There is demand for micropropagated Cannabis sativa liner plants, because they are uniform, vigorous, and pathogen free; however, availability is limited because of challenges with in vitro culture decline and ex vitro rooting. Ex vitro rooting success of microcuttings was evaluated for ‘Abacus’ and ‘Wife’ when cultures were 6, 9, 12, 15, and 18 weeks old from initiation. Microcuttings of ‘Wife’ harvested from 6, 9, and 12-week-old cultures rooted at or above 80%, but rooting declined to 50% and 30% for 15- and 18-week-old cultures, respectively. Rooting for ‘Abacus’ remained relatively constant between 47% and 70% for microcuttings harvested from 6- to 18-week-old cultures. ‘Wife’ plants grown from microcuttings, stem cuttings, and retip cuttings (cuttings taken from new shoots on recently micropropagated plants) had equivalent total shoot length, number of shoots, and flower dry weight, whereas micropropagated ‘Abacus’ plants had less shoot length and flower dry weight than plants from stem cuttings. However, when micropropagated ‘Abacus’ plants were provided an extra week of vegetative growth to reach an initial size equivalent to stem and retip plants, all plants performed the same. Propagation method did not change cannabinoid content for both ‘Abacus’ and ‘Wife’. Retip cuttings of ‘Abacus’ and ‘Wife’ rooted at 76% to 81% without rooting hormone, which is comparable to rates reported for stem cuttings of C. sativa treated with rooting hormone. Propagators should consider retipping to expand their liner production, because retips root well and possess the same desirable attributes as micropropagated plants.
Lauren E. Kurtz, Lillian N. Borbas, Mark H. Brand, and Jessica D. Lubell-Brand
Muhammad S. Islam, Alessio Scalisi, Mark Glenn O’Connell, Peter Morton, Steve Scheding, James Underwood, and Ian Goodwin
Automatic in-field fruit recognition techniques can be used to estimate fruit number, fruit size, fruit skin color, and yield in fruit crops. Fruit color and size represent two of the most important fruit quality parameters in stone fruit (Prunus sp.). This study aimed to evaluate the reliability of a commercial mobile platform, sensors, and artificial intelligence software system for fast estimates of fruit number, fruit size, and fruit skin color in peach (Prunus persica), nectarine (P. persica var. nucipersica), plum (Prunus salicina), and apricot (Prunus armeniaca), and to assess their spatial and temporal variability. An initial calibration was needed to obtain estimates of absolute fruit number per tree and a forecasted yield. However, the technology can also be used to produce fast relative density maps in stone fruit orchards. Fruit number prediction accuracy was ≥90% in all the crops and training systems under study. Overall, predictions of fruit number in two-dimensional training systems were slightly more accurate. Estimates of fruit diameter (FD) and color did not need an initial calibration. The FD predictions had percent standard errors <10% and root mean square error <5 mm under different training systems, row spacing, crops, and fruit position within the canopy. Hue angle, a color attribute previously associated with fruit maturity in peach and nectarine, was the color attribute that was best predicted by the mobile platform. A new color parameter—color development index (CDI), ranging from 0 to 1—was derived from hue angle. The adoption of CDI, which represents the color progression or distance from green, improved the interpretation of color measurements by end-users as opposed to hue angle and generated more robust color estimations in fruit that turn purple when ripe, such as dark plum. Spatial maps of fruit number, FD, and CDI obtained with the mobile platform can be used to inform orchard decisions such as thinning, pruning, spraying, and harvest timing. The importance and application of crop yield and fruit quality real-time assessments and forecasts are discussed.
