Predicting pre-harvest sprouting susceptibility in barley: Looking for “sensitivity windows” to temperature throughout grain filling in various commercial cultivars

Pre-harvest sprouting (PHS) is common in cereals that lack grain dormancy if maturing grain is exposed to rain. This phenomenon leads to immediate loss of seed viability, and since the malting process requires germination, its occurrence is highly undesirable in malting barley crops. Dormancy release rate is genetically and environmentally controlled. We evaluated the effect of temperature during grain filling on the dormancy release pattern (and then on the PHS susceptibility) of grains from five malting barley (Hordeum vulgare L.) cultivars widely sown in Argentina, with the aim of predicting PHS susceptibility of a barley crop from easy-to-gather data. Barley cultivars (Quilmes Ayelén, Q. Palomar, Q. Painé, B1215 and Scarlett) were sown on different dates over a 3-year period for generating variability in the thermal environment during grain filling. The period from pollination to physiological maturity (PM) was adjusted to a thermal time (TT) scale, which was then arbitrarily divided into 50 °C d intervals. Mean air temperature within each interval and for the whole filling period was calculated for the different sowing dates. Dormancy release pattern was followed by determining a weighed germination index (GI) throughout grain filling and maturation. We sought a linear relationship between temperature during grain filling and GI at some moment after PM. For all barley cultivars, except B1215, a significant (p < 0.001) and positive correlation was found between the GI of grains with 10–20% moisture content (fresh basis) and mean temperature within TT intervals located at the last stages of seed development. Then, simply temperature-based models for predicting crop PHS susceptibility were generated for each barley cultivar. Moreover, we intended a single, universal prediction model constructed with data from all cultivars. Two general forms were proposed, but the relationships were slightly less tight when each barley cultivar model was used. A preliminary validation for each cultivar model was done for three genotypes with independent data from four sites of the major barley production area in Argentina. When comparing experimental and field data regressions we did not find significant differences in slope for any cultivar (p > 0.25). However, most of the observed GIs were higher than predicted. This upwards displacement of GI–temperature relationship suggests the role of other environmental factors (i.e. water and soil N availability, day length), differing among tested locations. We are currently evaluating and quantifying the effect of these factors with the aim of improving PHS susceptibility prediction in malting barley crops.     

Seed dormancy and dormancy‐breaking methods in Leymus chinensis (Trin.) Tzvel. (Poaceae)

Leymus chinensis (Trin.) Tzvel. is a perennial grass with high productivity and forage value; however, poor stand establishment, often due to seed dormancy, limits its widespread use for forage production. To investigate the mechanism of seed dormancy and to develop effective methods of improving germination, the contribution of each part of the caryopsis to dormancy was investigated, and a number of single or combined dormancy‐breaking pre‐treatments were conducted using three seed lots. The palea, lemma, pericarp/testa, and endosperm all contributed to seed dormancy. The contribution of each part to dormancy was 23·4%, lemma; 6·2%, palea; 28·4%, pericarp/testa; and 42·0%, endosperm. Hull (palea and lemma) removal, pericarp/testa piercing, and soaking in distilled water or 30% sodium hydroxide (NaOH) significantly decreased the percentage of dormant seeds (i.e. increased germination). Treating hull‐removed and pericarp/testa‐pierced seeds with gibberellic acid (GA₃) also significantly decreased the percentage of dormant seeds. Compared with each of the single pre‐treatments, the combined pre‐treatment of pre‐soaking in water for 1 d, then 30% NaOH for 60 min and treating with 300 μm GA₃ resulted in the highest germination (89%); and seed viability was 91%.     

