Giant Pollen Research Articles

Effects of sexual polyploidization on reproductive development in a full-sib poplar family

Populus is an important source of woody biomass in the Northern Hemisphere. Sexual polyploidization plays a valuable role in the genetic improvement of Populus, resulting in tremendous variation in phenotypic traits. Most studies have focused on the variations in the vegetative growth of allopolyploid Populus; however, variations in the reproductive development of different polyploid genotypes of the progeny remain unclear. In this study, catkin traits, pollen size and viability, meiotic development, and reproductive ability were analyzed based on a full-sib family including diploid and triploid hybrids of (Populus pseudo-simonii × P. nigra ‘Zheyin3#’) × (P. × beijingensis) to understand the effects of sexual polyploidization on reproductive development in Populus hybrids. Catkin traits varied among the genotypes in the full-sib family. A ploidy change resulted in significant variation in male catkin length and male flower number per catkin but not in female catkin traits, suggesting that Populus catkin development may be more sensitive to respond to a change in ploidy level in male plants than in female plants. The male diploid hybrids had significantly smaller pollen grains, but higher pollen germination rates than the triploid hybrids. Giant pollen grains with large diameters were recorded in all-male diploid and triploid hybrids, which were speculated to be unreduced gametes. Premature cytokinesis, misorientation of the spindles, and aberrant cytokinesis were observed in a cytological analysis, which explained the production of unreduced pollen. Premature cytokinesis was only detected in triploid hybrids, which might be attributed to a ploidy change. The frequencies of meiotic abnormalities, such as precocious chromosomal migration, chromosome bridges, and micronuclei in the triploid hybrids were higher than those in diploid hybrids, suggesting that the unbalanced chromosomes in the triploid hybrids caused more complex meiotic chromosome behaviors. Backcrosses with the triploid hybrids resulted in low seed sets and seed germination rates, suggesting that polyploidization reduced pollen viability. Our findings provide new insight into the effect of sexual polyploidization on reproductive development in Populus and could be used to guide a Populus polyploid breeding program.

Inducing 2n pollen to obtain polyploids in tulip

Polyploids display desirable traits such as high yield, big flower, vigorous growth and strong resistance. Sexual polyploidization using 2n pollen induced by nitrous oxide (N2O) was an effective method to obtain polyploid tulips. In this study, two diploid tulip cultivars ‘Synaeda Amor’ and ‘Carnaval de Rio’ were used as materials to obtain 2n pollen and polyploids. Their bulbs undergoing meiosis were treated with N2O at six atmospheres for 24 h. The 2n pollen was identified based on the change of pollen diameter of parents and the ploidy of progenies. The results showed 2n pollen was successfully induced from these two diploid tulip cultivars by treatment with N2O. However, it was significantly different in induction efficiency of 2n pollen between them. The 2n pollen productivity of ‘Synaeda Amor’ was 16.0%, while that of ‘Carnaval de Rio’ was 26.7%. The maximum pollen grains diameter of ‘Synaeda Amor’ increased from 66.72 to 88.70 µm and ‘Carnaval de Rio’ from 65.24 to 97.66 µm, diploid to polyplod, respectively. Pollen mixtures containing giant pollen grains from ‘Synaeda Amor’ and ‘Carnaval de Rio’ were crossed with diploid cultivars ‘Salmon Dynasty’ and ‘Cheers’. Triploids were detected in the progenies of the four cross combinations, with the polyploidy ratio ranging from 4 to 18%. Whereas polyploids were not found in the progenies from control crosses without treatment. This research revealed that 2n pollen can be produced using N2O treatment and can be applied to induce polyploidy in tulip.

