Interactive Effects of Intraspecific Competition and Drought on Stomatal Conductance and Hormone Concentrations in Different Tomato Genotypes

Plant physiological responses to various stresses are characterized by interaction and coupling, while the intrinsic mechanism remains unclear. The effects of intraspecific competition on plant growth, stomatal opening, and hormone concentrations were investigated with three tomato genotypes (WT-wild type, Ailsa Craig; FL-a abscisic acid (ABA) deficient mutant, flacca; NR-a partially ethylene-insensitive genotype) under two water regimes (full irrigation, irrigation amount = daily transpiration; deficit irrigation, 60% of irrigation amount in full irrigation) in this study. Three kinds of competitions were designed, i.e., root and canopy competition, non-root competition, and non-canopy competition, respectively. Intraspecific competition reduced plant leaf area and stomatal conductance (gs) of wild-type tomato, accompanied by ABA accumulation and ethylene evolution. Intraspecific competition-induced decrease in gs was absent in FL and NR, indicating ABA and ethylene involved in plant response to intraspecific competition. As soil water becomes dry, the competition decreased gs by elevating ABA and ethylene accumulations. Under severe drought, the competition-induced decline in gs was covered by the severe drought-induced decrease in gs, as hydraulic signals most probably dominate. The absence of canopy competition insignificantly influenced plant stomatal opening of well-watered tomato, as canopy separation minimized the plant neighbor sensing by ethylene and other signals. Whereas under water deficit condition, the absence of canopy competition significantly reduced ABA accumulation in roots and then stomatal conductance, indicating the belowground neighbor detection signals maybe enhanced by soil drought. The absence of root competition increased ethylene evolution, confirming the importance of ethylene in neighbor detection and plant response to environmental stress.

The Influence of Rootstock on Fruit Ethylene, Respiration, Index of Absorbance Difference, Fruit Quality, and Production of ‘Aztec Fuji’ Apple under a Full-crop Condition

Selection of dwarfing rootstocks that facilitate optimum production of high-quality fruit is crucial in modern high-density apple orchards. In addition to tree growth and yield, rootstocks can influence fruit maturity of scion cultivars in apples. In this study, the impact of 17 rootstocks on fruit maturity, yield, and quality attributes of ‘Aztec Fuji’ apples (Malus domestica Borkh.) at harvest were evaluated in a season when all trees were in a “full-crop” condition. Keeping sealed fruit at room temperature, a typical climacteric pattern was observed in ethylene evolution, respiration, and oxygen consumption, peaking after 5–7 days in fruit from trees on all rootstocks. During the ripening period, ethylene evolution and respiration rates in fruit from trees on Supp.3, G.3001, and G.202 were often in the high-range category, whereas those on CG.4004, CG.4214, G.41N, and B.9 were in the midrange category and those on M.9Pajam2, M.26EMLA, and G.11 were in the low-range category. Evolved ethylene and respiration in fruit from trees on M9.T337 steadily and slowly increased from 7 days after harvest (7DAH) to 13 days after which harvest (13DAH) ethylene sharply increased, signaling occurrence of climacteric peak, while respiration declined after the peak of 13DAH. In fruit from trees on most rootstocks, the rates of oxygen consumption had inverse relationships with the rates of respiration, so that fruit from trees on M9.T337 had higher and those on G.41N and Supp.3 had lower rates of oxygen consumption. Trees on G.41N, CG.4004, and M.26EMLA had higher and those on CG.4003 had lower yield per tree than trees on other rootstocks. Trees on B.9 and M.9T337 were most yield efficient among trees on all rootstocks. Trees on CG.4004 had larger fruits than those on other rootstocks. Considering all fruit maturity, quality, and yield attributes, CG.4004 seems to be a good choice of rootstock for ‘Aztec Fuji’ under the conditions of this study.

Interactive Effects of Intraspecific Competition and Drought on Stomatal Conductance and Hormone Concentrations in Different Tomato Genotypes

We elucidated the effects of intraspecific competition on plant growth, stomatal opening and hormone concentrations in different tomato genotypes under different water regimes. Intraspecific competition reduced plant leaf area and stomatal conductance (gs) of wild-type tomato (Ailsa Craig), which was accompanied by abscisic acid (ABA) accumulation and ethylene evolution. Intraspecific competition-induced decrease in gs was absent in flacca, an ABA-deficient mutant, and in never-ripe, a partially ethylene-insensitive genotype, indicating ABA and ethylene involved in plant response to intraspecific competition. As soil water becomes dry, the competition decreased gs by elevating ABA and ethylene accumulations. Under severe drought, the competition-induced decline in gs was covered by the severe drought-induced decrease in gs, as hydraulic signals most probably dominate. Absence of canopy competition had no significant influence on plant stomatal opening of well-watered tomato, due to canopy separation minimized the plant neighbor sensing by ethylene and other signals. Whereas under water deficit condition, absence of canopy competition significantly reduced ABA accumulation in roots and then stomatal conductance, indicating the belowground neighbour detection signals maybe enhanced by soil drought. Absence of root competition increased ethylene evolution, confirming the importance of ethylene in neighbor detection and plant response to environmental stress.

