Differential cold sensitivity of pollen grain germination in two Prunus species

Summary Pollen grains from selected cutivars of almond [Prunus dulcis (Mill.) D. A. Webb] and peach (Prunus persica Batsch L.) were exposed to a range of temperatures between 1°C and 34°C on a thermogradient plate. Pollen germination at temperatures below 9°C was conspicuously greater in almond than peach. Miximal germination percentages were attained at about 16°C (almond) and 23°C (peach). The two species did not differ in their capacity for pollen tube elongation over a broad range of temperatures. Maximal pollen tube elongation occurred at temperatures 5°C to 8°C higher than maximal pollen germination. Species affiliation appeared to be of much greater consequence than chilling requirement or bloom date of the sporophyte in predicting gametophytic response to temperature.     

Location of the self-incompatibility gene on the almond linkage map

A progeny obtained from the almond cross ‘Ferragnès’בTuono’ (Prunus amygdalus Batsch) was used to study the self-incompatibility trait in three different ways: fruit set, pollen tube growth and stylar ribonuclease activity. As expected from the genotypes of the parents, all progeny appeared phenotypically as self-compatible. However, the progeny could be scored for the segregation of stylar ribonuclease isozymes and thus allowed the incompatibility locus to be placed on the almond linkage map.     

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 retention following natural self pollination in peach,almond, and peach × almond hybrids

Summary Retention of pollen grains following natural self-pollination was evaluated in 15 cultivars (cvs.) of almond, 4 peach and 2 nectarine cvs., and 37 interspecific peach × almond hybrids compared to 7 almond seedlings. The level of pollen retention was presumed to reflect and integrate the degree of homogamy, the amount of pollen produced by the flower, the extent of anther-stigma contact during anthesis, and the level of pollen germination. Pollen retention averaged 5 times greater in the peach and nectarine cvs. than in the almond cvs. The greater pollen retention, characteristic of the peach, was dominant in expression in the interspecific F₁ hybrids over the lower levels of pollen retention, characteristic of the almond. Thus, gametophytic self-incompatibility is not the only trait supporting outcrossing in the almond. Our data are consistent with the concept of co-evolution of floral traits relating to different breeding strategies. The level of pollen retention could often be anticipated at anthesis on the basis of blossom phenotype. That is, stigma-anther contact was observed frequently in the blossoms of peach, nectarine, and the peach × almond F₁ hybrids, but only infrequently in almond.     

Nut set evaluation in inter-specific almond × peach backcross progenies for self-compatibility selection in almond breeding programme

Self-compatibility was examined in 22 almond samples that were selected based on their generic and physiological characteristics. Polymerase chain reaction was also done with consensus primers. Pollen tube growth and nut set analyses were carried out on partially bagged limbs after self-pollination treatment. In spite of the fact that all genotypes had the S _f-allele and pollen tube growth were similar, nut set exhibited an alternate year characteristic that ranged from 16.2% to a maximum of 24.7%. This was the highest treatment after self-pollination. Difference existed between genotypes could be due to the genetic constitution of each genotype, is explored in set that is diminished by inbreeding, which diminish gene aggregation in different members of a progeny. In addition, flower morphology could also influence set in bagged limbs. Furthermore, with regard to flower sterility and bud density in relation to both pollination success and ecological condition availability, these traits must be considered when examining production in self-compatible almond orchards, e.g.,—the impacts accompanying inbreeding and effective autonomous self-pollination.     

Osmoregulation in birdseed millet under conditions of water stress II. Variation in F3 lines of Setaria italica and its relationship to plant morphology and yield

We report, for the first time, there generation of four homozygous lines in sweet cherry (Prunus avium L.) byin situ parthenogenesis followed by embryo and cotyledon culture. The sweet cherry cultivar ‘Altenburger’ was pollinated with marked pollen irradiated by γ-rays at doses ranging from 250 to1200 Gy. Pollination with such irradiated pollen affected fruit set and the quality of the embryos, and induced the formation of parthenogenic embryos. The immature embryos extracted from the stones, 35 or 75days after pollination, were cultivatedin vitro in an embryo or cotyledon culture. Although flow cytometrical analysis demonstrated the diploid level for all regenerants, four lines could be characterized as homozygous using isoenzyme analysis. This revised version was published online in July 2006 with corrections to the Cover Date.     

On genetically remodeling the almond tree

Summary Dwarf peach trees require only 1/4th the space of standard trees and thus reduce the cost of experiments in which the tree is the experimental unit, by 75%. Or, put another way, they facilitate estimates of tree performance, in experiments of the same size, that are 50% more precise than those obtainable from standard trees. The objective of this study was to determine if the almond tree could be genetically compressed (dwarfed) to facilitate discrimination of genetic and cultural manipulation on its productivity, to facilitate genetic manipulation, and to increase its productive efficiency.The results obtained indicate the almond tree can be dwarfed (compressed), by the dw gene of peach. interspecific crosses of dwarf (dw/dw) peach, P. persica, with almond, P. amygdalus, followed by backcrosses to almond revealed: 1. Plant stature and node density vary widely among the dwarf (dw/dw) inter species hybrids. The heritabilities of these traits are high. 2. Spur density also varies widely. Its mean is high and its heritability is very high. 3. The dwarf inter species hybrids produce flowers copiously. However, at 22 months of age the flowers of most seedlings are sterile, apparently due to abnormal pistils. Consequently, average productivity is very low. However, some of these dwarf P. persica × P. amygdalus hybrids do express moderate to high productivity. Further, the heritability of productivity, among the seedlings expressing some degree of fertility, is very high. Consequently, further backcrosses to almond are expected to rapidly restore fertility and productivity. The yield potential of dw/dw dwarf almonds will remain unknown until fertility is restored.     

