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Ling Wang, Yu-jia Liu, Nai-xin Liu, Yue Gong, Ya-nan Li and Jing-hong Wang

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David H Suchoff, Frank J. Louws and Christopher C. Gunter

Interest and use of grafted tomato (Solanum lycopersicum) in the United States continues to grow. Pioneered in Asia, herbaceous grafting is a commonly used cultural practice to manage many soilborne pathogens. Bacterial wilt (BW), caused by the pathogen Ralstonia solanacearum, is an aggressive soilborne pathogen that affects tomato grown in the southeastern United States. Traditional fumigation methods have limited effectiveness in the management of this pathogen. The present study was conducted to compare the bacterial wilt resistance of three commercially available tomato rootstocks, which are purported to be resistant to bacterial wilt: ‘Cheong Gang’, ‘RST-04-106-T’, and ‘Shield’. The determinate hybrid tomato ‘Red Mountain’, which is susceptible to bacterial wilt, was used as the scion and nongrafted control. Three locations were used over 2 years in North Carolina: an on-farm site with a history of bacterial wilt and two North Carolina Department of Agriculture Research Stations with no recent history of bacterial wilt. No disease symptoms were observed in any of the three grafted treatments, whereas the nongrafted controls showed between 30% and 80% disease incidence at the on-farm location. The resultant rootstock-imparted resistance improved marketable yields by between 88% and 125% compared with the nongrafted plants. When grown in locations lacking BW there were no yield benefits to grafting with any of the three rootstocks.

Open access

Elsa Sánchez, Maria Gorgo-Gourovitch and Lee Stivers

Hispanics residing in the United States are playing a larger role in agriculture. For example, in Pennsylvania, this group comprises the largest increase in new farmers, according to the 2012 Census of Agriculture. Efforts to connect with this population can be improved. Hispanic farmers and farmworkers face access barriers to agricultural programming that need to be addressed to more effectively “reach and teach.” Over a 1-year period, 22 to 25 agricultural educators attended a three-workshop training series focused on increasing knowledge and skills for planning, designing, advertising, and delivering agricultural programs inviting to Hispanic farmers and farmworkers. The workshop series included an expert on the science of inclusion, a specialist in Latino community studies, and several representatives from organizations with long histories of connecting with Hispanic farming audiences. Through guided activities and facilitated discussion, participants developed strategies for creating programming welcoming to the Hispanic farming community. This workshop series was highly rated by participants. After the first workshop, one participant stated that it was the best diversity workshop he had attended in his 22-year career. In a follow-up survey 1 year after the final workshop, the majority of respondents had made efforts to build relationships through agricultural programming for Hispanic farmers and farmworkers. Here, we are providing the methods we employed to serve as a model for others working to connect with this or other underserved or nontraditional farming audiences.

Open access

Thomas O. Green, John N. Rogers III, James R. Crum, Joseph M. Vargas Jr. and Thomas A. Nikolai

Results suggest that sand topdressing was more consistent at reducing dollar spot (Clarireedia jacksonii) in fairway turfgrass more so than rolling. This practice could be an effective cost-saving alternative to reduce frequent fungicide applications. Research was conducted from 2011 to 2014 on a simulated golf fairway and examined dollar spot severity responses in a mixed-stand of creeping bentgrass (Agrostis stolonifera) and annual bluegrass (Poa annua ssp. reptans) to sand topdressing and rolling. Treatments consisted of biweekly sand topdressing, rolling at three frequencies (one, three, or five times weekly), a control, and three replications. Infection was visually estimated. Sand topdressing significantly (P < 0.05) reduced disease up to 50% at the peak of the dollar spot activity in 2011, 2013, and 2014. Results on the effects of rolling on dollar spot were inconsistent.

