In vitro germination and viability of buckwheat (Fagopyrum esculentum Moench) pollen

An in vitro method for the germination of common buckwheat pollen was developed. Pollen grains were successfully germinated in an artificial medium consisting of 0.2 g each of MnSO₄, Ca(NO₃)2.4H₂O and KNO₃, 0.04 g H₃BO₃, 15 g sucrose and 30 g polyethylene glycol (molecular weight approximately 20,000) dissolved in 100 ml of double distilled water. The viability of pollen was assessed by in vivo and in vitro germination tests at 20 °C and 25 °C over a 38 h time period. Pollen grains were collected and germinated at 4 h intervals from freshly harvested flowers grown under 16 h day length and a constant temperature. Maximum pollen viability was found 2 h and 6 h after first light when plants were maintained at 25 °C and 20 °C, respectively. Viability, as measured by germination percentage, was similar at both temperature regimes. Some pollen remained viable for approximately 34 to 38 h in intact flowers, but all pollen lost viability in less than an hour when stored at room temperature without humidity control. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of pre-incubation humidity and temperature treatment on the in vitro germination of avocado pollen grains

Optimum in vitro germination of pollen grain of the avocado cultivars Fuerte, Nabal, Ettinger, Bacon and Zutano occurred at 25 °C. However, there were significant differences between cultivars in percentage germination and relative humidity (RH) requirements for optimum pollen grain growth. The most sensitive cultivar to relative humidity was Fuerte, in which the germination of pollen grain rose from 11.4%, at 40% RH, to about 50%, after one hour at 100% RH. The germination% of Nabal pollen grain was already high at 40% RH and was not increased by higher relative humidity. Increased relative humidity also helped to sustain the viability of avocado pollen. At 30 °C and 5% RH the pollen grains of Fuerte quickly lost its ability to germinate, at 40% RH for 1 hour, germination was reduced spectacularly compared to pollen kept in saturated with moisture environment where it was not affected the first 24 hours. The effects of temperature and relative humidity on fruit-set and yield of avocado are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

The viability and storage of strawberry pollen

Investigations were carried out in 1990 and 1991 to estimate the pollen viability of five strawberry genotypes and their suitability for storage. Pollen viability was assessed by acetocarmine staining, in vitro germination, and in vivo assays. Pollen was stored in darkness at ?18°C for 1 year, and pollen viability was estimated every 4 months during storage. The highest percentage of stained and in vitro germinated pollen grains, respectively, was shown by fresh pollen of cv. ‘Dukat’ (91 and 45%). The lowest values of these characteristics were observed in pollen of cv. ‘Paula’ (48% and 20%, respectively). The best response to storage at ?18°C occurred in pollen of the breeding clone ‘B-302’ and the cv. ‘Redgauntlet’. ‘Paula’ pollen responded least favourably to this. Pollen of the cvs. ‘Dukaf’. ‘Senga Sengana’, and clone ‘B-302’ after storage for 4 months, still had sufficient capacity for fruit set after cross-pollinations.     

Hybrid Tea-rose pollen. I. Germination and storage

Summary Germination and storage trials were carried out with pollen of several rose varieties. The pollen grains germinated well in a 15% sucrose solution with 40 ppm boric acid. Staining the pollen with a 0.1% tetrazolium solution and standardizing the degree of colour at which the pollen grains are counted as viable, provided a good viability estimate, simpler to carry out than in vitro germination. Germination capacity and staining ability of the pollen were greatly impeded-about halved-by dehydration during storage in desiccators at low humidity. This effect could be corrected by humidifying the pollen beforehand for about one hour, though this pre-treatment increased the percentage of germinated pollen grains more than the percentage stained. There was no difference between the two percentages in fresh or in deep-frozen pollen.Pollen stored at 1°C and high relative humidity soon lost its germination capacity: between 0 and 20% humidity a considerable proportion of the pollen remained viable for 9 months and longer. Storage for the same period in vacuum-sealed glass tubes at –24°C maintained viability as well or better and would probably prolong it further. Some of the cold-stored pollen induced a reasonable seed set after one year, a low seed set was obtained even after two years of storage at 1°C and low humidity.     

