An experiment was conducted in 2017 and 2018 to determine the sensitivity of common garden annuals to sublethal rates of 2,4-dichlorophenoxyacetic acid (2,4-D) and dicamba with or without glyphosate. Sublethal rates corresponding to 1/10×, 1/100×, and 1/300× of the full labeled rate (1×) of 2,4-D (1.0 lb/acre), 2,4-D plus glyphosate (1.0 lb/acre plus 1.0 lb/acre), dicamba (0.5 lb/acre), and dicamba plus glyphosate (0.5 lb/acre plus 1.0 lb/acre) were applied to ‘Prelude’ wax begonia (Begonia ×semperflorens-cultorum), ‘Wizard’ coleus (Solenostemon scutellarioides), ‘Pinto’ zonal geranium (Pelargonium ×hortorum), ‘Dazzler’ impatiens (Impatiens walleriana), ‘Bonanza’ french marigold (Tagetes patula), ‘Hurrah’ petunia (Petunia hybrida), ‘Titan’ madagascar periwinkle (Catharanthus roseus), and ‘Double Zahara’ zinnia (Zinnia marylandica). Visible injury, plant height, number of flowers, and dry weight were recorded at specific time intervals after treatment. When averaged across all annual plant species, the 1/10× rate of 2,4-D plus glyphosate resulted in 51% injury 28 days after treatment, whereas the 1/10× rate of dicamba plus glyphosate resulted in 43% injury. Treatments causing the greatest injury also resulted in the greatest reduction of dry weight, height, and flower production. Coleus was the most sensitive species in the study; dry weight was reduced by 16% and 18% compared with the nontreated controls from 1/300× rates of 2,4-D plus glyphosate and dicamba plus glyphosate, respectively. French marigold and zonal geranium had greater sensitivity to treatments containing 2,4-D, but coleus and zinnia had greater sensitivity to treatments containing dicamba. Petunia exhibited a high tolerance to 2,4-D or dicamba applied alone (>6% injury) but was highly sensitive when glyphosate was added to 2,4-D and dicamba (<65% injury). The 1/100× and 1/300× rates that are likely to equate to sublethal rates in field settings, resulted in less than 15% injury across all flower species except coleus and petunia.
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Brian Dintelmann, David Trinklein and Kevin Bradley
Wenjing Guan, Dean Haseman and Dennis Nowaskie
Grafting technology is increasingly being accepted in the United States, particularly for tomato (Solanum lycopersicum) production under protected structures. There is a great potential to expand this technology to other high tunnel crops. Using grafting technology in cucumber (Cucumis sativus) production is widely adopted in Asia to enhance cucumbers’ tolerance to low temperatures. But this technique is rarely used in the United States mainly because of the lack of information on the performance of the grafted plants under local production systems. Figleaf gourd (Cucurbita ficifolia), Cucurbita moschata, and squash interspecific hybrid (Cucurbita maxima × C. moschata) are the most used cucumber rootstocks worldwide. But their comparative performance was largely unknown for cucumber production in high tunnels in the Midwest United States. This study was therefore designed to compare the major types of cucumber rootstocks with the goal of identifying a rootstock with the maximized benefits for high tunnel cucumber production in the area. Nongrafted ‘Socrates’ and ‘Socrates’ grafted with Cucurbita moschata, squash interspecific hybrid, and figleaf gourd rootstocks were evaluated in high tunnels from March to June or July in 2016–19 at the Southwest Purdue Agricultural Center in Vincennes, IN. Transplant establishment, vine growth, and yield in early- and main-crop seasons were investigated. Grafted plants regardless of rootstocks ensured transplant survival even when the soil temperatures were dropped below 10 °C. Suboptimal soil conditions were encountered in the first month after transplanting. Grafted cucumbers with squash interspecific hybrid rootstock significantly increased vine growth from March to April and increased early-season yields (yield before 15 May) by 1.8 to 18.2 times compared with the early-season yields of the nongrafted cucumbers. The benefits provided by using grafting technology dismissed around middle May. Only squash interspecific hybrid rootstock improved cucumber yields in the entire production seasons. Cucumbers grafted with figleaf gourd rootstock had the lowest yield and the least plant growth after mid-May, indicating figleaf gourd rootstock may not be suitable for cucumber production under the current production system. Overall, squash interspecific hybrid was the most promising rootstock for early-season high tunnel cucumber production in the Midwest United States.
