Environmental and genotypic effects on bulb development in onion – a review

Environmental and genetic factors influence growth and bulb development of onions by affecting their physiology. Photoperiod plays critical a role in bulb development and determines the suitability of a cultivar for a particular region. Long days and high temperatures promote onion bulbing. Bulbing is regulated more by temperature than photoperiod, as determined by growing degree days. Far-red light promotes bulbing most effectively. High-temperature storage of sets (above 20–25°C) results in increased total bulb yields, while very high temperature (25.5–31°C) or temperature below 0°C depresses yield. Plant density has an impact on bulb size: the higher the plant density the smaller the bulb size. Onion is more sensitive to water stress during bulb formation and enlargement than during the vegetative stage. Nitrogen improves bulb development, but too much nitrogen promotes excessive vegetative growth and delays maturity. Growth hormones (gibberellins and ethrel) promote the growth and development of bulbs. Flowering and bulb formation in onion is regulated by different (Flowering Locus T) FT genes. Two antagonistic FT-like genes regulate bulb formation. AcFT1 promotes bulb formation, while AcFT4 prevents AcFT1 up-regulation and inhibits bulbing. There is a need to link our research with the genetics and physiology of onions, to enhance bulb yield.     

Effect of bulb storage temperature on leaf emergence and plant development during scale propagation of Lilium longiflorum ‘White American’

Effects of temperature and duration of bulb storage on leaf emergence of scale bulblets and on the type of plant development were investigated in Lilium longiflorum ‘White American’. After the parent bulbs had been stored for 0, 5, 10 or 15 weeks at 30, 20, 10, or 0°C, scales collected from different parts of a bulb were scale-propagated at 25 or 14°C, or under the temperature regimes normally used in The Netherlands. Independently of the scale position, a higher storage temperature promoted leaf emergence from scale bulblets, whereas a lower temperature delayed it. Higher storage temperatures produced more epigeous type plants, especially from outer and middle scales. Sprouting of the parent bulb had no effect on leaf emergence from the scale bulblets nor on the type of plant development.     

An analysis of the growth of forced tulips. 1. Changes in plant fresh and dry weights during growth at two temperatures

Changes in the fresh and dry weights of the component parts of plants of tulip cv. ‘Apeldoorn’ were followed in bulbs kept at low and high temperatures (9 and 18°C respectively) from the time of completion of flower differentiation until anthesis.There were marked differences between shoot dry weights at the two temperatures. At 9°C the stem, leaves and flower grew exponentially throughout the whole period, but at 18°C the specific growth rate of the stem and leaves declined throughout the period of the experiment. At 9°C the proportion of total dry weight in shoots and daughter bulbs was higher than at 18°C, and the proportion in the mother bulb was correspondingly smaller.At both temperatures the $\text{fresh weight}\text{dry weight}$ ratios of the mother bulb, shoot and daughter bulbs declined during dry storage, the decline being greater at 9°C. After planting, the ratio for all plant parts increased at 9°C, but scarcely changed at 18°C.These results are discussed in relation to dormancy, to the low-temperature requirement for successful and rapid flowering and to flower quality.     

Growth and flowering of Nerine flexuosa alba

N. flexuosa alba is a perennial bulbous member of the Amaryllidaceae and an attractive new ornamental. In the bulb, inflorescence buds are formed periodically under any circumstances which allow growth. The problem was that quite often these buds do not elongate, and desiccate prematurely, so that poor flowering results.Light was found not to be a factor in flowering, neither energetically nor photo-periodically, but temperature turned out to be limiting. Good flowering occurred after growth at temperatures of 9 or 13°C, 17 and 21°C being too high. The combination of 9°C during growth and 21°C during storage resulted in 100% satisfactory flowering and an acceptable bulb growth. Gibberellic acid did not effect flowering.     

Effects of pre- and post-bloom temperature regimes on development of Lilium longiflorum Thunb.

