The effects of trunk girdling and crop load levels on skin color, juice composition, and root elongation of a red table grape, ‘Aki Queen’ (Vitis labrusca L. × V. vinifera L., tetraploid) were investigated. The treatment of a low crop load with girdling significantly elevated the anthocyanin concentration in berry skin compared to that of a high crop load without girdling. The total soluble solid content of berries was significantly greater in a low crop load with girdling than in other treatments. Titratable acidity was not different among treatments. Root elongation stopped for two weeks as a result of the girdling treatment, regardless of the crop load level. Root elongation after girdle healing was vigorous when the crop load was low.
The anatomical development of cell wall ingrowth (phi thickening) in the cortical tissue adjacent to the endodermis and Casparian strip in endodermal cells was investigated in loquat roots. Phi thickening initially appeared simultaneously approximately 10 mm from the root tip and expanded as the distance from the root tip increased. Phi thickening was observed with increased age in several layers of cortical tissue. Then, the phi thickening attained full size at approximately 30 mm from the root tip. When phi thickening began around the cortex, the initiation of Casparian strip formation appeared as a dot in the endodermis. At the next stage, the Casparian strip appeared partly in several endodermal cell walls facing the phloem sectors before eventually appearing in all endodermal cells. Phi thickening developed considerably before the completion of the Casparian strip in loquat roots. When the development of the Casparian strip finished in the endodermis, the cortical tissue with the phi thickening shed from the endodermis. Upon separation of the cortex and endodermis, the pericycle layers increased laterally to a thickness of 2 to 3 cells and accumulated auto-florescent substances in their cell walls. The Casparian strip appeared further away from root tip in young and white roots than in the old and light brown roots. When roots were sampled from trees planted under drought stress conditions, phi thickening was observed to have developed dramatically compared to normal conditions. The development of phi thickenings of cortex in loquat roots under drought conditions may be regarded as a defense mechanism against water stress.
The salt tolerance of native Asian pear species, Pyrus betulaefolia Bunge., P. pyrifolia Nakai, and P. xerophila Yu, and native Mediterranean ones, P. amygdaliformis Vill. and P. elaeagrifolia Pall., were examined by irrigating them with 75 mM and 150 mM NaCl solutions for 30 days. Native Mediterranean species did not develop leaf injury during the 30-day NaCl treatments, but native Asian species developed leaf injury. Concerning the shank, fine roots, and whole plant, bioregional differences in Na and Cl contents were small. However, the Na and Cl contents of the leaves of native Mediterranean species were markedly less than those of native Asian species in both NaCl concentrations. Therefore, the native Mediterranean P. amygdaliformis and P. elaeagrifolia may have some salt exclusion mechanisms in the shank which restrict Na and Cl transport to the leaves. The stem water potential and Ci/Ca ratios were decreased by NaCl treatments in native Mediterranean and native Asian species. Thus, the photosynthetic decline by NaCl treatment observed in these species might have been caused by stomatal closure, which is likely to be induced by decreased water potential in the plant body. However, the photosynthetic rate of native Mediterranean species under NaCl stress was higher than native Asian species. Therefore, low concentrations of Na and Cl in the leaves of native Mediterranean species might prevent crucial decreases of photosynthetic rates under NaCl stress. The present results imply that native Mediterranean P. amygdaliformis and P. elaeagrifolia have a higher salt tolerance than native Asian P. betulaefolia, P. pyrifolia and P. xerophila. These native Mediterranean species would be useful in providing genetic resources as salt-tolerant rootstock for the Japanese pear.
To clarify the effects of changes in the sensitivity to temperature on skin coloration during ripening, potted ‘Aki Queen’ grapevines (3-year-old) were used. Short-term temperature treatments (1 week) were conducted in two glass growth cabinets under two conditions: low temperature (23°C daytime, 7:00–19:00/18°C nighttime, 19:00–7:00) and high temperature (33°C daytime/28°C nighttime). Temperature treatments were conducted during four different ripening stages. The treatment periods were 4–11 days (Stage I), 11–18 days (Stage II), 18–25 days (Stage III), and 25–32 days (Stage IV) after the onset of coloring. High temperature inhibited skin coloration at all stages except for the first few days of Stage I. Low temperature enhanced skin color from 5 days after the beginning of Stage I to 3 days after the beginning of Stage III. Low-temperature treatments in Stage II caused the greatest increase in skin anthocyanin concentration. These results indicate that the period between 8 and 21 days after the onset of coloring was critical for coloration. The effects of temperature on titratable acidity varied among stages, and low-temperature treatments in Stage I greatly inhibited the decrease of titratable acidity.
