Lack Of Dormancy Research Articles

Himalayan orogeny and monsoon intensification explain species diversification in an endemic ginger (Hedychium: Zingiberaceae) from the Indo-Malayan Realm

The Indo-Malayan Realm is a biogeographic realm that extends from the Indian Subcontinent to the islands of Southeast Asia (Malay Archipelago). Despite being megadiverse, evolutionary hypotheses explaining taxonomic diversity in this region have been rare. Here, we investigate the role of geoclimatic events such as Himalayan orogeny and monsoon intensification in the diversification of the ginger-lilies (Hedychium J.Koenig: Zingiberaceae). We first built a comprehensive, time-calibrated phylogeny of Hedychium with 75% taxonomic and geographic sampling. We found that Hedychium is a very young lineage that originated in Northern Indo-Burma, in the Late Miocene (c. 10.6 Ma). This was followed by a late Neogene and early Quaternary diversification, with multiple dispersal events to Southern Indo-Burma, Himalayas, Peninsular India, and the Malay Archipelago. The most speciose clade IV i.e., the predominantly Indo-Burmese clade also showed a higher diversification rate, suggesting its recent rapid radiation. Our divergence dating and GeoHiSSE results demonstrate that the diversification of Hedychium was shaped by both the intensifications in the Himalayan uplift as well as the Asian monsoon. Ancestral character-state reconstructions identified the occurrence of vegetative dormancy in both clades I and II, whereas the strictly epiphytic growth behavior, island dwarfism, lack of dormancy, and a distinct environmental niche were observed only in the predominantly island clade i.e., clade III. Finally, we show that the occurrence of epiphytism in clade III corresponds with submergence due to sea-level changes, suggesting it to be an adaptive trait. Our study highlights the role of recent geoclimatic events and environmental factors in the diversification of plants within the Indo-Malayan Realm and the need for collaborative work to understand biogeographic patterns within this understudied region. This study opens new perspectives for future biogeographic studies in this region and provides a framework to explain the taxonomic hyperdiversity of the Indo-Malayan Realm.

Novel loci and a role for nitric oxide for seed dormancy and preharvest sprouting in barley.

Barley is used for food and feed, and brewing. Nondormant seeds are required for malting, but the lack of dormancy can lead to preharvest sprouting (PHS), which is also undesired. Here, we report several new loci that modulate barley seed dormancy and PHS. Using genome-wide association mapping of 184 spring barley genotypes, we identified four new, highly significant associations on chromosomes 1H, 3H, and 5H previously not associated with barley seed dormancy or PHS. A total of 71 responsible genes were found mostly related to flowering time and hormone signalling. A homolog of the well-known Arabidopsis Delay of Germination 1 (DOG1) gene was annotated on the barley chromosome 3H. Unexpectedly, DOG1 appears to play only a minor role in barley seed dormancy. However, the gibberellin oxidase gene HvGA20ox1 contributed to dormancy alleviation, and another seven important loci changed significantly during after-ripening. Furthermore, nitric oxide release correlated negatively with dormancy and shared 27 associations. Origin and growth environment affected seed dormancy and PHS more than did agronomic traits. Days to anthesis and maturity were shorter when seeds were produced under drier conditions, seeds were less dormant, and PHS increased, with a heritability of 0.57-0.80. The results are expected to be useful for crop improvement.

Clinal population divergence in an adaptive parental environmental effect that adjusts seed banking

Bet-hedging via between-year seed dormancy is a costly strategy for plants in unpredictable environments. Theoretically, fitness costs can be reduced through a parental environmental effect when the environment is partly predictable. We tested whether populations from environments that differ in predictability diverged in parental effects on seed dormancy. Common garden-produced seeds of the two annual plant species Biscutella didyma and Bromus fasciculatus collected along an aridity gradient were grown under 12 irrigation treatments. Offspring germination was evaluated and related to environmental correlations between generations and their fitness consequences at the four study sites. One species exhibited strong seed dormancy that increased with unpredictability in seasonal precipitation. The parental effect on seed dormancy also increased proportionally with the environmental correlation between precipitation in the parental season and seedling density in the following season; this correlation increased from mesic to arid environments. Because fitness was negatively related to density, this parental effect may be adaptive. However, the lack of dormancy in the second species indicates that bet-hedging is not the only strategy for annual plants in arid environments. Our results provide the first evidence for clinal variation in the relative strength of parental effects along environmental gradients.

