Estimates of genetic variability and heritability for vegetative and reproductive characters of kiwifruit (Actinidia deliciosa)

The results of this study indicated a great deal of genetic variation in a number of characters of horticultural interest in kiwifruit seedling populations, and therefore, a potential to improve kiwifruit by vine selection. High narrow sense heritability was shown for pedicel length(0.62) and flowering duration (0.50) in male vines, and pedicel length (0.67),floral shoot percentage (0.54), leaf length-width ratio (0.64), fruit elongation (0.64) and fruit weight (0.52) in female vines. For these traits, selection of superior seedlings should lead to rapid genetic improvement in these populations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Sex modification in Actinidia deliciosa var. deliciosa

Summary The aim of the trial was to determine whether growth regulators and injuries could affect sex expression in the cultivated kiwifruit. Growth substances (NAA, BAP, GA, ethephon, ABA, TIBA, and CCC) were applied at 1% concentration in lanolin (w/w) to shoots of 17-year old plants of the staminate clone Matua and the pistillate clone Hayward. Injuries consisted in shoot defoliation or removal of a ring of phloematic tissue from the laterals. Both the application of growth regulators and injuries were done about 5 weeks before anthesis. In the pistillate clone, no treatment resulted in overcoming pollen grain sterility; ABA and GA mereased the stigma-style number as well as the density of papillae on the stigma surface. A positive correlation was found between stigma-style number and pedicel length (r=0.660). In the staminate clone, pollen grain viability was significantly altered by treatment; the highest (79.2%) and lowest (10.3%) values were recorded for ABA and GA, respectively. A negative correlation was found between pollen grain viability and pedicel length (r=–0.648). As a general rule, treatments which depressed pollen grain viability allowed the development of a variable number of styles. About 20 styles were consistently produced when GA was applied; the gibberellin-caused feminization of kiwifruit was confirmed in a repeated trial. The data collected also suggest that sex expression can be slightly changed by injuries; contrariwise, rather good results can be achieved by using a growth regulator earlier in the season or before flower initiation.     

Variability and inheritance of flowering time and duration in Actinidia chinensis (kiwifruit)

We investigated the variability and inheritance of flowering in a seedling population of diploid Actinidia chinensis Planch. We found considerable variation in time to reach 50% flowering (D50) and flowering duration (FD). D50 was highly heritable (h ² > 0.85) suggesting that this trait would respond well to selection in this population, whereas FD was greatly affected by the environment (h ² < 0.20). The results also showed that the flowering times of male vines were more sensitive to the environment than those of female vines. However, significant specific combining ability (SCA) effects could be achieved by targeting specific bi-parental combinations for breeding and selection of flowering time. The diversity in flowering traits among males will facilitate the selection of male pollinizers that coincide in flowering time with present or future female cultivars. The possibility of breeding female cultivars with a short flowering period to improve the consistency of fruit maturity at harvest is discussed.     

Inheritance of taste characters and fruit size and number in a diploid Actinidia chinensis (kiwifruit) population

We investigated the variability and inheritance of taste components and fruit size and number in a seedling population of diploid Actinidia chinensisPlanch. We found significant variation in all characters measured. Narrow-sense heritability estimates were high for vitamin C content, titratable acidity (TA), soluble solids content (SSC), fruit weight and dry matter content (DM), but low for glucose content, quinic acid content, and fruit number per vine. The genetic correlations between sugars (except myo-inositol), acids (except quinic acid), TA, vitamin C content, SSC and DM tended to be positive and moderate to high. However, correlations between these characters and fruit weight tended to be negative and moderate to high. The standardised coefficients () of multiple regression showed that SSC was highly dependent on the levels of fructose content, sucrose content and TA. Estimates of relative selection efficiencies (E) suggested that selection using SSC could be an efficient and convenient alternative to direct selection for improvement of sugar levels in kiwifruit. However, selection strategies based on SSC need to take account of its moderate negative correlation with fruit weight. Male and female parents useful for improving acid and sugar composition and fruit size were identified. One family was outstanding, as it combined large fruit size with high levels of SSC and DM.     

