Fertility,plant morphology,and transmission rates of the extra chromosome in single and double trisomics of Solanum tuberosum L. Group Tuberosum

Summary Initial single and double trisomics of S. tuberosum Group Tuberosum cv. Gineke were successfully crossed with and backcrossed to clones obtained through inbreeding of self-compatible dihaploids of the same variety. Some trisomics showed reduced flowering or flower abnormalities and contributed therefore only to a small extent. Berry-set and seed-set varied considerably. There was no relation between these phenomena, nor was there any relation between either berry-or seed-set and the identity of the extra chromosome in the female parent. Seed-set seemed to be influenced by the male parent. When a more inbred male parent was used in the crosses with trisomics this often resulted in less seed per cross. There was no clear relation between seed-set and stainability of the pollen grains, but both the strong selection for good pollen and the high level of self-compatibility, have apparently contributed to the success of the crosses. The double trisomic plants yielded less seed than most single trisomics. Only three of the single trisomics produced stainable pollen and two of them yielded progeny when used as male parent in crosses or selfings.In the progenies several of the trisomic types could be distinguished on the basis of plant morphology in the young seedling stage. For ten different trisomics the morphotype is being described. The average rate of female transmission of the extra chromosome was about twenty per cent, but there was a wide variation, both between and within the various trisomic types. The results indicated that for chromosomes 3 and 8 the rate of transmission was higher than the average value. In one out of two trisomic types male transmission of the extra chromosome occurred, with a rate of 4.7%. The possible causes for the observed differences in female transmission of the extra chromosome are being discussed.     

Production of intraspecific aneuploids in the genus Solanum. III. Intraspecific aneuploids

Summary The triploids recovered from 4x×2x crosses in three Solanum species were very vigorous and although few seeds/fruit were obtained when the triploids were crossed to diploids, the extensive crossing programme produced sufficient seed of four species cph, chc, pnt and tar. The average seed set for the 3x-2x crosses was an extremely low 3.5 seeds/fruit.Approximately 90% of the progeny of the 3x–2x crosses were aneuploids with chromosome numbers of 2n=25–29. The frequency of the aneuploids in the three species that were studied was chc 93%, pnt 94% and tar 92%. The aneuploids of chc and tar were extremely vigorous and fertile and they were used as females in crosses to the marker stocks. The aneuploids of pnt were vigorous, but the crossability barrier of pnt prevented their use in crosses to the marker stocks. A number of the aneuploids produced seed upon being selfed, but the ability to produce self seed may be related to the pseudo-compatibility of the parental clones. In only 7 aneuploids was there an indication that the self fertility was due to overcoming the self-incompatibility barrier as a result of competition-interaction of the aneuploid gamete.Plants in the families from the triploid-diploid crosses had a tremendous amount of variation in morphological characteristics (leaf shape, size and color; berry shape, color and degree or verrucose spotting: and plant habit and vigor). A large portion of variation exhibited in these families was due to the normal genetic segregation of the heterozygous parents. It was impossible to distinguish the aneuploids from their diploid sibs especially those having only one or two additional chromosomes because they were as vigorous and fertile as the diploids.There were some preliminary indications of the existence of distinct morphological characteristics among the aneuploids (separate petals, long berries, and extreme verrucose berries). However, there was no indication that these traits were due to the dosage effect of the extra chromosome. If it should be determined that this was true, it would be extremely useful in associating genes with chromosomes and determining the phenotypic effects due to the presence of an additional chromosome.Cooperative investigations of the College of Agriculture and Life Sciences, University of Winconsin and the Agricultural Research Service, U.S. Department of Agriculture, Madison, Wisconsin. Supported in part by grants from the Research Committee of the Graduate School, University of Wisconsin.First and third author respectively, formally Graduate Research Assistant Department of Horticulture, University of Wisconsin, Madison, and Geneticist Agriculture Research Service, U.S. Department of Agriculture, University of Wisconsin, Madison. Present address: Department of Genetics. University of Wisconsin, Madison, Wisconsin 53706 and Head Breeding and Genetics Department, International Potato Center, Lima, Peru.     

