Tetraploid Parents Research Articles

Genetic variation, heritability and genotype by environment interaction of morphological traits in a tetraploid rose population.

BackgroundGlobal trade has ensured that the ornamental horticulture continues to grow worldwide, with rose hybrids being the most economically important genus (Rosa x hybrida). Due to changes in global trade and an increase in energy costs the ornamental industry has seen a shift in the production and sale of flowers from the US and Europe alone to production in Africa and Latin America. As Kenya is a major exporter of roses to Europe we studied the genetic variation and heritability of specific morphological traits in a tetraploid population grown in the Netherlands and in Kenya. The aim was to estimate genotype by environment interaction (G × E) and to investigate the implications of (G × E) for rose breeding.ResultsA tetraploid rose population (K5) from a cross between two tetraploid parents was field tested over two seasons in the Netherlands (summer and winter) and two locations in Kenya (Nairobi and Njoro). Ten traits were compared per genotype across the four environments. There were differences in trait association across the four environments showing that the traits were partially influenced by the environment.The traits that had a low ratio of σ2ge/σ2g also showed a high value for heritability. For the traits number of petals, prickles on petioles, prickles on stems the interaction is minimal. For the traits chlorophyll content, stem width and side shoots we observed a much higher interaction ratio of 0.83, 1.43 and 3.13 respectively. The trait number of petals had the highest heritability of 0.96 and the lowest σ2ge/σ2g ratio (0.08). The trait number of side shoots (SS) with the lowest heritability (0.40) also had the highest σ2ge/σ2g ratio of 3.13.ConclusionAttained by this experiment showed that we have different magnitudes of non-crossover G × E interactions. For the traits number of petals, prickles on stems and prickles on petioles with a low interaction and high heritability, selection can be done at any of the environments. Thus, these traits can be confirmed at the breeding site. For the traits stem width, side shoots and chlorophyll content that had a higher interaction selection for or against these traits should be done at the production location or at least be verified there.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-014-0146-z) contains supplementary material, which is available to authorized users.

Ploidy Level Affects Important Biomass Traits of Novel Shrub Willow (Salix) Hybrids

Polyploidy is a common observation in the genus Salix, including some of the shrub willow species currently being bred as a potential bioenergy feedstock. Breeding of shrub willow has produced new species hybrids, among which a disproportionate number of high-yielding genotypes are triploid, produced from crosses between diploid and tetraploid parents. These novel hybrids display significant variation in biomass compositional quality, including differences according to ploidy. The triploid and tetraploid genotypes possess lower lignin content than diploid genotypes. Biomass composition was also significantly different across the 3-year growth cycle typical of bioenergy plantings. There were differences in syringyl/guaiacyl (S:G) lignin ratios among the 75 genotypes examined, in addition to significant correlations with willow growth traits, yield, and composition. These differences suggest that a long-term strategy of breeding for triploid progeny will generate cultivars with improved growth traits and wood composition for conversion to biofuels.

Production of Colchicine-induced Autotetraploids in Pummelo (Citrus grandis Osbeck) through Indirect Organogenesis

Colchicine-induced stable autotetraploid plants were recovered through indirect organogenesis from stem sections of in vitro-grown zygotic seedlings of pink/red-fleshed pummelo (Citrus grandis L. Osbeck) selections cybrid Hirado Buntan (C-HBP) (pink), 5-1-99-3 (dark pink), and HBJL-5 (red), all derived from Hirado Buntan pink pummelo. Multiple shoot induction was achieved through indirect organogenesis from the callus produced from the cut ends of the treated explants. Ploidy levels of regenerated plantlets were determined through flow cytometry at a stage when recovered shoots had one to two expanded leaves. Recovered tetraploids proved to be stable after 2 years in the field. As expected, higher colchicine concentrations and treatment durations decreased the survival rates of the regenerated plantlets. Colchicine concentrations of 0.05% and 0.1% produced the most tetraploids; of the 19 total tetraploids produced, 10 were produced from the treatment with a colchicine concentration of 0.1% and six were produced from treatment with a concentration of 0.05%. After flowering, these stable pink/red-fleshed tetraploid plants generated should be useful as breeding parents in our grapefruit/pummelo improvement program, especially if any show canker tolerance or reduced furanocoumarins. Use of monoembryonic tetraploids in interploid citrus crosses eliminates the need for embryo rescue to recover seedless triploid progeny; this research expands our pool of available high-quality monoembryonic tetraploid parents.