Fruit and vegetative characteristics of endosperm-derived kiwifruit (Actinidia chinensis F) plants

Summary Four hundred and thirty-eight endosperm-derived plants of kiwifruit (Actinidia chinensis) were observed. The plants were field planted in 1982 and all had flowered annually since 1986. A sample of these plants was assessed for leaf morphology, growth characteristics, flowering, sex expression, chromosome number, and fruit quality characteristics. The chromosome number of the endosperm plants varied from 58 to 146; most were aneuploid. A few triploid plants (2n=3x=87) were obtained; none of these were parthenocarpic. Segregation of sex expression was observed in progeny from one endosperm-derived callus.     

Arabinogalactan proteins may facilitate the movement of pollen tubes from the stigma to the ovules in Actinidia deliciosa and Amaranthus hypochondriacus

Sexual plant reproduction is a complex process that involves a series of interactions between the male gametophyte and the different cell types of the pistil. These interactions are believed to direct the pollen tube growth until its final target, the embryo sac. Arabinogalactan proteins are complex proteoglycans that are believed to be involved in these processes. The pistil is enriched in these highly glycosylated proteins and we provide results that show the selective presence of different AGP epitopes at the surface of the cells or in the ECM of the tissues that correspond exactly to the pollen tube growth pathway in Amaranthus hypochondriacus and Actinidia deliciosa. We also show that in Actinidia deliciosa, which is a dioecious plant with the male flowers having rudimentary ovaries where fertilization does not occur, there is no presence at all of the epitopes recognised by the monoclonal antibodies utilized in this study. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic relationship of Mediterranean mandarins (Citrus deliciosa Tenore) using RAPD markers

Summary Random amplified polymorphic DNA (RAPD) analysis was carried out to evaluate polymorphism and genetic similarity between 39 Mediterranean mandarin genotypes. One hundred eleven amplification products were identified using 21 random primers. An average of 2.2 RAPD markers was obtained for each primer, corresponding to 42% of the amplification products. Genotype-specific RAPD markers were also found, mainly in known hybrids. UPGMA cluster analysis revealed the low level of genetic variation between accessions of Mediterranean mandarins, whereas their hybrids with other Citrus species showed greater genetic dissimilarity. Twenty accessions yielded very similar patterns, suggesting either that they could be a single clone, or that the technique was not able to detect genomic variation. However, for the other specimens genetic polymorphism can easily be detected by RAPD, although the genetic variation between accessions was quite low. The large number of hybrids and the low polymorphism between accessions support the hypothesis that Mediterranean mandarins are all true hybrid of Common mandarins (Citrus reticulata Blanco).     

Family selection in plant breeding

Summary Plant breeding programmes rarely take explicit practical account of the two sources of genetic variance, namely between and within full-sib families, even though existence of these two sources of variation has long been recognised. This paper refers to inbred and clonal crops, not to outbred, seed-propagated species. Theory suggests that the two variances should be of similar size, sometimes very similar. Good comparisons have never been made because variance within families is laborious to estimate. It is proposed that sets of families be assayed as to means in formal trials and only the best few, judged against standards as having potential for superior segregates, should be exploited thoroughly. The calculation as to approximate equality of genetic variances between and within families is important. The vast majority of families should probably be discarded without further ado, and at considerable economy. Sensible decision-making requires an economic component in order to exploit the trade-off between the cost of the initial trial and families discarded without further cost. The object of this paper is a critical review of practical principles, not a general review of a large and diffuse literature.     

