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Light duration alters carbon partitioning among carbohydrates (CHOs) in source leaves. The current experiments were designed to determine how light duration affected the metabolism of newly fixed and reserve CHOs in various organs of apple and whether longer durations favored sorbitol (sor) synthesis. One-year-old `Gala' apple plants that experienced a 1-, 4-, 7-, 10-, or 14-h photoperiod for 7 d were exposed to 14CO2 for 15 min. Individual CHO concentrations and the activity of newly-fi xed [14C]CHOs in leaves, stems, and roots were analyzed during different intervals after labeling. In source leaves, sor increased significantly, whereas sucrose (suc) did not change as light duration increased from 1 to 10 h, resulting in increased sor/suc ratios from 2.6 in the 1-h to 4.3 in the 10-h light duration. The increased sor/suc ratios may be due primarily to the preferential carbon partitioning into sor in longer light durations. Longer light durations enhanced the sor export rate from source leaves, resulting in higher sor in stems and sink tissues. In roots, starch increased significantly over increasing light durations. A major portion of starch in roots may be converted from newly fixed CHO. Our results suggest that light duration alters the metabolism of sor and other CHOs in source and sink tissues of apple and that the changes in CHO concentrations result from different rates of carbon synthesis, partitioning, and export.
Sorbitol synthesis in apple leaves requires NADPH, a product of photosynthetic light reactions. Light duration directly affects NADPH production, thus, variation in light duration may influence sorbitol synthesis and alter the ratios of sorbitol to other carbohydrates. Our experiments were designed to determine whether light duration altered photosynthate partitioning among carbohydrates and whether longer light durations favored sorbitol synthesis. One-year-old `Gala' apple plants that experienced a 1-, 4-, 7-, 10-, or 14-hour photoperiod for 7 days were exposed to 14CO2 for 15 minutes. Individual carbohydrate concentrations and the activity of newly-fixed [14C] carbohydrates were analyzed during different intervals for 24 hours after labeling. Sorbitol and fructose concentrations increased significantly as light duration increased from 1 to 10 hours, then remained stable at a light duration of 14 hours, whereas starch concentration increased linearly over increasing light durations. Sucrose and glucose concentrations were not significantly altered by light duration. The sorbitol: sucrose ratios increased while sorbitol: starch ratios decreased as light duration increased from 1 to 14 hours. Newly-fixed [14C] carbohydrates varied diurnally. Similar changes during the different light duration periods were found for individual [14C] carbohydrates and unlabeled carbohydrate concentrations. Our results suggest that longer light durations favored sorbitol synthesis over sucrose, and NADPH concentration may become a rate-limiting factor for sorbitol synthesis during short light durations.
Flower development in opium poppy (Papaver somniferum L.) has been divided into four phases from emergence to anthesis, which mark changes in its sensitivity to photoperiod: a photoperiod-insensitive juvenile phase (JP), a photoperiod-sensitive inductive phase (PSP), a photoperiod-sensitive post-inductive phase (PSPP), and a photoperiod-insensitive post-inductive phase (PIPP). To predict flowering time under field conditions, it is essential to know how these phases are affected by temperature. Plants were grown in artificially lit growth chambers and received three temperature treatments: 15/10, 20/15, and 25/20°C in a 12-hr thermoperiod. Plants were transferred within each temperature regime from a non-inductive 9-hr to an inductive 16-h photoperiod or vice versa at 1- to 4-day intervals to determine the durations of the four phases. Temperature did not affect the durations of the first two phases (i.e., JP lasted 3 to 4 days and PSP required 4 to 5 days). The most significant effect of temperature was on the duration of PSPP, which lasted 28, 20, and 17 days at 15/10, 20/15, and 25/20°C, respectively. The temperature effect on PIPP was small (maximum difference of 3 days for treatments) and the data too variable to indicate a significant trend. Our results indicate that PSPP is the only phase that clearly exhibits sensitivity to temperature.