Teratomorphism of pollen of Larix sibirica Ledeb. (Pinaceae Lindl.) in the Arctic urbanized territory

This article presents data of palynological research of Larix sibirica Ledeb. (Pinaceae Lindl) in the Arctic climate of Murmansk city, located in the Far North of Russia. The purpose of this study is to research the teratogenesis of the Larix sibirica pollen in the conditions of the Arctic climate and technogenic pollution of the city of Murmansk and holding the palynoindication of the environment. In the tested samples of pollen of L. sibirica, five morphological anomalies of the development were defined: pollen without protoplast, with plasmolysed protoplast, with damaged exine, giant pollen grains and dwarfed. The proportion of teratomorphs in the samples varies from 76 to 81%, which is above the control values of 2.5 – 3 times. Most of the abnormal grains are represented by pollen with plasmolysed protoplast (58 – 64%) and without protoplast (11 – 18%). Giant, dwarf pollen grains and pollen with exine damage are much less common. High level of teratogenesis of L. sibirica allows us to draw a conclusion about the critical level of pollution of the city environment.

Introgression of Black Rot Resistance from Brassica carinata to Cauliflower (Brassica oleracea botrytis Group) through Embryo Rescue.

Black rot caused by Xanthomonas campestris pv. campestris (Xcc) is a very important disease of cauliflower (Brassica oleracea botrytis group) resulting into 10–50% yield losses every year. Since there is a dearth of availability of resistance to black rot disease in B. oleracea (C genome), therefore exploration of A and B genomes was inevitable as they have been reported to be potential reservoirs of gene(s) for resistance to black rot. To utilize these sources, interspecific hybrid and backcross progeny (B1) were generated between cauliflower “Pusa Sharad” and Ethiopian mustard “NPC-9” employing in vitro embryo rescue technique. Direct ovule culture method was better than siliqua culture under different temperature regime periods. Hybridity testing of F1 inter-specific plants was carried out using co-dominant SSR marker and Brassica B and C genome-specific (DB and DC) primers. Meiosis in the di-genomic (BCC) interspecific hybrid of B. oleracea botrytis group (2n = 18, CC) × B. carinata (2n = 4x = 34, BBCC) was higly disorganized and cytological analysis of pollen mother cells revealed chromosomes 2n = 26 at metaphase-I. Fertile giant pollen grain formation was observed frequently in interspecific F1 hybrid and BC1 plants. The F1 inter-specific plants were found to be resistant to Xcc race 1. Segregation distortion was observed in BC1 generation for black rot resistance and different morphological traits. The At1g70610 marker analysis confirmed successful introgression of black rot resistance in interspecific BC1 population. This effort will go a long way in pyramiding gene(s) for resistance against black rot in Cole crops, especially cauliflower and cabbage for developing durable resistance, thus minimize dependency on bactericides.

Unreduced 2n Pollen Production in ‘Nishiuchi Konatsu’ Hyuganatsu as Inferred by Pollen Characteristics and Progeny Ploidy Level

Hyuganatsu is a self-incompatible Citrus species with no parthenocarpic traits. Pollinizer requirements and seedy fruit production are therefore a limiting factor for Hyuganatsu growers. ‘Nishiuchi Konatsu’, a bud mutation of Hyuganatsu, can set fruit by self-pollination and aborts most seeds. To obtain a better understanding of the reproductive mechanisms of ‘Nishiuchi Konatsu’, its pollen was characterized by pollen observation and viability testing in vitro in addition to pollen tube observation of the pistil following various pollination combinations. Furthermore, the ploidy level of ‘Nishiuchi Konatsu’ and the progenies obtained after controlled pollination were analyzed using a flow cytometer. As a result, ‘Nishiuchi Konatsu’ pollen was shown to be functional in vitro, as indicated by both the pollen germination test and FDA staining. A curious feature of ‘Nishiuchi Konatsu’ pollen is that a giant pollen of about 42–44 μm in diameter, which is about 1.3-fold the average diameter of original Hyuganatsu pollen (33.4 μm), was partially produced. Observation of in vivo pollen germination and pollen tube elongation revealed that Hyuganatsu (or ‘Nishiuchi Konatsu’) × ‘Nishiuchi Konatsu’ showed imperfect incompatibility; that is, some pollen tubes were able to enter the style while others could not. Flow cytometry analysis indicated that ‘Nishiuchi Konatsu’ is diploid while all of its self-pollinated progenies, which were rarely obtained as normal seeds, were tetraploid. Progenies from other combinations were diploid. These results strongly suggest that unreduced 2n pollen production occurred in ‘Nishiuchi Konatsu’. In addition to self-compatibilty and seed abortion of ‘Nishiuchi Konatsu’ self-pollination, it has been reported that the proportion of normal to aborted seeds differs according to the cultivar of the seed parent crossed with ‘Nishiuchi Konatsu’ pollen (Honsho et al., 2009). Taking into account the unreduced pollen production as well as the effect of polyploidization on self-incompatibility and embryo development, we finally discussed why such a phenomenon was induced by pollination with ‘Nishiuchi Konatsu’ pollen and why ‘Nishiuchi Konatsu’ became self-compatible.

