Intensity Of Dormancy Research Articles

A comprehensive phenotypic and genotypic evaluation of Spanish groundnuts from diverse crosses to identify superior and stable donors for fresh seed dormancy

Breeding high yielding groundnut cultivars with 2–3 weeks of fresh seed dormancy, particularly in Spanish-type cultivars, enhances the sustainability of agriculture in groundnuts. In this context, we conducted a comprehensive phenotypic and genotypic evaluation of advanced breeding lines developed in the genetic background of Spanish types. By employing multi-phenotyping and marker data, we identified PBS 15044, 16004, 16013, 16015, 16016, 16017, 16020, 16021, 16026, 16031, 16035, 16037, 16038, 16039, 16041, and 16042 with 2–3 weeks dormancy (> 90%).The various parametric and non-parametric estimates identified the stable fresh dormant genotypes with one or more superior economic trait. PBS 16021, 15044, 16038, and 16039 identified with high hundred pod weight (HPW) were also reported having high intensity of dormancy (> 90% for up to 3 weeks); PBS 15044, 16016, PBS 16038 and PBS 16039 with high hundred kernel weight (HKW) also reported with up to 3 weeks fresh seed dormancy; and PBS 16013, 16031, and 16038 with up to 3 weeks fresh seed dormancy had high shelling percentage (SP). They can be used to develop lines with the desired level of dormancy, and high yields, by designing appropriate breeding strategies.

Effects of agroclimatic conditions on sunflower seed dormancy at harvest

At harvest sunflower seeds (Helianthus annuus L.) are dormant and poorly germinate at 10 and 25 °C. Seed sensitivity to low temperatures (10 °C) results from an embryo dormancy whereas the envelopes (pericarp and seed coats) inhibit the germination at 25 °C. Removal of pericarp greatly improved seed germination when the germination of whole achenes was higher than the critical value of 20 %. Using 107 seed batches corresponding to 26 genotypes cultivated in 2015, 2016 and 2017 in various production areas in France (Center and South) and Spain (South), we investigated the effects of agro-environmental factors on the depth of dormancy at harvest. A principal Component Analysis (PCA) performed with all the seed batches did not show any significant effect of the genotype (variety or female) and year of production on the intensity of dormancy, but it revealed the role of agro-climatic conditions. Experimental field trials performed with plants treated by a chemical desiccant after flowering demonstrated that accelerated desiccation during seed maturation on the mother plant was associated with lower dormancy. Our data also suggest that the longest the duration of the developmental cycle from sowing to harvest, the lowest the dormancy at harvest. We provide new insights into the modulation of dormancy intensity by genetic and environmental factors which might have practical applications in seed production.

Perubahan Perilaku Dormansi selama Proses Desikasi pada Benih Kacang Bambara (Vigna subterranea L. Verdc.)

Bambara groundnut seeds often show unsynchronized and slow germination even though on newly harvested seeds. This might be due to the presence of seed dormancy. Therefore, the objective of this research was to obtain the information on seed dormancy and germination behaviour of bambara groundnut seeds during desiccation. The experiment was arranged in a nested design. Dormancy breaking treatments (untreated, mechanical scarification, soaking in 1% KNO3 for 2 hours, mechanical scarification followed by KNO3 soaking) were nested in each of the desiccation levels (fresh seeds with 54.7% moisture content (mc), desiccated seeds with 44.4%, 18.0%, 15.4%, and 12.1% mc). The results showed that newly harvested seeds were in dormant state. Seed desiccation did not increase the intensity of seed dormancy, even resulted in an increase in field emergence (at 30 days after planting) from 43.9% in fresh seeds to around 70% in dry seed (12-15% mc). Seed desiccation (from 44.4% mc to 12.1% mc) increased the field emergence, although it was inadequate to break the dormancy completely. Meanwhile, seed desiccation tended to increase the GA/ABA ratio, but the seed permeability was decreased. The fact showed that seed desiccation reduced the intensity of dormancy of bambara groundnut seed, therefore, it is suggested to modify the drying method in order to accelerate the increasing of GA/ABA ratio while keeping the testa permeable.
 Keywords: after-ripening, GA/ABA ratio, hard seed, kacang bogor, permeability

Dynamics of the diaspore and germination stages of the life history of an annual diaspore-trimorphic species in a temperate salt desert.

