Segregation of bunch orientation in plantain and banana hybrids

Bunch orientation is an economically important trait in plantain (Musa spp. AAB group) and banana (Musa spp. AAA or ABB groups). Pendulous bunches are more symmetrical than subhorizontal, horizontal, or erect bunches and are, therefore, better adapted for transportation. Erect, horizontal, subhorizontal, and pendulous bunches were observed in segregating populations derived from crosses between plantains and bananas and among bananas. A proposed genetic model controlling this trait was tested in four populations. The true breeding diploid banana line, 'Calcutta 4' shows a pendulous bunch and has recessive alleles at three bunch orientation loci. The diploid banana cultivar 'Pisang lilin', which is heterozygous for the three loci, has a subhorizontal bunch. The triploid AAB plantain cultivar 'Bobby Tannap' has two simplex and one duplex loci, which also results in subhorizontal bunch orientation. The other plantain cultivar, 'Obino l'Ewai', which is simplex for two loci and nulliplex for the third, has a pendulous bunch due to dosage effects at the triploid level of the recessive alleles at simplex loci. Two tetraploid hybrids (TMPx 582-4 and 1187-8) have a subhorizontal bunch because of its duplex genotype for two loci and simplex genotype for the other locus. Bunch orientation might be an oligogenic trait regulated by the epistatic effects of at least three dominant loci. This revised version was published online in July 2006 with corrections to the Cover Date.     

Estimating genetic effects in maternal and paternal half-sibs from tetraploid-diploid crosses in <Emphasis Type="Italic">Musa</Emphasis> spp.

Ploidy manipulations and interspecific crosses have allowed considerable genetic progress in Musa breeding, but estimation of genetic parameters for parental selection remains a major challenge. This study aimed to determine the components of genetic variance and the relative contribution of genetic effects to phenotypic variation of yield and phenological traits in secondary triploid hybrids from tetraploid–diploid crosses. The hybrids were evaluated in two consecutive growth cycles on a tropical forest site. Non-genetic effects accounted for a large fraction of the variation observed for most traits, except bunch weight. Partitioning of genetic variance into additive and dominance components confirmed the predominant role of additive genetic effects on the expression of bunch weight, fruit filling time, fruit length, plant height, and number of leaves while primarily non-additive effects accounted for suckering behavior and fruit circumference. Maternal general combining ability (GCA) effects accounted for the additive genetic variation in plant height and number of leaves, suggesting that selection for these traits should be carried out in tetraploid clones. Conversely, paternal GCA effects were the primary causes of genetic variation for fruit filling time, bunch weight, and fruit length, suggesting that these characters should be selected for in diploid clones. Specific combining ability (SCA) effects were observed for all traits, except fruit filling time, suggesting that additional genetic gain could be achieved through recombinative heterosis for these traits.     

Effect of the black sigatoka resistance locus bs 1 and ploidy level on fruit and bunch traits of plantain-banana hybrids.

Summary Plantain (Musa spp., AAB group) cultivation is threatened by black sigatoka, an airborne fungal (Mycosphaerella fijiensis Morelet) leaf spot disease. Several traits in plantains and bananas are mainly affected by major genes. The host resistance response to black sigatoka is under the control of at least three different genes, one major recessive gene bs ₁ and two other independent additive alleles. Diploid and tetraploid plantain hybrids were evaluated for bunch weight, fruit weight, fruit length and fruit circumference. The F₁ euploid hybrids were derived from interspecific crosses between the resistant diploid wild banana Calcutta 4 and the susceptible triploid plantain cultivars Obino l'Ewai and Bobby Tannap. Linear and multiple regression models, coefficients of determination, and Durbin-Watson statistics were used to determine the single and combined effects of the major locus for black sigatoka resistance and ploidy on the different traits in the progenies. Differences in yield were mainly due to changes in weight and girth of fruit, which are affected by black sigatoka disease. The combined effect of ploidy and resistance to black sigatoka was partially responsible for the quantitative trait variation in yield. As a result of the gene interaction in the black sigatoka resistance locus bs ₁, the partially resistant and less susceptible phenotypes showed higher yield than their more susceptible full sibs.     