Associations between caryopsis dormancy, α-amylase activity,and pre-harvest sprouting in barley

Pre-harvest sprouting (PHS) is a concern for barley (Hordeum vulgare L.) producers, grain processors, and researchers worldwide. Pre-harvest sprouting has been mainly attributed to low dormancy, which is determined by genotype, stage of plant maturation, and environmental conditions during caryopsis development. Fourteen barley genotypes were sown in field experiments at two sites in North Dakota in 2004 and 2005. Spikes were harvested at four different stages: ≈500 g kg⁻¹ moisture content, physiological maturity, harvest maturity, and post-harvest maturity. Results indicated that barley genotypes were released from dormancy at different rates. The 14 barley genotypes were divided into three classes based on their dormancy loss rate during caryopsis development. C93-3230-24 was highly dormant, and ‘Stander’ and ‘Legacy’ were highly susceptible to PHS due to lack of dormancy from as early as 20 d after heading date. All other genotypes fell into the third group that had intermediate dormancy loss rate. No significant correlation was detected between barley α-amylase activity and germination percentage. A moderate association between malt α-amylase activity and caryopsis dormancy suggested that cultivars with increased malt α-amylase activity tend to have low dormancy and may be more prone to PHS.     

Reduction of Seed Dormancy in Echinacea pallida (Nutt.) Nutt. by In-dark Seed Selection and Breeding

Strong seed dormancy has been an obstacle for field production of Echinacea species. Previous research on overcoming Echinacea seed dormancy has been extensive and focused on treatment methods, which involve time and expense, and are incompatible with organic production if synthetic chemicals are used. We have attempted to genetically reduce seed dormancy through selection and breeding in Echinacea, by using Echinacea pallida as a model species. Three accessions were used in this study. Nine parent plants of each accession selected from early, in-dark germinated seeds (in-dark plants) or from late, in-light seeds (in-light plants) were planted and grouped by accession and germination treatment method for seed production through a polycross method. Germination tests indicated that these in-dark plants produced seed (in-dark seed) with significantly reduced seed dormancy when tested under light or dark condition in comparison to the seed of the in-light plants (in-light seed). Among the three accessions, the in-dark seed germinated at much higher rates than did the in-light seed, more than 2× at 25 °C under light and up to an 83× increase in darkness, and up to an 8× increase over the corresponding parental seed lots under comparable germination conditions. In addition to these increases in germination, the in-dark seed showed early and synchronized germination as compared to the in-light seed. Since these results were achieved through only one cycle of selection and breeding, they strongly suggest that we have developed a very effective method for modifying seed dormancy in Echinacea.     

长江中下游麦区主要小麦品种穗发芽抗性及鉴定方法比较

为了解长江中下游麦区当前推广小麦品种抗穗发芽的特性,采用整穗发芽法、整粒发芽法和半粒发芽法鉴定了20个小麦品种的穗发芽抗性。结果表明,品种间穗发芽抗性存在显著差异,扬麦16、扬麦18、扬麦20、扬麦22、扬辐麦4号、宁麦16等13个品种穗发芽抗性较好,宁麦17、宁麦19、镇麦6号、镇麦8号、镇麦9号、扬麦13和扬麦14等6个品种穗发芽抗性中等,郑麦9023易穗发芽;20个品种的整穗发芽率和取穗当天整粒发芽率差异不显著,且两种方法的发芽率呈极显著正相关,说明整穗发芽法和整粒发芽法都可用于穗发芽抗性鉴定;整粒发芽法中取穗当天与取穗10d后籽粒发芽率较为一致,且极显著正相关,说明这一时段内都可进行抗穗发芽鉴定;取穗30d后所有红粒品种的发芽率都极显著提高,说明此时种子休眠开始解除。18个红粒小麦品种的半粒发芽率极显著高于整粒发芽率,说明种皮对穗发芽有较强的抑制作用。白粒品种郑麦9023收获30d后发芽率与收获当天穗上发芽率、籽粒发芽率,整粒法与半粒法发芽率差异均不显著,说明该品种几乎无休眠特性,且其种皮对穗发芽的抑制作用较小。     

Anatomical Changes during in Vitro Direct Formation of Shoot Bud from Root Tips in Garlic (Allium sativum L.)