Patrick J. Conner
Andre Luiz Biscaia Ribeiro da Silva, Joara Secchi Candian, Elizanilda Ramalho do Rego, Timothy Coolong and Bhabesh Dutta
The use of resistant cultivars against Xanthomonas campestris pv. campestris (Xcc) is considered a critical management practice for black rot (BR) management in cabbage (Brassica oleracea var. capitata). Although most studies that have evaluated resistance to BR were conducted in greenhouses without accounting for yield, there is a clear need to investigate cultivar performance under field conditions. The objectives of this study were to evaluate commercial cabbage cultivars for resistance to BR and determine yield and head quality under field conditions. Field experiments with eight cultivars (Acclaim, Bravo, Capture, Celebrate, Cheers, Melissa, Monterey, and TCA-549) were conducted in two cabbage growing seasons, Fall 2018 and Spring 2019. Fields were spray-inoculated with Xcc (3 × 105 cfu/mL) at 35 and 49 days after transplanting in Fall 2018 and Spring 2019, respectively. Cabbage BR severity was evaluated at weekly intervals starting from 7 days postinoculation (DPI) until harvest. Marketable and unmarketable yields and cabbage head quality were measured at harvest. Cabbage BR symptoms were detected in all tested cultivars for both growing seasons with initial symptoms observed as early as 28 and 21 DPI in Fall 2018 and Spring 2019, respectively. Severity of cabbage BR at harvest was significantly greater in Fall 2018 compared with Spring 2019, whereas marketable yield was significantly higher in Spring 2019 (45,169 lb/acre) compared with Fall 2018 (26,370 lb/acre). In both growing seasons, ‘TCA-549’ had the lowest severity of BR and ‘Melissa’ had the highest severity of BR. Area under the disease progress curve (AUDPC) was 175 and 13 for ‘TCA-549’ in Fall 2018 and Spring 2019, respectively. The AUDPC for ‘Melissa’ in Fall 2018 and Spring 2019 were 2376 and 905, respectively. Regardless of growing season, cabbage marketable yield was higher for ‘Acclaim’ (51,760 lb/acre) compared with all other cultivars; however, there was no significant difference between Acclaim and TCA-549 (42,934 lb/acre) for cabbage marketable yield. Cabbage marketable yield was the lowest for cultivars Melissa (18,275 lb/acre) and Capture (24,236 lb/acre). Overall, there was a significant correlation between BR disease severity and cabbage marketable and unmarketable yields. Increasing the BR severity decreased cabbage marketability due to an increase in unmarketable yields. Continued development of cultivar resistance to BR is important for cabbage production in the southeastern United States, given the favorable conditions for disease development. The use of cultivars with low susceptibility, pathogen-free seeds, crop rotation, and proper spraying programs should be considered the best management practice for BR disease.
Jehanzeb Khan, Yubin Yang, Qiang Fu, Weiqiang Shao, Jianke Wang, Li Shen, Yan Huai, Guy Kateta Malangisha, Abid Ali, Ahmed Mahmoud, Yi Lin, Yongyuan Ren, Jinghua Yang, Zhongyuan Hu and Mingfang Zhang
Watermelon (Citrullus lanatus) is an important horticultural crop that is sensitive to heavy metals such as lead (Pb) in polluted water or soil. However, there are no available data regarding Pb tolerance phenotyping in watermelon. Watermelon seedlings were exposed to various Pb doses (0, 20, 40, 60, 80 µm·L–1 Pb) for 14 days, after which 20 µm Pb was identified as the optimal treatment for lead tolerance analysis in watermelon because it caused significant symptoms (leaf chlorosis, stubby and yellow roots) but little damage to seedlings. Subsequently, the Pb responses were analyzed in eight watermelon varieties (V1–V8), and membership function analysis was used to determine a single Pb tolerance index. Of the eight watermelon varieties, V4 and V7 were ranked the most Pb tolerant; V1, V2, V5, and V6 were moderately Pb tolerant; and V3 and V8 were the most Pb-sensitive varieties. Compared with most Pb-sensitive varieties (V3 and V8), the most Pb-tolerant varieties (V4 and V7) maintained high antioxidant activity, and had lower malondialdehyde (MDA) and total soluble protein (TSP) contents. In addition, carotenoid and chlorophyll (both a and b) contents were stimulated and inhibited, respectively, in leaves of high-Pb translocation varieties (V4 and V8). Principal component analysis (PCA) revealed relative root length as an indicator of Pb tolerance because it correlated significantly with shoot growth. These results provide useful insight into the mechanism of Pb tolerance in cucurbit crops, as well as information regarding the breeding of watermelon with enhanced tolerance to this heavy metal (Pb).
