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  • Author or Editor: Aref A. Abdul-Baki x
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Abstract

It is beyond the purpose of this presentation to review all the definitions for the term “vigor” as applied to seeds. So far, no one definition has been accepted, and perhaps it is not yet time to settle on one definition until we know more about the subject.

Open Access

Selected breeding lines and cultivars of tomatoes (Lycopersicon esculentrum Mill.) were evaluated for heat tolerance in the greenhouse (39°C day and 28°C night) and field using flowering, fruit-set, yield, fruit quality, and seed production as criteria. Under high temperature, heat tolerant lines performed better than the other two groups in all evaluation criteria except for seed production. The opposite was found under normal field conditions where heat sensitive commercial cultivars outyielded the heat tolerant lines and cultivars. Production of viable seeds under high temperature was severely reduced regardless of the heat tolerance level exhibited by the line or cultivar. Some of the heat tolerant lines could provide valuable sources of plant material for physiological studies to establish the molecular basis of heat tolerance and also could provide excellent germplasm sources for breeding heat tolerant tomato cultivars.

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Nine heat-tolerant tomato [Lycopersicon esculentum (Mill.)] breeding lines, four heat-tolerant cultivars, and four heat-sensitive cultivars were evaluated in the greenhouse under high temperature (39C day/28C night) and in the field. Criteria for heat tolerance included flowering, fruit set, yield, fruit quality, and seed production. Under high-temperature conditions, the group of heat-tolerant lines, the heat-tolerant cultivars, and the heat-sensitive cultivars produced, respectively, the following per plant: flowers, 186, 94, and 55; fruit set 70%, 52%, and 30%; yield, 410, 173, and 11 g; and normal mature fruit, 72%, 37%, and 7%. Yields of heat-tolerant lines under high temperature in the greenhouse ranged from 118% to 31% of their respective yields in the field. Yields of heat-tolerant cultivars were 62% of those in the field. In contrast, yields of heat-sensitive cultivars under high temperature were < 1% of their respective yields in the field. High temperature induced flower abscission, reduced fruit set and yield, and increased the incidence of abnormalities. Major fruit abnormalities with high temperatures included cracks, blossomed rot, watery tissue, and small, immature fruits. Production of viable seeds under the high-temperature regime was severely reduced or totally inhibited regardless of the heat-tolerance level exhibited by the line or cultivar. The failure of heat-sensitive and most heat-tolerant cultivars or lines to produce viable seeds under such a high temperature suggests that a lower level of heat stress than that applied in these experiments could allow the production of enough seeds to test the relationship between heat tolerance in a genotype and its ability to produce viable seeds under high temperature. The results indicate that certain lines have high tolerance to heat and, therefore, could provide valuable sources of plant material for physiological studies to establish the physiological and molecular bases of heat tolerance. Some of the heat-tolerant lines might also serve as excellent germplasm sources in breeding heat-tolerant tomato cultivars.

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A procedure is described for determining pollen viability in tomatoes (Lycopersicon esculentum Mill.) by growing pollen in a growth medium containing 0.29 M sucrose, 1.27 mm Ca(NO3)2, 0.16 mm H3 BO3, and 1 mm KNO3 (pH 5.2) to which 0.001% fluorescein diacetate (FDA) was added. Pollen viability can be evaluated within 30 min by determining percent fluorescing pollen in a sample. The procedure further allows the determination of percent germination in vitro and pollen tube growth within 1.5 hours. Neither the germination medium nor FDA has any adverse effects on germination and pollen tube growth. Percent fluorescent pollen and percent total pollen germination were highly correlated, suggesting that fluorescence is a good measure of pollen viability. The combined fluorescence-germination procedure is simple and adapted to routine screening of many samples.

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The diffusion coefficient of CO2 in `Russet Burbank' potato (Solanum tuberosum L.) tubers was determined under steady-state conditions at 10 and 27C. The data showed that the skin is the main barrier to gas diffusion, with an average diffusion coefficient of 6.57 × 10-7 and 7.61 × 10-7 cm·s-1 at 10 and 27C, respectively. The flesh also presents an appreciable barrier to gas diffusion. The average diffusion coefficient of CO2 in the flesh was 2.00 × 10-4 and 2.24 × 10-4 cm·s-1 at 10 and 27C, respectively. Under regular storage conditions, the tuber is well aerated and the concentration of O2 at the center of the tuber is sufficient to maintain aerobic respiration.