Growth performance comparison of intercross-triploid, induced triploid, and diploid rainbow trout

Abstract Use of all-female triploids (3N) instead of diploids (2N) can be advantageous in rainbow trout ( Oncorhynchus mykiss ) aquaculture and fisheries management due to sterility and the consequent superior growth and feed conversion achieved at reproductive age. Triploid trout are currently produced by pressure or temperature shock of the zygote (induced-triploid, 3NP). An alternative procedure to create triploids that may have fewer negative effects on embryonic development and result in 100% triploids is to mate a tetraploid (4N) parent with a 2N parent (intercross-triploid, 3NC). We compared growth performance of nine sets of families each consisting of 3NP, 3NC, and 2N siblings through two years of age. The 2N and 3NC fish exhibited greater body weight than the 3NP fish throughout most of the study; however, by the end, body weight of the 3NC fish exceeded that of the 2N and 3NP fish, which were similar. Condition factor was lowest for 3NC and highest for 3NP fish throughout most of the study. Higher rates of vertebral compression in the 3NP fish affected body weight, fork length, and condition factor in this group. The correlations of body weight among families for the three ploidy types ranged from R 2 below 0.03 around 8–9 months post-hatch, to above 0.5 around 18–19 month post-hatch, supporting family differences in growth response to triploidization and triploidization strategy. Nevertheless, a greater correlation between 2N and 3NC values than 2N and 3NP values, particularly at body weights above 1 kg, supports greater potential to improve 3NC growth performance compared to 3NP performance when genetic selection is based on the 2N phenotype.

Comparison of disease resistance between diploid, induced-triploid, and intercross-triploid rainbow trout including trout selected for resistance to Flavobacterium psychrophilum

All-female triploid fish are advantageous in rainbow trout (Oncorhynchus mykiss) aquaculture due to sterility and the consequent superior filet quality, growth, and feed conversion achieved at reproductive size. Triploid fish are commonly produced by pressure or temperature shock of the zygote (induced-triploids, 3NP), but can also be produced by mating a tetraploid parent with a diploid (2N) parent (intercross-triploids, 3NC). Little is known about the disease resistance of 3NC fish. In this study, we measured post-challenge survival of genetically-related 2N, 3NP and 3NC families after exposure to Flavobacterium psychrophilum the etiological agent of bacterial cold water disease (BCWD). The families used in this study originated from either an unselected commercial stock or BCWD resistant or susceptible line of rainbow trout. The overall survival of 2N fish was slightly higher than the respective 3NP and 3NC fish. Although 3NC fish tended to show higher survival than 3NP fish, this response was not sufficiently consistent to promote intercross production of triploids for increasing disease resistance. The survival of ten sets of 3NP, 3NC and 2N families, created from BCWD resistant and susceptible line parents, demonstrated overall similar inherent relative survival differences among the ploidy types both among families and between lines, although family differences in response to triploidization and triploidization strategy were observed. In summary, minimal survival difference between 3NP and 3NC families following experimental challenge suggests that innate resistance to F. psychrophilum is not substantially altered by the triploidization strategy and progress in family-based selective breeding of diploid fish for BCWD resistance will substantially translate into improved survival when triploids are derived either by shock treatment or intercross breeding.

Double hypoploid of Allium tuberosum Rottl. ex Spreng. (2n = 4x = 30): its origin and cytology

