Pre-selection for juvenile period,flowering and picking time in apple seedlings

The length of the juvenile period was found to be associated with the degree of juvenility (degree to which seedlings show juvenile symptoms) and with the time leaf buds break in spring. The time of bud break was also related to time of flowering; bud break and juvenility were not interrelated. The observations suggest that preselection on the basis of a low degree of juvenility and early bud break together would substantially increase the proportion of early-bearing and, to a smaller extent, that of early-flowering seedlings in the selected material. The shift towards earlier flowering was not accompanied by an advance of the date at which flowering ended, at least when the selection limit is based on the progeny mean. The degree of leaf fall (colour) during autumn appeared to be closely related to the time the fruits become picking ripe; no significant relation existed between this parameter and juvenility or bud break. The degree or time of leaf fall (colour) is a possible pre-selection criterion of the time of picking.     

A comparison of apple and pear seedlings with reference to the juvenile period I. Seedling growth and yield

Summary Several thousand apple and pear seedlings of many progenies were studied in connection with their juvenile period (J.P.). The initially significant inverse relation between the vigour (stem diameter) and the J.P. of the seedlings became insignificant as the trees grew older, due to a retardation of growth occurring when the seedlings become generative. This relation can be used effectively in pre-selecting for vigour in the nursery. Cumulative yields were higher when the J.P. was shorter, but there was no evident link between the J.P. and annual yield in full bearing, that is to say, precocity and preductivity are not directly connected. Better growing conditions and pre-selection have shortened the mean progeny J.P. of either crop by three years since the 1950's. Generally, the pear seedlings appear to grow faster, to become generative slower and to yield lower than comparable apple seedlings. The mean J.P. of apple and pear progenies averaged 4.2 and 6.0 years respectively. The difference between apple and pear may be attributable to a greater selection pressure on both precocity and productivity with apple than with pear.This possibly also led to a smaller tree in the productive phase on the assumption that tree size at first flowering-small at a short, large at a long J.P.-expresses reproductive efficiency and as such is reflected in the size of the adult tree.Also presented at the Juvenility Symposium held at West-Berlin, November 1976.     

Juvenile phase and growth of apple and pear seedlings

It was investigated whether and to what extent the duration of the juvenile phase of pear and apple seedlings is related to their vegetative growth. The juvenile phase was defined as the period in years that the seedling remains vegetative; the trunk diameter served as a measure of vegetative vigour. The following observations were made:

1. 1)

   A significant negative correlation exists between the duration of the juvenile phase and the vigour of the seedling (as measured by trunk diameter).

2. 2)

   Environmental conditions with respect to weather, soil and cultural practices which promote or restrict growth, tend to shorten or lengthen the juvenile phase accordingly by their influence on the time required for the attainment of a certain minimum size which at least partly determines the attainment of the flowering condition.

3. 3)

   The weak rootstock M. IX significantly accelerated the onset of flowering of apple seedlings by about 1 1/2 years; this rootstock appears to combine a retarding effect on growth with a specific influence on flowering.

     

Precocity and productivity of propagated apple and pear seedlings as dependent on the juvenile period

Summary Adult apple and pear seedlings varying in juvenile period were propagated on rootstocks. They were subsequently found to be more precocious and more productive when the juvenile period had been shorter. In view of the significant relation between vigour measured by stem diameter) and precocity of both seedlings and propagated trees, it is possible to pre-select for the potentially more precocious seedlings on the basis of vigour.Samenvatting De vruchtbaarheid van vegetatief vermeerderde appel- en peerzaailingen in verband met hun jeugdperiode Reeds vruchtdragende appel- en perezaailingen, waarvan de voormalige jeugdperiode sterk varieerde, werden op onderstam geoculeerd. Het bleek dat de bomen gemiddeld vroeger vruchtbaar en productiever waren naarmate de voormalige jeugdperiode korter was geweest.De al eerder geconstateerde relatie tussen groeikracht en jeugdperiode (kortere jeugdperiode naarmate de bommen dikker zijn), bleek ook na vermeerdering te bestaan, d.w.z. de dikkere bomen bloeiden eerder dan de dunnere. Daar deze samenhang erfelijk bepaald is, biedt dit de mogelijkheid om de potentieel vroeg-vruchtbare zaailingen reeds in het kwekerijstadium op basis van groeikracht te selecteren.     

