Variegation in Vitis hybrids was investigated to confirm the inheritance as a single, recessive gene as previously proposed and commonly observed in breeding programs. Variegated leaves have ornamental appeal, but the phenotype is sublethal in some environments. Twenty-nine grape families were characterized for variegation including F1, S1, and S2 populations. The majority segregated 3 wild type (WT):1 variegated and were supported by chi-square tests. Four populations had segregation ratios supporting 15:1 or 1:1 models, and a unique flecking phenotype was identified in a Landot 4511 S1 population that suggested the interaction of two recessive loci. A variegated parent was selfed to produce progeny with no WT offspring and was segregated 0:1. Marker trait associations including bulk segregant analysis (BSA), genome-wide association mapping, and quantitative trait loci (QTL) mapping was used on three populations. On chromosome 14, Lvar1 was identified and mapped to 24.5 to 29.5 Mb and associated closely with rhAmpSeq marker 14_27607541. Lvar2 was associated with rhAmpSeq marker 11_18433819 on chromosome 11 at 12.2 to 18.4 Mb. The identification of two loci and the segregation data in some populations suggest that grape breeding germplasm segregates for two recessive loci. The pedigree records suggest that ‘Frontenac’ inherited one of these loci, and that Landot 4511, an ancestor of many populations tested in this experiment, may carry two loci. A total of 252 candidate genes were identified at these loci, including a key target—adenosine triphosphate (ATP)-dependent zinc metalloprotease FtsH6, involved in photosystem II and similar to the var2 mutant in Arabidopsis. This knowledge can help breeders select for ornamental grapevines or eliminate variegation from their breeding programs.
Jack Olson, Cheng Zou, Avinash Karn, Bruce Reisch, Lance Cadle-Davidson, Qi Sun, and Matthew Clark
Yi-Xing Hou, Yi-Shan Hu, Chia-Min Chen, and How-Chiun Wu
This study investigated the effects of different sucrose, ventilation, and paclobutrazol (PBZ) treatments on the growth of potato plantlets cultured in modified temporary immersion culture vessels. Temporary immersion culture vessels were modified to enable the plantlets to be cultured on semi-solid growth medium and provided with forced ventilation. The plantlet responses to two sucrose concentrations (15 g⋅L−1 and 30 g⋅L−1) in combination with two forced ventilation treatments (5 min/2 h and no ventilation) and three PBZ concentrations (0, 0.2, and 0.4 mg⋅L−1) were studied. Shoot growth was severely inhibited by PBZ in the growth media, whereas leaf formation was promoted by ventilation irrespective of the PBZ concentration. In nonventilated vessels, it is noteworthy that PBZ was able to increase the number of leaves formed in plantlets grown on medium supplemented with 30 g⋅L−1 sucrose, but not on medium with 15 g⋅L−1 sucrose. In growth media without PBZ, a high percentage of potato plantlets was able to produce secondary axillary shoots when provided with 30 g⋅L−1 sucrose. However, their ability to produce secondary shoots was reduced when PBZ was included in the growth medium, particularly those with 15 g⋅L−1 sucrose. Plantlets grown in ventilated culture vessels combined with 30 g⋅L−1 sucrose in the growth medium produced more than three times more shoots than the other treatments. Under ex vitro conditions, plantlets that had been grown in ventilated vessels had fewer leaf deaths, and the inclusion of PBZ in the growth media further reduced the number of dead leaves. Findings of this study showed that PBZ had a key role in the responses of potato plantlets to ventilation and sucrose treatments, as well as their tolerance to ex vitro conditions. The modified temporary immersion system can be used for the in vitro culture of potato plantlets on semi-solid medium and provide forced ventilation to improve their growth.
Alessandra Carrubba, Roberto Marceddu, and Mauro Sarno
Humulus lupulus is a dioecious twining herb, with an outstanding vertical development capacity. Hop plants are usually grown on trellises up to 4.5 to 6.0 m high, whose management requires intense use of water, fertilizers, pesticides, and labor. In semiarid Mediterranean areas, where native resources are often scarce, the adoption of low-trellis farming systems could be a sustainable option for hop cultivation. With the aim of evaluating hop suitability to low-trellis cultivation in a Mediterranean environment, in 2018 and 2019 three traditional hop genotypes (‘Cascade’, ‘Chinook’, and ‘Nugget’) were grown, and their development rate was evaluated and put in relation with the plants’ cone, root, and biomass yield. Moreover, organic (fragmented pine bark) and synthetic [black polyethylene (PE) plastic film] mulches were applied on the same cultivars, and both epigeal and hypogeal development were evaluated. The results showed that the faster the growth in the first two phases of plant elongation (up to 50% of the height of the upper wire), the lower the yield in both cones and total epigeal biomass. A fast growth rate was instead associated with a higher hypogeal biomass production. Mulching was able to significantly affect the hypogeal biomass, specifically for cv. Cascade, where the use of synthetic mulching allowed significant root biomass increases. The analysis of the results obtained showed that hop’s suitability to a low-trellis farming system is highly variable among varieties in the semiarid Mediterranean environment.