Viability and storage of bromeliad pollen

Several bromeliad species from two different subfamilies, were used to develop a reliable method to evaluate pollen viability. Pollen germination on a medium containing 20% sucrose, 0.001%H₃BO₃ and 0.5% agar was comparable to germination on a compatible stigma. Maximum germination was reached within 2 to 10 hours depending on the species. Based on this test, six species were considered as being good pollen donors with germination percentages between 49%and 83%. Furthermore, pollen from these species and cultivars could be stored in liquid nitrogen (–196 ^°C) without a considerable loss of viability. For all species, a dehydration period of 4 hours prior to cryopreservation and a rehydration period of 1 hour after cryostorage were essential. Greenhouse humidity influenced anther moisture content and cryostorability. This revised version was published online in July 2006 with corrections to the Cover Date.     

Production of polyhaploids of hexaploid wheat using stored pearl millet pollen

The effects of drying and freezing on viability of pearl millet pollen were examined with the aim of using stored pollen in polyhaploid production of hexaploid wheat. Freshly collected pollen of pearl millet line NEC 7006 with 55% water content, germinated at a frequency of 80%. Pollen that was dried for two hours to 6% water content showed 50% germination frequency and maintained similar frequencies after the freezing process. In crosses of hexaploid wheat variety Norin 61 with fresh pearl millet pollen, embryos were obtained at a frequency of 27.6%. In crosses with pollen stored at -196 °C, -80 °C and -20 °C for one month, embryo formation frequencies ranged from 27.5 to 17.4%. After five and twelve months of storage, the frequencies ranged from 29.7 to 14.6% at storage temperatures of -196 °C and -80 °C, and from 8.0 to 3.2% at -20 °C, indicating significant differences among storage temperatures. However, no significant frequency difference was found among pollen water contents at the time of collection. All plants regenerated from crosses with pearl millet pollen stored for five months were wheat polyhaploids. These results suggest that stored pearl millet pollen is an efficient medium for producing polyhaploids in hexaploid wheat. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of short-term storage on germinability of pistachio pollen

The effects of short‐term storage under room conditions (constant 25°C and 35% relative humidity), refrigeration (4°C) and freezing (‐20°C) on the germinability of pollen of pistachio, Pistacia vera L., were studied and the effects of desiccation and pollen age on its germinability were reassessed. It was found that: (1) weight loss as a result of desiccation was positively correlated with germinability; (2) pollen grains stored in room conditions only germinated after prehydration, which restored germinability even after 7 days of exposure; (3) refrigerated (4°C) pollen grains retained their germinability for at least a week; (4) frozen pollen grains irreversibly lost most of their germinability; (5) 2‐day‐old pollen grains, within the anthers, retained their germinability under room conditions. These findings will contribute to the improvement of pistachio pollen preservation and help to find a simple and inexpensive method for its short‐term storage, while retaining its germinability.     

Storage of avocado pollen

Summary Avocado pollen was stored at a range of temperatures and relative humidities (RH) for up to one year and the pollen was tested for viability in vivo.Pollen stored for one month was capable of germination on the stigma and penetrating the ovule when stored at 4°C with <1,23,55 and 75% r.h. and at -196°C with 0% r.h. Most pollen samples stored at 25 and -15°C at a range of r.h. would germinate on the stigma but none would penetrate the ovule.After one year of storage, pollen at 4°C and <1 and 23% r.h. would germinate on the stigma but would not penetrate the ovule. There was no germination of pollen stored at 4°C and 55 and 75% r.h. Only pollen stored at -196°C and 0% r.h. would penetrate the ovule, but thawing and refreezing once during the year destroyed the viability.     