Interrelations among vegetative,yield and bunch quality traits in short-tem oil palm progenies

Summary Breeders usually obtain information on a large number of traits in their breeding and selection programmes. However, since some or many of these traits could be related, it is desirable to reduce the number being handled to the barest minimum without sacrificing efficiency. Breeders often use correlations, stepwise multiple regressions and path coefficient analyses to determine the nature of relationships among such characteristics. The objective of this study was to use these statistical methods to determine traits that could be useful in predicting number of bunches (NB), fresh fruit bunch yield (FFB) and mean bunch weight (MBW) for 13 backcross progenies of oil palm (Elaeis sp.) grown in four replications with 12 palms per replication. Data were collected over a period of 3 or 11 years, depending on the trait. Progeny means and individual palm data, averaged across replications and years, were used for each of these analyses.Results showed that correlations involving individual palm data were similar to the progeny mean correlations. Five to seven traits accounted for about 70–90% of the variations in the dependent variables. Traits that showed the highest correlations with the dependent variables always accounted for the largest proportion of the variation (r²) in multiple regression models, but did not always have the highest direct effect (i.e. path coefficients) in path analysis of the dependent trait. Number of leaves per palm had the highest correlation (r=0.729) with, and accounted for 53.2% of the variation in NB. Path analysis however showed that percentage fruit per bunch (% F/B) was the most important determinant of NB. It exerted the highest direct effect of 0.537. The highest correlation with FFB involved number of leaves (r=0.660), which, in multiple regression models also accounted for the largest proportion (44.0%) of the variation in FFB. Path analysis showed that percentage mesocarp per fruit gave the highest direct effect (p=–0.974) for this trait. It was concluded that various combinations of number of leaves per palm, sex-ratio, percentage fruit per bunch and percentage mesocarp per fruit would be effective as indirect selection criteria for NB, FFB and MBW in this set of material.     

Crossability between cultivated and wild tuber-and non-tuber-bearing Solanums

The cultivated potato has over 200 extant wild relatives many of which contain genes valuable for disease resistance, hardiness, processing and agronomic traits. Crossability of these wild species directly with the cultivated potato is complicated by several reproductive phenomena such as stylar and ploidy barriers and Endosperm Balance Numbers (EBN). However, a systematic analysis of crossability with many of these wild relatives has never fully been examined. Reciprocal crosses were made between cultivated potato and over 400 wild potato accessions; stylar barriers and 2n gamete production were examined as was the fertility of many of the putative hybrids. Generally, the seed/fruit ratio increased the more closely related the species were to the cultivated potato. However, a few crosses were successful in spite of predicted failure due to ploidy or EBN differences. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phenotypic diversity and relationships of fruit quality traits in peach and nectarine [<Emphasis Type="Italic">Prunus persica</Emphasis> (L.) Batsch] breeding progenies

Agronomic and fruit quality traits were evaluated and compared for three consecutive years on 1,111 seedlings coming from 15 peach and nectarine breeding crosses, grown under a Mediterranean climate. Significant differences among and within the different progenies were found for most of the traits analyzed. The breeding population segregated for several Mendelian characters such as peach or nectarine fruit, round or flat fruit, yellow or white flesh and freestone or clingstone. In addition, aborting fruit and flat fruit trees were found in our progeny, and our data seem to support multi-allelic control of both flat shape and aborting fruit. The variation within the progenies of some traits such as blooming and harvesting date, yield, fruit weight and SSC was continuous, suggesting a polygenic inheritance. Relationships between qualitative pomological traits and these agronomic and fruit quality parameters were also found. Valuable correlations among agronomic and fruit quality parameters were found, although coefficients of variation depending on the progeny should be considered. In addition, principal component analysis (PCA) revealed several relationships among quality traits in the evaluated progenies. Based on this evaluation, 26 outstanding genotypes were pre-selected from the initial breeding population for further studies.     