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.     

Pollen grain germination inside the anthers of two chasmogamous angiosperms: Almond (Prunus amygdalus L. Batsch) and apple (Malus pumila Mill.)

Summary Pollen grain germination inside anthers has so far been known in only eleven chasmogamous angiospermous species. The discovery of this phenomenon in some varieties of Prunus amygdalus (almond) and Malus pumila (apple) is therefore significant. The anomaly appears to be genetically controlled, the gene expression occurring under specific environmental conditions.     

An extended interspecific gene pool available to peach and almond breeding as characterized using simple sequence repeat (SSR) markers

Genetic diversity, as revealed by eighteenSimple Sequence Repeat (SSR) markers inthirty almond [P. dulcis (Mill.) D.A.Webb], twenty fresh-market peach [Prunus persica (L.), Basch], fifteenprocessing clingstone peach cultivars, andten rootstocks, established the geneticrelatedness among cultivars andcharacterized the variation within andbetween species. One accession each of thewild Prunus species, P.davidiana [(Carriere) Franch] and P.webbii [(Spach.) Vieh.], was included inthe analysis. The number of presumedalleles revealed by the SSR analysis rangedfrom one to six in peach whereas almondcultivars showed a range of three to nine.Peach cultivars clustered into ten groups,which are in general agreement withdocumented origin. Most processingclingstone peach cultivars clusteredseparately from fresh-market freestonecultivars supporting a distinct origin. Twomajor clusters were observed in almond withone containing California cultivars and theother containing European cultivars and theimportant California cultivar Mission.Results establish the value of SSR markersfor distinguishing different geneticlineages and characterize an extensive andlargely unexploited inter-species gene poolavailable to peach and almond breedingprograms.     

桃花粉活性检测和离体萌发特性的研究

果树花粉活力直接影响授粉、受精乃至座果。为了解果树品种的花粉生活力,给引种栽培和杂交育种工作创造有利条件,以桃花粉为试验材料,采用染色方法检测花粉的活性。试验结果表明,含有蓝墨水的花粉培养基,花粉萌发率可以达到64.67%,与对照相比差异不明显,因此该方法比较适合于快速检测花粉活性;固体培养基培养2个品种桃花粉,萌发率比液体培养基培养分别高25%和20%。另外温度、花粉密度、培养基中蔗糖及硼酸浓度都对花粉萌发率和花粉管长度有影响,在温度为24℃、1粒花药/100 μL、10%的蔗糖或100 mg/L的硼酸的条件下,均有利于花粉萌发和花粉管生长。     

The breeding system of rubber (Hevea brasiliensis): an evaluation of controlled hand pollination methods

Summary Controlled hand pollinated pistils of rubber were observed using fluorescence microscopy to assess the efficiency of the universally-employed method for the production of progeny for plant breeding. The controlled hand pollination method conducted in the morning resulted in the deposition of a mean of 15.6 pollen grains on the stigma, with no stray pollination observed. Over 36% of the pistils had the potential to set fruit.Pollinations conducted in the afternoon at the normal time of anthesis, had double the fruit set potential of morning pollinations as measured by penetration of ovules by pollen tubes. Pollinator efficiency also varied, with excessive damage to stigmas resulting in reduced pollen germination and tube growth. There were differences between clones in both female and male fertility, in the proportion of pistils with more than three carpels and in the production of small abnormal stigmas. There was no difference in pollen tube growth following self- or cross-pollination, indicating that the self-sterility mechanism of rubber operates in the ovary. Pollen could be stored for 5 days at 5°C and 75% RH with a 22% loss of fertility.     

A practical method for almond cultivar identification and parental analysis using simple sequence repeat markers

Early and accurate identification of almond [Prunus dulcis (Mill.) D.A. Webb] cultivars is critical to commercial growers and nurseries. Previously published simple sequence repeat loci were examined for their ability to distinguish commonly grown almond cultivars. Twelve highly polymorphic loci were selected for their ability to uniquely identify a set of 18 almond cultivars commonly grown in California, many of which are closely related. These markers also allow an accurate assessment of parent/progeny relationships among cultivars. This system can reliably identify at an early stage of development all major California almond cultivars in current production.     