Cryopreservation of Delphinium pollen at –30 °C

Pollen of garden varieties and species of Delphinium that was cryopreserved at –30 ^°C after 3 hours of air drying and storage on silica gel, had high germination and pollen tube growth in vitroeven after 180-day storage. On the other hand, pollen stored at 25 ^°C showed a marked decrease in the germination rate within 10 days. The best in vitro germination of Delphinium pollen was on a 1% water agar containing 15% sucrose and 0.005 to 0.01% boric acid and at 15 to 20 ^°C. Field pollination with the cryopreserved pollen showed higher fruit and seed set than pollination with pollen stored at 25 ^°C, and was not significantly different from fresh pollen. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pollen storage at low temperature as a procedure for the improvement of cold tolerance in spring rape, Brassica napus L.

The possibility of selecting spring rape for cold tolerance at the mature pollen grain stage was studied by investigating the effects of pollen storage at low temperatures on the quality of pollen grains and on the cold tolerance of the plants generated from them. Pollen treatments of F¹ hybrids affected fertilization ability much more than viability and even after 10 days storage at 3 or 10°C the pollen germination percentage was reasonably high. Pollen storage for 7 or 10 days at 3 or 10°C significantly increased the cold tolerance of F² seed germination, with 3°C being more effective. Pollen storage for a shorter time had no effect upon the number of resulting genotypes tolerant to low temperature. This approach may be successfully applied in plant breeding to enrich segregating plant populations with cold-tolerant genotypes.     

美国梾木(Cornus spp.)花粉活力及萌发特性

为了了解美国梾木花粉活力及萌发特性,采用扫描电镜技术对13个美国梾木无性系花粉形态进行观测与方差分析,并采用荧光显微技术和TTC染色法对无性系2号花粉萌发特性及花粉活力进行观察。结果显示:(1)不同无性系间花粉大小差异不显著,但外壁纹饰差异较大,极面沟距的变异系数最高且遗传最为稳定。(2)花序开花率为75%时花粉活力最高,整花4℃条件下短期保存花粉活力较高。(3)授粉后,多数花粉可在柱头上正常萌发,72 h后花粉管即可进入子房。研究认为,花粉外壁及极面沟距可作为鉴定美国梾木无性系的形态指标,美国梾木花粉活力及萌发特性是抗逆及丰产杂交组合的重要保证。     

The effects of high-temperature stress on the germination of pollen grains of upland cotton during square development

The reproductive stage of flowering plants is sensitive to high-temperature stresses. High temperature is a major factor influencing pollen grain viability in upland cotton (Gossypium hirsutum). The objective of this study was to identify the relationship between cotton pollen germination percentage and temperature by assaying the pollen germination of four upland cotton cultivars in vitro at different temperatures during the blooming period. The results showed that in vitro pollen germination percentage was related to the culture temperature of pollen germination and the temperature of the square development process. High temperature affected pollen development and germination, and high-temperature tolerance differed among the cotton cultivars. The pollen germination percentage decreased rapidly with changes in the culture temperature from 30 to 39 °C. A culture temperature of 35 °C might be a critical temperature for the pollen viability transition and could be used to screen cotton cultivars that have pollen grains with high-temperature resistance. Before the high-temperature stage, cultivars with rates of decrease in the percentage of pollen germination of less than 41 % at 35 °C relative to the rates at 30 °C might be considered as high-temperature tolerance cultivars, and cultivars with rates of decrease in the percentage of pollen germination greater than 41 % might be considered as susceptible cultivars. The high-temperature stress for pollen grain germination in vitro was greater than 30 °C, and the high-temperature stress for square development might be greater than 33 °C. Boll retention was significant; it was positively correlated with the pollen germination percentage and negatively correlated with temperature during the high-temperature stage. This study provided a method for rapidly screening cultivars (lines) with high-temperature tolerance pollen in upland cotton breeding.     