Diallel study of open-pollinated maize varieties in Trinidad

Summary In Trinidad, maize (Zea mays L.) is primarily harvested in the immature stage as green ears for human consumption. The purchase of popular imported hybrid seed has become a substantial component of the economic inputs of maize production. The objectives of this study were to investigate combining abilities and heterotic patterns among available open-pollinated varieties and to assess correlations among five important traits: time to silking, plant height, grain yield, ear size, and marketable ears per hectare. General combining ability was significant for all traits. Specific combining ability was significant for all traits except ear size. Three intervarietal crosses showed moderate levels of heterosis (10–27%), and several yielded similarly to the control hybrids, Pioneer X304 and Pioneer 3078. The cross Acid Soil Tolerant 1991 SA-3 X ICTA Farm Corn was selected as the most suitable base population for mass selection. Phenotypic and genotypic correlations among the five traits studied were all positive and significant. Populations which flowered early were shorter and yielded less than the late flowering and taller populations and population crosses included in this study.     

Candidate traits for index selection in choice of oil palm ortets for clonal propagation

Summary The objective of the study was to examine the usefulness of: principal component scores (PC), factor analysis cum stepwise regression identified traits (FASR) and selected traits based on their higher heritabilities and genetic correlations to the objective traits (HGC); as selection traits in a desired gains selection index (Yamada et al., 1975) to improve objective traits (oil yield, kernel oil yield, height increment, bunch index and leaf area ratio) as compared to those based on all the observed traits (AO); in selecting oil palm ortets for cloning.Based on the required selection intensities (i^*) to achieve the desired gains AO indices having smaller i^*'s were most efficient followed by PC, HGC and FASR indices. Expected selection response (1/i^*), however, is expected to increase with additional selection traits. As such HGC (bunch number, kernel to fruit and mesocarp to fruit) and FASR (mesocarp to fruit, fresh fruit bunch yield, fruit to bunch and average bunch weight) indices would be useful as they achieved expected selection responses close to AO indices with a small number of traits and would also minimise the contribution of highly correlated traits to sampling errors. The results also suggested considering selection indices for only two objective traits-oid yield and kernel oil yield-instead of all five objective traits in which case screening of impracticably large populations is needed to obtain desired genetic gains.     

Polyploidy and sexual polyploidization in the genus Vaccinium

Genus Vaccinium,consisting of blueberries, cranberries, lingonberries and many related wild species, includes diploid, tetraploid, and hexaploid species. Most evidence indicates that the tetraploid species are autotetraploids, with non-preferential bivalent chromosome pairing. Although homoploid interspecific crosses usually produce numerous fertile hybrids if the parents are from the same section of the genus, inter sectional crosses at the diploid level normally produce no seedlings, weak seedlings, or seedlings that are very low in fertility. There is a strong but not complete triploid block within Vaccinium. Even with insections, tetraploid × diploid (and the reciprocal) crosses normally give only a few tetraploid and a few triploid hybrids. Hexaploid × diploid crosses within sections are very hard to make, and the few hybrids that have been obtained are pentaploid. The frequency of 2n gametes varies,both among genotypes within species and among species. Vaccinium pollen is normally shed in tetrads, and the frequency of large pollen grains shed in dyads can be used to estimate 2n gamete frequency. Cultivated blueberries occur at both the tetraploid and the hexaploid levels, and there are important genetic resources in the diploids. Unreduced gamete production has permitted transfer of genetic material from the diploid to the tetraploid level and from the diploids and tetraploids to the hexaploid level via triploid hybrids. Intersectional crosses can occasionally produce tetraploid Vaccinium hybrids that appear to behave as amphidiploids and have medium to high fertility. CommercialVaccinium cultivars are normally propagated by cuttings. Intersectional hybridization, chromosome doubling, and asexual propagation could permit the production of novel hybrid combinations with value as ornamentals or in fruit production. This revised version was published online in July 2006 with corrections to the Cover Date.     