The effect of arbuscular mycorrhizal (AM) inoculation and activated charcoal on growth and nutrition in peach seedlings treated with peach root-bark extracts was studied under greenhouse conditions. Peach root-bark extracts significantly inhibited growth in both mycorrhizal and non-mycorrhizal seedlings, although mycorrhizal seedlings demonstrated better growth and biomass yield. Activated charcoal slightly alleviated the negative effects of root-bark extract treatment but reduced the benefits derived from mycorrhizal symbiosis. The initiation of mycorrhizal symbiosis may be delayed by activated charcoal through the adsorption of signal chemicals from host plants. Generally, mycorrhizal seedlings had better P and Ca nutrition. There were no differences in mycorrhizal infection among the inoculated plants, but there was increased sporulation in root-bark extract treatments without activated charcoal. These results suggest that activated charcoal should be applied after mycorrhizal symbiosis has been established.
Cucumber green mottle mosaic virus (CGMMV), which is easily transmitted via foliage contact, soil contamination, and seeds, is one of the major diseases affecting melon (Cucumis melo L.). However, no commercial cultivars resistant to CGMMV are available. In melon, only the symptomless carrier-type accessions ‘Phoot’ and ‘Kachri’ (var. momordica Duthle and Fueler) have been reported to be resistant to CGMMV. Therefore, to identify CGMMV-resistant accessions, 152 melon accessions were screened for resistance to CGMMV by mechanical inoculation. Only plants of the Korean accession ‘Chang Bougi’ (var. makuwa Makino) were resistant to the SH isolate (CGMMV-SH). The influences of temperature on symptom development and CGMMV accumulation in ‘Chang Bougi’ plants were studied. At 24°C, no symptoms were observed in the upper leaves of ‘Chang Bougi’ plants at 25 days after inoculation. In contrast, at 30°C, chlorotic spots were observed in the upper leaves from 15 to 20 days after inoculation. Under greenhouse conditions at an average temperature of 27.3°C, mosaic and chlorotic spots were observed in the upper leaves of ‘Chang Bougi’ plants from 30 days after inoculation. The accumulation patterns of CGMMV in the inoculated portions of ‘Chang Bougi’ and ‘Perlita’ (susceptible control) cotyledons were almost identical. CGMMV was detected in the uninoculated portions of ‘Perlita’ cotyledons from 4 days after inoculation, but was not detected in the uninoculated portions of ‘Chang Bougi’ cotyledons until 10 days after inoculation. Symptoms were observed, and the virus was detected in the upper leaves of ‘Chang Bougi’ plants inoculated with the watermelon isolate (CGMMV-W) or Kyuri green mottle mosaic virus (KGMMV). These results indicate that virus movement was restricted and that growth at 30°C enhances symptoms in this accession. Moreover, the resistance to CGMMV in this accession was specific to the SH isolate.
Hypersensitivity is induced in many species of Acanthaceae and Gesneriaceae by local mechanical wounding. Once a plant of these species sustains a wounded leaf, it exhibits a temporary hypersensitive state and severe injury easily occurrs even in unwounded leaves. Locally wounded African violet (Saintpaulia sp.) plants sometimes show severe injury even at a noninjurious temperature for this species. This study was aimed to clarify changes in the temperature sensitivity of hypersensitivity-induced African violet plants by local wounding. The basal leaves of African violet ‘Ritali’ plants were cut as a local wounding treatment. The locally wounded plants were transferred to growth chambers at various temperatures and we evaluated the degree of leaf injury using an analysis software. In locally wounded plants, temperature sensitivity increased and leaf injury was observed even at 11°C, which is a noninjurious temperature for unwounded African violet. Such a wound-induced sensitivity to low temperature treatment (7°C for 1 h) quantitatively increased with local wounding severity. For the investigation of time-course changes in the hypersensitive state (wounding memory) of locally wounded plants, the plants were transferred to low temperature conditions at various intervals after the wounding treatment. The wounding memory was short-lived, that is, it was generally observed immediately after local wounding and then almost disappeared 30 min after. In conclusion, the low temperature sensitivity of African violet plants was enhanced by prewounding treatment.
1-Methylcyclopropene (1-MCP) strongly inhibits ethylene-mediated ripening effects. Since 1-MCP binds irreversibly to ethylene receptors, and ethylene sensitivity is recovered through the appearance of new ethylene receptors, it is important to characterize ethylene receptor genes to understand 1-MCP efficacy. We isolated three putative ethylene receptor genes from apple fruit and examined Md-ETR1, Md-ERS1, and Md-ERS2 expression patterns in 1-MCP-treated and -untreated fruit of ‘Orin’ and ‘Fuji’. In both cultivars, treatment with 1-MCP suppressed ethylene production and rapidly decreased expressions of Md-ERS1 and Md-ERS2, but Md-ETR1 mRNA was slightly reduced by the application of 1-MCP. One possible explanation for the high 1-MCP efficacy in apple fruits is that 1-MCP suppresses ethylene production and Md-ETR1 is expressed in 1-MCP-treated fruit. Md-ERS1 and Md-ERS2 mRNAs accumulated more abundantly in untreated ‘Fuji’, which has a long shelf life, than in ‘Orin’. Since ethylene receptors negatively regulate ethylene signaling, differences in expression levels between the cultivars might be reflected in differences in ethylene sensitivity.