Sean M. Campbell, Brian J. Pearson and S. Christopher Marble
Butterfly pea (Clitoria ternatea) is a unique perennial and leguminous plant that produces brightly colored flowers that can be used as a pH-dependent natural food colorant in culinary and cosmetic preparations. Butterfly pea is commonly propagated from seed. Because of the increased interest in its commercial applications, effective production techniques are necessary to ensure consistent and successful commercial production. The objective of this research was to determine the influence of the substrate type and temperature on butterfly pea germination. Two substrate types (rockwool and commercial soilless substrate mix) and three temperatures (70, 80, and 90 °F) were evaluated to determine their effects on germination of butterfly pea seed. Collected and calculated germination data included germination capacity (G), mean germination time (MT), coefficient of variation of the germination time (cv t), mean germination rate (MR), uncertainty of the germination process (U), and synchrony of the germination process (Z). Differences were observed among substrate temperatures for the MT, cv t, and MR values, with germination greater at both 70 and 80 °F than at 90 °F. Similarly, significant differences among substrate types were observed for the G, MT, cv t, and MR values, with germination of seeds in rockwool outperforming seeds in soilless substrate mix. Because of the high priority for successful and uniform germination in commercial plant production operations, the results suggest that commercial germination of butterfly pea would be best in rockwool at 70 °F. Results of this study can be used for the commercial production of butterfly pea, for which propagation from seed is the primary means of plant production.
Charlie Garcia and Roberto G. Lopez
Supplemental lighting is required for the production of high-quality vegetable transplants in greenhouses when the photosynthetic daily light integral (DLI) is low. Light-emitting diodes (LEDs) are a promising alternative to high-pressure sodium (HPS) lamps. However, there are a limited number of studies that have evaluated how LED supplemental lighting spectral quality beyond blue (B) and red (R) radiation influences plant growth and development. Seeds of hybrid greenhouse seedless cucumber ‘Elsie’ (Cucumis sativus), tomato ‘Climstar’ (Solanum lycopersicum), and pepper ‘Kathia’ (Capsicum annuum) were sown and placed into a dark growth chamber until radicle emergence. Seedlings were grown in a greenhouse at a 25 °C constant temperature set point and under five lighting treatments. The supplemental lighting treatments delivered a total photon flux density (TPFD) of 120 μmol·m−2·s−1 for 16 h·d−1 based on an instantaneous threshold from HPS lamps or LEDs [three treatments composed of B (400–500 nm), R (600–700 nm), white, and/or far-red (FR; 700–800 nm) LEDs], and a control that delivered 25 μmol·m−2·s−1 from HPS lamps (HPS25). The LED treatments defined by their wavebands (TPFD in μmol·m−2·s–1) of B, green (G, 500–600 nm), R, and FR radiation were B20G10R75FR15, B25R95, and B30G30R60; whereas the HPS treatments emitted B7G57R47FR9 (HPS120) and B1G13R9FR2 (HPS25). Generally, cucumber, pepper, and tomato transplants under B30G30R60 and HPS120 supplemental lighting had the greatest stem diameter. Fresh weight and leaf area of all three species was greater when G radiation replaced R or B radiation. For example, leaf area and fresh weight of cucumber, tomato, and pepper increased (by 33%, 22%, and 49%; and 35%, 14%, and 56%, respectively) for plants under B30G30R60 supplemental lighting compared with plants under B25R95 supplemental lighting. The most compact cucumber and pepper transplants were those grown under B25R95 supplemental lighting, and the most compact tomatoes were those grown under the HPS25 (control) and B25R95 supplemental lighting. Tomato transplants under treatments providing ≥30 μmol·m−2·s−1 of G radiation had an increased incidence of leaf necrosis. From this study, we conclude that plant responses to supplemental lighting quality are generally genera-specific, and therefore high-wire transplants should be separated by genera to optimize production and quality. However, additional studies are required to provide complete LED supplemental lighting recommendations.