Abstract

The germination and emergence of soybean [Glycine max (L.) Merr.] can be adversely affected by the presence of excessive water as a result of continuous rainfall. The pre-germination flooding-tolerant cultivars can be tolerant to hypoxia in the flooding field. The objective of this study was to clarify the relationship between germination under hypoxia at different temperatures and pre-germination flooding tolerance. Seeds of 6 soybean cultivars were subjected to 5 oxygen concentrations and 3 temperatures. Seeds of all 6 cultivars hardly germinated under an oxygen concentration of 20 mL L^–1, but germinated with increasing oxygen concentration regardless of temperature. The pre-germination flooding-tolerant cultivar ‘Peking’ exhibited poorer germination under hypoxia than the other cultivars. Seed coat of ‘Peking’ did not dehisce when seeds did not germinate under hypoxia regardless of temperature. The pre-germination flooding-susceptible cultivar ‘Nakasennari’ exhibited higher seed coat dehiscence, but the dehiscence mostly occurred on the seed surface rather than micropyle under hypoxia at 25°C and 30°C. Seven days after termination of 3-d hypoxia treatment at 30°C, the percentage of seedlings with root hairs and/or lateral roots relative to that after ambient oxygen treatment was maintained in ‘Peking’ but decreased in the other cultivars, especially in ‘Nakasennari’. Pre-germination flooding-tolerant cultivar, especially ‘Peking’, is characterized by a delay in germination processes under hypoxia, and exhibits vigorous germination after release from hypoxia.     

Three-year field evaluation of early and late 20th century spring wheat cultivars to projected increases in atmospheric carbon dioxide

Carbon dioxide (CO₂), along with light, water and nutrients, represents an essential resource needed for plant growth and reproduction. Projected and recent increases in atmospheric carbon dioxide may allow breeders and agronomists to begin intra-specific selection for yield traits associated with CO₂ sensitivity. However, selection for maximum yield, particularly for cereals, is continuous, and it is possible that modern cereal cultivars are, in fact, the most CO₂ sensitive. To test CO₂ responsiveness, we examined two contrasting spring wheat cultivars, Marquis and Oxen, over a 3-year period under field conditions at two different planting densities. Marquis was introduced into North America in 1903, and is taller, with greater tiller plasticity (i.e. greater variation in tiller production), smaller seed and lower harvest index relative to modern wheat cultivars. Oxen, a modern cultivar released in 1996, produces fewer tillers, and has larger seed with a higher harvest index relative to Marquis. As would be expected, under ambient CO₂ conditions, Oxen produced more seed than Marquis for all 3 years. However, at a CO₂ concentration 250 μmol mol⁻¹ above ambient (a concentration anticipated in the next 50–100 years), no differences were observed in seed yield between the two cultivars, and vegetative above ground biomass (e.g. tillers), was significantly higher for Marquis relative to Oxen in 2006 and 2007. Significant CO₂ by cultivar interaction was observed as a result of greater tiller production and an increased percentage of tillers bearing panicles for the Marquis relative to the Oxen cultivar at elevated carbon dioxide. This greater increase in tiller bearing panicles also resulted in a significant increase in harvest index for the Marquis cultivar as CO₂ increased. While preliminary, these results intimate that newer cultivars are not intrinsically more CO₂ responsive; rather, that yield sensitivity may be dependent on the availability of reproductive sinks to assimilate additional carbon. Overall, understanding and characterizing vegetative vs. reproductive sink capacity between cultivars may offer new opportunities for breeders to exploit and adapt varieties of wheat to projected increases in atmospheric carbon dioxide concentration.     