Cytotoxic effect of benzo(a)pyrene on development and protein pattern of sunflower pollen grains

Benzo(a)pyrene (BaP) is an important part of diesel exhaust particles (DEP). The overall objective of this research was to elucidate some microscopic effects of BaP on the formation, development, and structure of pollen grains and its proteins in sunflower (Helianthus annuus L). Sunflower plants were grown in experimental pots and treated with the different concentrations of BaP. Flowers and young buds were removed, fixed in FAA70 (formalin:acetic acid:ethanol, 2 : 1 : 17) and subjected to developmental studies. Our results show that BaP-treatment causes abnormalities during pollen development. Shape of microspore tetrads changed from spherical to polygonal or irregular. Pollen grains in normal plants are spherical in both equatorial and polar views; in BaP-treated plants, they changed into irregular shapes in equatorial view and triangular shape in polar view. Delay in degeneration of the tapetum layer in anther, and formation of giant, irregular, and non-fertile pollen grains are other results of BaP treatment. Gel electrophoretic studies revealed that a band with a molecular mass of 30 kDa disappeared in the BaP-treated group and two new proteins with molecular masses of 15 and 20 kDa were formed. Some pollen proteins may act as allergens, considering the fact that pollen allergy frequency is increased in polluted areas, especially DEP-polluted ones; the possibility arises that BaP, as an important part of DEP, could be an effective agent entailing formation of detoxifying proteins which, on the other hand, can also act as allergens.

Production of viable male unreduced gametes in Brassica interspecific hybrids is genotype specific and stimulated by cold temperatures.

BackgroundUnreduced gametes (gametes with the somatic chromosome number) may provide a pathway for evolutionary speciation via allopolyploid formation. We evaluated the effect of genotype and temperature on male unreduced gamete formation in Brassica allotetraploids and their interspecific hybrids. The frequency of unreduced gametes post-meiosis was estimated in sporads from the frequency of dyads or giant tetrads, and in pollen from the frequency of viable giant pollen compared with viable normal pollen. Giant tetrads were twice the volume of normal tetrads, and presumably resulted from pre-meiotic doubling of chromosome number. Giant pollen was defined as pollen with more than 1.5 × normal diameter, under the assumption that the doubling of DNA content in unreduced gametes would approximately double the pollen cell volume. The effect of genotype was assessed in five B. napus, two B. carinata and one B. juncea parents and in 13 interspecific hybrid combinations. The effect of temperature was assessed in a subset of genotypes in hot (day/night 30°C/20°C), warm (25°C/15°C), cool (18°C/13°C) and cold (10°C/5°C) treatments.ResultsBased on estimates at the sporad stage, some interspecific hybrid genotypes produced unreduced gametes (range 0.06 to 3.29%) at more than an order of magnitude higher frequency than in the parents (range 0.00% to 0.11%). In nine hybrids that produced viable mature pollen, the frequency of viable giant pollen (range 0.2% to 33.5%) was much greater than in the parents (range 0.0% to 0.4%). Giant pollen, most likely formed from unreduced gametes, was more viable than normal pollen in hybrids. Two B. napus × B. carinata hybrids produced 9% and 23% unreduced gametes based on post-meiotic sporad observations in the cold temperature treatment, which was more than two orders of magnitude higher than in the parents.ConclusionsThese results demonstrate that sources of unreduced gametes, required for the triploid bridge hypothesis of allopolyploid evolution, are readily available in some Brassica interspecific hybrid genotypes, especially at cold temperatures.