Flower development in opium poppy (Papaver somniferum L. `album DC') is enhanced by long photoperiods (PP ≥ 16-hours). Predicting time to flower in field-grown opium poppy requires knowledge of which developmental stages are sensitive to PP and how the rate of flower development is changed by changes in PP. The objective of this work was to determine when poppy plants first demonstrated developmental changes in response to PP and how long PP continued to influence the time to first flower under consistent temperature conditions. Plants were grown in artificially lit growth chambers with either a 16- (inductive) or a 9-hour PP (noninductive). Plants were transferred at 1 to 3-day intervals from a 16- to a 9-hour PP and vice versa. All chambers were maintained at a 12-hour thermoperiod of 25/20°C. Poppy plants demonstrated developmental changes in response to PP four days after emergence and required a minimum of four inductive cycles before the plant flowered. Additional inductive cycles, up to of a maximum of nine, hastened flowering. After 13 inductive cycles, flowering time was no longer influenced by PP. These results indicate four phases between emergence and first flower: 1) a photoperiod-insensitive juvenile phase (JP); 2) a photoperiod-sensitive inductive phase (PSP); 3) a photoperiod-sensitive post-inductive phase (PSPP); and 4) a photoperiod-insensitive post-inductive phase (PIPP). The minimum durations (days) of these phases under the conditions of our experiment were JP = 4, PSP = 4, PSPP = 9, and PIPP = 14.
Burrowing nematode, Radopholus similis, reduces flower-yield-infected anthurium fields. Genetic resistance is one alternative to chemical control of the disease in anthurium. Seventeen commercial anthurium varieties, established in vitro on anthurium nutrient medium, were inoculated with burrowing nematodes to screen for tolerance. Three months after inoculation, plant responses were compared by number of nematodes recovered and by symptom index and plant weight loss with respect to non-inoculated plants. Results show that `Mauna Kea' and `Flamingo' anthuriums are among the most tolerant, while `Ozaki' is one of the most susceptible. These results are consistent with grower field evaluation. Nematode count is positively correlated with symptom index and weight loss. The mechanism of tolerance or resistance of anthurium toward burrowing nematode is unclear. However, due to the fact that burrowing nematode is a migratory endoparasite, a preinfectional resistance or tolerance mechanism is more likely to take place.
Flowering time, growth, and opium gum yield from five seed sources (T, L, B1, B2, B3) of opium poppy (Papaver somniferum L.) collected from different latitudes in three Southeast Asian countries were determined. Plants were grown in six growth chambers at a 11-, 12-, 13-, 14-, 15-, or 16-hour photoperiod with a 12-hour, 25/20 °C thermoperiod. Flower initiation was observed under a dissecting microscope (40×) to determine if time to floral initiation was identical for all accessions across a wide range of photoperiods. The main capsule was lanced for opium gum at 10, 13, and 16 days after flowering (DAF). Plants were harvested at 21 DAF for plant height, leaf area, and organ dry-weight determinations. In a 16-hour photoperiod, flower initiation was observed 10 days after emergence (DAE) for B1 vs. 8 DAE for the other four accessions. Flowering time was affected most by photoperiod in B1 and least in B2. Flowering times for B3, L, and T were similar across the range of photoperiods. B2, B3, and L had the highest gum yields per capsule; even though B1 had the greatest total plant biomass, it produced the lowest gum yield. There was no difference among accessions in the average ratio of gum: individual capsule volume. For the ratio of gum: capsule dry weight, only the difference between T and B1 was significant. Capsule size did affect these ratios slightly. T had a larger gum: volume ratio for larger capsules, and B3 had a smaller gum: dry-weight ratio for heavier capsules. Flowering time varied up to 40%, capsule dry weight up to 41%, and opium gum yield up to 71% for the five accessions across all treatments. No relationship was found between flowering time and the latitude where the seed sources were collected. Time to flower initiation could not be used to predict time to anthesis because floral development rates varied significantly among accessions and photoperiods. Capsule volume and dry weight were useful in estimating gum yield.
