The performance of double or mixed pollinations with compatible and self-incompatible or incongruous pollen of pear and apple

Summary Six pear and five apple trials were carried out to ascertain the outcome of combinations of compatible pollen (C) with self (S) or incongruous pollen (I) as to the pollination index (PI=seeds/pollinated flower). The PI of the mixture C+I (1:5) was consistently depressed as compared to that of the control C. The results of the double pollinations S/C and I/C were affected by the temperature at pollination; their PI's at <15°C were twice as high as those at >15°C, being well above and below the PI of C in the former and latter case respectively. The opposite was true for the C/S combination, the PI of which increased with the pollination temperature; the PI of C/I did not differ much from the PI of C, irrespective of temperature. The conclusion was reached that the interaction previously and presently found between compatible and self-incompatible pollen also exists to a fair extent between compatible and incongruous pollen. However, in pear neither the mentor nor the pioneer pollen technique proved to aid its hybridization with apple, the formation of self seed was not observed either. In apple the production of apple × pear hybrids was likewise doubtful, but the double pollinations S/C and C/S formed 4–10% self seed.     

Pollen and pollination experiments. V. An empirical basis for a mentor pollen effect observed on the growth of incompatible pollen tubes in pear

Summary The self-incompatible pear cultivar Doyenne du Comice was selfed with the aid of the mentor pollen technique (self pollen mixed 1:1 with compatible pollen) and the pioneer pollen method (compatible pollen applied 14 h in advance of the self pollen). Observations on tube growth in the style showed that inviable methylated pollen was ineffective either as mentor or pioncer pollen, having no effect on the performance of the self pollen which stopped growing at about one quarter of the style from the stigma. Calculations made on the basis of the obtained data indicated that the viable untreated or irradiated pioneer and mentor pollen, the former somewhat better than the latter, aided the self pollen tubes to reach the base of the style.     

Use of irradiated pollen as mentor pollen to induce self-fertilization of two self-incompatible Upper Amazon cacao clones

Summary Two self-incompatible Upper Amazon cacao clones, T85/799 and T79/501, were pollinated with compatible Amelonado pollen subjected to varying doses of gamma irradiation (10–100 Gy). The proportion of flat non-viable beans to fully formed, viable beans in the pods increased with an increase in dosage of gamma rays. At 60 Gy all the beans produced were flat and non-viable, beyond this dosage fruit set was zero. Pollinating the self-incompatible cacao clones with a 1 : 1 mixture of compatible mentor pollen irradiated at 60 Gy and normal self pollen produced a mixture of flat, non-viable beans and fully-formed viable beans. Similar experiments using irradiated pollen with a marker gene suggested that the fully-formed viable beans resulted from selfing. Increasing the proportion of the radiation-treated compatible pollen in the mixture increased the number of fully-formed beans. However, when compatible pollen which had been treated either at 80 Gy or with temperatures of 35° C, 40° C and 45° C for periods of five, ten and fifteen minutes in factorial combination were mixed with self pollen, no successful pollinations were achieved. Pollen viability tests indicated that, whilst pollen treated at 60 Gy were about 50% viable, those treated at either 80 Gy or with temperatures of 35–45° C were mostly not viable. This suggests that, to overcome the incompatibility in cacao, the tubes of the mentor pollen grains used should at least grow into the style. The possible causes for overcoming the self-incompatibility in cacao are discussed.     

Compatibility and incompatibility in witloof chicory (Cichorium intybus L.). 4. Formation of self-seeds on a self-incompatible and a moderately self-compatible genotype after double and triple pollinations

Summary After double or triple pollinations including selfing and the use of one-day-old compatible foreign pollen a severely self-incompatible clone could be forced to develop a reasonable amount of self-seeds per flower head. This number of self-seeds increased when the foreign pollination was delayed for e.g. 240 minutes in the double pollination experiment. Even more self seeds were obtained in the triple pollination experiment with a delayed second selfing.The influence of the old foreign pollen may be caused by a mentor pollen or a pioneer pollen effect.     