Individuals of the annual halophyte Atriplex centralasiatica produce three kinds of diaspores that differ in dispersal, dormancy/germination response and type of seed bank formed, which likely is a bet-hedging strategy in the rainfall-unpredictable environment on the semi-arid, saline Ordos Plateau in Inner Mongolia, China. Seasonal fluctuations in environmental conditions provide germination cues for the establishment of seedlings at the right time and place to ensure plant survival and population regeneration. Diaspore heteromorphism is a phenomenon in which diaspores with stark qualitative differences in morphology and ecology are produced by the same maternal plant. Germination responses and dispersal times of the annual halophyte Atriplex centralasiatica were examined to determine the role of diaspore heteromorphism in its adaptation to salt desert conditions. A. centralasiatica is a tumbleweed that produces three types of diaspores that differ in morphology and ecophysiology. The relative potential dispersal ability and intensity of dormancy of the three diaspore types was type A (fan-shaped diaspores with yellow fruits) < type B (fan-shaped diaspores with black fruits) < type C (globular diaspores with black fruits). In the field, type A retained high germinability, but all of them were depleted from the (transient) soil seedbank in the first growing season. Types B and C cycled between dormancy and nondormancy, and 0 and > 90.0% remained in the soil seedbank 2years after dispersal, respectively. The dormancy, dispersal and salt tolerance of type B diaspores were intermediate between those of A and C. Type A exhibited low dispersal-nondormancy, type B exhibited intermediate dispersal-intermediate dormancy and type C exhibited high dispersal ability-high dormancy. In the unpredictable salt desert habitat, the functional differences in germination and dispersal of the three diaspores act as a bet-hedging mechanism and ensure population establishment in different years by spreading germination over time and space.

Water absorption and physiological responses of hog plum tree diaspores to storage

Abstract Hog plum tree seeds (Spondias mombin L.) have a complex dormancy mechanism, which causes slow germination and great unevenness. At present, there are no efficient methods to promote seed germination. The objective of the study was to evaluate the effect of storage on overcoming seed dormancy of this Anacardiaceae. Diaspores of two hog plum trees were used, identified as Mother plant 1 and Mother plant 2, established in Tomé-Açu city, PA. Initially, it was investigated whether the structures surrounding the seeds (internal mesocarp and endocarp) prevent water absorption. For this, the diaspores of the two mother plants were sown between blotting paper, with an adequate level of water and, periodically, in the total of 144 hours, the water content of the seeds was computed. The storage studies involved two experiments. In the first, diaspores from both mother plants with a water content of around 5.0% were stored in impermeable packages, for one year, under the following conditions: natural environment of Belém, PA (average temperature of 26.8 °C) and at temperatures of 6 ± 1 ° C and minus 18 ± 2 °. The germinative response of the stored diaspores was compared with those of non-stored diaspores. Prior to storage, selection was made on the diaspores, discarding the small ones. In the second experiment, the germinative response of the diaspores of the two mother plants, stored for zero, one, two, three, four, five and six months, under natural environment conditions of Belém, PA, was evaluated. It was observed that the structures that cover the seeds do not offer restrictions to the water absorption, thus discarding the hypothesis of physical dormancy, without, however, excluding the possibility of mechanical dormancy. The storage of diaspores for one year, regardless of the storage condition, did not affect the germination power of the seeds. On the other hand, responses of great magnitude, in terms of reducing the time required for germination, were obtained when the diaspores were stored under natural conditions and at minus 18±2 °C, indicating that dormancy is naturally overcome by storage . Overcoming dormancy was a little slower when the diaspores were stored at a temperature of 6±1 °C. It was found that the storage of diaspores in an environment with an average temperature of 26.8 °C for three months provides the overcoming dormancy of most of the seeds. The intensity of dormancy varied within and between mother plants.