A comparison of apple and pear seedlings with reference to the juvenile period. II. Mode of inheritance

Summary Analysis of two incomplete half-diallel schemes of crosses, involving 22 apple and 33 pear progenies with 2500 and 5400 seedlings respectively, showed a highly significant GCA and an insignificant SCA variance for the juvenile period (J.P.). This indicates that the inheritance of the J.P. is of an additive nature, a mode of inheritance which is a function of the inheritance of a complex of factors governing growth. The mean J.P. of apple progenies varied between 3.4 and 5.0 years, that of pear progenies between 4.7 and 7.0 years. The implications for breeding are discussed.Also presented at the Juvenility Symposium held at West-Berlin, November 1976.     

Heat stress in crop plants: its nature,impacts and integrated breeding strategies to improve heat tolerance

Increasing severity of high temperature worldwide presents an alarming threat to the humankind. As evident by massive yield losses in various food crops, the escalating adverse impacts of heat stress (HS) are putting the global food as well as nutritional security at great risk. Intrinsically, plants respond to high temperature stress by triggering a cascade of events and adapt by switching on numerous stress‐responsive genes. However, the complex and poorly understood mechanism of heat tolerance (HT), limited access to the precise phenotyping techniques, and above all, the substantial G × E effects offer major bottlenecks to the progress of breeding for improving HT. Therefore, focus should be given to assess the crop diversity, and targeting the adaptive/morpho‐physiological traits while making selections. Equally important is the rapid and precise introgression of the HT‐related gene(s)/QTLs to the heat‐susceptible cultivars to recover the genotypes with enhanced HT. Therefore, the progressive tailoring of the heat‐tolerant genotypes demands a rational integration of molecular breeding, functional genomics and transgenic technologies reinforced with the next‐generation phenomics facilities.     

Hordeum chilense resistance to powdery mildew and its potential use in cereal breeding

Summary Hordeum chilense is a wild barley with high crossability with Triticum, Hordeum and Secale. Its amphiploid with wheat, tritordeum, has potential as a new crop. H. chilense is highly resistant to the powdery mildew diseases of both wheat and barley. Whereas tritordeum is resistant to barley powdery mildew, its reaction to wheat powdery mildew is similar to that of its wheat parent. However H. chilense contributes to a reduced density of mildew colonies. This quantitative resistance of tritordeum is diluted at higher ploidy levels.     

Microbial growth in turbulent suspension and its relation to marine aggregate formation

Microbial growth and respiration responses to seston of differing organic composition revealed two different mechanisms of marine aggregate formation: an almost immediate physicochemical aggregation of fine (<8 μm) particles and a longer-term (48 hrs) production of large, robust aggregates, mediated by bacterial activity. Suspensions of fine Spartina alterniflora fragments and a glacial till from Nova Scotia were used to stimulate bacterial and protozoan growth while maintained in turbulent suspension. Under high (6 to 11 mg·dm⁻³) DOC concentrations bacterial responses were rapid and, after 48 hrs, resulted in large, robust flocculated aggregates. With only the till in suspension, DOC levels were low (<3 mg·dm⁻³) yet the bacterial reponse was still rapid. Initial flocculation due to physical factors was evident in the till-only experiment and was either masked or not important in the high DOC experiments. Bacterial respiration per cell was 2 to 3 times as high under low DOC conditions as under high DOC and initial bacterial attachment to particle surfaces was significantly higher. Significant aggregate formation occurred after 48 hrs and appeared to be due to relict exudates from attached bacteria, in spite of low numbers of attached bacteria at the time of flocculation.     

