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Kimberly Moore, Charles Wajsbrot, Cristina Burgart and Luci Fisher

Because salts in irrigation water decrease plant growth, we wanted to develop a quick and easy method for evaluating salt tolerance that could be used in the greenhouse. Using plastic containers with lids, sea salt, and rooted cuttings, we monitored changes in plant quality, growth, and leaf water potential as electrical conductivity (EC) and sodium (Na) levels increased. In the first of two experiments, we compared sea hibiscus (Hibiscus tilliaceus) leaf water potential and plant quality in solutions with an EC of 0, 2.1, 4.2, 6.1, or 8.2 dS·m−1 (0, 240, 420, 610, or 1010 mg·L−1 Na). After 14 days, sea hibiscus quality in solutions with an EC of 6.1 or 8.2 dS·m−1 was less than plants in solutions of 0, 2.1, or 4.2 dS·m−1. There was no difference in quality among plants in 0, 2.1, or 4.2 dS·m−1 solutions. To test this method, in Expt. 2, we compared coleus (Coleus ×hybridus), copperleaf (Acalypha wilkesiana), ficus (Ficus benjamina), jasmine (Jasminium multiflorum), and plumbago (Plumbago auriculata) plant quality and growth in solutions with an EC of 0, 1.3, 2.1, 4.2, 5.6, or 6.1 dS·m−1 (0, 170, 240, 420, 520, or 610 mg·L−1 Na). Coleus quality declined at an EC greater than 1.3 dS·m−1, whereas jasmine and plumbago quality declined at an EC greater than 2.1 dS·m−1 Copperleaf and ficus declined at an EC greater than 4.2 dS·m−1. Plant response did vary with low to medium salt-tolerant plants tolerating at an EC up to 1.3 and 170 mg·L−1 Na, whereas plants with a greater salt tolerance tolerated at EC and Na values up to 4.2 dS·m−1 and 420 mg·m−1 Na, respectively. The use of this method benefits growers by determining upper EC and Na limits when faced with poor-quality water resulting from saltwater intrusion or when using reclaimed wastewater with greater EC and Na levels.

Open access

Noa K. Lincoln, Theodore Radovich, Kahealani Acosta, Eli Isele and Alyssa Cho

Breadfruit (Artocarpus altilis) cultivation is gaining momentum throughout the tropics due to its high yield and nutritious fruit. One impediment to expanding production of breadfruit is the lack of agronomic research related to production management. We examined foliar nutrient concentrations of different leaf positions and leaf parts to assess within- and between-tree variance to inform an effective sampling protocol. We further validated the sampling protocol on 595 trees at 87 sites that were assessed for yield and productivity. Foliar nutrients differed significantly by categories of productivity. For the first time, breadfruit-specific standards of foliar nutrient concentrations are presented for consideration. In conclusion, we recommend that foliar sampling use petioles harvested from leaves in the third position from the branch tip using sun-exposed leaves in the midcanopy of each tree.

Open access

Fekadu Fufa Dinssa, Peter Hanson, Dolores R. Ledesma, Ruth Minja, Omary Mbwambo, Mansuet Severine Tilya and Tsvetelina Stoilova

Amaranth (Amaranthus sp.) is an important leafy vegetable in Africa where most farmers grow unimproved landraces. Information about amaranth genetic diversity and its adaptation to different environments will help breeders develop improved commercial varieties that meet market requirements. The objectives of this study were to investigate the performances of amaranth entries for vegetable yield across locations and seasons, assess the relative contributions of genetic vs. environmental sources of variation to yield, and cluster locations into mega-environments (MEs) to suggest future test sites. Twenty-six diverse entries were evaluated for vegetable yields in replicated trials at five locations in wet-cool and hot-dry seasons in Tanzania. Season explained the highest proportion (52.1%) of the total sum of squares followed by entries (24.9%) and locations (23.0%). Mean yield across the hot-dry season trials (27.7 t·ha−1) was 47.3% greater than the mean yield across wet-cool season trials (18.8 t·ha−1). Differences among entries in vegetable yield were higher in the hot-dry season than in the wet-cool season, indicating that gain from selection is likely to be greater in the hot-dry season. Most entries performed well in either wet-cool or hot-dry season but a few entries were adapted to both seasons. Two MEs were identified, one characterized by lower altitudes, higher temperatures, and less fertile soils, and a second ME associated with higher altitudes, lower temperatures, and more fertile soils. Each ME may serve as an initial selection site for their respective target environment. Targeting a specific season may give a better chance of finding high-yielding varieties.

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Xun Chen, Nai-xin Liu, Li-juan Fan, Yu Du and Ling Wang

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Qiang Zhang, Wenting Dai, Hui Yang, Wenting Jia, Xuefei Ning and Jixin Li

In this study, newly harvested ‘New Queen’ melons were treated with calcium chloride (CaCl2) and 1-methylcyclopropene (1-MCP) alone or in combination before storage. The results show that respiration rate, ethylene release, activity, and gene expression of pectinases such as polygalacturonase (PG), pectin methylesterase (PME), and pectate lyase (PL) in ‘New Queen’ melons decreased dramatically when treated with 2% CaCl2 and/or 1 μL·L–1 1-MCP. In addition, climacteric behavior and flesh hardness reduction were inhibited. It was also discovered that softer melon flesh was more conducive to the growth and reproduction of decay-causing microorganisms, according to their growth curves in melons that were different in flesh hardness, suggesting inhibiting fruit softening can slow down the growth of microorganisms in fruit flesh and thus reduce fruit decay rate. The combined use of CaCl2 and 1-MCP was more effective in suppressing respiration rate, ethylene release, and protopectin hydrolysis, which could greatly delay the softening, reduce the decay rate, and extend the shelf life of ‘New Queen’ melons.