Multi-environment evaluation of Spanish bunch groundnut genotypes for fresh seed dormancy

The present study was carried out to evaluate eight promising Spanish bunch groundnut genotypes during four consecutive year (2014, 2015, 2016, 2017) to study genotype × environmental interactions and to identify stable sources of fresh seed dormancy in Spanish background in groundnut. Pooled analysis of variance revealed highly significant differences among the genotypes and genotype × environmental interactions for fresh seed dormancy at weekly intervals indicating that differential behavior of genotypes for fresh seed dormancy over the environmental conditions. Based on the results of intensity and duration of dormancy and germination stability index, identified four stable advanced breeding lines viz., PBS 12192, PBS 12187, PBS 12191 and PBS 12190 having high fresh seed dormancy of three week and two stable advanced breeding lines viz., PBS 12189 and PBS 12171 having high fresh seed dormancy of two week. Therefore, these genotypes can be used as novel genetic stock of fresh seed dormancy in Spanish bunch and they can be integrated into breeding programs to develop high yielding Spanish bunch cultivars with 2-3 weeks of fresh seed dormancy to avoid yield losses due to in-situ germination at the time of crop maturity.

Water stress, temperature regimes and light control induction, and loss of secondary dormancy in Brassica napus L. seeds

AbstractThis study investigated the induction and loss of dormancy in oilseed rape (Brassica napus). Twenty genotypes were preliminary screened; from these, two genotypes, RGS003 and Hayola 308, which possess high potential for dormancy induction (HSD) and medium potential to induce secondary dormancy (MSD), were selected. The stratification of seeds at alternating temperatures of 5–30°C (in dark) significantly relieved secondary dormancy, but dormancy was not fully released. The ψb(50) values were −1.05 and −1.06 MPa for the MSD and the HSD before dormancy induction. After inducing dormancy, the ψb(50) values for the MSD and the HSD were increased to −0.59 and −0.01 on day 0 stratification at 20°C. The hydrothermal time (θHT) value was low for one-day stratification for HSD in comparison with other stratification treatments. Water stress can induce dormancy (if the seeds have the genetic potential for secondary dormancy) and warm stratification (in dark) can only reduce the intensity of dormancy. The seeds with a high potential of dormancy induction can overcome dormancy at alternating temperatures and in the presence of light. It can, therefore, be concluded that a portion of seeds can enter the cycle of dormancy ↔ non-dormancy. The secondary dormant seeds of B. napus cannot become non-dormant in darkness, but the level of dormancy may change from maximum (after water stress) to minimum (after warm stratification). It seems that the dormancy imposed by the conditions of deep burial (darkness in combination with water stress and more constant temperatures) might be more important to seed persistence than secondary dormancy induction and release. The dormancy cycle is an important pre-requisite in order to sense the depth of burial and the best time for seed germination.

Dormancy and bud burst in sultana vines

Dormancy and bud burst have been studied for sultana vines in the Murray Valley, Australia. The vines are in deep dormancy at the beginning of autumn and the intensity of dormancy decreases gradually during autumn and winter. Bud burst of cuttings taken during the dormant period occurs the more rapidly the higher the temperature at which they are held. There is evidence to suggest that sultanas have no chilling requirement and no clear distinction between organic and enforced dormancy. Treatment with 3 ml of ethylene chlorhydrin in a.201 container for 24 hours is effective in breaking dormancy. The most effective treatment veries slightly with the intensity of dormancy. Removing the outer bud scales or soaking buds in water decreases the intensity of dormancy. The pattern of bud burst found on canes in the field is established on pruned canes at least one month before the shoots appear. Both auxin and gibberellin will delay bud burst and reduce the proportion of buds which burst but auxin will not affect a bud above the point of application whereas gibberellin will do so.