Effect of storage temperature and extraction methods on dormancy and germination of true potato seed

Seed treatments, methods of extraction and storage temperature were examined for effects on viability and dormancy of true potato seed. Dormancy of 4x?2x (S. tuberosum ×S. phureja) hybrids was eliminated after 7 months at room temperature and after 10 months at 4 C. However, data on the velocity and uniformity of germination (coefficient of velocity) revealed the presence of a residual dormancy that persists for nearly two years in seeds stored at 4 C, but which is largely eliminated after one year in seeds stored at room temperature. Seed viability was not affected by blender extraction, although seed extracted by hand gave a significantly lower initial coefficient of velocity (CGV). Application of gibberellic acid (GA, 1000 ppm) as a 24-hour soak to freshly extracted seed eliminates dormancy as effectively as GA applied during germination, and produces no deleterious effects on seed viability up to two years in storage. There were genotypic differences for seed dormancy within the tetraploid and diploid groups examined. SeveralS. tuberosum cultivars displayed a dormancy effect (lower CGV’s) in fresh seed that was not completely eliminated by GA, but which declines over time in storage.     

Grain composition of Virginia winter barley and implications for use in feed,food, and biofuels production

Grain compositional components impacting barley (Hordeum vulgare L.) use in food, feed and fuel products, must be combined with improved agronomic traits to produce a commercially viable barley cultivar. Little current information is available on grain composition and variability among winter barley genotypes. This study was conducted to determine the variability among modern hulled and hulless winter barley genotypes in grain composition. Barley types varied significantly in grain and kernel weight, starch, beta-glucan, oil and ash content, but not in protein concentration. Hulless barley had significantly higher grain test weight and starch concentration than hulled and malting types, and significantly higher beta-glucan than malting barley. Hulless barley had significantly lower kernel weights, oil, and ash concentrations than hulled and malting types. Higher starch and lower fiber and ash in grain of hulless barley versus hulled feed or malting type barley are characteristics that increase hulless barley desirability. Selection for high starch concentration among all barley types is feasible and will facilitate development of barley cultivars better suited for use in feed, malt, and ethanol production.     

Some effect fluid-sowing, pre-germination, irrigation and soil covering on the establishment and growth of seedlings of white clover slot-seeded into permanent pasture

Seeds of white clover ( Trifolium repens ) were sown alone or in fluid, or pre-germinated in fluid on to the soil surface of slots cut in an old Agrostis/Festuca sward. Seeds were left uncovered or covered with a thin layer of soil and irrigated from the outset or after 14 days delay.
With irrigation from the outset, seedlings established soonest from pre-germinated seeds but final percentage establishment ranged only from 50 to 63% for the three states of seed. With delayed Irrigation, however, few pre-germinated s1 survived and although germination of dry seed was delayed, final percentage establishment was unaffected. Soil covering increased establishment slightly. The number of leaves per seedling was greatest with pre-germination and early irrigation and least with pre-germination and delayed irrigation. Delayed irrigation also decreased the number of leaves per seedling for seedlings grown from dry seed.
The effects of early irrigation persisted so that at 84 days it significantly increased total yield of clover from all three states of seed, on average threefold, but much more from pre-germinated than from dry seed. Soil covering greatly increased yield, especially where irrigation had been applied from the outset. The interaction of early irrigation and soil covering was even more pronounced for stolon weights, and stolon growth of Individual seedlings appeared to benefit more from soil covering than from early irrigation.
The results showed the importance of early seedling emergence, but no advantages of fluid sowing per se. They also indicated large overall beneficial effects of early irrigation and its additive interaction with soil covering.     

Comparative Enzyme Kinetics of Two Allelic Forms of Barley (Hordeum vulgare L.) Beta -amylase

