Morphological and physiological changes during maturation and ripening of eight Asian pear cultivars grown in the southeastern United States were evaluated. Fruit size increased throughout maturation. Flesh firmness decreased as fruit matured and averaged ≈30 to 35 N at harvest maturity. The average TSS in mature fruit ranged from 10% to 13%, with `Shinko' having the lowest and `Shinsui' having the highest. TSS increased during 4 weeks of storage at 1C, but the increase was greater in immature fruit than in mature fruit. Respiration rate declined as fruit matured. Ethylene production was low in `Hosui', `Kosui', `Nijisseiki', `Shinseiki', `Chojuro', and `Shinko' fruit. Mature `Ichiban' and `Shinsui' fruit produced high amounts of ethylene. `Kosui', `Shinsui', `Chojuro', and `Ichiban' fruit showed a climacteric rise in respiration and ethylene production at 20C, while `Hosui', `Nijisseiki', `Shinseiki', and `Shinko' behaved as nonclimacteric fruit. Ethylene production by 1C-stored `Kosui', `Shinsui', `Chojuro', and `Ichiban' fruit was increased on removal to 20C. Glucose and fructose were low during early maturation but sharply increased ≈80 to 85 days after full bloom (DAFB). Sucrose was low in immature fruit but accumulated rapidly late in maturation ≈100 to 107 DAFB. In mature `Hosui', `Kosui', `Nijisseiki', `Shinsui', `Shinko', and `Ichiban' fruit, fructose was the predominant sugar, while in `Shinseiki' and `Chojuro' fruit, sucrose was the predominant sugar.
Nihal Rajapakse and William C. Newall
Nihal C. Rajapakse and William C. Newall
Changes in sugar composition during maturation and ripening of eight Asian pear cultivars were evaluated. Total soluble sugars (TSS) increased gradually throughout the maturation and averaged 10% to 13% in mature fruit. All cultivars, except `Shinko' and `Nijisseiki', had accumulated ≥10% TSS by 100 days after full bloom (DAFB). Starch accumulated during early stages of Asian pear fruit development but decreased as the maturity progressed coinciding with the rise in soluble sugars. Sorbitol, a sugar alcohol, was predominant in immature fruit and accounted for 35% to 60% of TSS fraction depending on the cultivar. Fructose rapidly increased during early maturation. Glucose increased during early maturation, but the increase was much smaller than that of fructose. Sucrose was low (<4%) in immature fruit but accumulated rapidly late in the maturation and continued to increase until harvest. In mature `Hosui', `Kosui', `Nijisseiki', `Shinsui', `Shinko', and `Ichiban' fruit, fructose was the predominant sugar which accounted for 47% to 60% of the TSS fraction. Glucose and sucrose accounted for 13% to 17% and 7% to 12%, respectively, in those cultivars. In mature `Shinseiki' fruit, sucrose was the predominant sugar (44% of TSS), while fructose and glucose accounted for 33% and 8%, respectively. Sucrose and fructose were present in equal amounts (29%) in mature `Chojuro' fruit. Late accumulation of sucrose in Asian pear cultivars suggest that sufficient time should be allowed before harvesting to obtain sweeter fruit.
Sandra B. Wilson and Nihal C. Rajapakse
Plant response to photoselective plastic films with varying spectral transmission properties was tested using lisianthus (Eustoma grandiflorum) `Florida Pink', `Florida Blue', and `Florida Sky Blue'. Films were designated YXE-10 (far-red light-absorbing film) and SXE-4 (red light absorbing film). Light transmitted through YXE-10 films reduced plant height compared to control plants by 10% (`Florida Blue'), and stem dry weight by 19% to 40%, but the response varied by cultivar. Internode length was reduced by 10% to 19% when `Florida Pink' and `Florida Sky Blue' plants were grown under YXE-10 films. Leaf and root dry weights were not affected by YXE-10 films, with the exception that `Florida Sky Blue' plants had a lower leaf dry weight than the control plants. Light transmitted through SXE-4 films increased plant height of `Florida Pink' plants by 15% but not of `Florida Blue' or `Florida Sky Blue.' Regardless of cultivar, dry weight of leaf, stem and root tissue was not affected by SXE-4 films as compared to control films. The average number of days to flower and bud number were not affected by YXE-10 or SXE-4 films, regardless of cultivar. The results suggest that selective reduction of far-red wavelengths from sunlight may be an alternative technique for greenhouse production of compact plants, but the magnitude of the response is cultivar specific.