Phenotypic,genotypic and environmental correlation in tomato (Lycopersicon esculentum)

Summary Twelve inbred lines of tomato and their 132 hybrids (reciprocals were considered separately) were studied in four environments: glasshouse and open air, with and without plastic cover. Nine characters were recorded and the phenotypic and environmental correlations between them were obtained within environments and for the complete set of data. Characters showing the highest phenotypic correlation with yield were fruits per cluster and earliness in harvesting, but neither of them is useful for indirect selection for yield. To the contrary, leaves between racemes can be used when selecting for fruits per cluster. Environmental correlations were generally low, excepting total yield in fruits per cluster.Broad sense heritabilities were obtained, which were rather high for fruit weight, locules per fruit, fruits per cluster and leaves between clusters. Some cases in which phenotypic correlations were rather constant for the different environments in spite of the great differences recorded for the genotypic correlation coefficients, are explained because of the great weight (i.e., considering heritabilities) of environmental correlations on phenotypic correlations.     

Overcoming hybridization barriers in potato

The cultivated potato is a major crop worldwide. It is a high input crop with complex quality requirements at harvest and during storage. Potato breeders are fortunate to have access to a very diverse and accessible germplasm resource. Wild Solanum relatives provide genetic diversity as well as genes for valuable production and quality traits. In most cases, crossing success can be predicted based on endosperm balance number (EBN), or effective ploidy, of the parents. Crossing barriers between most wild species and the cultivated potato are the consequence of differences in EBN and can be easily overcome using ploidy manipulations and bridge crosses. The most common ploidy manipulations include haploid extraction to reduce EBN and 2n gamete production to increase EBN. Additional methods to produce fertile interspecific hybrids include mentor pollination, embryo rescue, hormone treatments, reciprocal crosses, selection of cross‐compatible genotypes and somatic fusion. Knowledge of crossing barriers and mechanisms to overcome them allows potato breeders access to the rich gene pool in the genus Solanum.     

Effects of Inbreeding and Genetic Variation on Forage Quality Traits and Dry Matter Yield in Dactylis glomerata L. Subspecies

Cultivated 4× clones, 2× germplasm and their respective S; progeny were utilized in this study. Dry matter yield and forage quality data (in vitro dry matter disappearance, cell wall constituents, total nitrogen) were obtained on composited vegetative plant material harvested during four successive 4-week growth periods in the greenhouse. There was no detectable average inbreeding effect for any of the traits. The group mean of the diploids was significantly lower for in vitro dry matter disappearance than the tetraploid group mean. However, two out of six diploid 51 families exceeded the highest tetraploid family for this trait. The diploids had significantly higher cell wall constituents than tetraploids except for acid detergent lignin. There was more variation for any trait at the diploid level than at the tetraploid level among S₁ families as well as within families. Dry matter yield and total nitrogen were significantly correlated in diploids and in tetraploids. However, little variation was detected lot total nitrogen at either ploidy level. The results suggest that selection for improved quality in progeny from interploidy crosses may be more efficient by first selecting at the diploid level followed by scaling to the tetraploid level, rather than selection at the tetraploid level after hybridization.     

Leaf stomatal conductance and stomatal morphology of Musa germplasm

Drought tolerance combined with resistance to black sigatoka (BS) disease are two desirable traits for plantains in some parts of the tropics. Field evaluation of leaf stomatal conductance, single leaf transpiration rate, photochemical efficiency, and role of stomata in BS resistance, was done for 18 genotypes of Musa spp., which included diploid and triploid banana and plantains and tetraploid plantain hybrids, at a sub-humid and a humid site. Conductances were significantly (P ≤ 0.01) higher for leaf abaxial than adaxial surfaces (S), while clonal (C) differences were significant (P ≤ 0.05). Interactions between sampling period (T: morning vs afternoon) and location (L), and clone and location (C × L) were significant for both conductance and transpiration; (C × T × L) interaction was significant for conductance. Significant interactions for (C × L) and (C × T) suggested that conductance and transpiration of a specific clone need to be considered for a given environment. Total variation in conductance was explained by the following variables: S, C, (C × L), (C × T), and (C × L × T). In general, ABB cooking banana had higher conductances than other Musa taxonomic groups (AAB, AA, AAA, and AAAB). Evaluation of morphological and physiological traits of leaf stomata indicated that the resistance to BS disease is due to non-stomatal mechanisms. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of ploidy on stomatal and other quantitative traits in plantain and banana hybrids