BUD DORMANCY INTENSITY IN PEACH TREE CULTIVARS BY BIOLOGICAL AND TETRAZOLIUM TEST

ABSTRACT Temperate climate fruit trees often exhibit uneven budding and flowering, due to the low number of chilling hours that determine the occurrence of dormancy and its depth. The objective of this study was to determine the depth of bud dormancy in peach tree cultivars and evaluate the efficiency of the tetrazolium test for dormancy and comparing with biological test. Branches of the cultivars Aurora 1, Chimarrita, Chiripá, Coral, Eldorado, Granada, Leonense, Maciel, Marli, Premier, and Vanguard were collected between May and August 2008 at two locations: Curitiba and Lapa. The evaluation of dormancy was performed using a biological test of single node cuttings through the parameters: average time for bud burst, velocity of bud burst, final rate of bud burst and rate of vigorous bud burst. For the tetrazolium test, 300 mg of buds was used and the color intensity readings were obtained using a spectrophotometer. The peach tree cultivars evaluated differ in the intensity of dormancy in late fall. The most intense endodormancy cultivars found were: Chiripá, Leonense and Eldorado cultivars, and the weaker cultivars found were: Aurora 1 and Maciel. The tetrazolium test was efficient at estimating the intensity of dormancy in peach trees when the occurrence of cold was suitable for installation endodormancy. At a location with the lowest occurrence of cold (Curitiba), the tetrazolium test did not simulated successfully the biological test results.

Pre-treatments for overcoming dormancy in Sida alnifolia L.

Seeds of Sida species are reported to exhibit seed coat imposed dormancy posing serve problems in germination. In the present study some Pre-treatments for overcoming dormancy in Sida alnifolia L. were standardized. Among the eighteen pre-treatments tried for improving germination, chemical scarification using concentrated H2SO4 was significantly superior and recorded higher germination percentage and speed. Untreated seeds failed to germinate. Scarification of seeds with concentrated H2SO4 for higher duration of 30 minutes was selected as the best pre-treatment considering improvement in water imbibition, germination percentage, speed of germination, growth and vigour of the seedlings alongwith significant reduction in the intensity of dormancy.

Trade-offs between seed dispersal and dormancy in an amphi-basicarpic cold desert annual.

Several studies have demonstrated trade-offs between depth of seed dormancy and dispersal ability for diaspore-dimorphic species. However, relatively little is known about trade-offs between these two life history traits for a species that produces more than two diaspore morphs. The aim of this study was to investigate the relationship between seed dormancy and dispersal in Ceratocarpus arenarius, an amphi-basicarpic cold desert annual that produces a continuum of dispersal unit morphs. A comparison was made of dispersal and dormancy breaking/germination responses of dispersal units from ground level (a), the middle of the plant canopy (c) and the top of the plant canopy (f). Various features of the morphology and mass of dispersal units and fruits (utricles) were measured. The role of bracteoles in diaspore dispersal by wind, settlement onto the soil surface and dormancy/germination was determined by comparing responses of intact dispersal units and fruits. Movement of dispersal units by wind and animals, seed after-ripening, germination phenology and the presence of water-soluble germination inhibitors in bracteoles were tested using standard procedures. Dispersal units a, c and f differed in morphology and mass; in the majority of cases, extremes were exhibited by a and f, with c being intermediate. Overall, relative dispersal ability was f > c > a, whereas relative intensity of dormancy was a > c > f. Bracteoles increased dispersal distance by wind, enhanced settlement of diaspores onto the soil surface and mechanically inhibited germination. The results provide evidence for a model in which there is a continuous inverse-linear relationship between diaspore dispersal ability and depth of dormancy. Thus, dispersal unit heteromorphism of C. arenarius results in a continuum, from no dispersal ability/high dormancy (dispersal unit a) to high dispersal ability/low dormancy (unit f), which may be a bet-hedging strategy in the cold desert environment.

Seed dormancy and germination characteristics of Astragalus arpilobus (Fabaceae, subfamily Papilionoideae), a central Asian desert annual ephemeral

