brassica carinata), and turnip ‘Purple top forage’ (B. rapa); good quality compost and mustard meal amendment. The experiments were established as on-farm trials in 2016 and 2017 with prevalent Rhizoctonia solani population in propagation beds. All three biofumigant cover crops, arugula ‘Astro’, mustard green ‘Amara’, and turnip ‘Purple top forage’ in combination with solarization were able to reduce the Rhizoctonia root rot in flowering cherry ‘Kwanzan’ plants in nursery propagation beds. Compost amendment increased the flowering cherry rooted cuttings growth (plant weight, root weight, and plant height) compared to other treatments. Soil solarization in combination with cover crops and organic inputs could be used as part of an integrated approach to manage Rhizoctonia root rot in nursery crop propagation beds.

Yield, Quality, and Performance of Organic Sweetpotato Slips Grown in High Tunnel Compared with Open Field

Sweetpotatoes (Ipomoea batatas) are nutritious, easily stored, and well adapted to a variety of organic farming operations. This widely consumed root crop is propagated through the use of cuttings, known as slips. Slips are commercially grown primarily in the southeastern United States, and growers in the central United States still have limited access to sweetpotato planting material. Production of organic slips in high tunnels (HTs) could be a profitable enterprise for growers in the central United States given the season extension afforded by controlled-environment agriculture, which could allow growers to diversify their operations and facilitate crop rotation. In trials conducted in 2016 and 2017 at two research stations in northeast and south central Kansas, a systems comparison was used to evaluate the yield and performance of organic sweetpotato slips grown in HT as compared with the open field (OF), with four to six replications at each location. Propagation beds planted with ‘Beauregard’ seed roots in 2016 and ‘Orleans’ in 2017 were established in HT and OF under similar cultural methods and planting schedules. Slips were harvested from both treatment groups and transplanted to field plots to investigate the impact of production system on transplant establishment and storage root production. Slip yield from HT was greater than OF at both locations in 2016 (P ≤ 0.001), but this trend was inconsistent in 2017. Slips grown in HT were on average 12% less compact (slip dry weight per centimeter length) with fewer nodes than their OF counterparts in 2016. Nonetheless, mean comparisons for vine length, stem diameter, and total marketable storage root yield were not significant between HT and OF treatments (1.7 and 2.1 lb/plant, respectively). Similarly, the number of marketable storage roots for HT and OF groups was comparable (3.4 and 3.8 storage roots/plant, respectively). Although more research is needed to evaluate the feasibility of slips grown in HT and to determine recommendations for seed root planting densities, results from this study suggest that HT organic sweetpotato slip production could be a viable alternative to OF production as it relates to slip performance. According to this study, HT production could be a useful mechanism for growing sweetpotato slips, which could provide regional growers more control over planting material. Furthermore, HT slip production could promote the adoption of an underused vegetable crop that can be grown throughout many parts of the United States.

Tolerance of Sweetpotato to Herbicides Applied in Plant Propagation Beds

AbstractField and greenhouse studies were conducted in 2016 and 2017 to determine sweetpotato tolerance to herbicides applied to plant propagation beds. Herbicide treatments included PRE application of flumioxazin (107 g ai ha−1),S-metolachlor (800 g ai ha−1), fomesafen (280 g ai ha−1), flumioxazin plusS-metolachlor (107 g ai ha−1+ 800 g ai ha−1), fomesafen plusS-metolachlor (280 g ai ha−1+ 800 g ai ha−1), fluridone (1,120 or 2,240 g ai ha−1), fluridone plusS-metolachlor (1,120 g ai ha−1+ 800 g ai ha−1), napropamide (1,120 g ai ha−1), clomazone (420 g ai ha−1), linuron (560 g ai ha−1), linuron plusS-metolachlor (560 g ai ha−1+ 800 g ai ha−1), bicyclopyrone (38 or 49.7 g ai ha−1), pyroxasulfone (149 g ai ha−1), pre-mix of flumioxazin plus pyroxasulfone (81.8 g ai ha−1+ 104.2 g ai ha−1), or metribuzin (294 g ai ha−1). Paraquat plus non-ionic surfactant (280 g ai ha−1+ 0.25% v/v) POST was also included. After plants in the propagation bed were cut and sweetpotato slip number, length, and weight had been determined, the slips were then transplanted to containers and placed either in the greenhouse or on an outdoor pad to determine any effects from the herbicide treatments on initial sweetpotato growth. Sweetpotato slip number, length, and/or weight were affected by flumioxazin with or withoutS-metolachlor,S-metolachlor with or without fomesafen, clomazone, and all fluridone treatments. In the greenhouse studies, initial root growth of plants after transplanting was inhibited by fluridone (1,120 g ai ha−1) and fluridone plusS-metolachlor. However, by 5 wk after transplanting few differences were observed between treatments. Fomesafen, linuron with or withoutS-metolachlor, bicyclopyrone (38 or 49.7 g ai ha−1), pyroxasulfone with or without flumioxazin, metribuzin, and paraquat did not cause injury to sweetpotato slips in any of the studies conducted.