Open access

Ebrahiem M. Babiker, Stephen J. Stringer, Hamidou F. Sakhanokho, Barbara J. Smith and James J. Polashock

Species of Botryosphaeria and Neofusicoccum are major pathogens of blueberry worldwide. Accurate identification of these species is essential for developing effective management practices. A multigene sequencing strategy was used to distinguish between six isolates of stem blight pathogens collected from two different regions of the United States. The temperature growth study revealed that the optimal temperature for growth of five of the tested isolates ranged from 25 to 30 °C, although no significant difference was detected for the growth of Neofusicoccum spp. isolate SD16-86 at 20, 25, 30, and 35 °C. In vitro fungicide assays showed four fungicides, cyprodinil + fludioxonil, propiconazole, pyraclostrobin + boscalid, and azoxystrobin, were effective against the tested isolates with isolate SD16-86 being less sensitive compared with the other isolates. In a detached stem assay, none of 39 blueberry accessions displayed immunity or a high level of resistance to the two tested isolates, and no significant difference in lesion length was detected among the seven tested Vaccinium species inoculated with the two isolates.

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Jules Janick

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Tyler J. Simons, Christopher J. McNeil, Aubrey D. Pham, Carolyn M. Slupsky, Mikeal L. Roose and Jean-Xavier Guinard

‘DaisySL’ mandarins (Citrus reticulata Blanco) grafted to Schaub Rough lemon (C. jambhiri Lush; SHRL) Carrizo citrange (Citrus sinensis Osb. × Poncirus trifoliata L. Raf.; CARR), and Rubidoux Trifoliate [Poncirus trifoliata (L.) Raf.; RUBT] rootstocks were measured to determine their liking by adults and children, sensory properties, and targeted metabolomics over the course of 2 consecutive years. Chemical measurements showed differences in sugars, acids, and ethanol content, whereas a descriptive analysis found variations in sweetness, mandarin flavor, juiciness, and peelability. During both years, adults significantly preferred ‘DaisySL’ mandarins grafted to CARR and RUBT over those grafted to SHRL (P ≤ 0.05). Children liked the fruit grafted to CARR and RUBT rootstocks significantly more than fruit grafted to SHRL during the first year, but they did not prefer fruit grafted to any rootstock during the second year. This research found that ‘DaisySL’ mandarins are a well-liked variety of mid-to-late season mandarin capable of filling the seasonal gap between clementine and W. Murcott varieties. We concluded that the rootstock can affect the chemical composition, sensory profile, and consumer preferences for ‘DaisySL’ mandarins.

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Yu Liu, Miao He, Fengli Dong, Yingjie Cai, Wenjie Gao, Yunwei Zhou, He Huang and Silan Dai

The NAC transcription factor is a peculiar kind of transcription factor in plants. Transcription factors are involved in the expression of plant genes under different conditions, and they play a crucial role in plant response to various biotic and abiotic stress. We transferred the ClNAC9 gene into Chrysanthemum grandiflora ‘niu9717’ by Agrobacterium tumefaciens–mediated transformation. The results of kanamycin-resistant screening, polymerase chain reaction (PCR) detection, and Northern blot analysis proved that the target gene had been integrated into the genome of the target plants. Wild-type (WT) plants and transgenic plants were treated with different concentrations of NaCl, NaHCO3, and drought stress, and physiological indexes, such as antioxidant system activity (superoxide dismutase, peroxidase, catalase), malondialdehyde accumulation, and leaf relative water content, were measured. We also observed changes in plant morphology. The physiological indexes’ changing range and extreme values suggested that transgenic plants’ resistance to salinity, alkali, and drought stress was significantly higher than WT plants. Transgenic plant growth was less inhibited compared with WT plants, indicating that the ClNAC9 gene increased the resistance of transgenic plants under the stress of salinization, alkalization, and drought.

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Masahiko Fumuro

To determine the potential of using own-rooted trees to lower tree height and delay the decline in tree vigor caused by root clogging, the growth, yield, and fruit quality of pot-planted ‘Aikou’ mango (Mangifera indica L.) trees propagated by air layering and grafting were observed for 8 years after planting. The trunk diameter of the own-rooted trees propagated by air layering (hereafter abbreviated as own-rooted trees) was significantly smaller than that of the grafted trees propagated by conventional methods (hereafter abbreviated as grafted trees), but there were no significant differences in the scion diameters of the grafted trees. Moreover, no significant differences were observed in leaf number or total length of green branches between the own-rooted and grafted trees during the final 3 years. The height of the own-rooted trees was significantly shorter than that of the grafted trees. Although no difference in the fresh or dry weight of the aboveground part and whole tree was observed between the own-rooted and grafted trees, the fresh and dry weights of the underground part of the own-rooted trees were significantly lower than those of the grafted trees. Furthermore, the T-R ratio (the weight of the aboveground part of the tree excluding the leaves/the weight of the underground part of the tree) of the own-rooted trees was significantly higher than that of the grafted trees. Overall, no significant differences in yield or fruit quality were observed between the two tree types, and the average yield per 1 m2 over 6 years was 2.9–3.1 kg. These results indicate that it may be possible to lower tree height, delay the decline in tree vigor caused by root clogging, and prolong the life span of pot-planted trees by using own-rooted trees.