Glasshouse grown ‘Ace’ and ‘Nellie White’ Easter lily plants were subjected to different temperature regimes to determine temperature requirements during pre- and post-bloom development. Rate of leaf- and flower-bud development and stem elongation on the primary (mother) axis were directly proportional to the range of temperatures used (6–24°C), and were equally effective in predicting crop development. Scale initiation on the secondary (daughter) axis during pre-bloom phases was proportional to growing temperature, reaching maximum activity at 18°C in ‘Ace’ and at 12°C in ‘Nellie White’. The shift from scale to leaf initiation and development following anthesis was favored by 12 rather than 18°C with significant reductions in leaf initiation in both cultivars at 24°C. No difference in secondary meristem diameter occurred with temperature during pre-bloom, but large dome size was associated with 12°C or lower during the post-bloom phase. Primary scale weight increase (filling), reached a maximum 50 days following anthesis, and was greatest at 18°C. Secondary scale filling reached a maximum 80 days after anthesis at both 18 and 24°C. The secondary axis became increasingly responsive to sprout-inducing temperatures with increasing age and development. Fifty days after anthesis, 12 and 18°C were equally effective in sprouting ‘Ace’ bulbs, while 12°C was more effective with ‘Nellie White’. Early leaf senescence, associated with high (24°C) temperature, did not favor increased bulb size, daughter leaf primordia count and meristem diameter, or sprouting.     

The Effect of Temperature on Floral Behaviour,Pollen Tube Growth and Fruit Set in the Avocado

Avocado plants were kept in growth cabinets at 33°C day, 28°C night (33/28); 25°C day, 20°C night (25/20); and 17°C day, 12°C night (17/12), with a 12-h photoperiod and light intensity of 26000 1x. At 33/28 and 25/20 flowers opened in the afternoon as females and again the following morning as males (type B floral cycle) with some overlap of male and female stages at 25/20. At 17/12 very few flowers had a female stage, the majority opening once only as males. The duration of the flowering period decreased with a rise in temperature as did total number of flowers opening. Reproductive growth was inhibited in favour of vegetative growth at 33/28, as exhibited by smaller floral parts and abscission of buds and flowers. The rate of pollen tube growth increased with a rise in temperature, but abnormal growth was frequently observed at 33/28 and tubes failed to reach the ovary at 17/12. Endosperm and embryo development was observed to occur at 25/20 but not at 33/28 or 17/12 although a positive effect of pollination on fruit retention was evident at 33/28. This effect also occurred at 25/20 but not at 17/12. The most suitable temperature regime for floral behaviour, pollen tube growth and embryo development was 25/20.     

Pecan nut germination — A review for the nursery industry

The shell of the pecan nut is freely permeable to water and gases, but retards germination by mechanically restricting growth of the radicle. This mechanical effect, which is pronounced at 20°C, can be overcome by germinating nuts between 30° and 35°C. Cool, moist stratification can substitute for the high-temperature germination-requirement in that following stratification nuts germinate equally well at 20°, 25° and 30°C. During stratification or incubation at high temperature, cytokinin and gibberellin levels increase in the embryo. This increase in endogenous promoter levels is closely correlated with the digestion of food reserves necessary for the resumption of embryo growth.     

The effect of 4 storage treatments on seed yield components of 3 onion inbreds

Onion bulbs of 3 inbred lines were stored during the winter in 4 different storage temperature regimes. Traits directly and indirectly associated with seed production were studied the following summers. The inbred lines differed in their responses and many traits were affected by the storage treatments. The storage treatment of 10°C for 12 weeks followed by 2° C for 12 weeks resulted in a significantly higher seed yield than did storage at 2° C throughout the entire period. Inbred 2399 had a higher seed yield than the other inbreds. Associated with high seed yields of 2399 was early flowering, a high number of leaves/bulb, tall seed stalks and a high number of florets/bulb.     

Postharvest sprouting of onion bulbs grown in different temperature and C02 environments in the UK

Summary

The effects of different mean growing season temperatures and C0₂ concentrations during bulb production on postharvest bulb sprouting in a common storage environment at Reading, UK, was examined in two cultivars of the Rijnsburger type of onion (Allium cepa L.). Crops were grown in the field in temperature gradient tunnels maintained at either 374 or 532 ppm C0₂. At crop maturity, cohorts of bulbs were harvested, transferred to a constant temperature room (at an average of 11.6°C) and the subsequent duration to sprouting recorded. The duration to the onset of sprouting (expressed as days in storage until the first bulb sprouted) was not affected by cultivar, mean growing season temperature or CO₂ concentration, and was 165 d. The subsequent rate of sprouting (expressed as bulbs per day) was a positive linear function of mean growing season temperature, but no effects of CO₂ or cultivar were detected. Mean rate of sprouting increased from an average of 0.036 bulbs per day at 12.3°C to 0.093 bulbs per day at 18.6°C. Rapid sprouting in storage was associated with lower levels of total non-structural carbohydrate in the bulbs at the time of harvest. Thus, postharvest susceptibility of onion bulbs to sprouting in storage is expected to increase in warmer crop production temperatures.     