Pollen and pollination experiments. IV. ‘Mentor pollen’ and ‘pioneer pollen’ techniques regarding incompatibility and incongruity in apple and pear

Summary It was attempted to overcome self-incompatibility in apple and pear and incongruity between these species with the aid of compatible mentor or pioneer pollen. The mentor pollen was applied in a mixture (1:1) with the incompatible/incongruous pollen and the pioneer pollen was applied one day in advance of the other pollination. Two trials in 1976 with dead methanol-treated mentor pollen on apple were moderately successful, probably because of the hot spring weather. In the apple and pear trials of 1979 neither the methanol-treated nor the viable irradiated (100 krad) mentor or pioneer pollen significantly improved the seed set by self pollen or that after intercrossing. Competition and early embryo abortion after selfing or intercrossing probably contributed to the lack of success of these methods. The viable irradiated pollen induced a rather high parthenocarpic fruit set, whether applied on its own or mixed with or in advance of the incompatible pollen; the inviable methanol-treated pollen had no such stimulating influence.     

Independence of self-compatibility and potentiality for self-pollination in peach x almond hybrids

Summary The almond of commerce (Prunus dulcis (Mill.) D.A. Webb) is self-incompatible (SI) and requires honey-bees to effect the transfer of pollen among cultivars that flower simultaneously. Four year old trees from the F₂ generation of several peach x almond hybrids were studied to determine whether self-compatibility (SC) and the potentiality for natural, i.e., abiotic, self pollination (NSP) are genetically related or are inherited independently. Both SC and the high potentiality for NSP are characteristic of peach (Prunus persica (L.) Batsch) but not almond. Forty percent of SC genotypes exhibited adequate NSP (SC, +NSP) for good fertility i.e., without insect-mediated pollination. The remaining 60% of SC genotypes (SC,-NSP) exhibited an average 61% reduction in fruit set on limbs bagged to exclude honeybees during anthesis relative to fruit set on open pollinated limbs. Our data are consistent with the concept that fertility is dependent upon the load of compatible pollen deposited on the stigma. Fruit set reduction on bagged limbs, compared with bagged and self-pollinated limbs, was presumably due to a) lack of/insufficient pollination for fertilization and/or b) post-zygotic abortion of genetically inferior recombinants. Selection following manual self-pollination may result in SC genotypes with or without the capacity for NSP. In contrast, significant fruit set on limbs enclosed during pistil receptivity necessitates that the genotype selected express both SC and the potentiality for NSP.     

Variation in pollen performance among plants of Fagopyrum esculentum

Summary In genetically-heterogeneous outcrossing species, there is the opportunity for selection based on the male gamete. Buckwheat (Fagopyrum esculentum Moench) is self-incompatible with one ovule per flower, so pollen competition at each ovule can be studied. The occurrence of selection among pollen parents was determined, as well as the relative importance of prezygotic and post-zygotic selection. Mixed pollinations from two donors produced nonrandom paternity, with one of the donors being favored about 2:1 on several females. Individual plants showed significant variation in the speed of pollen-tube growth. Therefore, prezygotic selection is likely to have occurred based on the speed of pollen tube growth. In single-donor pollinations, donors had equal success as expected in the absence of post-zygotic selection among donors. However, a significant male x female interaction was found, consistent with postzygotic selection against particular parental combinations. To test whether male fitness is reduced by increased allocation to seed filling during pollen production, large- and small-seeded lines were compared, both as pollen donor and as pollen recipient. The large-seeded line was better in both roles, thus there was no evidence that greater allocation to seeds reduced the quality of the pollen.     

Pollination with gamma-irradiated pollen and development of fruits,seeds and parthenogenetic plants in apple

Summary Four apple (Malus X domestica) genotypes, Erovan, Golden Delicious, R1-49 and X6677, were pollinated with a marked pollen irradiated by -rays at doses ranging from 125 to 1000 Gy. Pollination with such irradiated pollen affected fruit set, seed number and seed contents, and induced the formation of parthenocarpic fruits and the development of parthenogenetic embryos. The immature embryos extracted from seeds. 2 and 3 months after pollination, were cultured in vitro and germinated after 2 months of cold treatment (3°C). Haploid plants were obtained in all 4 genotypes, after pollination with pollen irradiated at doses from 200 to 500 Gy. The optimum conditions for induction of apple haploids, by irradiated pollen approach, have been established.     

Influence of timing of cross-versus self-pollination on self-incompatibility in Brussels sprout inbreds

Summary The impact of cross pollination 30 h, 4 h, and immediately prior to self-pollination, and self-pollination 2, 4, 8, 12, 24 and 30 h prior to cross-pollination was assessed for pollen tube number per style, seed number per siliqua, and proportion of self-seed (sibs) per siliqua, in two inbred lines of brussels sprout. Pollination procedure had a marked effect on the amount of sib-and hybrid seed produced. Cross pollination 30 h prior to self-pollination produced significantly greater numbers of sib progeny, as did self-pollination 8–12 h before cross pollination. Prior application of self pollen reduces the number of pollen tubes in the style. The results of this experiment suggest that self-incompatibility in brussels sprout could better be assessed by self-pollination with a subsequent cross pollination 8 h later, and the determination of amounts of sib and F₁ hybrid seed per siliqua.     

