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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.

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William G. Hembree, Thomas G. Ranney, Brian E. Jackson and Mark Weathington

Camellia L., the most speciose member of the diverse tea family Theaceae, has a long and complex horticultural history. Extensive cultivation and hybridization have produced thousands of varieties of Camellia, including commercially important crops such as cultivated tea, oilseed, and iconic flowering shrubs. Cytogenetics of Camellia and related genera is complicated; chromosome number and ploidy can vary widely between species, and interspecific and interploid hybridization occurs. However, specific information regarding cytogenetics of many species, cultivars, and modern hybrids is lacking. The objectives of this study were to compile a consolidated literature review of the cytogenetics of Camellia and related genera and to determine chromosome numbers, ploidy, and genome sizes of specific accessions of selected species, cultivars, and interspecific and interploid hybrids. A review of the existing literature regarding Theaceae cytogenetics is presented as a consolidated reference comprising 362 taxa. Genome sizes were determined with flow cytometry using propidium iodide as a fluorochrome and Pisum sativum ‘Ctirad' and Magnolia virginiana ‘Jim Wilson’ as internal standards. Chromosome numbers of selected taxa were determined using traditional cytology and were used to calibrate genome sizes with ploidy level. Our results confirmed a base chromosome number of x = 15 for Theeae including Camellia, x = 17 for Stewartiae, and x = 18 for Gordoniae. Surveyed camellias ranged from 2n = 2x = 30 to 2n = 8x = 120, including diploids, triploids, tetraploids, pentaploids, hexaploids, and octoploids. Previously uncharacterized taxa such as Camellia azalea, C. amplexicaulis, C. chrysanthoides, C. cordifolia, C. cucphuongensis, C. flava, C. nanyongensis, and C. trichoclada were found to be diploid. Ploidy was also newly determined for Schima argentea, S. khasiana, S. remotiserrata, and S. sinensis (all diploids). Both diploid and triploid Stewartia ovata were found, and a ploidy series was discovered for Polyspora that ranged from diploid to octoploid. Ploidy determinations were used to confirm or challenge the validity of putative interploid hybrids. Monoploid genome sizes varied among subfamily and genera, with 1Cx values ranging from 0.80 pg for Franklinia to a mean of 3.13 pg for Camellia, demonstrating differential rates of genome expansion independent of ploidy. Within Camellia, monoploid genome sizes varied among subgenera, sections, and some species (range, 2.70–3.55 pg). This study provides a consolidated and expanded knowledgebase of ploidy, genome sizes, hybridity, and reproductive pathways for specific accessions of Camellia and related genera that will enhance opportunities and strategies for future breeding and improvement within Theaceae.

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Cunquan Yuan, Zhiyi Qu, Huitang Pan, Tangren Cheng, Jia Wang and Qixiang Zhang

Heterostylous Primula forbesii is an important ornamental flower in China because of its long-lasting flowers and winter bloom. This study aimed to develop markers of expressed sequence tag–simple sequence repeats (EST-SSRs) that are associated with heterostyly and that can be used for molecular-assisted selective breeding in P. forbesii. We investigated 114,474 unigenes and identified 25,095 SSRs in P. forbesii. Dinucleotide repeats (46.14%), mononucleotide repeats (44.65%), and trinucleotide repeats (8.27%) were the most abundant SSRs. Among the 25,095 SSRs, 10,645 SSR primer pairs were successfully designed, of which 130 primer pairs were randomly selected for further amplification validation using eight accessions of P. forbesii; 98 pairs produced clear and stable polymerase chain reaction (PCR) products, and 28 pairs showed polymorphism. Bulked segregant analysis (BSA) was conducted for the F1 population with respect to thrum style and pin style by scanning 28 polymorphic SSR primer combinations. One SSR marker, c64326, linked to the heterostyly trait at a genetic distance of ≈3.70 cM was identified. The marker c64326 was further validated in two populations with an accuracy of 97.92% and 90.63%. The novel and linked EST-SSR markers can be valuable resources for genetic diversity analysis, mapping, and marker-assisted breeding in P. forbesii.