Although Astragalus is the largest genus of seed plants, it contains only a relatively few annual species, about which little is known with regard to seed dormancy and germination. Thus, seed dormancy-break and germination were investigated in the cold-desert annual Astragalus arpilobus Kar. et Kir. Most of the seeds had a water-impermeable seed coat that became permeable after mechanical or acid scarification, i.e. physical dormancy. Both wet heat and alternate wet heat and cold (ice water) made only a small portion of the seeds permeable, and neither exposure to high nor to low temperatures was effective in breaking dormancy. Scarified seeds germinated at temperatures ranging from 5/2 to 30/15°C, with 20/10°C and 25/15°C being optimal. Non-dormant seeds germinated to high percentages in light and in darkness across the range of temperatures. Germination percentages did not increase with duration of dry storage at room temperature. Scarified seeds germinated to nearly 100% at water potentials between 0 and −0.30MPa but to 0% at −0.77MPa. Seedling emergence was higher for seeds buried at soil depths of 1 and 2cm than at 0 or >2cm. Forty-three percent of the scarified seeds sown in July in an experimental garden under natural conditions germinated in autumn, and an additional 5% germinated in spring. In contrast, no non-scarified seeds germinated in autumn, and only 5.3% of them germinated in spring. Most of the non-scarified seeds that did not germinate became part of the persistent seed bank. Our results indicate that the high intensity of hard-seed dormancy in the annual A. arpilobus is similar to that reported for the perennial species of Astragalus.

Mode of overwintering of invasive Harmonia axyridis in the Netherlands

After establishment of Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) in Europe, population densities of native ladybird species have decreased. The post-hibernation onset of female reproduction, a key characteristic influencing population dynamics and competition with related species, was studied. Hibernating individuals were collected and transferred to outdoor cages to continue overwintering. Every two weeks a sample of individuals was transferred to long-day, warm conditions. Intensity of dormancy was studied by determining the pre-oviposition period and ovarian development. Pre-oviposition periods were short throughout our observations, indicating that Harmonia axyridis was not in diapause but in a quiescent state. H. axyridis becomes active rapidly when temperature rises in spring but is not active earlier in the year than native species. Neither the mode of overwintering, nor the onset of spring activity can explain the invasion success of H. axyridis.

Environmental control of germination and dormancy of seeds of two cytotypes of Lygeum spartum L., a perennial grass of semi-arid and arid areas in Algeria

Au moment de leur récolte, les unités de dispersion de deux cytotypes de Lygeum spartum L. sont dormantes. Cette dormance correspond à une germination difficile à toutes les températures ainsi qu’à l’optimum thermique (20-25 °C) et à une impossibilité de germer dans une large gamme de températures. Aucune semence ne germe au-dessous de 10 °C et au-dessus de 30 °C. À la température optimale, la germination est fortement inhibée par la lumière blanche continue et une réduction du potentiel hydrique du milieu à – 1MPa. L’élimination de la dormance par une conservation au sec de 12 mois à la température ambiante entraîne un élargissement de la gamme de températures permettant une germination rapide. Cependant, l’optimum thermique reste similaire à celui des semences fraîchement récoltées, c’est-à-dire 20-25 °C. La dormance résulte principalement des enveloppes, mais le caryopse nu joue aussi un rôle dans la photosensibilité des semences entières. L’intensité de la dormance dépend du lieu de récolte ; elle est plus profonde pour les semences récoltées dans la zone semi-aride (cytotype polyploïde, 2n = 40) que pour celles collectées sur les hauts plateaux arides (cytotype diploïde, 2n = 16). Le rôle écologique de la dormance et de la post-maturation au sec est discuté en relation avec l’établissement de cette espèce dans un environnement aride.

Phenotypic variation in caryopsis dormancy and seedling salt tolerance in wild barley, Hordeum spontaneum, from different habitats in Israel

The phenotypic variation in caryopsis dormancy and seedling salt tolerance was investigated in 16 wild barley ecotypes in Israel. Depth of dormancy, as reflected by the time to maximum germination percentage, ranged from 15 to 103 days under dormancy-break treatment. Lower dormancy was characteristic of the mesic ecotypes, whereas deeper dormancy was characteristic of the xeric ecotypes. Dormancy-break patterns were revealed by growth curves: the xeric ecotype showed an S-shaped curve, whereas the mesic ecotype displayed a reverse L-shaped curve. Seedling salt tolerance was assessed by the ratio of root or coleoptile length in a seedling grown in 100 or 200 mM NaCl solution to that of a seedling grown in water. The root- and coleoptile-length ratios of mesic ecotypes were much higher than that of the xeric ecotypes, except that there was no observable difference in coleoptile-length ratio at 100 mM NaCl. The mesic ecotype was more tolerant to salt than the xeric ecotype at the young seedling stage, and seedling salt tolerance was negatively correlated with caryopsis dormancy depth. Thus evolutionary background environments have had a strong effect on the intensity of caryopsis dormancy in wild barley. Through natural selection, wild barley has adapted to dry and hot environments by increasing dormancy but not young seedling salt tolerance.