Summary Ploidy polymorphism occurs in the hybrid offspring derived from interspecific crosses between triploid plantains (Musa spp. AAB group) and diploid bananas (M. acuminata). Therefore,Musa breeders are interested in the determination of ploidy and its effects on phenotypic expression of quantitative traits. The aim of this research was to examine the reliability of stomatal and other phenotypic traits to determine ploidy in segregating plantainbanana hybrid families. Stomatal density and size were significantly correlated (P<0.01) with ploidy, although the correlation coefficients were not high (r=–0.49 and r=0.47, for stomatal density and size, respectively). High density of small stomata was correlated with low ploidy level, and vice versa. However, stomatal size and density were also influenced by a significant genotype effect (P<0.001) within the same ploidy level. Ploidy had an important effect on fruit traits and plant height in the hybrids of Obino l'Ewai×Calcutta 4, but this was not so clear in Bobby Tannap×Calcutta 4 hybrids. Obino l'Ewai derived tetraploids have medium to tall plants with large bunches and big fruits. Most of the tetraploids derived from Bobby Tannap have short stature due to the gene action of the dwarf,dw, allele. Also, a few selected diploids derived from Bobby Tannap outyielded their non-selected tetraploid full-sibs. In conclusion, chromosoem counting remains the only accurate proof of ploidy levels inMusa germplasm.     

Analysis of parental effects on mean vine maturity and chip colour of 4x.2x potato progenies

Summary The parental effects on progenies from potato 4x.2x(FDR) crosses were analyzed to determine anether and to what extent selection criteria used for selecting tetraploid breeding lines have to be adjusted when selecting diploid breeding lines. For vine maturity and chip colour multiple regression analysis of progeny means on means of diploid and tetraploid parents revealed high coefficients of determination (R²) for both characters, indicating good predicting power of the performance of both diploid and tetraploid parents on the performance of their 4x.2x progenies. For vine maturity the multiple regression slope for the tetraploid perents was significantly larger than for the diploid parents, and progeny means were towards the tetraploid parents. This indicates that selection criteria for vine maturity may be less stringent at the diploid level. However, diploids may be earlier maturing than tetraploids and therefore selection criteria can better be similar at both ploidy levels. For chip colour, multiple regression slopes for diploid and tetraploid parents were similar and progeny means were towards the darkest coloured parent irrespective of its ploidy level. This indicates that selection of breeding lines for chip colour can be conducted similarly at both ploidy levels.     

Interspecific hybridization in <Emphasis Type="Italic">Sarcococca</Emphasis> supported by analysis of ploidy level,genome size and genetic relationships

Knowledge of ploidy level differences, genome size and genetic relationships between species facilitates interspecific hybridization in ornamentals. For Sarcococca (Buxaceae) only limited (cyto)genetic information is available. The aim of this study was to determine the genome size and chromosome number and to unravel the genetic relationships of a breeder’s collection using AFLP marker analysis. Based on these results, interspecific crosses were made and the efficiency and hybrid status was verified. Two groups of diploid plants (2n = 2x = 24) were observed, with either a genome size of 4.11–4.20 or 7.25–9.63 pg/2C. All the tetraploid genotypes (2n = 4x = 48) had genome sizes ranging from 7.91 to 8.18 pg/2C. In crosses between parents with equal ploidy level and genome size a higher crossing efficiency (on average 58% of the hybridizations resulting in fruits) and more true hybrids (on average 96% of the offspring) were obtained compared to crosses between plants with different genome size and ploidy level (on average 23% fruits and 24% hybrids, respectively). In none of the cross combinations, the ploidy level or genome size was found to be a complete hybridization barrier, although unilateral incongruity was found in some cross combinations. Distant genetic relationships did not hamper the hybridization within Sarcococca genotypes. Our findings will contribute to a more efficient breeding program and a faster achievement of hybrids with an added value.     