The breeding values of potato parents for field resistance to late blight measured by whole seedlings

Summary Parents used in a potato breeding programme were intercrossed in a multiple mating scheme. The resulting progenies were assessed for resistance to late blight, using as criteria the size and frequencies of lesions on leaves, on petioles and on stems, and an overall score. Analysis of variance showed that all the statistically significant genetic variation was attributable to general combining ability (GCA) differences. The seven variates were highly correlated.     

The use of honey-bees and bumble-bees in breeding work

Summary 1.The use of honey-bees and bumble-bees in breeding insect-pollinated crops can save a lot of labour. In addition better results are obtained.2.In isolation rooms of 5×3×2 m, being insect-proof compartments of a glass-house, the inter-pollination of groups of plants can be successfully effected by using small bee colonies in hives, but without a queen.3.In small isolation cages of glass of 0.8×0.8×2 m the crossing of two plants or the selfing of individual plants can best be effected by:a.diseased queens of bumble-bees. In addition male bumble-bees orPsithyri species can be used;b.very small queenless colonies of bees on miniature frames in small-sized boxes.4.Particulars of how to recognize the diseased bumble-bee queens and how to capture and treat bumble-bees, and also particulars of the raising of bee colonies of different sizes and their treatment are given.

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Samenvatting 1.Het gebruik van bijen en hommels bij de veredeling van insecten-bloeiers kan veel werk besparen. Bovendien worden betere resultaten verkregen.2.In isolatie-kamers van 5 × 3 × 2 m, gevormd door insecten-vrije afdelingen van een kas, kan de onderlinge bestuiving van groepen planten het best tot stand worden gebracht door kleine, koninginloze bijenvolken in kasten.3.In kleine, glazen isolatie-kastjes van 0,8 × 0,8 × 2 m kan kruising van twee planten of zelfbestuiving van afzonderlijke planten het best geschieden door:a.zieke hommel-koninginnen. Tevens kunnen hommel-darren ofPsithyrus soorten gebruikt worden;b.zeer kleine, koninginloze bijenvolken op miniatuurramen in kastjes van klein formaat.4.Bijzonderheden worden vermeld betreffende het herkennen van zieke hommel-koninginnen en het vangen en behandelen van hommels; verder over het kweken van bijenvolken van verschillende grootte en hun behandeling.

     

Linkage between tolerance to high soil acidity and genetically high protein content in the kernel of wheat,Triticum aestivum L. and its possible use in breeding

Summary The winter wheat variety Atlas 66 has both the characteristics high protein content in the kernel and tolerance to high soil acidity. In a group of 121 F₄ lines, all derived from crosses with Atlas 66, a correlation coefficient of 0.39 was found between the two traits. A comparable group of 49 advanced generation lines, reselected for high protein content behaved similar, with a correlation coefficient of 0.37.The frequency distribution over the different categories of tolerance to soil acidity was tested within F₃ and F₄ populations of each two crosses between an Atlas 66-derived high-protein selection and a HRWW-variety. Both crosses slightly differed in frequency distribution but there were no differences between F₃ and F₄ distribution curves of one cross combination.Samples of varieties were tested, each sample having a phenotypically different protein content. The results indicated that protein content per se did not influence the level of tolerance to soil acidity. So it is concluded that although the two characteristics are genetically different they are linked to a certain extent.Individual regression lines were calculated for separate groups of F₄ selections derived from one cross combination. Two groups deviated from the majority and general pattern in that they showed a negative correlation between high protein and better tolerance. One of them differed significantly. A hypothesis is suggested to explain these exceptions.It is possible to screen lines for tolerance to high soil acidity in order to select within segregating populations for high protein content in the kernel, provided that positive selection is applied and that one of the parents combines both characteristics.     