阔叶杨桐花粉离体萌发和花粉管生长特性的研究

研究了不同浓度的蔗糖和硼酸,在不同温度和培养时间内对阔叶杨桐花粉萌发率和花粉管生长的影响,以期为阔叶杨桐的繁殖育种研究提供依据.结果表明:1)不同浓度的蔗糖和硼酸处理组之间存在显著性差异,蔗糖和硼酸都能促进杨桐花粉萌发和花粉管的生长,但超过一定浓度则会起到抑制作用;2)随着培养温度的升高,花粉萌发率和花粉管长度呈先升后降的趋势;3)随着培养时间的延长,花粉萌发率和花粉管长度逐渐增加,但最初的前12h内花粉萌发快,在培养的前9h内花粉管生长较快.4)实验显示:阔叶杨桐花粉培养的最适培养基是15％蔗糖和0.02％硼酸,最适培养温度为25℃,培养24 h后花粉萌发率为84.32％,花粉管长达2 003.51 μm.     

Compatibility and incompatibility in witloof-chicory (Cichorium intybus L.). 1. The influence of temperature and plant age on pollen germination and seed production

Summary For the production of inbred lines and F₁ hybrids in witloof-chicory information is wanted on characteristics such as the incompatibility system. These characteristics can only be studied properly if the influence of temperature and physiological status of the plant on pollen germination and seed production is known. Investigations were carried out with 9 self-incompatible (SI) and 6 self-compatible (SC) clones in glasshouses of the IVT phytotron at constant temperatures of 10, 14, 17, 20, 23 and 26°C. In general, in vivo pollen germination percentages were rather low after self pollination with an optimum for germination around 17–20°C. No seeds were formed at the lowest temperature (10°C) while seed production for SC clones was usually (rather) good at higher temperatures. At 26°C seed production in some clones decreased. Both pollen germination and seed production decreased at the end of the flowering period. There was a rather positive relationship at e.g. 17 and 20°C between pollen germination after selfing and seed production. When no pollen germination was observed, no seed formation occurred. When pollen grains did germinate, seed development would not necessarily occur in all cases. So this relationship only enables negative mass selection for SC.     

Establishment of a long-term storage method for soft X-ray irradiated pollen in watermelon

A new method for preserving viable soft X-ray irradiated pollen for the production of seedless watermelons (Citrullus lanatus L.) from diploid plants was established by storing the pollen under N₂ at −25°C for 1 year. Pollen stored at 4°C had the ability to germinate until 28 days under all atmospheres tested except O₂. However, after storage at this temperature for 3 months it did not germinate in any treatment conditions. Pollen stored at −25°C for 1 year under N₂, CO₂ or under a vacuum had a germination rate of about 50%. Pollen stored in O₂ or in air had a much lower germination rate, less than 20% and 10%, respectively. Thus, it is important to store watermelon pollen at a low temperature when it is being stored for a long time. Nitrogen and CO₂ were effective in extending the life of watermelon pollen. On the other hand, it has been demonstrated that the viability of pollen was reduced by storage under O₂. The N₂ and CO₂ are thought to be effective because they are essentially inert to the living pollen. Also, a lot of pollen tubes were observed in a middle portion of an ovary pollinated with pollen stored at −25°C under N₂; however, pollen tubes were not observed in ovaries pollinated with pollen stored under a vacuum. It was revealed in 1 year storage experiments that viability of pollen stored under N₂ was higher than that stored under a vacuum. Seedless fruits produced with pollen stored at −25°C under N₂ had the same characteristics as the control fruit. Authors did this research in ‘Research and Development Program for New Bio-Industry Initiatives’.     

Effects of gamma irradiation on in vitro pollen germination of different Cucumis species

Summary Pollen grains of 14 Cucumis accessions were irradiated with 0, 1, 2, 3 or 4 kGy acute gamma rays and germinated in vitro directly afterwards. Pollen germination was significantly reduced by increasing irradiation dose for all species, except C. melo var. agrestis. Pollen tube growth was generally reduced likewise. Pollen of two C. anguria subspecies was most sensitive to irradiation. Sensitivity of the pollen with respect to pollen tube growth in relation to irradiation dose was inversely related to total DNA amount per nucleus. In vitro germination was not related to DNA amount per nucleus. Results show that the examined Cucumis species, especially C. melo var. agrestis, are sufficiently resistant to irradiation to be used as donor species for in vivo egg cell transformation of the cucumber.     