Qin Yang, Yan Fu, Tingting Zhang, Shu Peng, and Jie Deng
MicroRNAs (miRNAs) related to phytohormone signal transduction and self-incompatibility may play an important role in the xenia effect. However, associated research in this area is still lacking in rabbiteye blueberry (Vaccinium ashei). In this study, we identified miRNAs, predicted their target genes, performed functional enrichment analysis of the target genes, and screened for miRNAs related to phytohormone signaling and self-incompatibility. A total of 491 miRNAs were identified, of which 27 and 67 known miRNAs as well as 274 and 416 new miRNAs were found in the rabbiteye blueberry cultivars Brightwell and Premier, respectively. Compared with ‘Premier’, 31 miRNAs were upregulated and 62 miRNAs were downregulated in ‘Brightwell’. Kyoto Encyclopedia of Genes and Genomes (KEGG) functional enrichment analysis indicated that the 4985 target genes predicted were involved in biosynthesis of amino acids, plant–pathogen interaction, and spliceosome pathways. A total of 10, one, one, five, two, five, and two candidate miRNAs related to auxin, cytokinin, gibberellin, abscisic acid, ethylene, brassinosteroid, and salicylic acid signaling, respectively, in rabbiteye blueberry pollen were identified. Further analysis indicated that novel_miR_49 was a candidate miRNA related to self-incompatibility, and their target gene was maker-VaccDscaff21-snap-gene-21.37. In addition, the KEGG enrichment analysis of the target genes of novel_miR_49 showed that they were involved in the ribosome, aminoacyl-tRNA biosynthesis, and glycosylphosphatidylinositol-anchor biosynthesis pathways. The results revealed that the microRNAs of rabbiteye blueberry pollen regulated to phytohormone signal transduction and self-incompatibility signal transduction based on related to auxin, cytokinin, gibberellin, abscisic acid, ethylene, brassinosteroid, and salicylic acid signaling. Results suggest that more research of the effects of miRNAs on regulation of hormone signal transduction and self-incompatibility is necessary for elucidating the molecular mechanism of the xenia effect.
David P. Leon-Chang, David R. Bryla, Carolyn F. Scagel, and Bernadine C. Strik
Although northern highbush blueberry (Vaccinium corymbosum L.) fields are often fertigated using soluble or liquid fertilizers, recommendations for applying most nutrients to the crop, including K, are based on the use of granular fertilizers. The objective of the present study was to compare fertigation to granular application of K in a mature planting of Duke, a popular early season blueberry cultivar that ripens from June through July in Oregon and Washington. The plants were grown on raised beds and irrigated using two lines of drip tubing per row. Treatments were initiated in 2016 and included no K fertilizer, a single application of granular potassium sulfate (K2SO4) in April, and fertigation once a week from April to August with soluble K2SO4 or liquid potassium thiosulfate (K2S2O3). Each treatment was applied for 2 years at a total rate of 70 kg·ha−1 K per year. The plants were also fertigated with 168 and 224 kg·ha−1 N in 2016 and 2017, respectively, and 30 kg·ha−1 P per year. Although extractable soil K was initially low at the site (144 mg·kg−1), the treatments had no effect on plant dry weight, yield, fruit quality, or the concentration of K in recently expanded leaves. However, during the first year of the study, K fertigation with K2SO4 or K2S2O3 reduced soil pH and increased the concentrations of K+, Ca2+, Mn2+, and SO4 2− in the soil solution under the drip emitters compared with no K or granular K2SO4, whereas granular application of K2SO4 resulted in higher concentrations of K+ between the emitters than any other treatment. Fertigation also affected the concentration of K in the fruit during the first year, although in this case, the concentration was lower with K fertigation than with no K or granular applications of K2SO4. During the second year, fertigation and granular K continued to result in higher concentrations of K+ in soil solution under and between the drip emitters, respectively, but at this point, extractable soil K was higher with each of the K fertilizers than with no K. Consequently, the concentration of K in leaves sampled from entire plants in late September that year was higher with any of the K fertilizers than with no K. Potassium fertilization also altered concentrations of other nutrients in the plants, including Mg, S, B, Cu, and Mn in the leaves; Ca, Mg, and B in the fruit; Mn and Zn in the woody canes; and P, Mg, S, and Mn in the crown. In many cases, concentrations of these nutrients were higher with one or more of the K fertilizers than with no K. Thus, regardless of the application method, K2SO4 and K2S2O3 appear to be good sources for increasing availability of K and other nutrients in the plants and soil. However, the amount of K in the plants was sufficient at the site, and therefore, none of the fertilizers provided a short-term benefit to growth or fruit production in the present study.