Role of salicylic acid in regulating ethylene and physiological characteristics for alleviating salinity stress on germination, growth and yield of sweet pepper

Background During a preliminary study, effects of 0, 20, 40, and 60 mM NaCl salinity were assessed on germination rate in relation to electrolyte leakage (EL) in sweet pepper. Results explored significant rises in ethylene evolution from seeds having more EL. It was, therefore, hypothesized that excessive ethylene biosynthesis in plants due to salinity stress might be a root cause of low crop productivity. As salicylic acid is one of the potent ethylene inhibitors, thus SA was used to combat effects of ethylene produced under salinity stress of 60 mM NaCl on different physiological and morphological characteristics of sweet pepper. Methodology The effect of 0.05, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 mM SA was evaluated on seed germination, growth and yield of sweet pepper cv. Yolo wonder at salinity stress on 60 mM NaCl. Seeds were primed with SA concentrations and incubated till 312 h in an incubator to study germination. Same SA concentrations were sprayed on foliage of plants grown in saline soil (60 mM NaCl). Results Seeds primed by 0.2 to 0.3 mM SA improved germination rate by 33% due to suppression of ethylene from 3.19 (control) to 2.23–2.70 mg plate−1. Electrolyte leakage reduced to 20.8–21.3% in seeds treated by 0.2–0.3 mM SA compared to 39.9% in untreated seeds. Results also explored that seed priming by 0.3 mM improved TSS, SOD and chlorophyll contents from 13.7 to 15.0 mg g−1 FW, 4.64 to 5.38 activity h−1 100 mg−1 and 89 to 102 ug g−1 compared to untreated seeds, respectively. Results also explore that SA up to 0.2 mM SA applied on plant foliage improved LAI (5–13%), photosynthesis (4–27%), WUE (11–57%), dry weight (5–20%), SOD activity (4–20%) and finally fruit yield (4–20%) compared to untreated plants by ameliorating effect of 60 mM NaCl. Foliar application of SA also caused significant increase in nutrient use efficiency due to significant variations in POD and SOD activities. Conclusion Salicylic acid suppressed ethylene evolution from germinating seeds up to 30% under stress of 60 mM NaCl due to elevated levels of TSS and SOD activity. Foliar application of SA upgraded SOD by lowering POD activity to improve NUE particularly K use efficiency at salinity stress of 60 mM NaCl. Application of 0.2 and 0.3 mM SA emerged as the most effective concentrations of SA for mitigating 60 mM NaCl stress on different physiological and morphological characteristics of sweet pepper.

Flowering profile and ethylene production of a new carnation subspecies ‘Mini-tiara’

Ethylene is involved in the senescence of carnation flowers. It is synthesized abundantly after full opening of the flowers and accelerates wilting of petals, which results in withering of the flowers. We investigated the possible involvement of ethylene production in the loss of display value of cut flowers of ‘Mini-tiara’ carnation, a new subspecies derived from Dianthus caryophyllus L. by interspecific cross with wild-type Dianthus species (wild pinks). Flowers of ‘Mini-tiara’ carnation have a unique morphology with pointed-shaped petals, some of which in the middle part of the flowers stand straight and build a dome throughout the display time, and lose their display value when the dome collapses by bending all petals outside (full opening of flowers). Ethylene evolution from ‘Mini-tiara’ carnation was not detected from flowers with upstanding petals, but occurred several days after the collapse of the dome (after full opening of the flowers), the time they already lost their display value. These findings indicated that ethylene production is not engaged in the loss of display value of ‘Mini-tiara’ carnation.

AVG, NAA, boron, and magnesium influence preharvest fruit drop and fruit quality of ‘Honeycrisp’ apples

Preharvest fruit drop (PFD) of apple (Malus domestica Borkh.) can cause significant losses resulting in up to 50% reduction in yield in some years. In a 2-yr study, ‘Honeycrisp’ trees were treated with six foliar treatments including 20 mg·L−1 1-naphthaleneacetic acid (NAA) 2 wk before anticipated harvest (WBAH), 125 mg·L−1 aminoethoxyvinylglycine hydrochloride (AVG) 4 WBAH, AVG plus NAA 2 WBAH, and repeat sprays of 200 mg·L−1 B, and 2000 mg·L−1 Mg applied 48–93 d after full bloom to evaluate their effect on PFD and fruit quality. Fruit drop associated with broken pedicels and physiological causes was monitored. During a year with ∼43% PFD on untreated control trees, AVG retained up to ∼35% and NAA retained up to ∼27% of the total fruit number, relative to the control trees. The combination of AVG plus NAA had similar PFD compared with AVG alone, while B and Mg were similar to the control. The proportion of PFD associated with broken pedicels was ∼5%. Aminoethoxyvinylglycine delayed starch degradation, ethylene evolution, and blush skin colour development of fruit. This study supports the use of AVG 4 WBAH and NAA 2 WBAH to manage ‘Honeycrisp’ PFD, which may offer economic advantages for growing quality apples. Foliar sprays of Mg or B failed to reduce PFD.