Effect of Cutting Type, Collection Time of Cutting, Plant Sex, Stem Wounding Method and Presence or Absence of Leaves on Rooting and Growth of Jojoba Shrub Cuttings

A series of six experiments were conducted with an objective of studying the effect of cutting type, collection time of cutting, plant sex, presence or absence of leaves and wounding method on the rooting and growth of jojoba shrub cuttings during 2016-2017 in the Jojoba Naturals Company greenhouses at Sana’a, Yemen. The cuttings were collected, prepared and planted under the transparent plastic tunnel. Perlite medium and automatic mist irrigation were used in the propagation beds. Relative humidity was between 80-99% and the temperature range was not more than 40 o C. Different parameters of rooting and growth of rooted cuttings were determined. Semi-hardwood and softwood cuttings recorded higher rooting percentages (77.77% & 82.22%) respectively than hardwood cuttings (26.11%). The cuttings collected in the spring season gave the greatest value of rooting compared to those collected in autumn and winter season. The presence of leaves on the cuttings within rooting time affected significantly the rooting percentage in comparison with the cuttings without leaves. However, the plant sex and wounding method did not differ significantly in respect of the rooting percentage of semi-hardwood cuttings. By this investigation, an efficient protocol including collection time of cuttings, rooting medium, plant hormone with its concentration, cutting type and rooting conditions was standardized. Thus, jojoba rooted cuttings would be produced in commercial quantities. As rooting success ratio of cuttings exceeds more than 90%.

Optimizing Sweetpotato Seed Root Density and Size for Slip Production

There is a research gap with respect to documenting the effects of sweetpotato (Ipomoea batatas) seed root density and size on transplant yield and quality. Field studies were conducted in 2012 and 2014 to determine the effect of sweetpotato seed root (canner size) density [12, 24, 37, 49, 61, 73, and 85 bushels [bu (50 lb)] per 1000 ft2] on ‘Covington’ and ‘Evangeline’ slip production in propagation beds. Another field study was conducted in 2012 and 2013; treatments included canner, no. 1, and jumbo-size ‘Covington’ roots at 49 bu/1000 ft2, to determine the effect of seed root size on slip production. As seed root density increased in the propagation bed, transplant production increased with no change in slip quality as measured by node counts and slip length except for stem diameter. In 2012, the best marketable slip yield was obtained at root densities of 73 and 85 bu/1000 ft2. In 2014, marketable slip production of ‘Evangeline’ increased as seed root density increased at a greater rate than ‘Covington’. In 2014, the best seed root density for marketable slip production was 49 to 85 bu/1000 ft2 for ‘Covington’ and 85 bu/1000 ft2 for ‘Evangeline’. In 2012, potential slip revenues increased with an increase in seed root density up to 73 bu/1000 ft2. In 2014, revenue trend was similar for ‘Covington’ as 2012; however, for ‘Evangeline’, revenue was greatest at 85 bu/1000 ft2. Seed root size had no effect on marketable slip production when using a once-over harvest system. Results suggest growers would use a seed root density from 49 to 85 bu/1000 ft2 depending on variety, and any size roots for production of optimum marketable slips. Selection of optimum seed root density also depends on grower needs; e.g., high seed root density strategy will have a higher risk due to the upfront, higher seed costs, but potentially have higher profits at harvest time. Lower seed root density strategy would be a lower initial risk with a lower seed cost, but also potentially have lower net revenues.

Semi-sterilized Tissue Culture for Rapid Propagation of Grapevines (Vitis vinifera L.) Using Immature Cuttings