Rayada specialty: the forgotten resource of elite features of rice.

Crop domestication and thereafter gradual selection or directional breeding have narrowed the genetic diversity of elite varieties and even promoted gathering of deleterious mutations in their stress response mechanisms, whereas local ecotypes, landraces and wild relatives still growing on native environment and preferences keep the genetic diversities for features like stress tolerance. Rayada is such an exceptional ecotype, variant of typical deepwater rice, completely endemic to certain areas of Madhumati river tracts of Bangladesh and still shares some features of wild rices. Multiple physiological features of Rayadas are distinctly different from typical deepwater rice. Tolerance to prolonged flood, submergence and cold are special features along with strong photoperiod sensitivity and lack of dormancy. Moreover, longer root system and prompt recovery capacity make it as an elite resource of stress tolerance. However, it has long been neglected because of mainly its long life cycle and poor yield. This review examines the specialty of Rayada rice and the potential use of its unique traits.

DORMANCY INDEX OF APPLE TREE BUDS MEASURED BY THE SINGLE NODE CUTTING BIOLOGICAL TEST

In the test known as single node cutting biological test, which is widely used for dormancy intensity evaluation of temperate tree fruit buds, one-bud cuttings are placed in a local propitious for their growth and the average shooting time (AST) is directly related to the bud's dormancy intensity. However, AST analysis alone generates not so conclusive results since other factors such as final shooting (FS), shooting velocity (SV), and vigorous shooting final rate (VSR) are also indicators of dormancy. The objective of this work was to reunite these four parameters in a single formula so that dormancy may be more precisely evaluated by a dormancy index (DI). The data used to develop the DI were obtained by testing 1-year-old 'Imperial Gala' apple tree buds. DI was directly proportional to AST and inversely proportional to FS, SV and VSR. Each parameter was multiplied by a constant factor, according to its importance in the dormancy analysis. The general formula is DI = AST.(k.FS + w.SV + VSR) -1 . The constant variables k and w must be calculated accordingly to the species being studied. As for apple, they are k = 3 and w = 2. By using the DI, the dormancy intensity was classified in 5 groups: lack of dormancy (DI ≤ 2); weak dormancy (2 14). For other fruit species, a new DI should be formulated.

Microsatellite Fingerprinting of the USDA‐ARS Tropical Agriculture Research Station Cacao (Theobroma cacao L.) Germplasm Collection

Cacao (Theobroma cacao L.) is an important cash crop in many tropical countries. Cacao accessions must be propagated vegetatively to conserve genetic integrity due to its allogamous nature and its seed recalcitrance (lack of dormancy). Therefore, cacao germplasm is usually maintained as living trees in field collections and has resulted in varying rates of misidentification and duplication. Using a high throughput genotyping system with 15 microsatellite loci, all 924 trees in the USDA‐ARS Mayaguez cacao collection were fingerprinted. Nineteen accessions (12.3%) were found to have intraplant errors while 14 (9.1%) synonymous sets were identified that included replicates of 49 accessions. The average number of alleles (8.8; SE = 0.56) and gene diversity (HObs = 0.65; SE = 0.026) indicate a high allelic diversity in this collection. A distance‐based cluster analysis and a Bayesian assignment test showed that the cacao accessions can be classified into four distinct clusters, with their geographical origins covering most of the cacao growing regions in the Americas. Assessment of the representative diversity of the collection led to the identification of several genetic gaps, including underrepresented genetic populations and particular traits of economic and agronomic value. The improved understanding of identities and structure in the USDA‐ARS cacao collection will contribute to more efficient use of cacao in conservation and breeding.