The barley (Hordeum vulgare L.) varieties, Franklin and Schooner, contain two different allelic forms of beta -amylase (EC 3.2.1.2) encoded on chromosome 4H by the Bmy 1-Sd1 and Bmy 1-Sd2L alleles, respectively. The corresponding enzymes, referred to as Sd1 and Sd2L, were purified from both mature barley grain and germinated barley (green malt), and their physical and kinetic properties studied. Approximately 4 kDa were cleaved from both Sd1 and Sd2Lbeta -amylases after germination. The K_mvalue for green malt beta -amylase was less than that of mature grain beta -amylase for both varieties when potato starch was used as a substrate, although V_maxwas similar. This indicated that proteolysis after germination increased the affinity of beta -amylase for potato starch. No significant kinetic differences were observed between beta -amylase from mature grain and green malt of the two barley varieties when amylose (degree of polymerisation 100 and 18) and maltopentaose were used as substrates. Kinetic differences were also observed between the two allelic forms of beta -amylase. Sd1 beta -amylase from green malt exhibited a lower K_mvalue for potato starch than Sd2L beta -amylase, demonstrating that at non-saturating starch concentrations Sd1 beta -amylase is better able to hydrolyse starch than Sd2L beta -amylase. As the degree of polymerisation of the substrates decreased from approximately 740 (potato starch) to 5 (maltopentaose), the K_mvalues for beta -amylase increased, whereas V_maxvalues decreased. Maltose, the hydrolytic product of beta -amylase, was found to be a weak competitive inhibitor of both Sd1 and Sd2L green malt beta -amylases with respect to potato starch and amylose. Taken together the kinetic observations for bet a-amylase suggest that the allelic differences and C-terminal proteolysis might be exploited to improve the efficiency of starch hydrolysis during the mashing stage of the brewing process.     

Confirmation of Novel Quantitative Trait Loci for Seed Dormancy at Different Ripening Stages in Rice

Seed dormancy contributes resistance to pre-harvest sprouting.Effects on respective quantitative trait loci (QTLs) for dormancy should be assessed by using fresh seeds before germinability altered through storage.We investigated QTLs related to seed dormancy using backcross inbred lines derived from a cross between Nipponbare and Kasalath.Four putative QTLs for seed dormancy were detected immediately after harvest using composite interval mapping.These putative QTLs were mapped near C1488 on chromosome 3 (qSD-3.1),R2171 on chromosome 6 (qSD-6.1),R1245 on chromosome 7 (qSD-7.1) and C488 on chromosome 10 (qSD-10.1).Kasalath alleles promoted dormancy for qSD-3.1,qSD-6.1 and qSD-7.1,and the respective proportions of phenotypic variation explained by each QTL were 12.9%,9.3% and 8.1%.We evaluated the seed dormancy harvested at different ripening stages during seed development using chromosome segment substitution lines (CSSLs) to confirm gene effects.The germination rates of CSSL27 and CSSL28 substituted with the region including qSD-6.1 were significantly lower than those of Nipponbare and other CSSLs at the late ripening stage.Therefore,qSD-6.1 is considered the most effective novel QTL for pre-harvest sprouting resistance among the QTLs detected in this study.     

青稞主效休眠基因单倍型分布及利用

穗发芽严重降低谷物的产量和品质,种子休眠与穗发芽高度相关。为了解中国青稞品种休眠特性及其主效休眠基因AlaAT和MKK3的单倍型分布,以143份地方品种和42份育成品种(系)为材料,分别种植在四川雅安、什邡和西藏拉萨,进行大田种子休眠性鉴定;选择休眠性极端材料,分别利用2对引物对含有目标休眠基因功能性SNP的片段进行扩增、测序,并用于AlaAT 和 MKK3基因特异性KASP标记开发与供试材料的单倍型分析。结果表明,3个种植点,地方品种的发芽指数（GI）均高于育成品种（系）,但差异不显著;四川2个种植点间GI值差异不显著,但显著高于西藏种植点,说明青稞品种（系）普遍休眠性弱,高原气候条件显著促进种子休眠。KASP标记检测发现,AlaAT 和 MKK3的强优势单倍型均为弱休眠单倍型 （频率>80%）,供试材料中有4种单倍型组合,分别为AlaAT-ND+MKK3-ND、 AlaAT-ND+MKK3-D、 AlaAT-D+MKK3-ND和AlaAT-D+MKK3-D,频率分别为80.0%、12.4%、6.0%和1.6%,其GI值随强休眠单倍型数量增加而降低;3个环境下,含有组合AlaAT-D+MKK3-D的GI值最低,说明休眠基因具有加性效应,聚合优良单倍型的品种（系）具有稳定的休眠特性。青稞生产和育种应根据种植区域和用途选择与利用上述主效休眠基因单倍型。     