Effect of the water-soluble fraction of diesel exhaust particles on the development and protein patterns of pollen grains in bean plants (Phaseolus vulgaris L.)

Excessive air pollution may adversely affect plant growth and development. The overall objective of this research was to elucidate some microscopic effects of diesel exhaust particles (DEP) on the formation, development, and structure of pollen grains and its proteins in Phaseolus vulgaris L. Bean plants were grown in experimental pots and treated with different concentrations of the water-soluble fraction of DEP. Flowers and young buds were removed, fixed in FAA70 (formalin : acetic acid : ethanol, 2 : 1 : 17), and subjected to developmental studies. Our results show that DEP cause some abnormalities during pollen development. Pollen grains in normal plants are spherical in equatorial view and triangular in polar view; in DEP-treated plants, they were changed into irregular shapes in equatorial view and asteroidal in polar view. Delay in degeneration of the tapetum layer of the anther, and formation of giant, irregular, and non-fertile pollen grains are other results of DEP treatment. Gel electrophoretic studies revealed that a new protein with a molecular mass of 80 kD was formed in the DEP-treated group. Some pollen proteins may act as allergens, considering the fact that pollen allergy frequency is increased in polluted areas; the possibility arises that DEP could be an effective agent entail formation of detoxifying proteins which, on the other hand, can also act as allergens.

Occurrence and cytological mechanism of 2n pollen formation in Chinese Diospyros spp. (Ebenaceae) staminate germplasm

SummarySome Diospyros spp. (Ebenaceae) staminate germplasm (2n = 6x = 90) recently found in Hubei Province, China, was of potential value for breeding. This study evaluated the natural rate of occurrence and cytological mechanism responsible for the formation of 2n pollen in this staminate germplasm. The frequencies of giant pollen, dyads, and triads detected in all accessions were 0 – 2.3%, 0.8 – 2.2%, and 2.3 – 4.3%, respectively. The correlation coefficient (r = 0.98**; P < 0.01) between the frequency of giant pollen and those of dyads and triads was highly significant, which strongly suggests that the giant pollen was 2n pollen. Cytological analysis of pollen mother cell meiosis showed that the main cytological mechanisms responsible for the formation of 2n pollen were tripolar spindles and fused spindles, instead of parallel spindles and vertical spindles. In addition, an abnormal disintegration of sister chromatids, which also produced 2n pollen in the end, was occasionally found at metaphase II. Diploid (2n) pollen produced by tripolar spindles and fused spindles was equivalent to first division restitution (FDR) gametes. Therefore, this Diospyros spp. staminate germplasm may have value for sexual polyploidisation in breeding programmes of Japanese persimmon.

Production of 2n pollen of Asiatic hybrid lilies by nitrous oxide treatment

Tetraploid varieties of lilies have superior agronomic traits such as large flowers and resistance to physiological disorders. In the present study, we attempted to induce 2n pollen of Asiatic hybrid lilies by arresting the meiotic process with nitrous oxide (N2O) gas. To determine which meiotic stage is optimal for induction of 2n pollen, plants with attached buds at different meiotic stages were treated with N2O for 24 h in a pressure-tolerant cylinder. A few 2n pollen grains were induced using plants with anthers in prophase I, whereas mixed pollen grains of differing size were produced using plants undergoing meiotic metaphase predominantly in anthers. Although normal lily pollen grains are elliptical, nitrous oxide exposure induced giant pollen grains that appeared spherical. Flow cytometry analysis showed that the giant pollen grains were diploid. When mixed pollen that included normal and giant pollen was crossed to tetraploid cultivars, the resulting seedlings were tetraploid and aneuploid, indicating that the giant pollen grains were diploids that could generate tetraploid seedlings through fusion to diploid eggs supplied from a tetraploid female parent. Thus, treatment with N2O is useful for the production of 2n lily pollen and may provide a new approach for tetraploid lily breeding.