Bulbing responses of two cultivars of red tropical onions to photoperiod,light integral and temperature under controlled growth conditions

Summary

The effects of photoperiod, light intensity and temperature on bulb formation and bulb structure of two tropical onion cultivars were investigated. From an initial experiment it was observed that the number of true scales and sheath scales differed significantly between the cultivars ‘Red Creole’ and ‘Agrifound Dark Red’. When these two cultivars were given 11, 12 and 13 h photoperiod treatments, it was found that both cultivars needed at least 12 h photoperiod for bulb formation. Modify the R/FR ratio from 1.22 to 1.16 in the final hour of the 11 h light period did not induce bulbing. The 13 h photoperiod increased the number of true scales and decreased the number of sheath scales compared with the 12 h photoperiod in both cultivars but total scale + leaf sheath numbers remained nearly constant. When onion plants were grown under 0%, 25%, 50% and 75% shading treatments, (12 h photoperiod), only plants receiving 0% and 25% shading bulbed. Low light intensity decreased the number of true scales and increased the number of sheath scales. Four temperature regimes were compared in a growth room experiment. Plants under the 29°348C treatment bulbed within two weeks and matured within six weeks. However, plants receiving the 25°308C treatment delayed bulb initiation more than those plants receiving 17°228C and 21°268C treatments. At the lowest temperature, bigger bulbs with thick necks were produced. This may be due to changes in bulb structure since at low temperature, the number of sheath scales was increased, however the number of true scales remained relatively constant in both cultivars. Dormant leaf initials decreased with decreasing temperature while the number of secondary meristems significantly increased. The results suggest that ‘Red Creole’ was more responsive to shorter photoperiods, bulbing earlier than ‘Agrifound Dark Red’. There was no significant difference in time to bulbing in response to temperature between the two cultivars if measured by bulbing ratio however there were differences in bulb structure which suggested that ‘Red Creole’ bulbed earlier. These effects may be due to the breeding histories of the two cultivars. It is suggested that studying bulb structure may provide a useful method of interpreting onion bulbing responses.     

High-Temperature Treatment (Blindstoken) of Bulbs of Tulip cv Rose Copland for Flower Killing and Yield Improvement

A three-year experiment on the high-temperature treatment of tulip bulbs established that yield could be increased by between 8 and 31 % for bulb weight or between 14 and 29 % for numbers of large bulbs, depending upon season, associated with a near-complete flower kill. The optimum pre-treatment storage temperature was 17°C, and the best date (of the five tested) for starting blindstoken at 33°C for one week was 20th-21st September.

Yield increases were greater when the blindstoken treatment was applied to bulbs whose shoots were short; later treatment, or treatment after pre-treatments which allowed faster shoot growth, were less effective. For optimum flower kill and yield increase the shoot should be about 1 cm high at treatment. Bulb weight and large bulb number were correlated, suggesting that the treatment increases total bulb weight by increasing bulb size rather than by differentially affecting the growth of daughter bulbs.

No adverse effects of the treatments were observed when the bulbs were forced in a glasshouse the following season.     

A study of the effect of the environment during growth on sprouting of bulb onions in store

The partition of dry matter between leaf and bulb with sheath was studied in relation to the post-harvest physiology of cvs Bola and Robusta grown at three sites for two seasons and dried and stored under standardized conditions. Foliar fall-over was synchronous at all sites in each season but the effects of site showed that crops either partitioned dry matter to the bulb early, lost less fresh weight in drying and sprouted later in store, or partitioned dry matter late, lost more fresh weight in drying and sprouted sooner in store. Crops showing the former behaviour were associated with low rainfall and a high number of day degrees between 6° and 20°C during early growth. There was up to 10 days difference between the sites in 50% sprouting dates. Bulbs of cv Bola sprouted earlier than those of cv Robusta, and bulbs harvested when foliar fall-over was negligible sprouted before those from later harvests. There were no site effects on plant maturity, on bulb growth regulator content (cv Robusta one year only), on sugar content at harvest or during storage, on bulb respiration rates at the end of drying or in the spring, or on bulb weight loss during storage.     