Carbon Isotope Discrimination and Grain Yield Variations among Tetraploid Wheat Species Cultivated under Contrasting Precipitation Regimes

Nineteen accessions belonging to six tetraploid wheat species were evaluated and compared for carbon isotope discrimination and grain yield during two successive cropping seasons (1995 and 1996) under Mediterranean rainfed conditions. The two seasons differed markedly in precipitation regime. A wide variation for the measured traits was observed among the 19 accessions for carbon isotope discrimination and grain yield in both years. Significant differences were also noted between species accessions for Δ and grain yield. In both years, Triticum timopheevi (AG genome) showed lower Δ values than the other tetraploid species (all carrying the AB genome). Positive correlations were observed between Δ and grain yield in both years. The use of carbon isotope discrimination as an indirect selection criterion for yield under stress and the potential benefits of some alien tetraploid species in improving drought tolerance in durum wheat are discussed.     

Effects of divergent selection on correlations between morphological traits in white clover (Trifolium repens L.)

The effects of two generations of divergent selection for stolon diameter and stolon amount on the pattern of phenotypic correlations between important agronomic traits in white clover (Trifolium repens L.) were studied. The effects of selection were: the proportions of the variances of traits under direct selection were considerably lower within selection lines than overall and this was associated with a loss of correlation between traits. Unselected traits showed higher proportions of variances remaining within the selection lines and shifts from non-significant to significant correlations from the plants overall to selection lines. The significance of these results and their relevance to strategies of germplasm improvement is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Breaking the crossability barriers between disomic tetraploid Solanum acaule and tetrasomic tetraploid S. tuberosum

Summary A combination of compatible second pollinations and embryo rescue was applied for systematic production of true tetraploid hybrids from crosses between disomic tetraploid Solanum acaule and tetrasomic tetraploid potato, S. tuberosum. Several genotypes of tetraploid potatoes were pollinated with S. acaule, and the compatible second pollinations were made on the following day, with a genotype of S. phureja, IvP 35 to promote fruit development. Embryo rescue was carried out in 21 families, 14 to 27 days after the first pollination. A total of eight plants were obtained from the embryo rescue and their chromosome numbers were counted in the root tips. Three of the eight plants were identified as tetraploid, and five others as diploid. Morphology, isozyme banding patterns, and pollen stainability, as well as potato spindle tuber viroid (PSTVd) resistance, indicated the hybrid nature of the three plants. This is the first report of successful tetraploid hybrid production between disomic tetraploid S. acaule (4x) and tetrasomic tetraploid potatoes. Seed set from the crosses between one of hybrids and diploid potatoes indicated workable levels of both male and female fertility for introgression of valuable genes from S. acaule into the cultivated potato gene pool. The methodology used may be applied to other disomic tetraploid tuber-bearing Solanum species and with some modifications also to distantly related solanaceous species and genera.     

Silage yield and quality traits in elite maize hybrids and their relationship to elemental concentrations in juvenile plants

European silage maize is cultivated for animal feed and biogas production. We evaluated 210 factorial crosses of elite dent and flint lines in multilocation trials for agronomic and quality traits together with biomass and shoot concentrations of 10 elements in juvenile plants. Significant genotypic variances, mainly due to general combining ability variance of the dent lines, and high heritabilities were observed for dry matter yield (DMY) and quality traits. DMY was not correlated with quality traits, but methane fermentation yield (MFY) and metabolizable energy content (MEC) showed significant correlations with starch and fibre content. Concentrations of elements N,P,S,K were positively correlated with each other but only in few cases correlated with DMY and quality traits. Parent lines with contrasting P concentrations differed in root morphology traits. Results support DMY as primary trait for selection of silage maize hybrids, but MFY is of negligible importance in breeding for biogas contrary to MEC for animal feed. Neither biomass nor elemental composition of juvenile plants were of predictive value for final DMY or quality traits.