Aneuploids provide valuable tools for locating genes on specific chromosomes and for studying dosage effect of additional/missing chromosomes. Presently, a double hypoploid with 2n = 4x = 30 chromosomes was found for the first time among the seed progeny of a tetraploid plant growing in Jammu University Botanical Garden. These chromosomes on the basis of form/size formed six quadruples and two triplets, with six groups having single deviant chromosomes. Occurrence of single deviant members in most of the groups pointed towards the segmental allotetraploid nature of present strain. Like the normal tetraploids, most of the pollen mother cells (PMCs) of this variant had somatic number of chromosomes (2n = 30) present as univalents or multivalents and bivalents, a few cells had double the somatic number of chromosomes (2n = 60) which were always present as bivalents. Meiotic details in the PMCs with 30 chromosomes revealed that 15.21 % cells had 30 univalents, 10.86 % cells had 6IV + 2III and in 54.32 % cells had configurations as 6IV + 2II + 2I, 4IV + 3III + 2II + 1I, 3IV + 2III + 5II + 2I, 2IV + 2III + 8II. Presence of a few cells with 6IV + 2III and most of cells with lesser number of quadrivalents but more bi- and univalents as well as the fact that 30 chromosomes matched into six quadruples and two triplets with most of the groups having single deviant members indicates that the present variant represents segmental allotetraploid. At the same time, occurrence of few cells with penta-/hexavalents indicates the involvement of structural chromosomal alterations in the evolution of present cytotype. In order to identify the missing chromosomes, present karyotype has been compared with that of its tetraploid parent. This comparison indicated that the missing chromosomes of the former belong to groups VII and VIII. For having some clues regarding the origin of present strain, reduction division in the two tracks of its progenitor was also studied. In the female track, majority of embryo-sac mother cells (EMCs) of the parent plant had 64 chromosomes which were present as 32 bivalents at metaphase I, with clean 32:32 segregations at anaphase I whereas a few EMCs available with 32 chromosomes had multivalents and unequal segregations in half of the cells with this number at anaphase I. In the male track, majority of the PMCs with 32 chromosomes had either multivalents or univalents at metaphase I and unequal dis junctional patterns in 32 % of the cells. As EMCs with 32:32 segregations are expected to develop into embryo-sacs with eggs having 32 chromosomes and PMCs and EMCs with 32 chromosomes and unequal separation of chromosomes are more likely to form genetically imbalanced gametes, it seems that the present variant has originated by the formation and the fusion of aneuploid reduced gametes.

Cytotype coexistence leads to triploid hybrid production in a diploid–tetraploid contact zone of Chamerion angustifolium (Onagraceae)

Polyploids are often geographically segregated from their diploid progenitors, but the extent of sympatry and the consequences for reproductive isolation and coexistence are rarely quantified. • In this study, we document the distribution and co-occurrence of diploid and tetraploid Chamerion angustifolium among 57 populations within the diploid-tetraploid contact zone in the Canadian Rocky Mountains. Rates of hybrid mating in mixed-ploidy populations were inferred from the frequency of triploid offspring in open-pollinated seed families. • Twenty-three of 57 populations sampled contained a single cytotype; 20 (87%) were tetraploid and three (13%) were diploid. Thirty-four populations (60%) contained multiple ploidies. Diploid and tetraploid plants occurred in all mixed-ploidy populations; triploids occurred in 13 populations and averaged 1.4% of plants per population. The proportion of tetraploids in a population was negatively related to elevation (partial regression: F = 27.2, P <0.0001) and latitude (partial regression: F = 17.4, P < 0.0001). Triploids were detected in seed from all eight mixed-ploidy populations sampled ( = 3.7% of seed per population), comprising 7% of that expected with random mating (G = 2589.2, df = 1, P <0.0001, n = 2628), and were more often produced by diploid maternal parents than tetraploid parents. • Our results indicate that tetraploids regularly coexist with diploids in the contact zone and that this coexistence is likely promoted by both strong reproductive isolation and asymmetric intercytotype mating between diploid and tetraploid C. angustifolium.

Confirmation of cytotype stability in autotetraploid black wattle (Acacia mearnsii) trees using flow cytometry and size differences of the reproductive gametes