黄金梨胚珠、花粉发育及花粉败育过程的显微观察

观察了黄金梨的胚珠、胚囊、花粉发生发育过程中细胞形态变化特征。结果表明:黄金梨的胚珠、胚囊、花粉发育是在春季萌芽到开花过程中完成的。在开花前28d花芽萌动初期,胚珠原基出现,花药囊内为小孢子母细胞;花前21d胚珠原基分化出内外珠被,四分体开始出现;花前14d四分体出现率最高;开花时胚囊形成,花粉败育并形成空花药囊。造成黄金梨花粉败育的原因是小孢子母细胞减数分裂后形成的四分体及四分体分离后形成的早期花粉细胞无细胞核,早期花粉细胞液化不能形成较厚硬的外壁而解体。     

Factors affecting the response of tulips to gibberellin

Gibberellic acid (GA₃) treatment of forced tulip crops has potential for producing faster growth to anthesis in the glasshouse, for reducing losses due to floral bud blasting, and for reducing the duration of cold storage needed to obtain satisfactory flowers. Using partly and fully cooled direct-forced tulips, cultivar ‘Apeldoorn’, several factors (relevant to the definition of GA₃ treatments) were studied. Experiments confirmed the previously recorded effects of gibberellins in tulips: GA₃ injections reduced the duration of the glasshouse period, enhanced flower survival and flower length, and reduced stem length at flowering.Following bulb storage at temperatures from ?2 to 20°C, GA₃ reduced the glasshouse period by 15–25% and increased flower length, compared to controls, irrespective of storage temperature. Stem length was also reduced by GA₃, this effect being greater following a storage temperature of 5°C or lower. When GA₃ was applied during the period of 17°C-storage which precedes cool storage, or during or after storage at 5°C, it was found that treatments during or at the end of cool storage were more effective in producing the characteristic effects of GA₃ than were pre-cooling applications. In partly cooled bulbs (but not fully cooled ones), the GA₃-induced earliness of flowering was about doubled when GA₃ injections were given repeatedly at 2-week intervals throughout storage. The responses to GA₃ injections were found to be unmodified by early-lifting and heat-treatment (for earlier forcing), by delaying the start of 5°C storage (for later forcing), by glasshouse temperature (16 and 18°C), and by shading treatments; there was little effect of bulb size.     

Increases in ethylene and carbon dioxide production by Tulipa gesneriana L. ‘Prominence’ after completion of the cold-requirement

Bulbs of Tulipa gesneriana L. ‘Prominence’ were either specially pre-cooled at 5 ± 0.5°C or held at 17 ± 0.5°C in a flow-through system equipped for atmospheric sampling. Bulbs at 17°C had low CO₂ and C₂H₄ production rates until January when they began to increase. An initial peak of C₂H₄ production occurred during the 2nd week of pre-cooling, followed by a major increase after 12 weeks. In addition, bulbs were specially pre-cooled for periods of 2–16 weeks (2-week increments). The bulbs were then transferred to 17 ± 0.5°C, where initial periods of special pre-cooling of greater than 12 weeks resulted in a dramatic increase in respiration rate over bulbs cooled for less than 12 weeks. These increases in C₂H₄ and CO₂ liberation appeared to be related to completion of the bulb cold-requirement. However, no surge of shoot elongation occurred after 12 weeks of pre-cooling and transfer to 17°C.     

Effect of temperature on seed and fruit development in three mango (Mangifera indica L.) cultivars

The effect of diurnal maximum/minimum (20/10 or 25/15 °C) temperatures on seed and fruit development of ‘Irwin’, ‘Kensington’ and ‘Nam Dok Mai’ mangoes (Mangifera indica L.) was studied in a controlled-environment glasshouse. Exposure to low temperatures (20/10 °C day/night) 3 days after hand pollination significantly increased the percentage of stenospermocarpic fruit (nubbins), in which embryos were aborted at some stage during early fruit development. There were significant differences between cultivars in the percentage of nubbins produced out of the total fruit set following overnight exposure to 10 °C with 21% for ‘Nam Dok Mai’, 11% for ‘Kensington’ and 3% for ‘Irwin’. At 45 days after pollination, nubbin fruits were much smaller in size and weighed ca. 50% less than normal fruits. The lower percentage of nubbin fruits in ‘Irwin’ implies a greater adaptation to cool temperatures by this cultivar during fruit set and early embryo development.     