Rapid expansion of grapevine plantings in many parts of the world has led to increased demand for desirable planting stocks. In countries that rely on importing new varieties and have strict quarantine rules, such as Australia, vines need to stay under quarantine for ≈2 years before they are released, at which time there is very limited wood available. Hence, rapid expansion of propagating stock after release is the key to multiplying up new varieties. A novel method, referred to as Semi-sterilized Tissue Culture (SSTC) using immature single-node cuttings, was established and evaluated as a way of rapid expansion of grapevine (Vitis vinifera L.) planting stock. In the SSTC method, immature single-node cuttings were surface-sterilized using methylated spirits and then cultured in the root pulsing medium [1/2 Murashige and Skoog (MS) medium supplemented with 40 μM indole-3-butyric acid (IBA)] for 24 hours. They were then planted in sterilized aerobic rooting medium (sphagnum peat:coarse river sand:perlite = 0.5:1:2) and cultured in a tissue culture room for ≈4 weeks for root initiation and development. The rooted immature single-node cuttings were then transferred to normal propagation beds in a greenhouse and potted on for acclimatization. Tube stock generated by SSTC easily acclimatized with a 15 times higher root strike rate than cutting propagation. It also took at least 50% less time than fully sterilized micropropagation methods to produce planting stocks. The advantages of the SSTC method are that it can be conducted under semisterilized conditions, avoiding degeneration and bacterial contamination problems encountered in micropropagation methods. By removing the time-consuming steps of the explant establishment, proliferation, and maintenance in vitro, the propagation process was simplified compared with conventional sterile tissue culture procedures. The SSTC procedure removed the need for high operator skill levels, reducing expense and allowing easier commercial adoption.

Efficacy of Vapam fumigant against clubroot (Plasmodiophora brassicae) of canola

Clubroot, caused by Plasmodiophora brassicae, has become a serious threat to canola (Brassica napus) production in western Canada. Experiments were conducted under greenhouse and field conditions to assess the effect of Vapam fumigant (dithiocarbamate; sodium N‐methyldithiocarbamate) on primary and secondary infection by P. brassicae, clubroot severity, and growth parameters in canola. Preliminary trials showed a 12–16‐fold reduction in primary and secondary infection and clubroot severity at all of the Vapam application rates (0·4–1·6 mL L−1 soil) assessed. Vapam was also found to be effective in reducing clubroot severity and improving seed yield of canola under field conditions. Application of Vapam at soil moisture levels in the range of 10–30% (v:v) had a large effect on both disease severity and infection rates and plant growth parameters. The results suggest that Vapam can effectively reduce clubroot severity and may be useful for the treatment of transplant propagation beds in brassica vegetable production, and for the containment of small, localized clubroot infestations in commercial canola crops.

Pulsed electromagnetic fields effect in oregano rooting and vegetative propagation: A potential new organic method

Many types of magnetic fields have already been investigated in order to find new methods to enhance plant growth. This study reports the positive effect of pulsed electromagnetic field on the main root characteristics (fresh weight, dry weight, root surface and length) of unrooted oregano stem cuttings. For oregano, vegetative propagation is commonly used, with rooted or unrooted stem cuttings, because seed propagation is not suggested for commercial cultivation. Oregano seeds are very small and, thus, difficult to handle. Vegetative reproduction in organic cultivation faces the ethical problem of the use of hormones to induce the rooting process in propagation beds. The purpose of this study was to determine if magnetic field can replace hormones in plant propagation and what the results of the combination of both magnetic field and hormones would be. Two types of stem cuttings were used (apical and middle) and the experiment was established in two different seasons (spring and autumn). The findings showed that magnetic field alone stimulates the rooting process in plant material, with results similar to or even statistically significantly better than those obtained using hormones. However, the combination of magnetic field and hormones resulted in measurements statistically significantly lower than with magnetic field alone. Such methods can potentially be useful for plant materials growers, providing better oregano seedlings, especially in organic farming, where chemical compounds are forbidden.

Visual inspections of nursery stock fail to protect new plantings from Blueberry scorch virus infection

Blueberry scorch virus (BlScV) is one of the most pervasive pathogens of highbush blueberry. The virus is aphid-vectored and exhibits a latent period between infection and symptom expression in the host plant of up to 5 years. In many cases, we have observed BlScV symptom expression in new fields that appears inconsistent with aphid-vectored introduction and spread. It was, therefore, speculated that the virus may be introduced through infected nursery stock. To examine this possibility, we first surveyed selected nurseries to determine if mother plants, used for propagation by cuttings, were BlScV-infected. Two nurseries were found to harbor symptomless, infected, mother plants (cv. Duke). Cuttings from one nursery were collected from infected and non-infected plants and rooted in propagation beds. The survival and infection of cohorts from each mother plant were determined one year after planting. A significantly greater proportion of cuttings survived from non-infected mother plants (0.7) than from infected mother plants (0.5). Of the cohort from infected mother plants that survived, 40% tested positive for BlScV. We also surveyed the distribution of infected, symptomatic plants in recent ‘Duke’ plantings that originated from nurseries with BlScV-infected mother plants and compared distribution with older plantings with more advanced BlScV outbreaks. In all cases, the distribution of BlScV symptom development in young fields was random, which is consistent with introduction from planting stock. Older plantings showed a strong clustered distribution, which is consistent with aphid transmission. This study identifies infected nursery stock as an important source of BlScV dissemination and underscores the importance of having symptomless mother plants virus tested.