Bruce L. Dunn, Carla Goad, and Lynn Brandenberger
Uniconazole is approved for use as a chemical option on tomato (Solanum lycopersicum) for height control, but research is limited. In this study, 12 tomato cultivars were chosen with three cultivars each of indeterminate, determinate, heirloom, and container types. Plants were sprayed with a one-time application of 0, 2.5, 5, 7.5, or 10 mg⋅L–1 of uniconazole during the two- to four-leaf stage to evaluate height control. Results indicated no significant difference between concentrations for plant height, stem caliper, and plant dry weight. The greatest soil plant analysis development (SPAD) values were observed with the 10-mg⋅L–1 treatment. Flower response in ‘Brandywine’ to a single application of 0, 2.5, or 5 mg⋅L–1 of uniconazole demonstrated a greater number of flowers per plant at 5 mg⋅L–1, whereas no significant difference was shown for the number of flower clusters or the number of flowers per cluster at other treatment levels. Using 2.5 mg⋅L–1 uniconazole was effective for reducing plant height across all cultivars of greenhouse-grown tomato seedlings compared with the control, whereas addition of 5 mg⋅L–1 was shown to increase the number of flowers in the heirloom cultivar Brandywine.
Ricardo Goenaga, Angel Marrero, and Delvis Pérez
Little is known about the adaptability of lychee (Litchi chinensis) to acidic soils high in aluminum (Al). A 2-year greenhouse study was conducted to determine the effects of various levels of soil Al on dry matter production, plant growth, and nutrient concentration in shoots of lychee cultivar rootstock seedlings (maternal half-sibs) of cultivars Brewster, Bostworth-3 (Kwai May Pink), and Kaimana. Soil Al treatments were statistically different for all variables measured in the study but not rootstock seedlings. Total leaf, stem, and root dry weights significantly decreased at soil Al concentrations ranging from 0.42 to 12.69 cmol·kg−1. Increments in soil Al resulted in a significant reduction in the concentration of leaf calcium and phosphorus and a significant increase in leaf Al in cultivar rootstock seedlings. The concentration of leaf potassium, magnesium, iron, zinc, and boron were in the optimum range for lychee, whereas leaf nitrogen and manganese concentrations were above optimum. The results of this study demonstrated no cultivar rootstock seedlings differences for dry matter production in lychee trees grown under Al stress and demonstrate that lychee is highly susceptible to acid soils.
Ehtisham S. Khokhar, Dennis N. Lozada, Amol N. Nankar, Samuel Hernandez, Danise Coon, Navdeep Kaur, and Seyed Shahabeddin Nourbakhsh
Fruit architecture and morphology-related traits are among the determinants of fruit diversity and are major contributors to yield and yield potential in chile pepper (Capsicum spp.). This study aimed to characterize 105 genotypes of a Capsicum diversity panel consisting of cultivars, breeding lines, landrace, and wild species belonging to twelve different pod (fruit) types, for 32 morphometric Tomato Analyzer (TA) descriptors. Hierarchical cluster analysis grouped the genotypes into eight clusters based on the TA descriptors. A multivariate principal component analysis yielded two principal components, PC1 and PC2, which explained 53.24% and 10.11% of the variation in fruit diversity, respectively. The basic measurements—namely, perimeter, area, width midheight, maximum width, height midwidth, maximum height, and curved height were the most discriminating descriptors with a maximum contribution to the overall fruit shape. There was a strong, positive correlation for basic measurements and fruit shape index, whereas blockiness was negatively correlated with distal angle macro. Additive genetic effects and high heritability for the fruit traits were observed. Results of this study will provide valuable information to breed high-yielding chile pepper cultivars based on fruit morphology traits.