菠萝体细胞胚发育过程的形态学和解剖学研究

 以‘神湾’菠萝（Ananas comosus‘Shenwan’）愈伤组织为材料,对体细胞胚发育过程中的形态和组织结构变化进行了观察和石蜡切片研究。结果表明,菠萝体细胞发育过程可划分为原胚、球形胚、梨形胚、笋形胚和成熟胚等5个时期。原胚是由胚性细胞分化和分裂形成的多细胞结构,呈棒状至纺锤形,最粗处直径50 ~ 200 μm,灰白色,细胞较均匀一致,未出现组织分化。球形胚近球形,直径200 ~ 500 μm,已开始组织分化,在后期能清楚观察到一些原维管束组织存在。梨形胚呈上细下粗的梨形,长600 ~ 1 000 μm,最粗处在胚体中下部（直径400 ~ 800 μm）,已经具备轴向性和双极性,子叶原基组织呈帽状将胚芽原始体包在其中。笋形胚似冬笋状,长1 000 ~ 2 000 μm,下部最粗处直径600 ~ 1 000 μm,后期子叶原基、胚芽鞘原基和胚芽原基已清晰可见。成熟胚长2 000 ~ 4 000 μm,下部最粗处直径1 000 ~ 1 500 μm,胚芽端已具子叶、胚芽鞘、叶原基和胚芽生长点,而胚根原基分化较慢,外围有一层胚根鞘组织。胚芽和胚根内源生,子叶衣领状,第一枚叶（胚芽鞘）基部鞘状,胚轴短,叶原基呈莲座状着生在上胚轴顶端,是菠萝体细胞胚的重要特征。     

Flowering and fruit-set response to temperature in the avocado cultivar ‘Hass’

Avocado plants, cultivar ‘Hass’, were kept in growth cabinets at 33°C day, 28°C night ($\text{33}\text{28}$); 25°C day, 20°C night ($\text{25}\text{20}$); and 17°C day, 12°C night ($\text{17}\text{12}$), with a 12-h photoperiod and photon flux density of 400 μE m^?2 s^?1 (400–700 nm). At $\text{33}\text{28}$ and $\text{25}\text{20}$ flowers opened in the morning in the female stage and again in the afternoon of the following day in the male stage (Type A floral cycle). At $\text{17}\text{12}$ the flowers opened in the afternoon in the female stage and started to reopen in the male stage 2 days later during the afternoon. They remained open overnight and started to close the following morning. Pollen tube growth and ovule penetration occurred at all temperatures. Pollen tube growth was fastest at $\text{33}\text{28}$, but the pistils had lost the ability to support pollen tube growth by the second week of the experiment. A lower proportion of the ovules at $\text{17}\text{12}$ had an embryosac penetrated by a pollen tube. Embryo development occurred at all temperatures, but fruitlets were abscissed at $\text{33}\text{28}$ and embryo growth was very slow at $\text{17}\text{12}$. The most suitable temperature regime for floral behaviour, pollen tube growth and embryo development was $\text{25}\text{20}$.     

The Effect of Cold Storage and Treatment with Gibberellic Acid on Flowering and Bulb Yields of Dutch Iris

Iris bulbs of the varieties Wedgewood and Prof. Blaauvv were injected with 50 or 500 μg. gibberellic acid (GA) before or after cold storage (10° C.) of 18 or 35 days. GA injection accelerated flowering by up to 19 days ; it had little or no effect on length of leaves or flower stem. It was most effective when applied at an early stage after flower initiation.

GA injection reduced bulb yield of Wedgiwood plants, and had no effect on, nor increased bulb yield of, Prof. Blaauw plants.

GA spraying (seven times at 10^-2M of GA) accelerated flowering and increased foliage growth in both varieties. It increased flower stem elongation and reduced bulb yield in Wedgfcwood plants.     

栽培种培养时间对真姬菇产量和质量的影响

研究了栽培种培养时间对真姬菇搔菌后气生菌丝恢复生长、料面转色、现蕾和子实体发育的影响，发现培养75d的处理C和培养83d的处理D的现蕾情况最好，菇形最佳，产量最高，16瓶产量分别达2．261kg和2．364kg；培养61d的处理A和培养67d的处理B现蕾情况不好，子实体发育迟缓，栽培瓶之间差异较大；培养92d的处理E现蕾情况良好，但是在栽培后期易受杂菌污染。