Storage Does Not Influence Steryl Glucoside Concentration in Cycas micronesica Seeds

The concentration of two steryl glucosides and their sterol precursors were measured in gametophyte tissue of Cycas micronesica K.D. Hill seeds before and after two storage treatments. For one study, intact 14-month-old seeds were stored at room temperature for 10 months. For the second study, cleaned (sarcotesta tissue removed) 22-month-old seeds were sown in perlite propagation beds, and ungerminated seeds were harvested after 14 months. Concentration of the steryl glucosides and sterols in the gametophyte tissue did not differ between the fresh seeds and the seeds after storage. The function of these metabolites is not known, but their unexpected stability for up to 14 months of storage indicates they are not metabolized during storage and may be vital during germination and early seedling growth. Implications on human exposure to their neurotoxic effects from gametophyte flour ingestion are discussed.

Regeneration of Mugwort (Artemisia vulgaris) from Rhizome Sections in Sand, Pine Bark, and Soil Substrates

Abstract Regenerative potential of mugwort (Artemisia vulgaris L.) rhizome sections has not been quantified when rhizomes are transplanted into substrates encountered in landscapes and nursery fields, container nurseries, or propagation beds. Mugwort regeneration in pine bark, sand, and soil substrates was analyzed by rhizome color, length, and the presence or absence of a leaf scale. Color of rhizomes, which darken with time, did not account for differences in growth among treatments. Contrary to previous research, 85, 78, and 69% of 2 cm-long rhizome sections produced both roots and shoots when grown in pine bark, sand, and soil substrates, respectively, during 45-day trials. Slightly less than 31% of rhizome fragments 0.5 cm long without a leaf scale produced both roots and shoots in soil. Though fewer rhizomes survived in soil, root and shoot fresh weights were greater than in pine bark and sand. When rhizome sections included a leaf scale, survival, fresh weights of roots and shoots, shoot height, leaf number and root lengths were greater, regardless of substrate type. Root initials emerged both adjacent to leaf scales and in the internode between leaf scales. Shoot emergence preceded root emergence from rhizome sections.

Mugwort (Artemisia vulgaris) Rhizome Regeneration in Pine Bark, Soil and Sand Substrates

Mugwort, or false chrysanthemum (Artemisia vulgaris L) is a well-adapted invasive plant that presents increasing management challenges to agricultural producers, Green Industry professionals and homeowners across portions of the eastern U.S. The ability of mugwort to regenerate from cut rhizome sections has not been adequately quantified for substrates that are typical of landscapes and nursery fields, container nurseries, and propagation beds. Cut rhizome sections were analyzed by rhizome color, length, and the presence or absence of a leaf scale. Media substrates included pine bark, sand, and soil. Rhizomes darken with time and color did not account for differences in growth among treatments. When grown in pine bark, sand, and soil substrates during 45-d trials, 85%, 78%, and 69% of 2 cm-long rhizome sections produced both roots and shoots. These results contrast with previous research. When rhizome fragments 0.5 cm long did not include a leaf scale, slightly fewer than 31% produced both roots and shoots in soil. Fewer rhizomes survived in soil, but root and shoot fresh masses of soil-grown rhizomes were greater than rhizomes that were regenerated in pine bark and sand. When rhizome sections had a leaf scale, survival, fresh masses of roots and shoots, shoot height, leaf number and root lengths were greater, regardless of substrate type. Root initials emerged in the internode between leaf scales and also adjacent to leaf scales. Shoot emergence preceded root emergence from rhizome sections. Growers, landscape managers and homeowners should scout regularly and initiate aggressive controls when mugwort populations are found.

Fungal Pathogens Associated with Blueberry Propagation Beds in North Carolina

SUMMARY Death of blueberry cuttings in commercial rooting beds was observed due to abiotic and biotic causes. Abiotic causes included poor watering practices, water quality, rooting medium, and inadequate drainage due to poor rooting bed design. Biotic causes were attributable to fungi and included (1) non-pathogenic Basidiomycetes colonizing unsterilized rooting media, (2) airborne or rain-splashed pathogens infecting individual cuttings (Botryosphaeria, Pestalotia and other sp.), and (3) Cylindrocladium sp. that spread radially from the initial infection, producing circular dead spots in rooting beds. Re-use of Cylindrocladium-infested media resulted in complete loss of cuttings. Methyl bromide fumigation was successfully used to sanitize infested media.