The production of aneudihaploids in Solanum tuberosum L. group Tuberosum (the common potato)

Summary Trisomic cytotypes were produced in dihaploid (diploid) plants of Solanum tuberosum L. Group Tuberosum, the common potato, according to two methods. Firstly, the aberrant types were selected, through chromosome counting, from parthenogenic dihaploid offspring of tetraploid-diploid crosses. In dihaploid populations from twelve tetraploid potato varieties the frequencies of aneuploids ranged from 3.5 to 11.0%. About 95% of these aneuploids had only one, and the others not more than two extra chromosomes. Secondly, the aneuploids were produced from triploid-diploid crosses. Seedset strongly depended on the crossability of the parental plant material, and the best results were obtained when the motherplants were grafted onto tomato. On avarage the three most successful cross combinations resulted in approximately 0.7 berries per pollination and 6 seeds per berry. With regard to seedsize the seed could be divided in two groups, viz, normal and small seeds. Half of the seed did not germinate or produced inviable seedlings, especially among the small seed group. About 93% of the plants was neuploid, with 25, 26 and 27 being the predominant chromosome number. It was concluded that the production of trisomics was the most successful through triploid-diploid crosses. The results were discussed with reference to the chromosomal behaviour in the meiosis in triploid plants (Lange & Wagenvoort, 1973a). It thus was possible to relate the low seedset to the distribution of chromosomes in the meiotic anaphases. On the one side this distribution resulted in a limitation of the avalability of gametes with monohaploid and near-monohaploid chromosome numbers, while on the other side the macrospores with higher chromosome numbers seemed to be inviable. Finally a crossing scheme was presented for transmitting the trisomic condition into a genetic background with better homogeneity and more homozygosity.Extended version of a lecture presented at a Eucapia meeting about Potato Dihaploids, held at Wageningen (Netherlands). See Lange and Wagenvoort, 1973b.     

Identification of primary trisomics and other aneuploids in foxtail millet

A complete set of nine primary trisomics (2n+ 1) for cv.‘Yugu No. 1’of foxtail millet, Setaria italica (L.) Beauv. (2n= 2x= 18), was identified cytologically from progenies derived from crosses between autotriploids(2n= 2x= 27) and their diploid counterparts. Five autotriploid plants were identified from 2100 seedlings derived from 4x-2x crosses; the reciprocal crosses (2x-4x) failed to produce autotriploids. Autotriploids grew vigorously and were morphologically very similar to diploids. Theprimary trisomics (2n= 2x= 19) constituted ?32.5% of the total progeny from the 3x-2x crosses, whereas 59.8% of the descendants were aneuploids with chromosome numbers ranging from 20 (double trisomics and tetrasomics) to 37 (2n= 4x+ 1; or autotetraploid with one additional chromosome). The nine primary trisomics identified were self-fertile; seven had characteristic morphology, whereas trisomics VIII and IX resembled the disomics. The seed set for trisomic V was the lowest (20%), and trisomic VIII the highest (74%). Other aneuploids with 20 or more somatic chromosomes were either self-sterile or partially fertile with various, but low, levels of seed set. Each of the primary trisomics showed its unique transmission rate when self-pollinated; trisomic IX had the highest (45.8%), whereas trisomic V had the lowest (19.6%) transmission rate.     

携带抗白粉病基因Pm21的小麦–簇毛麦小片段易位染色体在不同小麦背景中的传递率及遗传稳定性

抗白粉病基因Pm21来自小麦近缘种簇毛麦。小麦一簇毛麦小片段顶端易位系NAU418(T1AS·1AL-6VS)和小片段中间插入易位系NAU419(T4BS·4BL-6VS-4BL)携带Pm21,高抗白粉病,是小麦抗病育种新种质。为了对其育种利用提供依据,以NAU418和NAU419为亲本分别与来源于不同生态区的郑麦9023等12个小麦品种杂交,杂种F_1再分别与来源于不同生态区的农艺亲本进行正、反回交,研究两种易位染色体在不同小麦背景中的遗传稳定性及其通过雌雄配子的传递规律。DNA分子原位杂交结果表明,在杂种F_1花粉母细胞减数分裂中期Ⅰ(Pollen Mother Cell,PMC MI),两种易位染色体分别可以与对应的小麦染色体配对形成棒状二价体。正、反交结果分析表明,NAU418中的小片段顶端易位染色体T1AS·1AL-6VS通过雌配子和雄配子的传递率分别为8.00%~50.98%和7.89%~45.07%,NAU419中的小片段中间插入易位染色体T4BS·4BL-6VS-4BL通过雌配子和雄配子的传递率分别为29.17%~52.38%和7.69%~47.06%。表明2个易位系中的易位染色体都可以通过雌、雄配子传递,但是其通过雄配子的传递率均显著低于通过雌配子的传递率。     