Correlations within and between characters between and within generations as a measure for the early generation selection in potato breeding

Summary The main objective was to determine the reliability of selection in early generations of a potato breeding programme. To that end data were recorded in the seedling generation, an early and a late harvested experiment of the first clonal generation and the late harvested second clonal generation on up to 30 genotypes of 55 populations from crosses of three Solanum tuberosum ssp. tuberosum cultivars and seven selected S. tuberosum ssp. andigena clones, adapted to the northern temperate zone. Phenotypic correlations were computed per population in almost all possible combinations within and between characters between and within generations. The mean across 55 comparable correlation coefficients was considered to be the best estimate of the relationship concerned.In all four experiments data were collected on number of tubers, tuber yield and mean tuber weight; in the three experiments of the two clonal generations in addition on date of emergence, number of stems, plant height, haulm type, and general impression of the underground plant parts and in the two late harvested clonal generations on date of maturity and under water weight.The results confirmed that general impression which is largely decisive for the selection in early generations, is a little reliable measure. However, from the magnitude of the mean correlations between experiments within characters it must be concluded that selection for most of these separate characters is hardly more reliable. An exception was date of maturity for which a mean correlation was determined of r=0.78 between the two clonal generations. The second strongest mean correlations, perhaps surprisingly, were for tuber yield, viz. r=0.52 between the seedling generation and the late harvested first as well as the second clonal generation and r=0.63 between the late harvested clonal generations. From the correlations between characters it appeared that for a high tuber yield, besides its components, in particular an early emergence, a large plant height, an attractive haulm type and a late maturity are of importance.The main conclusion is that, as long as not enough seed tubers are available for the layout of statistically sound experiments, a negative instead of a positive selection should be applied to avoid the rejection of most of the valuable genotypes in an early stage. On the basis of the results directives for the application of such a negative selection are given.     

Possibilities of selection for keeping quality in tulip breeding

Summary The vase-life in tulip (Tulipa L.) is an important character. Research was done on the possibilities of selecting for keeping quality. It was found that the keeping quality of undetached flowers was strongly correlated with the keeping quality of cut flowers at 17°C in a glasshouse. The period from flowering date till 50% discoloration appeared to be highly correlated with days to perianth drop. For practical reasons the latter trait has preference in selection work. The number of days to discoloration is also an effective selection criterion. Flower longevity in the field in April/May and in the glasshouse were significantly correlated; thus, already in the field a first selection on keeping quality can be carried out. The increase in height for flowering (adult) and non-flowering (juvenile) plants during forcing did not appear to be significantly correlated with flower longevity, so preselection on this character is not promising. Flower longevity was positively correlated with forcing period. This poses some problems in selection, as a long forcing period is considered an undesirable character. The daily water uptake of cut flowers was significantly correlated with flower longevity.     

Recurrent phenotypic selection for forage yield in rye

Summary Cultivars of Cucurbita pepo and other Cucurbita species were characterized by RFLP analysis using different fragments of the ribosomal intergenic spacer (IGS) of Cucurbita pepo as hybridization probes. Several cultivars could be distinguished by a specific rDNA restriction pattern, whereas some cultivars showed an identical RFLP pattern suggesting a closer relationship. Other species of the genus Cucurbita exhibited strong cross-reaction with the C. pepo spacer probes, in contrast to DNA of Cucumis species which did not cross-hybridize.Abbreviations IGS intergenic spacer - ITS internal transcribed spacer - kbp kilo base pairs - rDNA ribosomal DNA - RFLP restriction fragment length polymorphism - rRNA ribosomal RNA     

Preliminary results of using in vitro axillary and adventitious buds in mutation breeding of Chinese gooseberry

Summary Aseptically cultured shoots of Chinese gooseberry exhibited growth disorder and morphological aberrances, and some died after being exposed to sufficient gamma-ray irradiation. The death rate was dose dependant and the LD₅₀ was 80–90 Gy and 50–60 Gy respectively for cv. Hayward and clone 4. All petiole explants irradiated with gamma-ray could form calli as the control, but the rate of differentiation of adventitious shoots of the petiole explants decreased and was dependant on dose. Sensitivity of the shoot or petiole explants to gamma-ray irradiation varied with species. Gamma-ray irradiation did not deter either the 2-node segments from producing axillary shoots M₁, M₂, and M₃ or the advantitious shoots originating in the petiole explants and the M₃ shoots from forming advantitious roots. Therefore, using aseptically cultured axillary or adventitious buds for mutation breeding of Chinese gooseberry is feasible. A bacterium surviving in the explants lessened the efficiency of these two in vitro techniques in mutation breeding of Chinese gooseberry.Abbreviations IAA 3-indole acetic acid - IBA -indole butyric acid - MS Murashige & Skoog (1962)     