Open access

Shengrui Yao, Steve Guldan and Robert Heyduck

Late frost is the number one issue challenging fruit production in northern New Mexico. We had apricot (Prunus armeniaca) trees in an open field planting at Alcalde, NM, and not a single fruit was harvested from 2001 through 2014. Apricot trees in surrounding communities produce sporadic crops. In 2012, we planted apricots in two 16 × 40-ft high tunnels (9.5-ft high point). Trees were trained to a spindle system in one high tunnel and an upright fruiting offshoot (UFO) system in the other, and there were identical plantings in the open field for each high tunnel. Supplemental heating was provided starting at blooming time. There were five cultivars planted in each high tunnel at 4 × 8-ft spacing in a randomized complete block design with two replications (rows) and two trees per cultivar in each plot. In 2015, relatively high yields were obtained from all cultivars. The average yields for the spindle system were (lb/tree): ‘Puget Gold’ (29.0), ‘Harcot’ (24.1), ‘Golden Amber’ (19.6), ‘Chinese Apricot’ (18.6), and ‘Katy’ (16.7). Yields for the UFO system were (lb/tree): ‘Golden Amber’ (18.6), ‘Katy’ (14.9), ‘Puget Gold’ (11.3), ‘Chinese Apricot’ (10.2), and ‘Harcot’ (8.6). On average across all cultivars, the UFO system produced 60% of the yield of the spindle system in 2015. A heating device is necessary for high tunnel apricot fruit production in northern New Mexico because trees normally bloom in early to late March, depending on the year, while frosts can continue until mid-May. In years like 2017 and 2018 with temperatures below 10 °F in late February/early March, some of the expanded flower buds were killed before bloom. On those cold nights, one 100-lb tank of propane may or may not be enough for 1 night’s frost protection. Economically, it would not be feasible in those years. Only in years with a cool spring, late-blooming trees, and mild temperatures in April and May can high tunnel apricot production generate positive revenue with high, direct-market prices. High tunnel apricot production with heating devices is still risky and cannot guarantee a reliable crop in northern New Mexico or similar areas.

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Xiaojuan Zong, Brandon J. Denler, Gharbia H. Danial, Yongjian Chang and Guo-qing Song

‘Hansen 536’ (Prunus dulcis × Prunus persica) is an important commercial rootstock for peach and almond. However, susceptibility to wet soil and bacterial canker has limited its use primarily to areas with less annual rainfall. Genetic engineering techniques offer an attractive approach to improve effectively the current problems with this cultivar. To develop an efficient shoot regeneration system from leaf explants, 10 culture media containing Murashige and Skoog (MS) or woody plant medium (WPM) supplemented with different plant growth regulators were evaluated, and adventitious shoot regeneration occurred at frequencies ranging from 0% to 36.1%. Optimal regeneration with a frequency of 32.3% to 36.1% occurred with WPM medium containing 8.88 µm 6-benzylamino-purine (BAP) and 0.98 to 3.94 µm indole-3-butyric acid (IBA). The regenerated shoots had a high rooting ability, and 80% of the in vitro shoots tested rooted and survived after being transplanted to substrate directly. Transient transformation showed an efficient delivery of the β-glucuronidase (GUS) reporter gene (gusA) using all three Agrobacterium tumefaciens strains tested with a concentration of OD600 0.5 to 1.0 for 4 days of cocultivation. The protocols described provide a foundation for further studies to improve shoot regeneration and stable transformation of the important peach and almond rootstock ‘Hansen 536’.

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Christopher S. Imler, Camila I. Arzola and Gerardo H. Nunez

Unlike most horticultural crops, blueberry (Vaccinium spp. section cyanococcus) prefers low-pH (4.2–5.5) soils. Other plants can acidify their rhizosphere to create a hospitable microenvironment. Southern highbush blueberry (SHB; Vaccinium corymbosum interspecific hybrids) plants do not acidify their rhizosphere in response to Fe deficiency, but other factors that affect rhizosphere pH have not been elucidated. We report results from two hydroponic experiments exploring N uptake effects on the rhizosphere pH of ‘Emerald’ SHB. Ammonium (NH4 +) uptake led to rhizosphere acidification, whereas nitrate (NO3 ) uptake led to rhizosphere alkalization. When grown in a split-root hydroponic system, roots that took up NH4 + acidified the rhizosphere to a greater extent that roots not exposed to NH4 +. Rhizosphere acidification was observed even in a nontreated control. These results suggest that NH4 + uptake is the main driver of rhizosphere pH in SHB. N form effects suggest that fertilization with NO3 might lead to undesirable rhizosphere alkalization.