Shumin Li, Nihal C. Rajapakse and Ryu Oi
The far-red light intercepting photoselective plastic greenhouse covers have been shown to be effective in producing compact vegetable transplants. However, photoselective films reduce the photosynthetic photon flux (PPF) transmission compared to conventional plastic films because of the dye contained in the film. The low PPF in greenhouses covered with photoselective films may result in decreased plant dry matter production and could especially be a problem in the season with low light level and in northern latitudes. Therefore, this study was conducted to determine if covering at the end of the day (EOD) with photoselective films was effective in controlling height of vegetable seedlings. This will allow growers to maintain a high light level during daytime for optimum growth of plants. Cucumber seedlings were exposed to light transmitted through a photoselective film and a clear control film. Three exposure durations: continuous, exposure to filtered light from 3:00 pm to 9:00 am, and from 5:00 pm - 9:00 am, were evaluated. Results show that, after 15 days of treatment, about 25% of height reduction could be achieved by exposing the plants at the EOD from 3:00 pm to 9:00 am or from 5:00 pm to 9:00 am. Plants grown continuously under filtered light were the shortest. Compared to plants grown in photoselective chamber continuously, EOD exposed plants had greater leaf, stem and shoot dry weights, greater leaf area and thicker stem. Specific leaf and stem dry weights were also greater in EOD exposed plants. Number of leaves was not significantly affected by any exposure periods tested. The results suggested that the EOD use of photoselective film is effective in reducing height of cucumber seedlings. The responses of other crops need to be evaluated to test the feasibility of using photoselective film as a EOD cover on wide range of crops.
Shumin Li, Nihal C. Rajapakse and Ryu Oi
Growth chamber experiments were conducted to investigate the effectiveness of several photoselective plastic films in controlling height of `Sweet Success' cucumber, `Mt. Pride' tomato, and `Capistrano' bell pepper transplants. Four types of treatment films; a control, two far-red light intercepting films (YXE-1 and YXE-10), and a red light intercepting film (SXE-1), with R: FR ratios of 1.0, 2.0, 1.6, and 0.8, respectively, were used as the covering materials of experimental chambers. Photosynthetic photon flux (PPF) was adjusted to be the same in all chambers with cheese cloth. Treatment period for cucumber and tomato was 15 days and that for bell pepper was 20 days. At the end of the treatment, significantly shorter plants were found in both YXE-1 and YXE-10 chambers for all the three tested crops. However, YXE-10 was more effective than YXE-1 in producing compact cucumber, tomato and bell pepper transplants. SXE-4 film produced taller plants than control film. Magnitude of response to filtered light varied with the crop species. Number of leaves was not significantly affected by the light transmitted through photoselective filters, indicating that the height reduction was mainly caused by the reduction in internode length. With the commercial development of photoselective greenhouse covers or shade material in the near future, nursery and greenhouse industry could potentially reduce the cost for growth regulating chemicals, reduce the health risks to their workers and consumers, and reduce environmental pollution.
V.R. Kambalapally and Nihal C. Rajapakse
The role of light quality on growth, flowering, and postharvest characteristics of `Nellie White' Easter lilies (Lilium longiflorum Thunb.) was evaluated in two growing seasons using 4% CuSO4 and water (control) as spectral filters. The CuSO4 filter significantly reduced plant height and internode length. However, the height reduction was smaller in the 1994—95 season (9%) than in the 1995—96 growing season (32%). The number of days to flower bud appearance and flower opening, and the number and diameter of flowers were not significantly affected by the spectral filters in either season. The CuSO4 filters reduced flower longevity by 3 days in nonstored plants, and by 5 days when plants were subjected to 1 week storage at 4 °C prior to placing in the postharvest room. Results suggest that spectral filters are effective in controlling height and producing compact Easter lily plants without causing a delay in flowering or reducing number of flowers per plant but flower longevity can be adversely affected.