Cereal seed viability after 10 years of storage in active and base germplasm collections

Periodic testing of viability is crucial to operation of seedbanks because it permits the control of genetic erosion during storage. In this work, data obtained at the Spanish Genetic Resource Center (CRF-INIA) from the routine task of monitoring seed viability were analyzed. The accessions studied came from the active and base collections of oat, barley and wheat. All seed entered the cold chambers with a moisture content below 7% and the storage temperatures were −4°C for active collections and −18°C for base collections. Differences between initial and final germination after 10 years of storage were studied in 1770 seed samples: 342, 341 and 55 for active collections and 273, 723 and 36 for base collections of oat, barley and wheat, respectively. The percentage of barley and wheat accessions without significant changes in germination ranged from 84% to 89%. Oat seed showed larger deterioration and about 35% of the samples presented significant differences between initial and final germination. Besides, some underestimation of oat initial viability due to seed dormancy was detected.Under the conditions of the CRF seedbank and according to the FAO/IPGRI regeneration standards, 4.6% and 0.4% of the studied active and base samples, respectively, would need a regeneration after 10 years of storage. Possible reasons involved in the loss of viability such as initial seed quality, accession variability and storage conditions are discussed taking into account the available passport and germination information. In our conditions, cultivar variation and storage temperature appeared to be the most influential factors relating to seed storability.     

Evaluating pea and barley cultivars for complementarity in intercropping at different levels of soil N availability

Two field experiments were carried out on a temperate sandy loam using six pea (Pisum sativum L.) and five spring barley (Hordeum vulgare L.) cultivars to determine cultivar complementarity in the intercrop for grain yield, dry matter production and nitrogen (N) acquisition. Crops were grown with or without the supply of 40 or 50 kg N ha⁻¹ in the two experiments. Cultivars were grown as sole crops (SC) and as mixed intercrops (IC) using a replacement design (50:50). The land equivalent ratio (LER), which is defined as the relative land area under SC that is required to produce the yields achieved in intercropping, were used to compare cultivar performance in intercropping relative to sole cropping.Barley was the stronger competitor in the intercrops and as a result barley grain yield and nitrogen uptake in IC were similar to SC. The per plant pea grain production and aboveground N accumulation in IC were reduced to less than half compared to SC pea plants due to competitive interactions.Application of N caused a dynamic change in the intercrop composition. Competition from barley increased with N application and the pea contribution to the combined intercrop grain yield decreased. The LER values showed that in the intercrop plant growth resources were used on average 20% more efficient without N application and 5–10% more efficient with N application.The choice of pea cultivar in the intercrop influenced the intercrop performance to a larger degree than the choice of barley cultivar. Furthermore, pea cultivar×cropping systems interactions was observed, indicating that cultivars performed differently in sole and intercrops. An indeterminate pea cultivar competed strongly with barley causing a greater proportion of peas in the intercrop yield, but caused a reduced N uptake and yield of barley. Determinate peas with normal leaves caused the highest degree of complementary use of N sources by allowing barley to exploit the soil N sources efficiently, while they contribute with fixed N₂. However, difference in performance among cultivars was observed. Using the indeterminate pea cultivar combined IC grain yield was in general lower than the greatest sole crop yield and vice versa for the determinate pea cultivars. Up to 22% (LER=1.22) greater combined IC grain yield was observed in several mixtures using determinate pea cultivars.From the present study, it is was concluded that there is a need for breeding suitable pea cultivars for intercropping purposes, since cultivars bred for sole cropping may not be the types, which are the most suitable for intercropping. For optimized N-use in pea–barley intercrops it is concluded that important traits for the intercropped pea are: (1) determinate growth, (2) a medium competitive root system for soil inorganic N and other nutrients during early growth, (3) high light absorption capacity by peas growing underneath the canopy of the higher barley component and (4) early establishment of symbiotic N₂ fixation to support a high growth rate during early growth stages.Fertilized pea–barley intercrops gave a 15% higher net income than fertilized barley sole cropping and is regarded as a better safeguard for the farmer’s earnings compared to pea sole cropping known for variable yields and poor competitive ability towards weeds.     