Acacia mearnsii (black wattle) is grown commercially in South Africa for its timber and bark. However, the invasive nature of the species has resulted in it being considered an alien invader and for this reason research has been aimed at producing a sterile triploid variety that would be highly desirable for the South African commercial forestry industry. Tetraploids were successfully induced by soaking germinating diploid seeds in colchicine. Seed from these tetraploids was used to establish a field trial, where crossing diploid with tetraploid parent plants only produced diploid and tetraploid progeny and failed to produce any triploid progeny. Control-crossed seed set between diploids is generally low in A. mearnsii and, together with the possibility of an unstable tetraploid population, this could be reducing the chances of producing triploid seed. Thus identification and confirmation of stability within the existing advanced-generation tetraploid population (aged 10–11 years) was critical to ensure the production of sterile triploids. Flow cytometry was used to determine the stability of the ploidy of leaf vegetative tissues, whereas polyad and ovule size measurements were used to determine the stability of ploidy of the reproductive tissues. Results from the study revealed that the tetraploidy of within the leaf vegetative tissue was stable. For both the ovule and polyad size measurements, a size range was determined for diploids and tetraploids and, within the population under investigation, no overlap was apparent. This allowed for the conclusion that the advanced-generation tetraploid population was stable and that the absence of triploid progeny must be because of post-zygotic reproductive barriers within the ovary.

Biochemical Evaluation of Triploid Progenies of Diploid × Tetraploid Breeding Populations of Camellia for Genotypes Rich in Catechin and Caffeine

To verify the quality of triploid varieties of Camellia tea species at the secondary metabolite level, we tested caffeine and catechin profiles of 97 F(1) segregating progenies in two breeding populations with a common tetraploid parent and diploid parents of two geographic and varietal origins. Catechin and caffeine levels of the triploid progenies were quantified and compared against their diploid parent. Some of the progenies showed better performance than their diploid parent. Most of the progenies of the diploid C. sinensis × tetraploid cross showed heterosis for caffeine and EGCG. Progenies of the C. assamica subsp. lasiocalyx × tetraploid cross showed heterosis for +C, EC, EGC, and TC. The genomic contributions of the diploid parent seem to be the main factor in the variation between the two populations. Our studies showed quantitative enhancement of some of the quality-related parameters in tea, providing a platform to refocus on this classical breeding approach for developing quality cultivars in tea.

EXTENSIVE CITRUS TRIPLOID BREEDING PROGRAM BY 2X×4X SEXUAL HYBRIDIZATIONS

Production of seedless citrus fruits is required for the fresh market because consumers do not accept seedy fruits. Development of new seedless mandarin cultivars has a high priority for many citrus industries worldwide. The recovery of triploid hybrids is the most promising approach to achieve this goal, since triploids have a very low pollen and ovule fertility and usually are seedless or produce very low numbers of seeds, and do not induce the formation of seeds in other cultivars by cross pollination. The objective of our breeding program is to produce new high quality easy peeling and seedless mandarin cultivars. Citrus triploid plants can be recovered by 2jcx4y sexual hybridizations. Triploid embryos are found in normal and undeveloped seeds that do not germinate under greenhouse conditions. Extensive breeding programs based on this type of hybridization require very effective methodologies for recovery of new tetraploid parents, embryo rescue and ploidy evaluation. Different approaches have been implemented to obtain new tetraploid parents. Spontaneous autotetraploid plants of apomictic genotypes have been selected from seedbeds by flow cytometry and autotetraploid plants of non apomictic genotypes have been obtained by chromosome duplication with treatments of micrografted shoot tips with colchicine or oryzalin. Symmetric protoplast fusion is also used to produce tetraploid genotypes. So far, we have obtained more than 4,400 triploid hybrids from 77 parental combinations. Protection of Plant Breeder's Rights of a triploid hybrid named IVIA-600 obtained in a hybridization between 'Hernandina' clementine and tetraploid 'Orlando' tangelo has been requested. (Resume d'auteur)

The effect of temperature and relative humidity on Acacia mearnsii polyad viability and pollen tube development

Acacia mearnsii (black wattle) is a commercially important forestry species in South Africa, grown for its timber and bark. Due to its invasiveness, it is also considered be an alien invader species and for this reason the production of a sterile triploid variety would be highly desirable for South African commercial forestry. Previous research on crosses between diploid and tetraploid parent plants to produce triploid progeny has resulted in poor seed set. One possible barrier preventing seed set could be the effect of temperature and relative humidity, within the isolation bags used during cross-pollination operations. For this reason in 2011 diploid polyads were subjected to various temperature and relative humidity combinations, to simulate conditions recorded within the isolation bags being used in the 2010 flowering season in order to see if the conditions were detrimental to polyad viability. The results showed that when polyads were exposed to extreme temperatures (>30°C) and low relative humidities (RH's) (10%), polyad viability and pollen tube development, decreased significantly. In contrast the effect of high RH's in combination with low temperatures for long periods appeared to be beneficial to polyad viability and pollen tube growth. The results also indicated that the Australian Centre for International Agricultural Research (ACIAR) agar germination medium was superior to the Brewbaker and Kwack (BK) 30% agar germination medium for determining polyad viability as it resulted in greater number of pollen tubes per polyad, which were healthier in appearance. The Sigma® DAB peroxidase vital stain test overestimated polyad viability and showed no significant differences between the various treatments, highlighting its unreliability as a test. Polyad viability and pollen tube development were compared across three flowering seasons (2009, 2010 and 2011) and similar trends were apparent with some seasonal differences.