Venkat K. Reddy and Nihal C. Rajapakse
The response of `Bright Golden Anne' chrysanthemum plants grown under CuSO4 spectral filters to exogenous GA3 application was evaluated to determine the relationship between gibberellins (GAs) and carbohydrate levels. The CuSO4 filters removed far red (FR) wavelengths of light and increased red: far red (R:FR), blue: far red (B:FR), blue: red (B:R) ratios, and phytochrome photoequilibrium (Ø) values of transmitted light compared to water (control) filter. Plant height, internode length, and leaf and stem dry weights were significantly reduced by light passing through CuSO4 filters in spring and summer seasons. Weekly applications of exogenous GA3 reversed the reduction in height and internode length induced by CuSO4 filters. Plants grown under CuSO4 filters responded more to exogenous GA3 application with respect to height and internode length, suggesting that the sensitivity to GA was not lowered. Light passing through CuSO4 filters reduced the carbohydrate levels, but the response varied with the season. Weekly GA3 application increased the carbohydrate levels, but did not totally reverse the reduction in carbohydrate levels under the CuSO4 filters. Although GA3 application increased the carbohydrate levels partially in CuSO4 filter-grown plants, the inhibition of GAs may not be solely responsible for reduction of carbohydrate levels under CuSO4 filters, showing that exogenous GAs and carbohydrate levels are not well correlated under CuSO4 spectral filters.
Sonja L. Maki and Nihal C. Rajapakse
Endogenous gibberellins of chrysanthemum [Dendrathema×grandiflorum (Ramat) cv. Bright Golden Anne] were characterized in preparation for quantification of endogenous gibberellins in apices under control and CuSO4 spectral filters. Expanding shoots were separated into young expanding leaves and apices. Methanolic extracts of young expanding leaves were purified by solvent partitioning, PVPP column chromatography, and reversed-phase high performance liquid chromatography. Two bioactive regions corresponding to the HPLC retention times of GA and GA19 standards were detected in fractions using the recently developed non-dwarf rice bioassay. Dideuterated internal standards of GA12, GA53, GA19, GA20, and GA1 were added to similar extracts of shoot apices. The presence of endogenous GA53, GA19, GA20, and GA1 in chrysanthemum apices was confirmed by isotope dilution using gas chromatography–mass spectrometry-selected ion monitoring and Kovats retention indices. Ions for the deuterated internal standard of GA12 were detected, but not for endogenous GA12. The above results demonstrate that the early 13-hydroxylation pathway operates in chrysanthemum.
Nihal C. Rajapakse and John W. Kelly
Transpiration rates of chrysanthemum [Dendranthema ×grandiflorum (Ramat.) Kitamura] plants grown under spectral filters were evaluated as part of an investigation on using light quality to regulate plant growth. The 6% CuSO4·5H2O spectral filter reduced photosynthetic photon flux density in red (R) and far red (FR) wavelengths and increased the R: FR and blue (B): R ratios (B = 400 to 500 nm; R = 600 to 700 nm; FR = 700 to 800 nm) of transmitted light relative to the water (control) filter. After 28 days, cumulative water use of plants grown under CuSO4 filters was ≈37% less than that of control plants. Transpiration rates were similar among plants grown under CuSO4 and control filters when expressed as leaf area, a result suggesting that the reduced cumulative water loss was a result of smaller plant size. Plants grown under CuSO4 filters had slightly lower (10%) stomatal density than control plants. Light transmitted through CuSO4 filters did not alter the size of individual stomata; however, total number of stomata and total stomatal pore area per plant was ≈50% less in plants grown under CuSO4 filters than in those grown under control filters due to less leaf area. The results suggest that altering light quality may help reduce water use and fertilizer demands while controlling growth during greenhouse production.
Venkat K. Reddy and Nihal C. Rajapakse
The influence of removal of specific wavelengths [red (R), blue (B), and farred (FR)] from sunlight on the height of chrysanthemum plants was investigated by overlaying Roscolux™ colored acetate films on 4% CuSO4 or water (control) spectral filters. CuSO4 filters removed FR wavelengths and significantly reduced plant height and internode length compared to control plants that received B, R, and FR wavelengths of light. Plants grown under Roscolux blue filters did not receive R light and were significantly taller compared to plants from any other treatments. Plants grown under Roscolux red filters did not receive B light and were significantly shorter compared to plants from other treatments. Leaf area, leaf dry weight, and stem dry weight were highest in plants grown under Roscolux red and control filter combination. The amount of leaf chlorophyll and the ratio of Chl A: Chl B was highest in plants grown under Roscolux blue filters. In general, plants that received FR light (control + film) were taller than the plants that did not receive FR light in the corresponding (CuSO4 + film) filter combination. The influence of removal of specific wavelengths on plant height control and developmental physiology will be discussed.