Storage of maize (Zea mays L.) pollen at −196°C in liquid nitrogen

Summary The water content of pollen has a decisive influence on its storability in liquid nitrogen. Pollen with an initial high water content cannot be stored successfully at extremely low temperatures, so a certain degree of drying must be carried out before storage. Provided the viability of the pollen is not significantly reduced during drying, the pollen remains viable and fertile when kept at –196°C.     

Estimating pollen fertility in Solanum species and haploids

Summary Three staining methods (acetocarmine, fuchsin and oxidation of benzidine) and germination in vitro and in vivo were applied to estimate pollen fertility in Solanum species and dihaploids. Pollen was divided into six classes based on shape and contents of the grains. With acetocarmine, fuchsin, peroxidase and germination in vitro 4, 3, 2 and 1 classes, respectively, are supposed to be included in the percentage of good pollen as measured by these methods. This percentage therefore, in more than 96% of the cases studied, shows a decrease in the order indicated. Neither aging of pollen at room conditions nor collecting pollen from flowers on 1–9 days after anthesis does influence the percentage of good pollen with acetocarmine and fuchsin, whereas this percentage drops sharply to zero with peroxidase and germination in vitro. The latter two methods apparently measure as good pollen only the grains with living cytoplasm. When pollen is collected at three successive dates from the same flowers the percentage of good pollen drops sharply with all methods used. There is a relation between quantity of pollen per flower and pollen quality (% good), low-quantity pollen containing significantly lower percentages of good pollen than medium- and high-quantity pollen. The latter two are not significantly different in this respect.From calculations of correlation coefficients it is concluded that only germination of pollen in vitro is significantly correlated with berry and seed set and thus gives a reliable estimate of male fertility. This does not hold true for the two staining methods without due reserve. The peroxidase method is not useful for the Solanum material studied.After standardized pollination the average number of haploid pollen grains on diploid stigmata was found to be 1625±127, that of diploid pollen on tetraploid stigmata 2863±98.A. W. B. Janssen 1975.     

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. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Breeding tomato for pollen tolerance to low temperatures by gametophytic selection

Haploid selection for traits related to pollen cold tolerance in tomato was performed in segregating populations derived from a Lycopersicon esculentum × L. pennellii hybrid. BC₁ populations were obtained by combining normal and low temperature treatments on two stages of pollen development: pollen formation, and germination and pollen tube growth. F₁ hybrids were cultivated under low and normal temperatures and their pollen was used to pollinate L. esculentum plants at low and normal temperatures. The four BC₁ populations obtained were tested for the quality and quantity of pollen produced at low temperatures. The population obtained by cold treatment at both stages had a significantly improved pollen germination ability at low temperatures. The two other coldselected BC₁ populations showed no differences compared with the unselected BC population. A second cycle of pollen selection, corresponding to BC₂, was applied in order to test its persistence in the subsequent generations and the possibility to further improve the character. This second cycle showed no improvement although some plants retained the high pollen germination ability at low temperatures that was observed in the first cycle. Hence, gametophytic selection of some characters related with tomato pollen performance may be feasible, at least for the first cycle of selection.     

Evolution of reproductive behaviour in the genus eleusine

Summary The paper traces shifts in the reproductive behaviour as influenced by the selective pressures of crop domestication, in the genus Eleusine, from the wild species. E. africana to its domesticated form E. coracana. Among other changes we consider temporal features of flowering, nature of anthesis and dehiscence, the stigma to lemma length ratio determining the extent of stigma protrusion and the pollen grain to ovule ratio as important in changing the breeding behaviours. These changes are viewed as evolutionary responses of plants to their respective ecological niches.     

Pollen and pollination experiments. II. The influence of the first pollination on the effectiveness of the second one in apple

Summary Pollinating apple cultivars twice with compatible pollen at an interval of one or two days produced about twice as many seeds per pollinated flower as a single pollination. With the aid of scab- or mildew resistant marker pollen, it could be shown that the second pollen formed on average twice as many seeds as the first. The first pollen appears to pave the way-partly at its own cost-for the second and was therefore called pioneer pollen.     

Interspecific hybrid of Helianthus annuus × H. simulans: Characterization and utilization in improvement of cultivated sunflower (H. annuus L.)

The first success at interspecific hybridization between cultivated sunflower(H. annuus) and a diploid perennial species, H. simulans is reported. The F₁s from both direct and reciprocal directions exhibited dominance of the wild species phenotype and were pollen sterile. Meiosis was irregular in the F₁ hybrids and both univalents and multivalents were observed. Multiplication of the interspecific hybrids was achieved through in vitro culture of nodal sections on Murashige & Skoog medium supplemented with 0.5 mg l^-1 benzyladenine. Fertility of the interspecific hybrids was improved by subjecting the in vitro proliferating shoots to 0.001% colchicine incorporated in the shoot multiplication medium. The amphiploids serve as fertile bridges and facilitate interspecific gene transfer through conventional breeding. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pollination requirements for seed set in ulluco (Ullucus tuberosus)

Summary Pollination experiments were carried out on ulluco (Ullucus tuberosus), known as a very poor seed producer. All the clones used were diploids. The effect of self-vs. cross-pollination was studied in Experiment 1. Caged selfpollinated flowers produced no seeds. Different clones produced seeds in 0–8% of caged cross-pollinated flowers and in 5–19% of cross-pollinated non-caged flowers. Ulluco is thus basically an outbreeder.Experiment 2 studied whether seed set is limited by pollen availability. Total seed number per inflorescence number did not differ between plants treated with supplemental pollen and control plants; pollen availability thus did not limit seed set. The treated plants, however, produced more seeds in cross-pollinated than in other flowers on the plant, and the control flowers on treated plants produced fewer seeds than those on the control plants. In the treated plants, resources may have been allocated to artificially cross-pollinated flowers at the expense of other flowers. In some clones, seed set after artificial cross-pollination was at a level practicable for breeding work.     

Analysis of pollen tube growth in situ to investigate self-incompatibility in the wild potato Solanum commersonii

Summary Pollen tube growth was investigated in a diallelic crossing design with seven genotypes of the diploid wild potato species Solanum commersonii, accession O/S UR-9, CIP 762459. Pollen tube growth in the style was recorded using a combined quantitative and qualitative evaluation scale. Clear-cut differences in pollen tube growth behavior in compatible and in partially or completely incompatible crosses were detected. Diallelic crossing of the seven randomly chosen genotypes, intercrossing within two progeny families, and backcrossing of two progeny populations to the parents revealed the existence of a one-locus gametophytic system of stylar incompatibility. The S-allele status of all genotypes investigated was determined.