Amplified fragment length polymorphism as a tool for molecular characterization of almond germplasm: genetic diversity among cultivated genotypes and related wild species of almond,and its relationships with agronomic traits

Amplified fragment length polymorphism (AFLP) analysis is a rapid and efficient method for producing DNA fingerprints and molecular characterization. Our objectives were to: estimate genetic similarities (GS), marker indices, and polymorphic information contents (PICs) for AFLP markers in almond cultivars; assess the genetic diversity of almond cultivars and wild species, using GS estimated from AFLP fingerprints and molecular characterization; and facilitate the use of markers in inter-specific introgression and cultivar improvement. The genetic diversity of 45 almond cultivars from Iran, Europe, and America, were studied assaying 19 primer combinations. In addition, several agronomic traits were evaluated, including flowering and maturity times, self-incompatibility, and kernel and fruit properties. Out of the 813 polymerase chain reaction fragments that were scored, 781 (96.23%) were polymorphic. GS ranged from 0.5 to 0.96, marker indices ranged from 51.37 to 78.79, and PICs ranged from 0.56 to 0.86. Results allowed the unique molecular identification of all assayed genotypes. However, the correlation between genetic similarity clustering as based on AFLP and clustering for agronomic traits was low. Cluster analysis based on AFLP data clearly differentiated the genotypes and wild species according to their origin and pedigree, whereas, cluster analysis based on agronomic data differentiated according the pomological characterization. Our results showed the great genetic diversity of the almond cultivars and their interest for almond breeding.     

A major gene for flowering time in almond

Almond (Prunus amygdalus Batsch) is the earliest temperate fruit species to bloom. This restricts the economic growing of almond to frost free regions. Most almond-breeding programmes aim to develop lateflowering cultivars in order to avoid frost damage and take advantage of higher temperatures which are favourable for pollination and fertilization. Flowering time is generally considered to be inherited quantitatively but a single gene conferring very late flowering in a qualitative way has been identified in several progenies tracing back to a single mutant, ‘Tardy Nonpareil’. The effect of this allele has been studied in three progenies, showing that the effect of this major gene is modified by minor genes, quantitatively inherited, and probably influenced by inbreeding.     

Gamma-irradiation of cacao (Theobroma cacao L.) pollen: Effect on pollen grain viability,germination and mitosis and on fruit set

Summary Theobroma cacao pollen fertilization capability was studied after 0, 50, 100, 200, 500 and 1000 Gy gamma-irradiation. For all irradiation doses, no alteration of pollen grain viability and in vitro germination was observed. In situ, for all doses, pollen tubes penetrated into the styles and reached the ovules 20 hours after pollination. In vitro observations of the pollen grain nuclei after 20 hours incubation showed that pollen irradiation causes inhibition of the division of the generative nucleus. Fruit survival rate 30 days after pollination decreased as irradiation doses increased from 0 to 100 Gy, and over 100 Gy no fruit set was obtained. The possibility of using irradiated pollen as a method for obtaining haploid cacao plantlets is discussed.     

Increasing productivity in sweet almond using selected clones of bitter almond

Summary Eight controlled crosses were made between seven different sweet-kerneled almond cultivars (Prunus dulcis [Mill.] D. A. Webb), and five crosses were made between sweet x highly floriferous bitter almond clones. Sweet x bitter progenies out-yielded the sweet x sweet matings by more than three to one in the first year of production. This was attributable to greater cropping efficiency rather than to tree size or precocity. There was no pleiotropic association or association due to linkage between bitterness and yield. The selected Alnem (bitter) clones appear to be potentially useful progenitors for increasing almond yield capacity by conventional breeding methodology.     

Morphological variation within a sour cherry collection

Summary Morphological traits of 28 full-sib sour cherry (Prunus cerasus L.) families developed with pollen from European sour cherry selections were evaluated with principal component (PC) analysis. The traits which loaded on the first PC were size characters such as lateral length, leaf area, fruit weight, and trunk diameter increase. These character loading on the first PC could be interpreted as representing gradations between morphologies characteristic of the 2 presumed progenitor species, sweet cherry (P. avium L.) and ground cherry (P. fruticosa Pall.). Mean family differences in trunk diameter increase, lateral length, leaf area, and fruit weight varied approximately 12, 3.7, 2.5, and 2 fold, respectively. These results suggest that it may be possible to select sour cherry hybrids approaching the tree and fruit size of either progenitor species. The results are discussed in reference to germplasm collection and the potential of certain cultivars and hybrids as parents.     

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.     

Morphological variation within collections of Moroccan almond clones and Mediterranean and North American cultivars

Summary Cultivated almonds (Prunus dulcis (Miller) D.A. Webb) in Morocco are still propagated from seeds by farmers to overcome transplant failure of grafted trees. Almond collections in southern Morocco conducted since 1975 have resulted in the selection of clones planted at 3 experimental stations. Principal component analysis (PCA) was used to compare kernel, nut, leaf, and growth habit characteristics among 67 selected Moroccan clones and 14 introduced cultivars. Clustering of clones from similar countries and collection areas would suggest the existence of different almond populations. The Moroccan clones did not cluster separately from the foreign cultivars. Three Moroccan clones had exceptionally large nuts and kernels while 7 selections had high yield potential due to high spur density. Moroccan selections tended to be characterized by small leaves in comparison to foreign cultivars. No evidence was found to suggest the existence of separate populations within the Moroccan almond germplasm.