Insect resistance of a full sib family of tetraploid switchgrass Panicum virgatum L. with varying lignin levels

Little information is available on insect resistance mechanisms and inheritance in biomass grasses. Although reduction of lignin in biomass grasses in order to increase the efficiency of fermentation may result in increased susceptibility to insect feeding, other resistance mechanisms may be more important. Field grown leaves of two tetraploid parent (Kanlow N1, Summer) and 14 progeny switchgrass (Panicum virgatum L.) plant clones selected for a diversity of plant form and ranges in lignin levels were tested for leaf resistance to feeding by the fall armyworm (Spodoptera frugiperda J. E. Smith), a grass feeding insect pest. Although lignin generally appeared important as a resistance mechanism only at early season stages, replicate clones of two low lignin progeny plants generally remained resistant to fall armyworm feeding. Mechanical damaging increased resistance to fall armyworm feeding in several of these plants. Degrees of resistance were sometimes associated with leaf form of progeny. These results indicate there are likely multiple insect resistance mechanisms operating at different stages in switchgrass, and that segregation of some mechanisms appears related to growth form of the plants.

Regeneration and characterization of somatic hybrids combining sweet orange and mandarin/mandarin hybrid cultivars for citrus scion improvement

Protoplast fusion between sweet orange and mandarin/mandarin hybrids scion cultivars was performed following the model “diploid embryogenic callus protoplast + diploid mesophyll-derived protoplast”. Protoplasts were isolated from embryogenic calli of ‘Pera’ and ‘Westin’ sweet orange cultivars (Citrus sinensis) and from young leaves of ‘Fremont’, Nules’, and ‘Thomas’ mandarins (C. reticulata), and ‘Nova’ tangelo [C. reticulata × (C. paradisi × C. reticulata)]. The regenerated plants were characterized based on their leaf morphology (thickness), ploidy level, and simple sequence repeat (SSR) molecular markers. Plants were successfully generated only when ‘Pera’ sweet orange was used as the embryogenic parent. Fifteen plants were regenerated being 7 tetraploid and 8 diploid. Based on SSR molecular markers analyses all 7 tetraploid regenerated plants revealed to be allotetraploids (somatic hybrids), including 2 from the combination of ‘Pera’ sweet orange + ‘Fremont’ mandarin, 3 ‘Pera’ sweet orange + ‘Nules’ mandarin, and 2 ‘Pera’ sweet orange + ‘Nova’ tangelo, and all the diploid regenerated plants showed the ‘Pera’ sweet orange marker profile. Somatic hybrids were inoculated with Alternaria alternata and no disease symptoms were detected 96 h post-inoculation. This hybrid material has the potential to be used as a tetraploid parent in interploid crosses for citrus scion breeding.

Simultaneous estimation of genetic linkage and preferential pairing factor for a triploid population with unphased markers

Triploids, recognized to occur more frequently in natural and experimental populations of many species than previously appreciated, display important economic and biological values. Despite this, however, linkage analysis for triploids has not been well explored. We develop a statistical model for estimating and testing the linkage between molecular markers in a triploid population derived from a tetraploid and diploid parent. The model incorporates one important meiotic feature of tetraploids by which more homologous chromosomes pair with a greater likelihood than less homologous chromosomes. By implementing the EM algorithm within the maximum likelihood framework, the model provides a procedure for simultaneous estimation of the linkage and preferential pairing factor. The model accommodates the segregating patterns of pseudotest markers and intercross markers with different amounts of informativeness. The utility of the model was validated through a real data analysis and simulation studies. The model provides a statistical tool for linkage analysis in a triploid population by taking into account meiotic behavior of tetraploids. Results from the model will help to shed light on the genetic diversity and origin of a polyploid population.