Self-pollination vs. cross-pollination in almond: pollen tube growth, fruit set and fruit characteristics

Pollen tubes reaching the ovary, fruit set and the main fruit characteristics of six self‐compatible genotypes (‘Marta’, ‘Antoñeta’, ‘Guara’, ‘Lauranne’, ‘S2332’ and ‘S4017’) of almond were studied after self‐ or cross‐pollination. No significant differences after self‐ or cross‐pollination were found in the number of pollen tubes reaching the ovary, the percentage of ovaries finally penetrated, fruit set and fruit characteristics. The results showed the possibility of obtaining suitable fertilization, yields and quality of fruits by self‐pollination of self‐compatible almond cultivars in a single cultivar orchard.     

Pollen germination and pollen tube growth following self-pollination and intra- and interspecific pollination of Medicago species

Summary Pollen germination and pollen tube growth after self- and intra- and interspecific pollinations of annual [M. scutellata (L.) Mill., M. disciformis DC., and M. rigidula (L.) All.] and perennial (M. sativa L.) Medicago species were studied using a Carl Zeiss microscope with a fluorescence filter attachment.Self-pollination of self-fertile annual and intraspecific pollination of cross-fertile perennials were characterized by high pollen germination and rapid normal pollen tube growth. In contrast pollen germination percentages were very low and many pollen tube growth abnormalities occurred following interspecific pollination and self-pollination of self-sterile plants. The time period from pollination to fertilization for interspecific crosses was about double that following self-pollination of the annual species. However, fertilization occurred frequently following interspecific pollinations. Much of the sterility was due to factor(s) operating after fertilization.Cooperative investigations of the Kansas Agricultural Experiment Station, Dept. of Agronomy and the U.S. Department of Agriculture, Agricultural Research Service. Contribution No. 82-582-J- Mention of a trademark name or proprietary product does not constitute a guarantee or warranty by the U.S. Department of Agriculture, and does not imply its approval over other products that also may be suitable.     

Methods of overcoming interspecific barriers in Trifolium

Summary Barriers to interspecific hybridization in Trifolium were investigated by manipulation of mentor pollen treatments, ploidy levels, and compatibility and male sterility systems. Crosses involving the addition of mentor pollen produced fewer seeds and hybrids than crosses involving normal pollination. Lower seed set with mentor pollen was deduced to result from the use of less viable pollen, approximately half the pollen having been killed by alcohol. Pollinations at the diploid level resulted in more hybrids than at the tetraploid level, perhaps because genes for male sterility produced higher female sterility in the tetraploids. The self-compatible stock produced more seeds, mostly selfs, than the self-incompatible stock, but produced more hybrids only in one cross, T. pratense L. × T. diffusum Ehrh. The use of male-sterile female parents reduced selfing but produced fewer hybrids than male-fertile female parents. Techniques of this study were designed to affect prefertilization barriers, but the lack of effect may indicate that postfertilization barriers in Trifolium are of greater importance.Journal Article No. 98-3-208 of Kentucky Agricultural Experiment Station. Published with approval of the Director.     

Results of multiple pollination in blueberry (Vaccinium elliottii Chapm.)

Blueberry (Vaccinium section Cyanococcus, family Ericaceae) is a shrub that produces multiple-seeded berries in which only a fraction of the ovules develop into viable seeds. A recessive yellowleaf marker gene was used to evaluate the efectiveness of a single pollination versus multiple pollinations in producing seeds in Vaccinium elliottii Chapm. A multiple-pollination experiment was conducted to see if the first pollen applied or the second produced more progeny, and to see if multiple pollinations increased the number of seedlings produced. Flowers of diploid yellowleaf Vaccinium elliottii were pollinated from one to four times at daily intervals. Pollen from redleaf and yellowleaf plants was used to produce two types of seedlings that could be distinguished visually. Generally, percent berry set, seeds per berry, and seed germination were not increased by multiple pollination. After multiple pollination, the pollen applied first always produced the most seedlings. Prior pollination greatly reduced seed set from subsequent pollination, but subsequent pollination caused little or no decrease in the number of seeds set by the first pollination. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of mentor pollen on pistil-pollen incongruities among species of Cucumis L.