Cytometric and morphometric identification of diploid, tetraploid and pentaploid plants derived from Actinidia arguta (2n = 4x) crossed with A. deliciosa (2n = 6x)

Interspecific crosses between Actinidia arguta (In = 4x) and A. deliciosa (2n = 6x) were carried out in order to transfer cold resistance from a wild to the cultivated kiwifruit species. Of the 65 progenies obtained and analysed by flow cytometry, 16 were diploid, one was tetraploid and 48 were, as expected, pentaploid. Morphologically, the diploids can be distinguished from the pentaploids by their longer lamina. The existence of 5x progenies confirms the existence of gene flow between A. arguta and A. deliciosa, whereas the existence of 2x and 4x progenies provides evidence for parthenogenesis within the Actinidia genus following an interspecific cross. The study demonstrates the utility of flow cytometry for genomic analysis of progenies derived from interspecific crosses. Possible uses of both sexual and parthenogenetic progenies in the breeding and genetics of kiwifruit are discussed.     

Screening RAPD primers for molecular taxonomy and cultivar fingerprinting in the genus Actinidia

Summary Eighty ten-base long arbitrary primers were tested for PCR-based DNA amplification of three species of the genus Actinidia (A. deliciosa the kiwifruit, A. chinensis, and A. kolomikta), with the aim of screening species-specific and genotype-specific markers.Of the 80 primers tested, 30 gave an average of 3.5 bands which were monomorphic within one or two species and absent in the remaining one(s), thus resulting in useful markers for taxonomic and phylogenetic purposes. None of the primers tested produced bands linked to sex. Twenty primers out of the twenty-five selected from a preliminary screening showed high levels of polymorphism, producing two to eleven patterns each from the 13 kiwifruit cultivars examined.We found the Stoffel fragment and the Taq polymerase were both suitable for RAPD analysis, the most noticeable difference being the smaller size of fragments (0.4–1.2 kb) produced by the former in comparison to the latter (1.0–3.4 kb). We tested also three different annealing temperatures (35, 37, and 39° C) and found the intermediate one best for number of amplified bands and reproducibility of results.Abbreviations 2-BE 2-butoxyethanol - CTAB hexadecyltrimethylammonium bromide - MAS Marker-Assisted-Selection - PCR Polymerase Chain Reaction - RAPD Random Amplified Polymorphic DNA - RFLPs Restriction Fragment Length Polymorphisms     

Environment of selection and type of germplasm in barley breeding for low-yielding conditions

Summary Thee groups consisting of 332, 243 and 280 barley breeding lines (entries) of known selection history were evaluated in 10, 9 and 8 environments, respectively, to determine the relationship between grain yield in low yielding (LYE) or high yielding (HYE) environment, and selection history and type of germplasm. One cycle of selection in LYE produced on average five times more entries outyielding the best check in LYE than selection in HYE. A retrospective analysis indicated that the highest yielding lines in LYE were lower yielding (15%–28%) in HYE when compared with the best check, and by 20% and 38% compared with the best entries in HYE. In contrast, the highest yielding lines in HYE were lower yielding (4%–33%) in LYE when compared with the best check, and by 33% and 40% when compared with the best entries in LYE. The highest yielding lines in LYE did not differ consistently from the highest yielding lines in HYE for a number of morphological and developmental traits including days to heading. This suggests there are many paths to high yield in LYE and that analytical breeding based on individual traits may not be appropriate for variable environments. Only 0.07% of the highest yielding entries in LYE was selected for high yield in HYE conditions confirming previous results indicating that selection for high yield in HYE is an inefficient strategy for improving yield in low yielding conditions. This frequency is 28 times lower than the frequency of high yielding entries in LYE selected from landraces or crosses with landraces in low yielding conditions. The results imply that the most cost-effective strategy for barley breeding in low yielding conditions is to select repeatedly in low yielding conditions and to include adapted germplasm (landraces) in the breeding material.     