The Origin of Spelt and Free-Threshing Hexaploid Wheat

It is widely believed that hexaploid wheat originated via hybridization of hulled tetraploid emmer with Aegilops tauschii (genomes DD) and that the nascent hexaploid was spelt, from which free-threshing wheat evolved by mutations. To reassess the role of spelt in the evolution of Triticum aestivum, 4 disomic substitution lines of Ae. tauschii chromosome 2D in Chinese Spring wheat were developed and one of them was used to map the Tg locus, which controls glume tenacity in Ae. tauschii, relative to simple sequence repeat (SSR) and expressed sequence tag loci on wheat chromosome 2D. The segregation of SSR markers was used to assess the presence of Tg alleles in 11 accessions of spelt, both from Europe and from Asia. Ten of them had an inactive tg allele in the D genome and most had an active Tg allele in the B genome. This is consistent with spelt being derived from free-threshing hexaploid wheat by hybridization of free-threshing wheat with hulled emmer. It is proposed that the tetraploid parent of hexaploid wheat was not hulled emmer but a free-threshing form of tetraploid wheat.

Identification of pre-zygotic reproductive and morphological barriers limiting controlled crossed seed production of triploid Acacia mearnsii

A study of the reproductive biology of black wattle (Acacia mearnsii de Wild) was conducted, specifically with regard to the compatibility of the diploid×tetraploid cross to produce a triploid variety, together with identifying ways of increasing triploid seed production. Fluorescent microscopy was used to determine pollination and fertilisation rates and to identify any pre-zygotic barriers at the stigma, style and ovary. Both diploid and tetraploid families were tested as maternal parents to establish if this was imperative to producing a triploid. Morphological measurements were documented in order to determine any incompatibilities in the cross to produce a triploid. The in vivo results showed that successful fertilisation of the ovary was possible whether one used a diploid or tetraploid maternal parent. When the maternal parent was a tetraploid, however, the pollination rate (polyads adhering to the stigma) and ovary fertilisation rates were significantly (p<0.05) greater. Morphological measurements and observations also revealed that tetraploid floral parts were significantly (p<0.05) larger than the diploids. The morphological size differences between the diploid and tetraploid polyads and pistils did not appear to influence the fertilisation of the ovaries and thus did not pose any identifiable barrier in the cross to produce a triploid. When considering the results from the cross to produce a triploid (2n×4n or 4n×2n), the diploid polyads were significantly (p<0.05) more vigorous and suitable in fertilising the tetraploid ovaries as opposed to the reverse. Possible pre-zygotic barriers at the stigma, style or ovary were investigated and the only area that could be identified limiting seed production was within the ovary.

Variation of DNA methylation and phenotypic traits following unilateral sexual polyploidization in Medicago

Sexual hybridization is an important generator of biodiversity and a powerful breeding tool. Hybridization can also overcome ploidy barriers when it involves 2n gametes, as in the case of unilateral sexual polyploidization (USP) that has been utilized in several crops, among which alfalfa. This research was aimed at gaining insights into the effects of USP on genome methylation and on phenotypic traits in alfalfa, an important forage species. The Methylation-Sensitive Amplified Polymorphism technique was used to estimate the cytosine methylation changes occurring in a tetraploid (2n = 4x = 32) USP progeny from crosses between a diploid Medicago sativa subsp. falcata genotype that produces 2n eggs and a cultivated tetraploid Medicago sativa subsp. sativa variety. De novo methylation or demethylation in the USP progeny were observed for 13% of the detected genomic sites, indicating that methylation changes can be relevant. USP plants showed larger surface area of the leaf epidermis cells than both parents, but this did not result in larger leaf size or higher plant biomass. They displayed significant higher ovule sterility than the tetraploid parent, but normal fertility was observed in crosses with unrelated male testers. We conclude that hybridization and sexual polyploidization resulted in novel variation in terms of remodeling of the methylation landscape as well as changes in phenotypic traits in alfalfa.