Germination of Brassica pollen and expression of incompatibility in vitro

Summary Pollen derived from cabbage, broccoli, and collards (Brassica oleracea, var. capitata, Italica and acephala, respectively) will germinate in a synthetic medium consisting of sucrose, H₃BO₄, CaCl₂ and purified polyethylene glycol 20,000. The optimum levels of constituents varied from genotype to genotype. With one genotype of cabbage, a germination percentage of 84% and tube lengths of at least 3.5 mm long were obtained. Whereas pollen from broccoli germinated in 1 to 2 hours, cabbage pollen required a 3 to 4 hour incubation period. Optimum germination occurred at pH 5.8 and at a pollen density of 0.5–2.0 mg/ml for cabbage. The effect of flower age on pollen germination varied from genotype to genotype. Of 7 cabbage genotypes tested, pollen germination either increased, decreased or remained the same as flower age increased. Pollen germination in vitro required polyethylene glycol purified by dialysis or passage through Sephadex G-25. Cabbage stigmas release a heat-labile substance capable of inhibiting germination of self-pollen, but stigma extracts from a cross plant have no effect.     

Some consequences of pollen storage in the raspberry (Rubus idaeus L.)

Summary Raspberry pollen was stored at 5°C and –13°C for six months and then tested for its ability to induce pyrene set and the production of viable seedlings, and for its effect upon the segregation of a major gene s. Only pollen stored at –13°C gave a pyrene set and germination percentage adequate to produce sufficient seedlings for a breeding programme. It is suggested that tests of pollen viability in the raspberry should include studies of pollen germination, and the effect of this pollen on pyrene set and seed germination. Possible causes of the loss of viability in the pollen stored at 5°C are discussed.     

Assessment of Cold and Heat Tolerance of Winter-grown Canola (Brassica napus L.) Cultivars by Pollen-based Parameters

Winter‐grown canola (Brassica napus L.) production is limited mostly by frost and winter kill in the southern canola‐growing regions of the United States. Tolerance to cold and heat were assessed by studying percentage of pollen viability (PV), in vitro pollen germination (PG) and pollen tube length (PTL) for 12 field‐grown cultivars. Freshly collected pollen from all cultivars were incubated on artificial solid growth media at a constant temperature ranging from 10 to 35 °C at 5 °C interval for 30 h to determine PG and PTL. A modified bilinear model best described the temperature response functions of PG and PTL. Canola cultivars showed significant variability (P < 0.001) for PV (61.3 % to 89.7 %), PG (29.0 % to 48.2 %) and PTL (463 to 931 μm). The average cardinal temperatures, T_min, T_opt and T_max, for PG and PTL were 6.4, 24.3 and 33.7 °C, respectively. Principal component analysis revealed that maximum PG, PTL, T_min and T_opt of both PG and PTL were the most important factors in determining cold tolerance, whereas T_max of PG and PTL, and maximum PG and PTL were more responsible in separating the cultivars for heat tolerance. The canola cultivar, KS3077, was the most cold tolerant with the lowest T_min and the widest temperature adaptability range, and the cultivar Kadore was the most heat tolerant with the highest T_max for the PG. The identified cold‐ and heat‐tolerant cultivars may be useful in canola‐breeding programmes to develop cultivars suitable for a niche environment.     

Long-term storage of Narcissus anthers and pollen in liquid nitrogen

Summary Three methods for the long-term storage of narcissus pollen were compared; anthers in glass vials held in a desiccator with calcium chloride at 2°C, and polypropylene straws containing either anthers or naked pollen immersed in liquid nitrogen. Pollen from all storage treatments showed 15–16% germination in vitro after 3 days, compared with 27.4% for fresh pollen. Seed set per pod using pollen stored for 3 days was comparable to that of fresh pollen. However, after 351 days, pollen from anthers at 2°C exhibited only 0.1% germination and failed to set seed whereas no further change in germination rate was recorded for pollen from the two liquid nitrogen treatments and seed set was still equivalent to fresh pollen.