Protein and hordein content in barley seeds as affected by nitrogen level and their relationship to beta-amylase activity

Two barley cultivars differing in grain size and protein content were used to investigate the effects of nitrogen nutrition, cultivar and their interaction on grain protein content, hordein content and beta-amylase activity and the relationship between hordein content and beta-amylase activity during in vitro spike culture. The content of protein and hordein fraction, and beta-amylase activity in barley grains increased as the nitrogen level in culture solution increased. Grain protein content was significantly affected by nitrogen treatment and cultivar, and there was no significant interaction between nitrogen treatment and cultivar. Hordein content and beta-amylase activity were significantly affected by nitrogen treatment and cultivar as well as their interaction. Beta-amylase activity was positively correlated with grain protein and hordein contents, and the ratio of hordein B:C was negatively correlated with total protein content and beta-amylase activity.     

Modification of potato microtuber dormancy during induction and growthin vitro orex vitro

Prolonged or highly variable dormancy can be a significant impediment to the efficient use of potato (Solanum tuberosum L.) microtubers by the seed industry. In the present study, reductions in microtuber dormancy duration were obtained in cultivars commonly used by the processing industry (Kennebec, Russet Burbank and Shepody). This was achieved by modifying microtuber induction media and applying various dormancy-release treatments after harvest, with or without prior storage. An 8 h photoperiod, instead of continuous darkness during microtuber induction and development, increased microtuber yield while reducing dormancy duration. Dormancy duration was also shortened by increased sucrose concentration during microtuber induction under an 8 h photoperiod. As sucrose was increased from 4 to 16% under an 8 h photoperiod, mean dormancy duration decreased by 86 d for Shepody, 65 d for Kennebec and 46 d for Russet Burbank. During theex vitro storage period, 24 h treatment with bromoethane vapor (from 0.22 ml liquid BE per L volume) or bromoethane vapor followed by a 3 d treatment of 60% CO₂/ 20% O₂/ 20% N₂ resulted in a rapid dormancy release of freshly harvested microtubers. These dormancy-releasing treatments significantly increased minituber yields under greenhouse conditions for all cultivars when compared to untreated controls. Increased minituber yields were also observed when dormancy release treatments were applied to microtubers after storage at 6 C for 8 weeks. The results demonstrate that microtuber dormancy duration can be manipulated during growthin vitro orex vitro. However, optimization may require cultivarspecific protocols     

Relation of Seed Structures to Soybean Cultivar Difference in Pre-germination Flooding Tolerance

Abstract

Flooding during germination inhibits the sprouting and emergence of soybean [Glycine max (L.) Merr.], reducing subsequent growth and yield. Previous studies revealed that cultivars tolerant to pre-germination flooding have a mechanism of reducing water absorption speed (WAS) during the initial stage of inundation; however, seed structures involved in WAS have not been fully clarified to date. The objectives of this study were to identify possible seed structures responsible for cultivar difference in WAS and pre-germination flooding tolerance. WAS of two tolerant cultivars (Peking and Williams) and two susceptible cultivars (Nakasennari and Enrei), which were identified in our previous study, was compared in relation to seed structures. In Peking, WAS was markedly lower than that of the other cultivars, either in intact seed or seed with the seed coat removed, suggesting that both the seed coat and the embryo have a mechanism of reducing WAS in this cultivar. WAS of the hilum side tended to be higher than that of the back side, and sealing of the micropyle significantly lowered WAS, showing that the micropyle rather than the hilum appeared to be responsible for the higher WAS of the hilum side regardless of cultivar. A comparison of cross section area of the hilum revealed that the tolerant cultivars tended to have a larger area than the susceptible cultivars, suggesting that an inner space of the hilum can act as a reservoir at the initial stage of inundation, thereby reducing WAS in tolerant cultivars.