Unreduced pollen frequencies versus hybrid production in diploid-tetraploid Vaccinium crosses

Summary Reciprocal crosses were made between highbush Vaccinium corymbosum L. cultivars (4X) and high, medium and low frequency diplandroid pollen producing diploid clones of V. elliotti (Chapm.) and diploid pubescent forms of V. corymbosum. Pollination of 3,342 flowers produced 15 hybrids-11 tetraploids and 4 triploids. All V. elliottii hybrids were tetraploid while each successful diploid-tetraploid V. corymbosum cross produced at least one triploid. The ratio of tetraploid hybrids to 100 pollinations (H: 100P) was considered to be the best criterion for assessing crossability. Vaccinium elliottii produced a total of 8 4X hybrids while 2X V. corymbosum only produced 3. Vaccinium elliottii was more successful as a female parent and diploid V. corymbosum only produced hybrids as male parents. High frequency diplandroid clones showed a lower mean crossability as pollen parents (H: 100P=0.2) than medium frequency diplandroid clones (H: 100P=0.8). As predicted, 0% diplandroid clones wer unsuccessful as pollen parents. Unreduced pollen production was essential for tetraploid hybrid production in 4X×2X crosses. There appeared to be no consistent, inherent pattern between 2n pollen and 2n egg production in a clone nor was a tetraploid genotype effect on crossability consistently observed.Paper No. 10781 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC., 27695-7601     

Transmission of bacterial wilt resistance by First Division Restitution (FDR) 2n pollen via 4x×2x crosses in potatoes

Summary Resistance to bacterial wilt (Pseudomonas solanacearum) found in tuber-bearing Solanum species was transferred into a diploid potato breeding population. Simultaneous selections were made for agronomic characters, production of first division restitution (FDR) 2n pollen, and resistance. Diploid resistant genotypes were identified via inoculation with a virulent isolate (CIP-204) of race 3 of Pseudomonas solanacearum. These resistant diploid genotypes were crossed to susceptible tetraploid potatoes. An investigation was made to assess whether resistant diploid genotypes transmit resistance to bacterial wilt, which is a quantitatively inherited trait, to tetraploid potatoes via FDR 2n pollen. Tetraploid seedlings from 4x×2x crosses were inoculated with the same isolate CIP-204, and the percentage of surviving seedlings was scored. Some 4x×2x families from resistant diploid genotypes demonstrated a high level of survival rate. The transmission of bacterial wilt resistance was achieved by the use of FDR 2n pollen. It was speculated that a female x male interaction effect on the survival rate of the evaluated progeny may exist. Selecting proper 4x and 2x parents would be important for obtaining a higher frequency of transmission of resistance to bacterial wilt in the progeny.     

Crossability and embryo rescue enhancement in wide crosses between wheat and three Agropyron species

Summary Soft winter wheat lines were crossed with Agropyron intermedium, A. elongatum and A. trichophorum using pollen from single plants of Agropyron spp. to pollinate wheat spikes. Not only species but also individual plants within varieties of Agropyron species differed in percent seed set with a wheat genotype. In two arrays of crosses between two phenotypically different plants of A. elongatum and nine wheat lines, one Agropyron plant gave higher seed set (overall=27.1%) than the other (overall=3.7%). The differences were significant in seven of the nine cross combinations. Results are consistent with the hypothesis that these two plants differ in their crossability as pollen parents with wheat, and suggest the possibility of occurrence of crossability genes in wheatgrasses. The success rate of hybrid embryo rescue was higher (87.5%) with cold treatment (4°C) than without cold treatment (75.0%) of excised embryos on culture media. Results underscore the significance of genotype of the alien species for crossing with low crossable wheats, and of the physical factors for improving embryo rescue in wide crosses.Contribution No. 11,825, Purdue Agric. Exp. Stn., West Lafayette, Indiana 47907, USA. The research was supported in part by Public Varieties of Indiana.     