Sensory evaluation as a selection tool in apple breeding

Several conventional sensory methods were adapted to provide aprocedure that is suitable for screening apple (Malus × domestica) breeding selections for dessert quality. Trained judges were presented with randomized coded samples (apple slices) and asked to rate them on 0 to 9 bipolar hedonic (liking) scales for texture and flavour, and 0 to 9 unipolar intensity scales for skin toughness, crispness, hardness, juiciness, aroma, sweetness and sourness. Appearance liking was rated on coded samples of five whole apples, using the 0 to 9 hedonic scale. A minimum panel size of eleven judges was generally sufficient to obtain statistical discrimination of one point on the 0 to 9 scales. Panel mean scores for breeding selections relative to standards have been consistent from panel to panel and year to year. A subset of selections and cultivars was rated for appearance and taste by consumers in blind taste tests. In-house panel findings were comparable to consumer ratings for taste and appearance liking, with a few exceptions in appearance. Panel mean scores for texture and flavour liking were regressed on texture and flavour components. Crispness accounted for about 90% of the variation in texture liking. Juiciness, aroma, sweetness and sourness were all important to flavour liking, but their relative importance changed from year to year and in total accounted for only about 60% of variation in flavour liking. Perceived sweetness and sourness were better predictors of liking than analytical measurements of soluble solids and titratable acidity. Formal sensory evaluation can be used successfully for screening breeding selections, and may provide more reliable data than the opinions of only one or two people.     

Usefulness of the grid system in phenotypic selection for smooth bromegrass fiber concentration

Summary Grid selection was investigated as a means of reducing environmental variation prior to selection for low neutral detergent fiber (NDF) concentration in smooth bromegrass (Bromus inermis Leyss.). Eleven populations of 350 plants each were arranged into 10 grids of 35 plants each. Adjustment of NDF concentration by block means and standard deviations reduced the phenotypic variation to 50 to 94% of the original variance. Adjustment also reduced or eliminated spatial patterns of phenotypic variation in five of eight populations with significant patterns to original NDF values. Selection for low NDF tended to identify plants from blocks with a low mean NDF in some populations. When selection was based on t-scores, the number of plants representing each block was a random variable in each population. Use of grid selection with a t-score adjustment should increase the efficiency of phenotypic recurrent selection for low NDF concentration.     

Repetitive cycling and simple recurrent selection in traditional barley breeding programs

Summary A critical examination of three representative barley development programs from three barley producing areas of the world reveals that the evolution of each can be explained by the concepts of simple or phenotypic recurrent selection. Typically, each has utilized only 13 to 16 separate genetic sources in their program. Most of the sources were introduced over 50 years ago and have been progressively recombined through a simple recurrent selection process. The time period required for selection, testing, and reincorporation of improved genetic recombinants into the breeding program, or the completion of a cycle of recurrent selection, ranged from 6.5 to 10.5 years. If the major operative force in barley breeding is recurrent selection, then additional attention should be given to increasing the genetic base and reducing the time required to complete cycles of selection.     

Component analysis of plant dry matter production: a basis for selection of breeding parents as illustrated in carnation

Summary Improvement of dry matter production in the vegetative phase is a breeding objective in many crops, especially where whole plants or parts of plants in the vegetative phase constitute the commercial product. Dry matter production is a complex process and plant dry weight, as measured at a given date, is a complex character, of which initial weight of planting material and mean relative growth rate over the period of growth are the major components.The primary objective of the present paper is to demonstrate how a method of component analysis proposed by Sparnaaij and Bos can be used to facilitate breeding for a high rate of vegetative growth. The procedure is illustrated by data from a study of variation in forcing ability among 13 carnation cultivars. It involves a detailed analysis of mean relative growth rate over the period of vegetative growth, including components derived from observations on net rate of photosynthesis and dark respiration.It is shown how component analysis can be used (a) to quantify the relative contribution of initial plant weight and of mean relative growth rate and its components to the genetic variation in plant dry weight, thus allowing a judicious choice of selection criteria for breeding parents, and (b) to predict mean plant dry weight of F₁ hybrids obtained by crossing these parent genotypes, thus facilitating the choice of crosses to be made.