Free access

Abstract

Green and sun-bleached seeds of cultivars ‘G 2’ and ‘Green Fordhook 861’ lima beans (Phaseolus lunatus L.) were analyzed for total chlorophyll in whole seeds, and for soluble protein and rates of synthesis of carbohydrates, proteins, and lipids in excised embryonic axes. Bleached seeds were lower in total chlorophyll than green seeds. Embryonic axes from bleached seeds synthesized less carbohydrates and proteins, but more lipids than embryonic axes from green seeds. When held in water for 3 hours, embryonic axes from ‘G 2’ lima beans had about 65% more soluble protein, and respired 20% faster than embryonic axes from ‘Green Fordhook 861’. Whole ‘G 2’ lima bean seeds also emerged faster than ‘Green Fordhook 861’ seeds. In each cultivar, green seeds had a higher percent emergence than bleached seeds.

Open Access

Abstract

Green seeds from lima bean (Phaseolus lunatus L.) cvs. G 2 and Green Fordhook 861, contain chlorophylls a and b in a ratio of about 2:1. Chlorophyll content per seed increases during development, reaches a max about 5 weeks after pod formation, then declines sharply during maturation. Bleached seeds have less chlorophyll, especially chlorophyll a, and carotene than non-bleached seeds.

In developing and mature lima bean seeds max chlorophyllase activity appears during the stage which corresponds with max chlorophyll content rather than the stage of most rapid loss of chlorophyll. The enzyme is particulate, located in the chloroplast membranes, and has an optimum pH of 8.5 ± 0.2.

The low carotene content of seeds of green-seeded commercial cultivars might contribute to their sensitivity to light. Several cultivars that were obtained from other countries. (Plant Introductions) contain 10 to 20 times as much carotene as the commercial cultivars tested. These “Introductions” provide genetic material for increasing the carotene content of lima bean seeds. High carotenes would improve nutritional value of beans and might reduce or prevent bleaching.

Open Access

Growth analysis was used to document growth responses of staked, fresh-market tomatoes (Lycopersicon esculentum Mill.) to black polyethylene or hairy vetch (Vicia villosa Roth) mulches. Leaf area and dry mass of vegetation and fruit were measured weekly during two growing seasons. Growth was better early in the season but worse later in the season for plants grown with black polyethylene than with hairy vetch mulch. Unit leaf rate (rate of growth per unit leaf area) of fruit was higher with black polyethylene than with hairy vetch, whereas the reverse was true of vegetation. This relationship led to a higher leaf area ratio and leaf area duration of plants grown with hairy vetch than with black polyethylene. Consequently, tomatoes grown with black polyethylene produced higher early yield because of increased partitioning to fruit. However, tomatoes grown with hairy vetch eventually outgrew and outyielded those grown with black polyethylene because of increased partitioning to leaf area.

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A 3-year study was conducted at the Beltsville Agricultural Research Center, Beltsville, Md., to evaluate plant stand, growth, and yield of snap bean (Phaseolus vulgaris L.) cultivars Carlo and Matador grown with conventional tillage (CT) or with no-tillage hairy vetch (Vicia villosa Roth) (HV) mulch. Plant stand and dry mass of both cultivars in CT were similar to those in no-till HV. However, leaf area and yield with no-till HV were significantly higher than those with CT.

Free access

Stand, plant growth, and yield were determined on `Matador' and `Carlos' snap beans (Phaseolus vulgaris L.) that were planted as a summer crop in a 3-year study using conventional tillage (CT) and no-till hairy vetch (Vicia villosa L. Roth) mulch (HV) systems. The CT plots received (kg·ha–1) 67 N as ammonium nitrate at preplanting and both CT and HV plots received (kg·ha–1) 17N–34P–17K with the planter. Stand differences between CT and HV were not significant. Average yields in CT and HV over a 3-year period were 13.3 and 19.8 t·ha–1, respectively. Average plant dry mass 2 days before harvest was not significantly different between CT and HV. Leaf area per plant 2 days before harvest was 1992 and 3092 cm2 in CT and HV, respectively. Higher yield in the HV mulch system, as compared to CT, can be attributed to larger leaf area per plant, higher soil organic matter and water-holding capacity, and less soil compaction in the HV plots.

Free access