Cytological and Morphological Characterization of Pisum sativum and Pisum fulvum Tetraploids

Two colchicine-induced tetraploid lines, one belonging to Pisum sativum and the other to the wild species Pisum fulvum, were compared with their corresponding diploids and among themselves for chromosome number, meiotic behaviour and for pollen and pod fertility. For both lines, five generations were analyzed; the tetraploid level was maintained throughout the generations. In P. fulvum, aneuploids with 27, 29 and 30 chromosomes were observed, while in P. sativum aneuploids with 29 chromomes were found. Meiotic analysis evidenced a higher number of quadrivalents and a lower number of univalents in P. fulvum. This particular chromosomal behaviour may also have been responsible for determining the higher pollen and pod fertility in P. fulvum. Wild species of this genus seem to have better tolerance for ploidy variations.     

Aneuploids of perennial ryegrass (Lolium perenne)

Summary Aneuploid plants of perennial ryegrass (Lolium perenne L.) with 2n=15 to 30 chromosomes were obtained by crossing a near-triploid (2n=3x+1=22) with a diploid or on open-pollination with diploids and tetraploids. Aneuploids occurred with a frequency of 83% in near triploid × diploid progeny and 92% on open-pollination with diploid and tetraploid plants. Aneuploid plants with 15 to 18 chromosomes resembled diploids in morphology and those with 19 to 30 chromosomes were akin to tetraploids. Meiotic studies suggested that most aneuploid plants resulted from transmission of aneuploid egg cells (n=8 to 23). Aneuploid plants with 2n=27 to 30 chromosomes in the progeny of 22×14 cross originated from unreduced egg cells. Plants with 19 to 21 chromosomes were recovered only by immature seed culture. Aneuploid plants with 26 to 30 chromosomes and triploids (2n=21) had higher pollen fertility and bigger seeds than plants with 15 to 22 chromosomes.     

Development of a complete set of disomic rape-radish chromosome-addition lines

After crosses of multiple rape-radish chromosome additions with rape, nine different monosomic additions (2n = 4x = 38 + 1) of individual radish chromosomes, a–i, were isolated, having the genomic background of winter oil seed rape and radish cytoplasm. Extra chromosomes were identified with RAPD markers, specific for individual radish chromosomes. All radish-plasmic monosomic additions, except that of chromosome f, had low seed production due to pistilloid stamens. Rape cytoplasm was substituted by crossing the monosomic additions as pollinators to rape followed by reselection of the radish chromosome additions. The monosomic additions in rape cytoplasm showed normal male fertility. Average transmission rates of radish chromosomes via egg cells and pollen cells were 37% and 27%, respectively. Lowest male transmission was found for chromosomes e and f with 0.04 and 0.01. Monosomic additions were self-pollinated to produce disomic additions. Monosomic and disomic addition progenies were discriminated by a prescreening with quantitative double primer (dp) RAPDs and cytological confirmation of preselected candidates by FISH analysis using a Raphanus-specific probe. Usability of this complete set of nine disomic rape-radish additions (2n = 4x = 38 + 2) was discussed.     

Inheritance of sexual incompatibility in apricot

The study was carried out with 3- to 6-year-old apricot progenies from the breeding programmes of ARS in Fresno, California, USA and of CEBAS in Murcia, Spain. Progenies from 19 different crosses were studied to determine the inheritance of the genetic incompatibility trait. The 19 crosses included those where both parents were self-compatible or both self-incompatible, and also those where a self-compatible parent and another self-incompatible were crossed. Segregating progenies were studied either by bagging a sufficiently high number of flowers in balloon stage and determining the percentage of fruit set several weeks later or by following pollen tube growth with fluorescence microscopy. Results indicated that a monofactorial system with a multiallelic series appears to control the trait. Alleles for self-compatibility would allow the pollen tubes to grow in any style and reach the ovules. Alleles for self-incompatibility would stop the pollen tube growth if the same allele is present in the pollen grain and in the pistil.     

Chromosomal location of fertility restoring genes for ‘wild abortive’ cytoplasmic male sterility using primary trisomics in rice