Ping Yu and Stephen Christopher Marble
Pennsylvania bittercress (Cardamine pensylvanica) and other bittercress (Cardamine) species are among the most common and difficult-to-control weed species in container nurseries, and they have been vouched in most counties in Florida. Preemergence herbicides can provide control, but concerns over potential resistance development, environmental issues, and crop injury problems associated with herbicide use create the need for alternative weed control methods to be explored. Previous studies have shown the potential of mulch materials for controlling weeds in nurseries, but their use along with preemergence herbicides has not been extensively investigated. To compare the effects of different mulch materials and herbicides on Pennsylvania bittercress control, a full factorial designed greenhouse study was conducted. Three mulch treatments including no mulch, pine (Pinus sp.) bark, and rice (Oryza sativa) hulls were evaluated with three herbicide treatments, including water (i.e., no herbicide), isoxaben, and prodiamine applied at label rates. Twenty-five seeds of Pennsylvania bittercress were sown on the surface of each container and emergence (percent), coverage (square centimeters), seedhead number, and biomass (grams) were measured. The results showed that Pennsylvania bittercress in containers mulched with rice hulls had the lowest emergence throughout the experiment. For coverage, seedhead, and biomass parameters, Pennsylvania bittercress seeded in rice hulls treatments had significantly lower coverage, fewer seedheads, and lower biomass compared with those in nonmulched or pine bark treatments, regardless of herbicide treatment. With isoxaben and the water check, nonmulched treatments had the highest coverage/seedhead/biomass, whereas with prodiamine, Pennsylvania bittercress in pine bark mulched containers had the highest coverage/seedhead/biomass. In conclusion, applying rice hulls alone can provide better Pennsylvania bittercress control compared with isoxaben or prodiamine applied alone.
Kimberly Moore, Cristina Burgart, Samar Shawaqfeh, Luci Fisher, and Mica McMillan
Growers have different capabilities to alleviate salt stress in the growing substrate. One method to reduce substrate salt levels is to increase the volume of water applied during irrigation. This increases the leaching fraction (LF) which is the volume of water that drains from the growing substrate divided by the volume applied during irrigation. We can determine the leaching requirement (the minimum LF to maintain a desired substrate salt level) using the formula LF = ECw/5(ECe − ECw), where ECw is the electrical conductivity (EC) of the water and ECe is the desired EC of the substrate. We tested this formula to see if we could maintain an acceptable substrate EC of 4 dS⋅m−1 by modifying the LF for ‘Hope’ philodendron (Philodendron selloum) and ‘Tineke’ ficus (Ficus elastica) irrigated with tap water (EC 0.17 dS⋅m−1) or reclaimed wastewater (RWW) from Davie, FL, USA (EC 1.66 dS⋅m−1) and RWW from Hollywood, FL, USA (EC 2.93 dS⋅m−1). Shoot and root dry weight was greatest for both species with the tap water applied with a 5% LF. Increasing the LF to 15% for Davie RWW and a 55% for Hollywood RWW, produced acceptable growth for ‘Hope’ philodendron and ‘Tineke’ ficus. In our second experiment, we monitored the growth of ‘Looking Glass’ begonia (Begonia fibrous), ‘Freddie’ calathea (Calathea concinna), and ‘Déjà vu’ philodendron (Philodendron selloum) irrigated with tap water (EC 0.15 dS⋅m−1), salt water (EC 3.49 dS⋅m−1), or RWW (EC 3.48 dS⋅m−1) with LFs of 28%, 50%, or 65%. ‘Looking Glass’ begonia and ‘Freddie’ calathea growth was greater with 65% LF than 28% LF, respectively, for all three water sources. Philodendron growth was not different due to LF. However, philodendron, calathea, and begonia growth was greater with tap water and RWW than with saltwater. Although final leachate EC with saltwater and RWW was around 2 dS⋅m−1 using 50% LF, leachate sodium (Na) levels from salt watered plants was higher than for RWW or tap watered plants. We suspect that high Na levels in combination with lower potassium (K) and calcium (Ca) levels in the saltwater solution resulted in poor plant growth. Although the Na levels in leachate from RWW substrates was higher than tap watered substrates, Ca and K levels also were greater. Although we were able to use the salt equation to maintain substrate EC levels ranging from 2 to 4 dS⋅m−1, volumes of solution applied were two to three times higher when using RWW or salt water compared with tap water. We suspect that a balance between Na, Ca, and K supported better plant growth with RWW than salt water. However, additional work needs to be done on the benefits of supplemental Ca and K when using water high in salts or Na. This works suggests that in addition to monitoring EC, it also is important to monitor Na, Ca, and K concentrations.