Optimisation of pollen viability tests for Acacia podalyriifolia and two ploidys of Acacia mearnsii

Acacia mearnsii (black wattle) is a commercially important forestry species in South Africa, grown for its timber as well as its bark. It is, however, also considered to be an alien invader of indigenous vegetation and for this reason the production of a sterile variety would be highly desirable for commercial forestry in South Africa. Previous research on crosses between diploid and tetraploid parent plants to produce triploid progeny has resulted in poor seed set. One possible barrier preventing seed set could be the viability of the pollen used in the cross pollination operations. Thus a study was conducted to test the pollen viability. In vitro agar media germination tests (ACIAR and Brewbaker and Kwack media) were optimised on Acacia podalyriifolia pollen and then used together with vital stain tests (Sigma® DAB peroxidase and p-phenylendiamine) to test pollen germination and viability of A. mearnsii pollen. These were then compared to in vivo pollen germination on the stigma, and were conducted on both diploid and tetraploid pollen mixes. Results showed that the vital stain tests gave significantly ( p < 0.05) higher pollen viability than the agar germination tests and were more in agreement with the results from the pollen germination rate on the stigma. For both the diploid and tetraploid pollen mixes tested, there were no significant differences ( p > 0.05) between the two agar media germination tests and between the two vital stain tests.

Contribution of synthetic tetraploids (AAAA) and diploids (AA) to black Sigatoka resistance and bunch weight to their triploid progenies

The generation of banana triploids from tetraploid–diploid crosses requires knowledge on the influence of the parents on black Sigatoka resistance and agronomic traits to the triploid progenies. The objective of this investigation was to determine the influence of tetraploid and diploid parents on black Sigatoka resistance and agronomic traits in the triploid progenies generated from tetraploid–diploid crosses. The mating scheme was designed as a 4 × 5 North Carolina II mating design. Due to problems in seed set and germination, progenies from 2 male parents with 4 female parents were evaluated at two sites in Uganda. The results showed that the male-parent triploid progeny heritability estimate for the number of leaves at harvest was greater than the female parent estimate. The diploid parents had higher correlation coefficients for the total leaves at harvest with the triploid progenies than tetraploid parents with triploid progenies. Disease development over time took more days in diploid parents than in the tetraploid parents with the triploid progenies as intermediates. These results suggested that diploids transferred black Sigatoka resistance to the triploid progenies as measured by the number of standing leaves and disease development overtime. There was a positive correlation ( P < 0.05) between tetraploid female parents and triploid progenies for plant height and bunch weight. The triploid progeny–tetraploid female parent heritability estimates for plant height (0.92) and bunch weight (0.72) were highly significant. These results indicated that the female synthetic tetraploids influenced plant height and bunch weight in the triploid progenies. Therefore, it is important to select the tetraploids with heavy bunches to effectively improve yield in triploid progenies generated by tetraploid–diploid crosses. The tetraploid–diploid progenies had a significant ( P < 0.05) family-by-site interaction for bunch weight indicating that new banana genotypes need to be tested across different environments to select stable genotypes to promote to end-users.

A survey of β‐glucan and arabinoxylan content in wheat

Dietary fibre lowers the risk of coronary heart disease and colorectal cancer. This survey quantifies mixed link β-glucan (MBG) and arabinoxylan (AX) in wheat and investigates relationships between the grain carbohydrates. MBG and AX contents were measured in 500 and 200 wheat accessions respectively, including diploid, tetraploid and hexaploid genotypes comprising primitive, synthetic and elite lines. Overall, MBG contents ranged between 1.8 and 18.0 g kg(-1) grain dry weight. In wheat-barley addition lines and triticale hexaploids the levels were 9.0-11.3 and 3.5-9.6 g kg(-1) respectively. The amounts in synthetic wheats were nearer their tetraploid parents than their diploid parents. AX and total non-starch polysaccharide (NSP) contents ranged from 23.7 to 107.5 g kg(-1) and from 31.7 to 136.7 g kg(-1) respectively. Linear regressions showed that the relationships of starch and grain weight with NSP glucose were stronger than those with AX. The results indicated insufficient genetic diversity in the germplasm surveyed to initiate a breeding programme to increase the amount of MBG in wheat grain to 20 g kg(-1) , a level considered high enough to confer a 10-15% reduction in blood cholesterol.