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Quantification of seed dormancy has been achieved by measuring physiological, biochemical, and molecular changes accompanying dormancy release, as well as dormancy development. At the physiological level, dormancy is quantified in terms of stratification time, strength of embryo covering structures, embryo growth potential, responsiveness to light, and to temperatures and other changes. At the biochemical level, dormancy has been related to hormone (abscisic acid, gibberellin, etc.) levels, respiratory activity, and other metabolic functions. At the molecular and cellular level, dormancy has been associated with RNA and protein synthesizing ability and with gene expression. Our recent studies with lettuce seeds using gibberellin biosynthesis inhibitors indicate that the amount of gibberellin produced during seed soak may mediate dormancy release and is quantitatively related to the level of dormancy. Examples of quantifiable changes associated with dormancy will be described. Whether a quantifiable change reflects a causal relationship with dormancy release or development, or is a consequence thereof, will be discussed.
A gibberellic acid (GA) biosynthesis inhibitor, tetcyclacis, induced dormancy in nondormant seeds of lettuce (Lactuca sativa L.), tomato (Lycopersicon esculentum Mill.), pepper (Capsicum annuum L.), carrot [Daucus carota var. sativus (Hoffn.)], onion (Allium cepa L.), celery (Apium graveolens L.), and impatiens (Impatiens novette), as most of the seeds failed to germinate after washing under conditions that permitted germination before dormancy induction. In lettuce seeds, tetcyclacis and paclobutrazol were more effective in inhibiting germination in light than in darkness. A 16- to 24-h soak treatment with tetcyclacis was sufficient to induce dormancy in nearly all seeds. Tetcyclacis failed to induce dormancy if applied after 6 h presoak in water. Dormancy induced by tetcyclacis was released by GA4+7 (a mixture of gibberellin A4 and A7), light, and moist-chilling treatments. When GA4+7 was applied with tetcyclacis, dormancy induction was prevented under both favorable, e.g., 25C, and unfavorable, e.g., 5C, or low water potential (Ψ), germination conditions. Unlike tetcyclacis, abscisic acid (ABA) failed to induce dormancy in lettuce seeds. Thermodormancy induction in lettuce seeds at 35C was prevented by fluridone. However, neither ABA nor tetcyclacis countered its effect. Dormancy was also induced in lettuce seeds by ancymidol, flurprimidol, or paclobutrazol. Dormancy induced by tetcyclacis in pepper, tomato, carrot, and onion seeds was released by GA4+7, but not by irradiation or moist-chilling. Chemical names used: 5-(4-chlorophenyl)-3, 4, 5, 9, 10-pentaazatetracyclo [5.4.102,6.08,11]-dodeca-3, 9-diene (tetcyclacis); 1-(4-chlorophenyl)-4, 4-dimethyl-2-(1H-1, 2, 4-triazole-1-yl)-3-pentanol (paclobutrazol); α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidine methanol (ancymidol); α-(1-methyl)-α-[4-(trifluoromethoxy) phenyl]-5-pyrimidine-methanol (flurprimidol); 1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4 (1H)-pyridinone (fluridone).
ACC-derived ethylene production was used as an index of seed vigor of lettuce (Lactuca sativa L.), cabbage [Brassica oleracea (Capitata Group)], tomato (Lycopersicon esculentum Mill.), snap bean (Phaseolus vulgaris L.), and sweet corn (Zea mays L.) seeds. Seeds were aged at 40C and 93% relative humidity over saturated solution of KH2PO4 for various times to obtain seeds of differing vigor. Naturally aged lettuce seeds, differing in vigor, were also used. Depending on the seed type, 0.25 to 2 mm ACC (saturating dose) was needed to produce maximal amounts of ethylene. Seeds in the presence of ACC produced a much larger amount of ethylene than those in the absence of ACC, the ACC-derived ethylene could be detected before germination, and ACC had no adverse effect on germination. ACC-derived ethylene production paralleled vigor loss as determined by a decrease in percentage germination over a soak period required for complete germination of nonaged seeds (16 hours for lettuce, 24 hours for cabbage, and 48 hours for tomato and sweet corn), an increase in mean germination time (determined for lettuce only), and a decrease in seedling growth (determined for snap bean only). Second degree polynomial and logarithmic equations generated for the relationship of ACC-derived ethylene production to germination or growth parameters following seed aging, provided good to excellent fit. As a vigor test, the ACC-ethylene procedure has several advantages over the non-ACC ethylene procedure: It improves the sensitivity of the test by enhancing ethylene production, permits detection of small differences in vigor, and allows detection of ethylene before germination within a few hours of soaking. Chemical name used: 1-aminocyclopropane-1-carboxylic acid (ACC).