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Wenjie Ma, Wen Liang and Bing Zhao

The effects of different relative air humidity (RH) levels under high temperature and accompanying vapor pressure deficits (VPDs) on the physiology, photosynthesis, and anatomy of Rhododendron need to be better understood to help in reducing damage to leaves caused by high temperature. In this study, two Rhododendron cultivars were exposed at 45%, 55%, 65%, 75%, and 85% RH to a treatment of constant temperature at 38 °C for 14 days, resulting in a VPD of 3.64, 2.98, 2.32, 1.66, and 0.99 kPa, respectively. The results showed the least reduction of the net photosynthetic rate (Pn) under 75% RH treatment in R. ‘Fen Zhenzhu’ (decreased by 79.8%), and under the 85% RH treatment in R. ‘Zhuangyuan Hong’ (decreased by 75.4%). The decline in relative water content (RWC) was less under the 75% and 85% RH treatments, and electrolyte leakage showed a slight decrease under the 75% RH treatment in the two Rhododendron cultivars. The appearance of the two cultivars under greater RH showed less damage, probably because plants can avoid damage by increasing total chlorophyll content, decreasing stomatal area, stomatal density, and opened stomata ratio, enhancing enzymatic activity and osmoregulation substances, and improving leaf structure. The findings show that greater RH can alleviate damage caused by heat stress and improve thermostability.

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Fan Li, Shenchong Li and Qinli Shan

Temperature is one of the main factors that affects the growth pattern of Gerbera hybrida, which shows vast variation in morphology and stress adaptation among cultivars. However, little is known about temperature responses of plant growth among different cultivars. In this study, four cultivars were planted in different growth temperatures to investigate the effect of temperature on plant growth of Gerbera hybrida during their vegetative growth. Results showed that the optimum growth temperature of the four cultivars was 20 °C, of which plant height, root length, biomass accumulation, leaf area, and photosynthetic rate were enhanced significantly. Different cultivars showed diverse temperature adaptation ranges, which were related with their genetic background, and the temperature adaptability of cultivar Autumn was the best among the four cultivars. Temperature also had significant effects on photosynthetic rate, which was the main factor shaping plant growth. Our research provides the basic guidance for the growth temperature control in the cultivation of Gerbera hybrida.

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Marisa Y. Thompson, Jennifer Randall, Richard J. Heerema and Dawn VanLeeuwen

Successful commercial pecan [Carya illinoinensis (Wangenh.) K. Koch] production relies on mitigation of alternate bearing, which is a function of pistillate flower production. Mechanisms of floral initiation in pecan are not well understood. Our objective was to assess the impact of select plant growth regulators (PGRs) on return bloom for commercial application in pecan trees grown in the Southwestern United States. A 2-year study evaluated effects of ethephon, aminoethoxyvinylglycine (AVG), and gibberellin GA3 (GA3) on subsequent season return bloom in fruiting and nonfruiting pecan shoots. Cultivars used were mature Western and immature Western and Pawnee. Effects of PGRs on return bloom of nonfruiting shoots were different from fruiting shoots. As compared with untreated control, a GA3 treatment on fruiting shoots of mature ‘Western’ trees increased the number of flowers per new shoot by 125%. For nonfruiting shoots on the mature ‘Western’ trees, the number of flowers per new shoot decreased significantly by all PGR treatments and as much as 93% for AVG. In previously nonfruiting shoots on the immature ‘Western’ trees, a GA3 treatment reduced the number of flowers per new shoot in the next season by 88.2%. Results from immature ‘Pawnee’ shoots did not show statistically significant differences. The effects of these PGRs on subsequent season flowering in pecan are complex. This study suggests that PGRs can be used to increase or decrease cropload through effects on return bloom and therefore have potential uses for mitigating alternate bearing.