Sexual polyploidization in red clover

Because sexual polyploidization broadens genetic basis and supply plant breeders with more variability for the selection process, it can be useful in red clover breeding. This paper reports results of three crossing cycles, starting from a parental generation of tetraploid red clover plants (female parent), and diploids from the Quiñiqueli cultivar, selected for production of more than 1% of giant pollen grains (male parent) aiming to obtain tetraploid plants to be used in red clover breeding programs. Crosses in the next generations were performed by mutual cross-pollinations. Chromosome number chimerism and high pollen sterility were detected in F1, F2 and F3, but there was a trend towards increasing seed production and seed viability along the generations, probably due to successful competition between fertile and sterile gametes. The identification of fertile triploids, as well as their recurrent formation along the generations, indicates that triploid block is not complete in red clover, and that triploids may be successfully used as a bridge for the production of sexual polyploids.

Induction of 2n pollen in tulips by arresting the meiotic process with nitrous oxide gas

Triploid tulips have agronomically desirable traits such as vigorous growth and large flower size, but only a portion of all cultivated tulips is triploid. To apply 2n pollen to polyploid breeding of tulips, the polyploidizing agent, nitrous oxide gas (N2O), was applied to bulbs. In tulips, meiosis in anthers occurs inside the bulbs from mid- to late-October. When meiosis in anthers (excised from bulbs) reached metaphase I, we treated other bulbs of the same clones with N2O for 24–48 h. Most of the treated plants produced pollen grains with a wide-ranging or bimodal size distribution, indicating a mixture of n, 2n and aneuploid pollen grains. The use of pollen containing a relatively high proportion of giant pollen grains tended to yield larger numbers of triploids in the progeny. The number of giant pollen grains could be increased when N2O-treated pollen grains were suspended in 10% sucrose and then sieved through a nylon mesh. Very few polyploids were observed in some cross combinations, even those involving pollen with a relatively high proportion of giant grains. Even so, this low polyploid yield most likely is due to a triploid block, because the capsules obtained in the crosses of the diploid×N2O-treated plants contained some abnormal seeds, which were mostly triploid. Embryo culture was useful in rescuing abnormal embryos. The present study reveals that 2n pollen can be produced at high frequency using N2O during tulip breeding.

Selection for increasing 2n gamete production in red clover

Three selection cycles were performed in the red clover cultivars Quiniqueli, Redland and Keenland to increase the 2n gamete production. Unreduced gamete production was estimated by the giant pollen grain (GP) production. Plants with more than 1% of GP were selected as progenitors from the original population; plants with at least 2% and 3% of GP, respectively, we re selected and crossed for the second and third cycles. The GP production ranged from 1.4 to 7.5% in the first, 2.0 to 51.0% in t he second, and 3.0 to 46.7% in the third cycle. Considering the three cultivars together, there was a significant increase in GP production from the first (4.0%) to the third (8.9%) cycles. 'Redland' presented higher GP percentages in each cycle and signif icant and steady GP production increases along the three cycles: 4.8, 13.4 and 19.7%, respectively, and should be included in further attempts to obtain sexual polyploids.

Occurrence and cytological mechanism of 2n pollen formation in a tetraploid accession of Ipomoea batatas (sweet potato).