Purple blotch (Alternari a porri) and thrips (Thrips tabaci) can seriously reduce yields of short day onions in South Texas. The level of injury caused by these organisms is influenced by the concentration of nitrogen in leaf tissue. Lower levels of tissue nitrogen increase susceptibility to A. porri but decrease susceptibility to thrips. The purpose of this study was to evaluate the effect of tissue N levels on joint susceptibility of 4 onion cultivars to A. porri and thrips. Foliage was fertilized at 0, 4, 8, 12 or 16 lbs N/ac/wk for 6 weeks. Nitrogen concentrations in onion leaves varied over time and by leaf age, but showed very little effect due to foliar fertilization. Significant differences in thrips were noted among cultivars, but not among leaf N concentrations with cultivars. Purple blotch outbreak occurred late in the growing season and was not related to leaf N levels. Total N uptake failed to respond to foliar fertilization, therefore overall use efficiency of the foliar N applied averaged only about 10% relative to the amount taken up in the check plots.
Abstract
Head weights of ‘Nagaoka 55’ Chinese cabbage (Brassica rapa L. ssp. pekinenis (Lour.) Olsson) were 76–79% greater at a plant spacing of 43 cm than at 28 cm. Percentage salable and grade 1 heads both increased with increasing distance between plants. Seedlings were raised in cylindrical containers of 2.5, 3.75, 5 and 7.5 cm diameter × 6.4 cm depth for 3,4,5 and 6 weeks in a seedling house. Transplant age affected maturity time minimally and did not affect yield. Seedling fresh weight was greater in 7.5 cm containers than in the smaller containers at all transplant ages. Plants started in 7.5 cm containers matured 7.5 days earlier, produced 10% heavier heads and yielded 25–31% more than plants started in 2.5 cm containers. Plants from the larger containers probably performed better as a result of the more favorable physical properties or fertilization regime of the container media. The highest yields in these trials exceeded 3 MT/ha · day.
Nitrogen (N) deficiencies can significantly reduce plant growth as well as flower quantity and quality. However, excessive N application leads to increased production costs and may cause water contamination as a result of runoff. Ground-based remote sensing of plant chlorophyll content offers the possibility to rapidly and inexpensively estimate crop N status. The objective of this study was to test the reliability of three different Normalized Difference Vegetation Index (NDVI) measuring methods and Soil-Plant Analyses Development (SPAD) chlorophyll meter values as indicators of geranium (Pelargonium ×hortorum L.H. Bailey) N status. Two potted geranium cultivars, Rocky Mountain White and Rocky Mountain Dark Red, were supplied with N at 0, 50, 100, and 200 mg·L−1 levels, respectively. NDVI readings were measured at 45 cm above the canopy or media of individual plants or 45 cm above the canopy of a group of plants (four plants treated with the same N rate were placed together). Significant correlations existed between indirect chlorophyll content measurements of SPAD values and NDVI readings regardless of four-pot group or single-pot measurements with N application rates and leaf N concentration. Using a cross-validation technique in discriminant analysis, 70.8% to 79.2% of sample cases were correctly categorized to the corresponding N statuses including very deficient, deficient, and sufficient. Therefore, ground-based, non-destructive measurements of a chlorophyll meter and pocket NDVI unit were able to indicate N status. Considering that flower color can interfere with NDVI measurements, the chlorophyll meter may better determine N content when flowers are present.
Demand for organically grown produce is increasing, largely due to concerns of consumers about health and nutrition. Previous studies have not shown a consistent difference of essential nutrients, such as vitamins and minerals, between organic food crops and the conventional counterparts. However, to date, little consideration has been given to phytochemicals, secondary plant metabolites with potential health-promoting properties. We first discuss factors that can infl uence the levels of phytochemicals in crops, and then we critically review the results of published studies that have compared the effects of organic and conventional production systems on phytochemical contents of fruit and vegetables. The evidence overall seems in favor of enhancement of phytochemical content in organically grown produce, but there has been little systematic study of the factors that may contribute to increased phytochemical content in organic crops. It remains to be seen whether consistent differences will be found, and the extent to which biotic and abiotic stresses, and other factors such as soil biology, contribute to those differences. Problems associated with most studies tend to weaken the validity of comparisons. Given the limitations of most published studies, needs for future research are discussed.