1-aminocyclopropane-1-carboxylic acid (ACC) was used to measure seed vigor of lettuce, cabbage, tomato, snap bean and sweet corn seeds. Accelerated aging at 40C and 93% RH over saturated solution of KH2PO4 and natural aging under ambient storage conditions (5-7C, 28 to 60% RH) were used to obtain seeds of differing vigor levels. Depending on the type of seeds, the amount of ACC needed for maximal ethylene production (saturating dose) ranged from 0.25 to 2mM. Seeds produced much larger amounts of ethylene in the presence than in absence of ACC, the ACC-derived ethylene was detected prior to germination, and ACC had no adverse effect on germination. ACC-derived ethylene production paralleled vigor loss as determined by percentage germination, mean germination time (for lettuce only) and seedling growth (for snap bean only). Second degree polynomial and logarithmic equations generated for the relationship of ACC-derived ethylene production to germination or growth parameters following seed aging, provided good to excellent fit. As a vigor test, the ACC-ethylene procedure has several advantages over the non-ACC ethylene procedure: it greatly improves the sensitivity of the test by enhancing ethylene production, it permits detection of small differences in vigor levels and it allows detection of ethylene prior to germination within a few hours of soaking.
This research work was carried out for 2 years at Kelardasht-Mazandaran and Mardabad-Karaj Agricultural Research Stations to evaluate the rooting of selected and hybrid F12/l and Colt rootstocks under climatic conditions of Iran. Young F12/l and colt rootstocks (semi-hard wood and summer cuttings) available in Kelardasht Agricultural Research Station were used These rootstocks were also used for layering. Summer cuttings were taken in early July and, after wounding, were treated with IBA with 1000, 2000, and 3000 ppm and then put under mist. Three months later the rooted cuttings were evaluated on the basis of rooting percentage, number and the length of the main and the lateral roots and the length of the rooted section. The hardwood cuttings were prepared in two intervals (early Dec. and late March) and, when wounded, were treated with IBA with the same concentrations. Finally, the experiments were completed by horizontal layering of several rootstocks and covering them with soil. The results were used in a completely randomized block design in four treatments, and the averages were compared by Duncan test. The results indicate that the summer cuttings treated with 1000 ppm IBA have the highest rooting percentage in both rootstocks, while those treated with 2000 ppm gave the best results with regard to number and the length of the main root. The best result on the number and the length of the lateral roots are achieved in cuttings treated with 2000 ppm IBA. Number and the length of lateral roots in Colt and F12/l rootstocks are, respectively, high in cuttings treated with 2000 and 3000 ppm. IBA. In semi-hardwood cuttings, different concentrations of IBA were effective on callus formation and budbreak. Thus, there were more callus formation in high concentration and the number of budbreaks was reduced. Study on the layering method indicates that there are 6.1 and 3 rooted cuttings in every Colt and F12/l layered rootstocks respectively. The rooting percentage in the said rootstocks is 100% and 73.3%, respectively.
Abstract
Improved emergence rate and final stand occurred when ‘Ruby Queen’ beet seed pellets, amended with 1.10 to 3.95 mg polyethylene glycol 8000 (PEG) per seedball, were field planted. The number of seedlings per seedball 17 days after planting ranged from 1.39 to 1.60 for PEG-amended pellets, compared to 0.71 plants for non-PEG pellets or dry seeds. The PEG-amended seed pellets yielded 16 to 18 marketable roots per meter of row compared to 11 roots from non-PEG pellets.
Mango malformation is one of the major factors causing significant fruit loss in Pakistan. To investigate the role of malformation a long-term field experiment was established on 15 years old mango orchard. Malformation inflorescences were removed and counted in last week of April and fruit were harvested in July every year starting from 1989. Malformed inflorescence varied from plant to plant however, during 1990, 1991 and 1992 it decreased considerably over the control year (1989). The malformation was 77% during control year 1989, 57% during 1990, 57% during 1991 and 50% during 1992. Mango fruit yields were significantly decreased due to non-bearing malformed inflorescences. The mean yield decrease was 83 % during 1989 which relatively improved in later years and were 58% in 1990, 53% in 1991 and 54% in 1992.
The quality of three dragon fruit clones (Hylocereus spp.) was determined after x-ray irradiation for disinfestation of quarantine pests. Fruit were treated with irradiation doses of 0, 200, 400, 600, or 800 Gy and stored for 12 days at 10 °C. Irradiation did not affect soluble solids content, titratable acidity, or fructose concentrations. Glucose, sucrose, and total sugar concentrations decreased linearly as dose increased. Minimal softening occurred in the outer flesh layers for fruit treated with 400 or 600 Gy irradiation. Surface color, peel injury, and bract appearance differed among the three clones with irradiation stress, but in all cases, visible changes were minor. Fruit decay was absent or minimal, and disease ratings were not affected by irradiation. Irradiation treatment of dragon fruit at doses 800 Gy or less would ensure visual and compositional quality while providing quarantine security.