Dinâmica da dormência e brotação de gemas de vimeiro no Planalto Sul Catarinense

O objetivo deste trabalho foi avaliar a dinâmica e a heterogeneidade de dormência de gemas, e avaliar o efeito de diferentes épocas de colheita de ramos na brotação do vimeiro, no Planalto Sul Catarinense. Ramos de ano foram colhidos nos meses de abril a agosto de 2005, nos municípios catarinenses de Lages, Bocaina do Sul e Urupema. A dormência de gemas foi avaliada em estacas retiradas da base (0 a 12 cm), centro (12 a 24 cm) e ápice (24 a 36 cm) de ramos com comprimento superior a 150 cm. Foram utilizadas estacas com e sem redução para uma única gema. As brotações das plantas em campo também foram avaliadas. A dormência mais intensa de gemas de ramos de ano ocorreu em maio, quando a intensidade de dormência e a freqüência de gemas dormentes decresceram do ápice para a base do segmento basal dos ramos. A colheita do vime em abril induziu a brotação antes do inverno e prejudicou a brotação primaveril.

CALOGÊNESE EM DIFERENTES ESTACAS DE CAQUIZEIRO TRATADAS COM FRIO E ÁCIDO INDOLBUTÍRICO

Objetivou-se avaliar a influência da época de coleta, tratamento com frio e doses de ácido indolbutírico (AIB) na calogêneseem estacas de caquizeiro ‘Fuyu’. Formulou-se a hipótese que sendo o caquizeiro uma espécie que apresenta dormência em intensidades variadas durante o outono e inverno, então o crescimento celular necessário à calogênese é influenciado pela época do ano e pelo efeito do frio, que juntos podem tornar as células responsivas à ação das auxinas. Os ramos foram coletados em 29/08 (estacas lenhosas) e 21/02 (estacas semi-lenhosas) e em cada época, metade dos ramos foi tratada com 504 horas de frio (4 a 7° C) e metade foi submetidaà estaquia após tratamento com AIB (0, 1.000, 2.000 e 3.000 mg L-1). Determinou-se a velocidade de brotação das gemas e após 60 dias foram avaliadas a porcentagem de estacas com calo, brotadas, dormentes e mortas. A calogênese foi maior (20,83 %) nas estacas semi-lenhosas não tratadas com frio. Nas estacas lenhosas não houve formação de calos. Nas estacas semi-lenhosas a velocidade de brotação foi menor que nas estacas lenhosas mas nestas últimas houve maior mortalidade (90,04 %). O tratamento com AIB não influenciou a calogênese. Concluiu-se que a calogênese foi favorecida nas estacas semi-lenhosas não tratadas com frio. A velocidade de brotação foi mais intensa nas estacas lenhosas e tratadas com frio. As estacas semi-lenhosas apresentaram-se mais dormentes, principalmente as submetidas ao tratamento com frio. Houve um maior percentual de estacas mortas entre as estacas lenhosas tratadas com frio.

Etiolated growth in relation to energy reserves and winter survival in three temperate grasses