Summary The merits of mentor pollen in certain interspecific hybridizations in the genus Cucumis L. were evaluated. African wild cucumber species Cucumis metuliferus Naud. and C. africanus L. and Asian species C. sativus var. hardwickii Alef and var. sikkimensis Hook, were reciprocally crossed. Pollen tube growth was arrested halfway down the style in all combinations except in C. sativus × C. africanus. Mentor pollen irradiated with 100 and 200 krad grew through the style and into the ovules in all species. Fruitset was obtained in all cases when mentor pollen was used either alone or in mixtures. Fruits set after self pollination with mentor pollen yielded only seeds without embryos.In several crosses, aided by mentor pollen, a number of relatively large seeds (with enlarged embryosac) were obtained. A sample of these embryosacs contained a globular structure like an embryo. Embryosacs with embryo-like structures were explanted on several different media but no development was obtained.     

Pollen and pollination experiments. VI. Heat resistance of pollen

Summary Pollen of dry apple, pear, lily and rose pollen was heated up to 48 h at a range of temperatures. About half or more than half of the pollen grains survived 48 h at 40 C, 24 h at 50 C, 8 16 h at 60 C. 4 8 h at 70 C, more than one hour at 80 C. and between 10 and 20 min at 90 C. Presumably, pollen able to withstand low humidity is also heat resistant, a property which may be usable to make pollen virus free through heat treatment and perhaps to overcome incompatibility.     

Inheritance of pollen color in hazelnut

In contrast to the yellow color of pollen of European hazelnut (Corylus avellana L.) cultivars, an unusual cream color was observed in some seedlings from self-pollination of the Sicilian cultivar ‘Montebello.’ After elimination of accidental outcrosses, the segregation fit a 3 yellow: 1 cream ratio, indicating the possibility of simple genetic control. Two seedlings with cream-colored pollen were backcrossed to their parent ‘Montebello,’ and the progeny segregated 1 yellow: 1 cream for pollen color. When two seedlings with cream-colored pollen were crossed with each other, all of the resulting seedlings had cream-colored pollen. These segregation ratios indicate that pollen color in hazelnut is controlled by a single locus with yellow dominant to cream color. The symbol pc is proposed for this locus. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of γ-radiation on vitality and competitive ability of Cucumis pollen

Summary Pollen of 4 Cucumis sativus genotypes and of the related species C. metuliferus and C. zeyheri 2x was irradiated with four doses of -rays: 1, 2, 4 and 5 kGy. Higher radiation doses were found to inhibit germination and pollen tube growth in vitro with C. sativus, the most sensitive species.Irradiated pollen of cucumber never performed normal fertilization. However, after radiation with 1 kGy, cucumber pollen was able to occupy all available ovules, of which about 50% developed into empty seeds without embryo. This makes 1 kGy-irradiated maternal pollen less suitable to serve as mentor pollen in interspecific hybridizations. Doses of 2 kGy and more appeared to eliminate the ability to compete for ovules, while fruit set after a 2 kGy radiation was still high.     

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.     

A test of the mentor pollen technique in the genus Ipomoea

Summary A major barrier to hybridization of some Ipomoea species is located at the stigma-style interface. In 5 interspecific combinations examined with the aid of fluorescence microscopy, pollen was found to germinate and penetrate the stigma surface without, however, passing into the style. In the cross I. hederacea x 1. purpurea, pollen tubes were observed in the style and capsules were set, but no full seeds were produced. Attempts to facilitate hybridization among Ipomoea species using mentor pollen-foreign pollen mixes were unsuccessful.     

The progamic phase in Cichorium intybus L. Pollen tube growth in the style,incompatibility reaction and gametophytic competition

Summary Pollen germination and tube growth were studied following compatible, incompatible and pseudo-compatible pollinations in chicory. Pollen germination begins 3 minutes after compatible pollinations. The earliest pollen tubes reach the ovary 17 minutes later. Many of the later germinating pollen tubes are arrested and burst at the stigma papillae. In the transmitting tissue inhibitional effects due to negative interactions between pollen tubes are frequently observed. Complete self-incompatibility results in total inhibition of germination. In case of pseudo-self-compatibility, some pollen germinate but germination and stigma penetration are delayed and often result in pollen bursting. There is no self-incompatibility reaction in the transmitting tract but if the pollen tubes reaching this tissue are relatively numerous, negative interactions between them occur as after compatible pollinations. An hypothesis is presented which attributes the negative interactions between pollen tubes to the diffusion of a substance from the growing pollen tubes. This substance would also provoke pollen bursting on the stigma.