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Jianjun Li, Xiaoya Lian, Chenglin Ye and Lan Wang

Lonicera japonica Thunb., known as Japanese honeysuckle or golden-and-silver honeysuckle, belongs to the honeysuckle family and is native to eastern Asia, including China, Japan, and Korea. Microscopy, spectrophotometry, colorimetry, and the Royal Horticulture Society of Colorimetric Card (RHSCC) were used to compare and analyze the pigment distribution, content, and color variations in the Yujin 2 and Damaohua cultivars at different developmental stages. There were notable differences in the corolla color and the cross-section color between different developmental stages and different varieties. The lightness (L*), redness (a*), and yellowness (b*) values were calculated for each period for the two cultivars to observe variation trends. The chlorophyll content in the corollas of both cultivars showed declining trends with different rates. The chlorophyll content decreased rapidly from the young period to the two white period, and changed gradually from the two white period to the golden period. Moreover, the carotenoid content declined slightly from the young period to the silver period and rose sharply during the golden period. The ratio of these two pigment contents increased dramatically during the golden period: by 11.51 and 6.53 times in ‘Yujin 2’ and ‘Damaohua’, respectively. There were significant differences in corolla color, cross-section color, and the content of three pigments between the two varieties of honeysuckle. distribution and variation of pigments were the key factors affecting the flower color of honeysuckle. This study provides a basis for the identification and breeding of honeysuckle varieties and lays a foundation for further studies on the function and molecular mechanisms of pigments.

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Rumana Yeasmin, Stephen P. Bonser, Satoru Motoki and Eiji Nishihara

Environmental conditions, specifically heat stress, are important factors in asparagus crop production. Arbuscular mycorrhizal fungi (AMF) have been shown to increase plant growth. Effects of heat stress on nutrient uptake have rarely been examined in intact plants, but the limited results indicate that heat stress will decrease uptake; no studies have examined heat stress effects on asparagus nutrient uptake. We examined the effects of AMF, Glomus intraradices, on the growth, nutrient uptake, heat stress responses, and antioxidative activity in asparagus (Asparagus officinalis L.). We grew AMF-inoculated or non–AMF-inoculated asparagus plants in sand culture at 20 to 25 °C for 14 weeks in a greenhouse and subsequently subjected to three temperature conditions (control = 20 °C/25 °C night/day, mild heating = 30 °C/35 °C night/day, and severe heating = 37 °C/42 °C night/day) in growth chambers. Morphological and physiological growth parameters were compared between AMF-inoculated and non–AMF-inoculated plants. The mycorrhizal symbiosis markedly enhanced biomass production and heat stress responses negatively in plants compared with that in the non–AMF-inoculated plants. Plants grown under non–AMF-inoculated treatment had severe rate of leaf browning (80% to 100%), whereas the mycorrhizal plants showed a minimum rate of leaf browning under heat stress conditions. The results indicated mycorrhizal-inoculated plants showed an increase activity of antioxidative enzymes, such as superoxide dismutase and ascorbate peroxidase. The 2,2-diphenyl-1picrylhydrazyl radical scavenging activity also showed a greater response in mycorrhizal plants than in the control plants under each temperature treatment. Application of AMF enhanced plant growth and mineral nutrients and alleviated heat stress damage through an increased antioxidative activity and the mycorrhizal symbiosis significantly enhanced heat stress tolerance of asparagus.

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Rachel Leisso, Ines Hanrahan and Jim Mattheis

‘Honeycrisp’ apple is susceptible to the postharvest chilling disorder soft scald that renders fruit unmarketable. Reducing or preventing this disorder is an important component of ‘Honeycrisp’ postharvest management. In commercial settings, advanced fruit maturity and orchard history contribute to an estimation of soft scald susceptibility, but additional at-harvest information indicative of soft scald risk would enable better management decisions. In this study, we obtained fruit from commercial orchards for 3 successive years, and assessed field growing degree days (GDD), field chilling hours (CH), and fruit quality metrics at harvest, followed by soft scald incidence assessment at 12 weeks of cold storage. The analyses indicated starch index, soluble solids content (SSC), internal ethylene concentration, titratable acidity (TA), peel background color, firmness, GDD, or CH do not reliably indicate fruit susceptibility to soft scald. However, SSC and TA were elevated in fruit that later developed soft scald, and a higher number of GDD also sometimes preceded soft scald, which is consistent with advanced fruit maturity that can enhance soft scald risk. Overall, results suggest that other tools may be required to accurately predict postharvest soft scald on a quality control laboratory scale. The statistical analyses applied to the present study would have utility for assessing other soft scald prediction tools or markers.