We evaluated a 4x accession of Ipomoea batatas (L.) Lam. and four 2x accessions of Ipomoea triloba for 2n pollen production. Approximately 90% of the genotypes of accession 81.2 (I. batatas, 4x) produced 2n pollen with different frequencies. In contrast, none of the genotypes of I. triloba produced 2n pollen. The diameter of the 2n pollen was approximately 30% ((3) sqrt 2) larger than that of the n pollen, making it easy to identify, measure, and quantify. The correlation (r = 0.93**) between the frequency of giant pollen and the frequency of dyads and triads was highly significant, strongly suggesting that the giant pollen grains were 2n pollen. The 2n pollen producers presented either a parallel or tripolar spindle arrangement (Y shaped) at anaphase II instead of the normal 60 degrees crossed spindle orientation. These two abnormal spindle configurations produced dyads and triads, with different frequencies (13-67%), instead of tetrads. Occasionally a metaphase II spindle variation was found with a single fused spindle, which also forms a dyad. The correlation (r = 0.89**) between the frequency of 2n pollen and the frequency of parallel, fused, and tripolar spindle arrangements was also highly significant, suggesting that these abnormal spindle configurations are involved in the production of 2n pollen in I. batatas. When we evaluated the efficiency of 2n pollen in polyploidization using 4x x 4x (2n) crosses, all progenies were 4x, suggesting the existence of barriers to crossability between 4x genotypes and their 2n pollen-producer counterparts.

Origin of Tetraploid Progenies in 4x*2x Crosses of Cyclamen(Cyclamen persicum Mill.).

The origin of tetraploids from 4x × 2x cyclamen crosses was examined by using the diploid pollen parents with and without giant pollen grains, and by pollinating tetraploid cultivars with sieved giant and normal-sized pollen grains borne on diploid plants. The developing pollen mother cells were observed after the second meiotic division in the diploids with and without the giant pollen grains. Tetraploid progeny production in the crosses was obviously related to the giant pollen grains. Tetraploid F1 progenies were produced in the crosses by using pollen from diploid plants that produce giant pollen ; no seed was obtained in the crosses by using pollen from diploids, which produce no giant pollen. More seeds were obtained when sieved giant pollen grains were used for the crosses than when non-sieved pollen grains with giant pollen were used, whereas no seed was obtained in the crosses using only normal-size pollen grains from diploids. Thirteen to 27% of pollen mother cells in the diploids with giant pollen grains formed pollen dyads or triads after the second meiotic division, whereas few pollen dyads and triads were formed in those without giant pollen grains. These observations suggest that most giant pollen grains in diploid cyclamen are unreduced male gametes. Therefore, the origin of tetraploids derived from 4x × 2x cyclamen crosses is the results of fertilization between an unreduced pollen grain from the diploid plant and a normally reduced egg cell from the tetraploid. Furthermore, the use of sieved giant pollen grains was efficient for the production of tetraploid progenies.

A tetraploid hybrid plant from 4x × 2x crosses in Vitis and its origin

To study the origin of unreduced (2n) gametes in diploid Vitis cultivars, we surveyed the occurrence of tetraploid hybrid seedlings from 40 interploid crosses with five tetraploid and seven diploid cultivars. A total of 250 seedlings from the interploid crosses were established through embryo culture and by seed sowing. In 20 2x × 4x crosses, no tetraploid hybrid seedlings were derived from 8,902pollinations. In 20 4x × 2x crosses, two tetraploid hybrid seedlings were obtained from 8,057 pollinations. Investigation of isozyme genotypes of the two tetraploid seedlings using three variable enzyme systems indicated that one of the two seedlings resulted from the union of a diploid egg with a 2n male gamete and that failure of second meiotic division resulted in the formation of the 2n male gamete. The percentage of giant pollen grains in `Muscat Bailey A', a pollen parent of the tetraploid seedling, was relatively high(about 5.9%) and 10.9% of the giant pollen grains germinated on agar medium. These results suggested that 2n pollen of diploid cultivars are useful for breeding tetraploid grape.

Production of Nonaploid (2n = 9x) Japanese Persimmons (Diospyros kaki) by Pollination with Unreduced (2n = 6x) Pollen and Embryo Rescue Culture

To produce nonaploid Japanese persimmon (Diospyros kaki L.f.) by artificial hybridization, we surveyed the natural occurrence of unreduced (2n) pollen among hexaploid cultivars and sorted them from normal reduced (n) pollen. The sorted 2n pollen was crossed with a hexaploid female cultivar and the resultant embryos were rescued by in vitro culture techniques to obtain plantlets. Three out of six male-flower-bearing cultivars (2n = 6x = 90) produced 2n pollen at rates of 4.8% to 15.5% varying with the cultivar, which was estimated by both pollen size and flow cytometry. After sorting giant (2n) from normal pollen grains by using nylon mesh, they were crossed with a hexaploid female cultivar. The seeds obtained from pollination with normal pollen were perfect, but those obtained from pollination with giant pollen were mostly imperfect, with embryo growth being suspended at the globular stage. Although the rate of survival was very low, some embryos at the globular stage were rescued successfully and grown in vitro. Both flow cytometric analysis and chromosome counting proved that the plantlets obtained were nonaploid.