Summary Identification and location of fertility restoring genes facilitates their deployment in a hybrid breeding program involving cytoplasmic male sterility (CMS) system. The study aimed to locate fertility restorer genes of CMSWA system on specific chromosomes of rice using primary trisomics of IR36 (restorer), CMS (IR58025A) and maintainer (IR58025B) lines. Primary trisomic series (Triplo 1 to 12) was crossed as maternal parent with the maintainer line IR58025B. The selected trisomic and disomic F₁ plants were testcrossed as male parents with the CMS line IR58025A. Plants in testcross families derived from disomic F₁ plants (Group I crosses) were all diploid; however, in the testcross families derived from trisomic F₁ plants (Group II crosses), some trisomic plants were observed. Diploid plants in all testcross families were analyzed for pollen fertility using 1% IKI stain. All testeross families from Group I crosses segregated in the ratio of 2 fertile: 1 partially fertile+partially sterile: 1 sterile plants indicating that fertility restoration was controlled by two independent dominant genes: one of the genes was stronger than the other. Testcross families from Group II crosses segregated in 2 fertile: 1 partially fertile+ partially sterile: 1 sterile plants in crosses involving Triplo 1, 4, 5, 6, 8, 9, 11 and 12, but families involving triplo 7 and triplo 10 showed significantly higher X² values, indicating that the two fertility restorer genes were located on chromosome 7 and 10. Stronger restorer gene (Rf-WA-1) was located on chromosome 7 and weaker restorer gene (Rf-WA-2) was located on chromosome 10. These findings should facilitate tagging of these genes with molecular markers with the ultimate aim to practice marker-aided selection for fertility restoration ability.     

Ploidy manipulation and introgression breeding in Darwin hybrid tulips

Meiotic polyploidisation via crossing with 2n gamete producing genotypes and interploidy crosses are two of the main methods currently used to obtain polyploid tulips. In our study diploid 2n gamete producing F₁ hybrids of Darwin hybrids (Tulipa gesneriana × Tulipa fosteriana) and triploid hybrid resulting from ‘Rhodos’ × ‘Princeps’ cross were used as pollen donor and crossed with cultivars of T. gesneriana in the following combination: 2x × 2x, 3x × 2x, 2x × 3x, and 3x × 3x. The progenies resulting from crosses at diploid level were mostly diploid, whereas a few seedlings were triploid. In 3x × 2x crosses aneuploids with chromosome constitution in between triploid and tetraploid (43–45 chromosomes) were predominant, but also one tetraploid (2n = 4x = 48) and four pentaploids (2n = 5x = 60) were obtained. In 2x × 3x crosses most progenies were triploid with the exception of a few aneuploids (3x + 1 and 3x ? 1), whereas in 3x × 3x cross diploid and aneuploid genotypes were recorded with chromosome number varied from 27 to 34. These results indicate that triploid parents produced aneuploid as well as euploid (x, 2x, 3x) gametes and that success in ploidy manipulation in tulip depends to a large degree on the ploidy level of the parental genotypes used for hybridization. Genome constitution of selected population of F1 and BC1 hybrids was analyzed through genomic in situ hybridization (GISH). GISH analysis of the BC1 showed a considerable amount of intergenomic recombination which is desirable for introgression breeding.     

A cytogenetic study of the progenies of hybrids between Brassica napus and Brassica oleracea, Brassica bourgeaui, Brassica cretica and Brassica montana

In this cytogenetic study the progeny of all crosses were investigated in F₁, F₂ and backcross (BC₁) hybrids. Brassica napus and F₁ hybrids between B. napus and B. oleracea, and between B. napus and three wild relatives of B. oleracea (B. bourgeaui, B. cretica and B. montana). Each of the wild relatives has 18 somatic chromosomes. Interspecific F₁ hybrids were obtained through ovary culture mean. These had 28 and 37 chromosomes and their mean pollen fertility was 10.7% and 93.0%, respectively. Many F₂ and BC₁ seeds were harvested from the F₁ hybrids with 37 chromosomes after self‐pollination and open pollination of the F₁ hybrids, and backcrossing with B. napus. Many aneuploids were obtained in the F₂ and BC₁ plants. It is evident from these investigations that the F₁ hybrids may serve as bridge plants to improve B. napus and other Brassica crops.     

Drought tolerance in sorghum by pollen selection using osmotic stress

A pollen selection study for drought tolerance using Poly Ethylene Glycol (PEG) as a selective agent was conducted in sorghum. Ten genotypes of sorghum suitable for post rainy season were crossed to cytoplasmic male sterile line 104A and three genotypes to 116A producing 13 hybrids. Two sets of 13 hybrids with and without pollen selection were produced. PEG at 36 per cent was applied to stigma and stylar tissue one hour before pollination for pollen selection (selective fertilization) and no treatment for control (nonselective fertilization). Hybrids thus produced through selective and non-selective fertilization were tested in moisture stress environment during post rainy season. The hybrids obtained through selective fertilization produced significantly higher mean grain yield compared to hybrids obtained through non-selective fertilization. The results indicate that selective fertilization through in vivo pollen selection using PEG as selective agent was effective in improving moisture stress tolerance of the progeny in sorghum genotypes studied. Further, the pollen selection also had influence on plant height, panicle length, panicle width, panicle weight and grain mass. Thus,the pollen selection had a significant effect on grain yield through its components and developmentally related traits. Pollen selection for osmoticstress tolerance in sorghum influences the growth and vigour of the plants resulting in superior progeny in moisture stress environment. The analysis of individual crosses indicated that pollen genotype selection was able to favour performance of the progeny. However, the pollen selection had positive effect in majority of the hybrids and the study demonstrates the transmission of the selected trait from pollen generation to progeny. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetics of the viability of pollen grain produced at low temperatures inLycopersicon Mill.