Chlorophyll Fluorescence and Vegetative Propagation of Taxus

Chlorophyll fluorescence over the course of stem cutting propagation was examined in 10 cultivars of Taxus ×media (Taxus baccata L. × T. cuspidata Sieb. & Zucc.), including `Brownii', `Dark Green Pyramidalis', `Dark Green Spreader', `Densiformis', `Densiformis Gem', `Hicksii', `L.C. Bobbink', `Runyan', `Tauntoni', and `Wardii'. The fluorescence value measured was the ratio of variable over maximum chlorophyll fluorescence (Fv/Fm). This value reflects the maximum dark-adapted photochemical efficiency of photosystem II (PSII) reaction centers involved in photosynthesis and is an indirect measure of plant stress. The objective of this study was to examine Fv/Fm as a method for stock plant selection and for monitoring rooting progress of various cultivars. Fv/Fm varied significantly (P ≤ 0.05) among cultivars, initially and over time. However, there was significant overlap among some cultivars. The Fv/Fm decreased dramatically during cold storage, but usually returned to original levels after several weeks in the propagation beds. This appeared to be a reflection of the reduction of water stress as the cuttings formed roots. Initial stock plant Fv/Fm was not correlated (P ≤ 0.05) with rooting percentage, root number, root dry weight, or root length, indicating that Fv/Fm is not a reliable indicator of stock plant rooting potential. Visual assessment is just as reliable.

336 A Comparison of Virus-free Versus Infected Sweetpotato Transplants for Cutting Propagation

Production of disease-free sweetpotato [Ipomoea batatas (L.) Lam.] transplants is of major importance to certified and foundation seed programs and producers. Sweetpotato roots are traditionally planted and cuttings are harvested from propagation beds. The objective of this study was to investigate the efficiency of producing cuttings in nursery containers. Virus-tested and virus-infected `Beauregard' sweetpotato transplants were harvested from planting beds for the purpose of producing cuttings for transplants. Cuttings were established in 3.7-L plastic nursery containers filled with 100% pine bark amended with either low, medium, or high rates of Osmocote 14-14-14 and dolomitic lime. Resulting transplants produced a greater number of cuttings and greater plant biomass with higher fertilizer rates. Increasing fertilizer rates also had a positive effect on cutting production and biomass. Dry weight and stem growth were similar for both virus-infected and virus-tested transplants following first and second harvests. Producing foundation cuttings in nursery containers filled with a pine bark medium proved to be an efficient method of increasing virus-tested sweetpotato cuttings.

Variability of Clonal Selections of Poinsettia `Eckespoint Monet'

The introduction of poinsettia (Euphorbia pulcherrima) cultivar Eckespoint Monet in 1994 provided a novelty bract color that promised to be a welcome addition to the array of poinsettia colors available. The light tan bracts of `Monet' are splashed with flecks of medium rose, with the flecks concentrated on the margins. In warm growing areas, the bracts' base color appears faded and the rose flecks are not intense, which delays time to market and reduces consumer acceptance. Plants with darker rose flecks were observed in 1994 and clonal selections were saved that had a range of very light to very dark rose flecks. Further selections within these clones were made in 1995 based on bract color and consistency. A cultivar trial in 1996 evaluated 26 of these clones compared to the true `Monet' and a `Dark Monet' from the Ecke Ranch. Single plants were grown in 20-cm containers and pruned twice. Data were recorded on plant height and diameter, days to first bract color, marketable, and anthesis, the percentage of mutant laterals, and bract color. Plant height and diameter and days to anthesis were not significantly different among the selections but the clones with darker bracts were marketable up to 5 days earlier than `Monet'. Selections with darkest rose flecks occasionally mutated to solid red but these laterals could be easily rogued in propagation beds by using the dark red petioles as a selection criterion. These selections can be too dark when grown in cool climatic areas but are more intense and acceptable in warm regions of the United States.

Phormium Yellow Leaf Phytoplasma Is Associated with Strawberry Lethal Yellows Disease in New Zealand

A yellows disease of strawberry plants was identified in propagation beds in New Zealand. Affected plants were flatter to the ground, showed purpling of older leaves, reduced leaf size, yellowing of younger leaves, and sometimes plant death. A phytoplasma was observed in the phloem of affected plants. The 16S rRNA gene of the phytoplasma was amplified by polymerase chain reaction from symptomatic plants and from one asymptomatic plant, but not from 36 other asymptomatic plants. Nucleotide sequence analysis of the 16S rRNA gene showed that the phytoplasma is closely related or identical to the phytoplasma associated with the yellow leaf disease of New Zealand flax (Phormium tenax).