493 Inducing Polyploidy Pollen in Apple Cultivars

To perform apple polyploid breeding the ways of inducing polyploidy pollen with temperature and chemicals were studied. Materials include 13 diploid cultivars: Red Chief, Dai Hong, Rose Red, Golden Delicious, Mollie's Delicious, Gala, Bella, Jonathan, Fuji, Qiu Kou Hong, and Yan Qing, OBIR-2T-47. Chemicals: Chloroform, N-nitroso-ethylurea. At the beginning of PMC meiosis, fruiting branching groups were covered with plastic bags to raise temperature or were treated with chemical. After covering, temperature during the day increased 2 °C, generally not lower than 0 °C. Whether branches received high temperature or chemicals treatment, polyploidy pollen was induced to produce. The pollen grain of CK is tricolporat, its polar view is triangular, and its diameter almost 40 μm, showing no difference in size. Rate of empty pollen grain is low. Pollen grains that were treated were different in size, and rate of empty pollen is high, part of pollen grains germinating colporat change into tetracolporat with a few polycolporat, its polar view is square, round, and oval. The diameter of large pollen grains was 45-48 μm, increased by 11-12%. Giant pollen grain are 50-68 μm, increased by 25%-70%. Rate of induction is different in different cultivars. For most cultivars, giant pollen grain is 0.3%-0.5%. Gala and OBIR-2T-47 were higher, reaching 2.5%-7%. Chemicals caused damage on cultivars. Delicious strains were easily damaged.

Varietal and Individual Differences in Cross-compatibility in the 2x*4x Crosses of Cyclamen (Cyclamen persicum Mill.).

Varietal and individual differences in cross-compatibility in the 2x×4x crosses of cyclamen, particularly those of diploid pistillate parents, were investigated. A factor of tetraploid formation and efficient methods to obtain progenies in the crosses are discussed. Different cross-compatibilities, depending upon the pistillate parents, were observed in the 2x×4x crosses, whereas pollen parents scarcely affected fruiting and seed production. There were individual and varietal differences, and all progenies in the crosses showed tetraploidy. All the diploid pistillate parents producing tetraploid progenies through crossing had giant pollen grains. These results suggest the possibility that fertilization between a reduced male gamete from a tetraploid plant and an unreduced female gamete from a diploid plant results in tetraploid progenies. The individual and varietal differences of cross-compatibility among parents also suggest that the selection of diploid pistillate parents decides the formation of seeds. Thus, the selection of diploid pistillate cultivars and individuals, which can produce the tetraploid progenies, should be effective in the inter-ploidy cross breeding of cyclamen.

Use of 2n Giant Pollen to Produce Nonaploid Japanese Persimmon

Distribution of pollen diameter of Japanese persimmon cv. Zenjimaru (2n = 6x, × = 15) was determined using pollen grains hydrated with CPW solution supplemented with 0.9 M mannitol. Mean diameter of giant pollen grains (65 μm) was 1.3 times longer than that of normal pollen grains (50 μm). The occurrence of giant pollen was estimated to be about 5% of the pollen population. The hydrated giant pollen grains could be sorted out from normal pollen grains by filtering through a layer of nylon mesh (62 μm). Flow cytometric analysis of nuclear DNA content confirmed that giant pollen was unreduced 2n pollen. 2n giant pollen grains were pollinated to cn. Jiro (2n = 6x) callie and plantlets could be obtained from immature embyros excised from seeds 70 days after pollination.