Effect of pre-soaking and pre-chilling treatments on seed germination of Pinus roxburghii provenances from western Himalaya, India

After subjecting the seeds to GA3, and H2O2 treatments for 24 h and chilling at 2–3°C for a period of 15 days, we conducted the seed germination tests for 21 different seed sources of Pinus roxburghii from western-central Himalaya under laboratory conditions at various temperatures viz., 20°C, 25°C and 30°C inside a seed germinator. The results reveal that the soaking of seeds in H2O2 (1% v/v) and GA3 (10 mg·L−1) solutions manifested 82.39% and 78.19% germination, respectively whereas untreated seeds exhibited 70.79% average germination. Both GA3 and H2O2 treatments caused an appreciable shortening of the germination period by 8 days and 10 days, respectively. Moist-chilling did improve the rate and percentage of germination when germinated at 20°C over 21 days; however total germination was not affected at temperatures 25°C and 30°C. Although the seeds of P. roxburghii germinate well due to lack of dormancy, the increasing demand for large quantities of seeds of P. roxburghii for reforestation programmes make pre-sowing treatments useful in improving the rate and percentage of germination.

Gherkin elite line selection

Gherkin lines were obtained by mass selection cycles in alteration with inbreeding cycles in a F population evaluated by Koch and Costa (1991). The purpose of the present study was to identify and select elite lines with plant uniform ity and desirable fruit characteristics. Seedlings of 71 lines were obtained in a greenhouse and transplanted to a bed covered wit h black polypropylene felt. The plants were grown prostate along the ground, without pruning, in a randomized complete block design, with three replicates and five plants per plot. Three criteria were trendsetters for line selection: lack of dormancy, plant and fruit uniformity, and yield components performance. Based on these parameters, the F 6M5S1 gherkin lines 1, 2, 3, 4, 5, 6, 8, 15, 20, 55, 60, and 63 were selected. These elite gherkin lines were called Paulista Gherkin, due to their contrastin g characteristics in relation to the common type.

Induced dormancy and colour polymorphism in seeds of the bull thistleCirsium vulgare(Savi) Ten.

AbstractTo colonize newly disturbed areas, weedy species must disperse their seeds in space and/or in time.Cirsium vulgarehas poor dispersal in space, but can form a persistent seed bank. Fresh seeds are capable of germinating in either light/dark or constant dark conditions under favourable diurnal temperatures of 25°C: 10°C. Despite this lack of dormancy, a large proportion of seeds do not germinate in the autumn after dispersal. Variation in germination requirements according to seed colour was also examined. Fresh seeds were placed under one of two overwintering treatments at 5°C, alternating light/dark or constant darkness. Some seeds of all colours: white, light, intermediate, dark and black germinated under these conditions. Six months later, ungerminated seeds subjected to the light/dark treatment did not require light for germination when placed under optimal temperatures. However, most seeds that had overwintered in constant darkness required light for germination. In the field, this induced dormancy would prevent seeds from germinating if buried or located in deep shade. Such seeds have the potential of forming a persistent seed bank. The proportion of dormant seeds did not appear to be associated with seed colour. Seeds incubated at 10°C following overwintering under light/dark conditions germinated to a higher percentage than seeds overwintered in darkness, regardless of the light conditions for germination. The results of this study help to explain the contradiction between delayed germination in the field and the lack of seed dormancy.

Abscisic acid controls dormancy development and bulb formation in lily plantlets regenerated in vitro

Plantlets of lily regenerated in vitro from scale explants consist of scales and leaves from which the base of the petiole has swollen to a scale. Fluridone, an inhibitor of ABA‐synthesis, applied during culture in vitro, inhibited the swelling of the petioles and promoted leaf formation. At high fluridone concentrations (10 or 33μM), swelling was completely blocked, and plantlets consisted of leaves only. Addition of ABA during the regeneration in vitro had the opposite effect and resulted in plantlets with scales only. When applied simultaneously with fluridone, ABA nullified the effect of fluridone. This demonstrates that bulb formation in lily is under the control of ABA. Lily plantlets regenerated in vitro on scale explants at 20 or 25°C were harvested after 11 weeks, and the leaves were removed from the bulblets. The bulblets were dormant and required a cold treatment to achieve rapid emergence after planting in soil. Fluridone added during the culture in vitro prevented the development of dormancy, and the bulblets did not require a cold treatment. The effect of fluridone was nullified by simultaneous addition of ABA. Bulblets harvested after 6 weeks of culture at 20°C had not yet developed dormancy. Bulblets regenerated at 15°C were only slightly dormant. In both types of bulblets, it is unlikely that the lack of dormancy was due to low ABA‐levels since addition of ABA did not affect the dormancy status. These data indicate that the level of endogenous ABA and an unknown additional factor play major roles in the development of dormancy.