Andrés Mayorga-Gómez, Savithri U. Nambeesan, Timothy Coolong and Juan Carlos Díaz-Pérez
Bell peppers (Capsicum annuum L.) are ranked eighth in value for vegetable production in the United States (USDA-NASS, 2019). Due to the high value of bell peppers, disorders such as blossom-end rot (BER) can cause significant losses in yield by up to 35% for growers. BER is the symptom of a calcium (Ca2+) deficiency that may occur during periods of cell expansion when the supply of Ca2+ may be lower than demand. In this study, we determined the temporal patterns of the fruit Ca2+concentration ([Ca2+]) and accumulation in three separate studies under field and greenhouse conditions. In the three experiments, [Ca2+] during fruit development showed varied patterns: it remained constant, decreased transiently during the cell expansion phase, or displayed a more gradual sustained decrease. However, in the three experiments, fruit Ca2+ accumulation increased during development as fruit size increased. In two experiments, the distal part of the fruit had lower [Ca2+] than the proximal end. However, there was no correlation between [Ca2+] in various fruit sections with BER incidence. Seeds and placental tissue had increased [Ca2+] and several other macro- and micronutrients; this spatial distribution of Ca2+ coupled with subcellular Ca2+ distribution should be explored in future studies. The temporal pattern of Ca2+ accumulation in this study suggests that fruit Ca2+ uptake continues throughout fruit development. Therefore, Ca2+ application during bloom and early fruit development may prevent or minimize Ca2+ deficiency disorders in bell pepper.
Wayne W. Hanna and Brian M. Schwartz
Suejin Park, Youyoun Moon and Nicole L. Waterland
Water deficit stress can reduce the postproduction shelf life and marketability of floriculture crops. To alleviate the damage by water deficiency, plants need to limit transpirational water loss by inducing stomatal closure. Osmotic stress induces stomatal closure like the response to water deficit stress. It could be used as a convenient tool to enhance water deficit stress tolerance by reducing water loss. The objective of this research was to investigate whether osmotic treatment with a high concentration of chemical solutions could trigger a response to osmotic stress so that stomatal closure can be induced, resulting in enhanced water deficit stress tolerance in viola (Viola cornuta ‘Sorbet XP Yellow’). Osmotic treatments with CaCl2, Ca(NO3)2, NaCl, NaNO3, BaCl2, Ba(NO3)2, and mannitol were applied at the osmotic potentials (ψS) of −1.3 and −2.0 MPa. Chemical treatments [except Ca(NO3)2, NaCl, and mannitol] helped to delay wilting and gave a longer shelf life, up to 5.2 days over that of the control, 2.5 days. However, leaf necrosis was observed on the violas treated with NaCl, NaNO3, BaCl2, Ba(NO3)2, and mannitol. CaCl2 was the most effective agent in delaying wilting under water deficit stress in viola without leaf necrosis. Compared with the control, violas treated with CaCl2 at 200 and 300 mm showed an increase in shelf life by 2.6 and 1.2 days, respectively. Stomatal conductance (g S) was reduced within 4 hours after treatment with CaCl2 compared with that of control violas. Leaf relative water content (RWC) of control violas was dramatically reduced 3 days after treatment and fell below 50% on day 4, while CaCl2-treated violas maintained higher leaf RWC (70% to 81%) during the water deficit period. These results indicated that osmotic treatment with the high concentration of CaCl2 caused stomatal closure, resulting in a reduction of water loss and an extension of shelf life under water deficit stress in viola.