Summary The different viabilities of pollen produced at low temperatures in intra- and inter-specific crosses of tomato were studied. Cultivars Red Top, Moneymaker, and Marroqui were crossed with cultivar E-15 and these four cultivars were hybridized with lines of the wild speciesL. pimpinellifolium PE-13,L. parviflorum PE-52,L. pennellii PE-47, andL. hirsutum PE-37 and PE-41. A six-generation family of the Moneymaker x PE-47 cross was obtained to carry out a more detailed genetical study of pollen grain viability at low temperatures. Pollen grain viability was evaluated during the winter via acetocarmine staining. When the parents were compared with their F₁, the intra-specific tomato crosses showed dominance to better-quality pollen, theL. esculentum x L. pimpinellifolium inter-specific crosses showed positive heterosis, while the crosses ofL. esculentum with the tolerant speciesL. pennellii andL. hirsutum showed intermediate inheritance. However, in theL. esculentum x L. pennellii family, the dominance and the non-allelic interactions (homozygosis x homozygosis) were the most important factors, so that dominance to better viability at low temperatures appeared to be the general mode of inheritance. Genetical control of pollen grain viability at low temperatures seemed to be polygenetic.     

Progenies of allotriploids of Oriental × Asiatic lilies (Lilium) examined by GISH analysis

With the aim of utilizing allotriploid (2n = 3x = 36) lily hybrids (Lilium) in introgression breeding, different types of crosses were made. First, using diploid Asiatic lilies (2n = 2x = 24), reciprocal crosses (3x − 2x and 2x − 3x) were made with allotriploid hybrids (AOA) obtained by backcrosses of F₁ Oriental × Asiatic hybrids (OA) to Asiatic cultivars (A). Secondly, the AOA allotriploids were crossed with allotetraploid (OAOA, 2n = 4x = 48), in 3x − 4x combination. Finally, the AOA allotriploids where crossed to 2n gamete producer F₁ OA hybrids (3x − 2x (2n)). Two types of triploids were used as parents in the different types of crosses, derived from: (a) mitotic polyploidization and (b) sexual polyploidization. Ploidy level of the progeny was determined by estimating the DNA values through flowcytometry as well as chromosome counting. The aneuploid progeny plants from 3x − 2x and reciprocal crosses had approximate diploid levels and in 3x − 4x crosses and 3x − 2x (2n) the progeny had approximate tetraploid levels. Balanced euploid gametes (x, 2x and 3x) were formed in the AOA genotypes. Recombinant chromosomes were found in the progenies of all crosses, except in the case of 2x − 3x crosses through genomic in situ hybridization (GISH) analyses. Recombinant chromosomes occurred in the F₁ OA hybrid when the triploid AOA hybrid was derived through sexual polyploidization, but not through mitotic polyploidization with two exceptions. Those recombinant chromosomes were transmitted to the progenies in variable frequencies.     

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.     

The effect of gibberellic acid on fruit and seed set in crosses of garden and winter hardy Rosa accessions

Summary The effect of gibberellic acid (GA₃) was studied on a wide range of crosses between various garden roses and two hardy breeding lines. Although there were fewer seeds per fruit, fruit set was higher in most crosses when GA₃ was applied to the stigma at the rate of 250 ppm ten days after pollination. However, higher fruit set did not result in more seeds per pollination for many crosses and seemed to be related to the degree of male parentage. Both parents used had a major effect on pollination success. Recently developed Rosa cultivars have a narrow genetic base and the use of distantly related cultivars as parents would possibly give a high seed set and greater numbers of progeny.Contribution No. 335/90.08.01R, Experimental Farm, L'Assomption; Contribution No. Ro 44, Research Program Service, Ottawa.