The role of energy reserves in development of winter hardiness was examined in timothy (Phleum pratense L.), orchardgrass (Dactylis glomerata L.) and perennial ryegrass (Lolium perenne L.) through periodically measuring etiolated growth (EG; shoot growth of crown under dark, warm and humid conditions following defoliation) and determining sugar profiles at critical stages of hardening and wintering. Seasonal changes in weight and duration of EG were monitored by sampling once or twice a month from September to the following April. In all species, total etiolated growth (TEG; total shoot production at each sampling time as determined by weekly or biweekly harvests until exhaustion of reserves) increased from September to reach peak levels during the second hardening stage in mid-November. Thereafter, TEG remained high until the following spring in orchardgrass while it declined linearly in timothy, which had the lowest TEG. The decline in TEG was intermediate in perennial ryegrass. Changes in the duration of EG were most marked in orchardgrass, as it required six weeks to produce about 150 mg g-1 TEG in early November but only one week in March. The results indicated occurrence of dormancy in apical meristems of orchardgrass at the end of the first hardening stage with temperatures above 0 °C, which roughly corresponded with the phase of dormancy in woody plants. Dormancy was weak in timothy and largely undetectable in perennial ryegrass, as measured by the EG technique. A positively significant correlation between total nonstructural carbohydrates (TNC) content and TEG was found in all species. Detailed analysis, however, showed that direct estimation of TNC content using TEG was difficult because TEG production per unit TNC was negatively correlated with TNC level, and the amount of TNC unused in early autumn was more than in the rest of the season. Changes in sugar profiles occurred at transition from the first to the second hardening stage with subzero temperatures and varied with wintering strategy of each species. Simple sugar content dramatically declined while fructan content increased in both timothy (cv. ‘Senpoku’) and orchardgrass (cv. ‘Wasemidori’), which were selected at sites covered with snow for more than 120 days. In contrast, a cold tolerant perennial ryegrass cv. `‘eveille’ selected in the Netherlands retained high amounts of simple sugars. The results suggest that EG technique is suitable to monitor physiological status (amount and rate of mobilization of energy reserves, intensity of dormancy and bud development) of plants expressing winter hardiness.

Dormancy, Cold Hardiness, and Spring Frost Hazard inVitis amurensisHybrids under Continental Climatic Conditions

Seven <i>Vitis amurensis</i> hybrid selections were studied for intensity of dormancy, winter hardiness, and earliness of budbreak during the 2000/2001 dormant season under continental climatic conditions in southern Missouri. Results of a budbreak assay demonstrated that buds from six of the seven hybrid selections could be released from dormancy under forcing conditions as early as October. Throughout November and December, the intensity of dormancy was lower in all <i>V. amurensis</i> hybrids than in the French-American hybrid variety Vignoles. These observations suggest that endodormancy is relatively short in <i>V. amurensis</i> hybrids. In these grapes, the first evidence of bud growth in the field was observed in early January, two to three weeks earlier than in Vignoles. Bud and shoot growth were several phenological stages in advance of Vignoles throughout late winter and early spring. The examination of buds at the end of the dormant season revealed that primary bud mortality was lower (<i>p</i> ≤0.05) in three of the <i>V. amurensis</i> hybrid selections than in Vignoles. A late spring frost event, however, destroyed large numbers of emerging shoots on the hybrid selections, killing 37 to 93% of the young shoots at node positions 1 through 5. All seven of the <i>V. amurensis</i> hybrid selections suffered greater spring frost damage (<i>p</i> ≤0.05) than Vignoles, which was at a considerably less advanced phenological stage. The data suggest that <i>V. amurensis</i> has limited value as a genetic resource in continental North America, where winters are characterized by widely fluctuating temperatures and spring frosts are common.

Changes in the Intensity of Bud Dormancy and Internal Compositions of Current Shoot in Fig

To estimate the intensity of bud dormancy in fig (Ficus carica L.) 'Masui Dauphine', current shoots in the field were collected monthly from July 1999 to March 2000 and cut at the 5th, 8th, 11th, 14th, 17th and 20th nodes. The cutting were kept in water at 25°C under fluorescent light (5klx) continuously. The percentage of budbreak within 20 days and the days to 80% budbreak were recorded. The water, carbohydrate, and abscisic acid (ABA) contents of each shoot were also measured. The percentage of budbreak within 20 days at 25°C on all nodal position was 40%, in late November; the basal nodes tended to have lower % budbreak than the upper ones. Water content increased with the growth of the current shoots, reaching over 60% during the introductory phase of endodormancy. The starch accumulated during this period; it was hydrolyzed to sugar at the onset of budbreak or the awaking phase. The ABA content increased only during the introductory phase of endodormancy. The endodormancy of the fig bud was classified into three phases, i.e., 1) introductory (early October to early November), 2) deepest (late November) and 3) awaking phases (middle December to late January). The fig shoot can be heated or headed back at any season to get fruitbearing shoots for double cropping or year-round production. These treatments force most buds to sprout within a short period, even when they are in the deepest phase of endodormancy.