Selection of Winter and Summer Annual Life Forms in Populations of Senecio sylvaticus L. )

This study has analyzed the occurrence of winter and summer annual life forms of Senecio sylvaticus and the selective factors regulating the co-occurrence. A difference in dormancy of achenes of Senecio sylvaticus is the first prerequisite for the selection of both life forms, with a lack of dormancy in the winter annual type and an endosperm- located dormancy in the summer annual type, which is heterogenous for this character. Frost resistance is only found in the winter annual life form, but it was insufficient to survive strong winters, so that a predominance of winter annual type is excluded. Further selective factors operating in different ways on both life forms are rabbits and voles, foraging on juveniles plants during winter, aphids and seed-head flies, affecting more the summer annual life form than the winter annual type. The importance of these factors for selection of both life forms is discussed.

Structural Diversity and its Adaptive Significancein Seeds of Vigna minima (Roxb.) Ohwi § Ohashi and its Allies (Leguminosae-Papilionoideae)

The surface features of seed coat, hilum and strophiole, histological aspects of hilum and strophiole, and mechanism of seed dormancy in Vigna minima, V. umbellata, V. dalzelliana and V. calcarata auct. pi. have been investigated. Scanning electron microscopy has revealed a substantial variability in seed coat microtopography, hilum and strophiole, which is of taxonomic and evolutionary significance. The histology of the hilum is uniform in all four taxa, but the structure of the strophiole shows differences between wild and cultivated species. All four taxa have hard seeds; those of V. umbellata have no dormancy but those of wild species have water-impermeable dormancy. Seed germination experiments using araldite-coated, and hilum-micropyle- and strophiole-plugged hard seeds of V. umbellata and water-impermeable seeds of V. minima, which were pin-pricked through the strophiolar groove, demonstrate that the zone of weakness to the permeability of water in hard seeds of these species is the strophiolar region, and not the seed coat, hilum or micropyle. The parenchymatous tissue of the strophiolar plug in the seeds of V. umbellatais associated with the lack of dormancy, whereas the sclerenchymatous tissue of the strophiolar plug in the seeds of V. minima is responsible for the water-impermeable seed dormancy. Under natural conditions, the water-impermeable dormancy of wild species breaks down as a result of the degradation of the hard seed coat, by microbial action, at the strophiolar groove.

Fonctionnement sympodial continu et multiplication végétative chez l’Arum italicum

The vegetative and floral development of Arum italicum Mill. displays no resting period under western European climatic conditions. Between two flowering seasons several sympodial units ending with an inflorescence are successively built. The meristem of each new unit is generally initiated in the axil of a sagittate leaf of the preceding unit but it can also grow in a nonaxillary position at the base of the meristem. The leaves of the first unit spend the winter season above the ground. Their petiole sheaths surround all the later sympodial units. On each sympodial unit a number of axillary buds give rise to tunicated bulbils which provide for the asexual multiplication of the species. The ontogeny of the bulbils on the mother plant and their behaviour after they become autonomous are described, as well as those of young plantlets grown from seed germination. In rhizomes, bulbils, and plantlets the shoot apex is in close contact with a subapical region (base plate) built from interlocked leaf or scale bases which are rich in storage products. This base plate will give rise to a new rhizome. Although Arum italicum has a tuberous rhizome with sympodial growth, it has nevertheless some characters of a bulbous plant (base plate and bulbils) but it differs from it by continuous growth and development and the lack of dormancy of the bulbils.