Yen-Hua Chen and William B. Miller
Water uptake is a critical issue for postharvest physiology of cut flowers. After harvest, cut flowers lose access to water from roots and sometimes develop emboli inside the xylem, which can disrupt water uptake and undermine flower longevity. The duration of dry storage (desiccation) before flowers are placed in a vase may affect rehydration capability. Despite the appreciated importance of desiccation time on water balance, the duration of desiccation that might cause irreversible damage in Lilium sp. L. is unknown. Therefore, we investigated effects of pre-vase dehydration on water uptake and postharvest quality of cut lilies. Stems of Lilium ‘Nashville’, ‘Santander’, and ‘Sorbonne’ were subjected to 0, 8, 24, or 48 hours of dehydration at 20 °C, then rehydrated in a solution containing 2% sucrose and a biocide. Water uptake in the first 24 hours of rehydration was significantly greater in dehydrated stems than in control (0 hour) stems. Although dehydration treatments increased water uptake in the first 24 hours after rehydration, total water uptake in dehydrated stems over the ensuing 9- to 10-day vase period was significantly less than in controls. In the vase, 48 hours of dehydration reduced the total water uptake in ‘Nashville’ by 27% and in ‘Sorbonne’ by 48%. Individual flower life and stem vase life were not affected significantly by dehydration treatment; however, ‘Sorbonne’ stems dehydrated for 24 or 48 hours had smaller flowers than controls and those that underwent the 8-hour dehydration treatment. ‘Nashville’ stems dehydrated for 24 hours showed visible leaf yellowing 3 days earlier than controls; ‘Sorbonne’ dehydrated for 48 hours showed leaf yellowing 2 days earlier. We conclude cut lilies have an ability to recover partially from significant dehydration and can restore water uptake initially, but pre-vase dehydration reduces total water uptake and affects some postharvest attributes negatively.
Clinton C. Shock, Erik B. G. Feibert, Alicia Rivera, and Kyle D. Wieland
Onion (Allium cepa L.) bulbs produced in the Pacific Northwest of the United States in 2014 and 2015 had unusually high incidence of internal decay. This decay was not detectable externally, leading to marketing problems when bulbs were packed and shipped to markets. The onion growing seasons in 2014 and 2015 were unusually hot, suggesting a connection of heat stress to bulb internal decay. Field studies to investigate the effect of temperature on onion bulb internal decay and yield were conducted in 2016–18 with drip-irrigated onions at the Oregon State University, Malheur Experiment Station located in eastern Oregon. Two long-day onion cultivars were submitted to four cultural practice variations to affect soil and bulb temperatures: bare soil check, supplemental heat using electric heat cables, white kaolinite clay application to the bulb sides and soil surface, and wheat (Triticum aestivum L.) straw mulch. The treatments established significant midafternoon average bulb and soil surface temperature gradients in the following order of increasing temperature: straw mulch, kaolinite, check, and supplemental heat. Averaged over years and cultivars, straw-mulched onions had the highest yield of bulbs larger than 102 mm diameter. Averaged over years and cultivars, onions receiving supplemental heat had the lowest total and marketable yield with no difference among the other treatments. Straw mulched onions had higher total and marketable yield than the bare soil check treatment in 2017, the hottest year. Averaged over the 3 years and two cultivars, marketable yield and yield of bulbs larger than 102 mm diameter decreased with increasing midafternoon bulb temperatures. Kaolinite application did not increase bulb yield nor bulb size compared with the bare soil check. The incidence of internal bulb decay was low all 3 years. In 2017, onions receiving supplemental heat had the highest internal decay and the straw-mulched onions had among the lowest internal decay. There was little difference in the measured soil moisture among treatments. Straw mulching may attenuate the negative effects of excessive heat on yield and bulb internal quality for long day onion production.
Chi D. Nguyen, Matthew Creech, Diying Xiang, German Sandoya, Dean Kopsell, and Heqiang Huo
Lettuce (Lactuca sativa L.) is one of the most consumed fresh vegetables in the United States. However, lettuce production is heavily limited to California and Arizona, posing a high risk to the supply chain. Hydroponic production is a soilless cultivation method and provides a sustainable alternative to growing lettuce in the field. Light is a critical factor in plant development, and light quality highly affects plant morphogenesis. The goals of this study were 2-fold, with the first to investigate the growth of 26 lettuce cultivars under a hydroponic system supplemented with fluorescent light to determine adaptability. Subsequently, the second goal was to determine how light-emitting diodes (LEDs) affect lettuce plant morphology and photosynthesis compared with fluorescent light for four lettuce cultivars. Results showed that 23 of 26 lettuce cultivars were grown successfully using a hydroponic system. However, lettuce grown under fluorescent light experienced stem elongation—a morphological response to low-light conditions known as shade avoidance syndrome. Stem elongation decreased significantly under LED light, whereas other morphological characteristics remained relatively the same between the two light treatments. Although there were no differences in dry weight and leaf area, the carbon assimilation rate increased significantly in lettuce cultivars Coastal Star, Muir, Green Butter, and Rouge d’Hiver when treated with LED light. Correspondingly, intercellular carbon dioxide (CO2) decreased in these four lettuce cultivars under the LED light treatment. Our study results indicate that LED light increased photosynthetic activity and reduced stem elongation to enhanced lettuce quality.