玉米的玉米芯育苗技术及其间作栽培试验效果

试验的玉米芯育苗技术合理实用,所有肥液处理下的都能增产。其中,3kg过磷酸钙／50kg水肥波浸泡处理玉米芯条件下的育苗移栽,增产最高,可达36．8％,人畜粪水,2．5kg尿素／50水、1．5kg尿素／50水和5kg复合肥／50水肥液浸泡处理条件下的,增产也在20％以上,2kg过磷酸钙／50kg水肥液浸泡的处理增产为16．7％。这些肥液浓度可能是该区玉米芯育苗较合理的处理浓度,但12～15d的浸泡处理时间太短．致使育苗成功率低,恰当的处理时间有待进一步研究确定。     

An induced brachytic mutant of chickpea and its possible use in ideotype breeding

Mutations were induced in chickpea (Cicer arietinum L.) cultivar ‘JG 315’ through treatment of seeds with ethyl methane sulphonate (EMS). One of the mutants, named JGM 1, had brachytic growth (compact growth), characterized by erect growth habit, thick and sturdy stem, short internodal and interleaflet distances and few tertiary and later order branches. It was isolated from M₂ derived from seeds treated with 0.6% EMS for 6 h. Segregation analyses in F₂ progenies of its crosses with normal chickpea genotypes (JG 315, ICC 4929, and ICC 10301) suggested that a single recessive gene controlled brachytic growth in JGM 1. This gene was not allelic to the br gene for brachytic growth in spontaneous brachytic mutant E100YM. Thus, the gene for brachytic growth in JGM 1 was designated br2 and the br gene of E100YM was redesignated br1. Efforts are being made to use JGM 1 in development of a plant type with short internodes and erect growth habit. Such plant type may resist excessive vegetative growth in high input (irrigation and fertility) conditions and accommodate more plants per unit area.     

Molecular assessment of genetic diversity in winter barley and its use in breeding

Summary During the last decades extensive progress has been achieved in winter barley breeding with respect to both, yield and resistance to fungal and viral diseases. This progress is mainly due to the efficient use of the genetic diversity present within high yielding adapted cultivars and – with respect to resistance – to the extensive evaluation of genetic resources followed by genetic analyses and introgression of respective genes by sexual recombination. Detailed knowledge on genetic diversity present on the molecular level regarding specific traits as well as on the whole genome level may enhance barley breeding today by facilitating efficient selection of parental lines and marker assisted selection procedures. In the present paper the state of the art with respect to virus diseases, i.e. Barley mild mosaic virus, Barley yellow mosaic virus, and Barley yellow dwarf virus is briefly reviewed and first results on a project aiming on a genome wide estimation of genetic diversity which in combination with data on yield and additional agronomic traits may facilitate the detection of marker trait associations and a more efficient selection of parental genotypes are presented. By field tests of 49 two-rowed and 64 six-rowed winter barley cultivars the genetic gain in yield for the period 1970–2003 was estimated at 54.6 kg ha⁻¹ year⁻¹ (r² = 0.567) for the six-rowed cultivars and at 37.5 kg ha⁻¹ year⁻¹ (r² = 0.621) for the two-rowed cultivars. Analysis of 30 SSRs revealed a non-homogenous allele distribution between two and six-rowed cultivars and changes of allele frequencies in relation to the time of release. By PCoA a separation between two and six-rowed cultivars was observed but no clear cut differentiation in relation to the time of release. In the two-rowed cultivars an increase in genetic diversity (DI) from older to newly released cultivars was detected.     

System analysis of frost resistance in winter wheat and its use in breeding

Morphophysiological and physicochemical parameters of sets of winter wheat genotypes were measured. High correlations were found between survival percentage of the winter wheat check variety under freezing and electroconductivity tests, stem electrical resistance after electric shock, and intensity of delayed leaf fluorescence at low temperatures. These correlations decreased when the number of varieties was increased to 35-100. Complex attribute of frost resistance was divided into large components using factor analysis. Biological interpretation was achieved for the first six components. Quantitative values for each component of frost resistance in the various genotypes were determined. The determination coefficient of multiple regression equations, where function was a level of frost resistance and arguments were the component's value for each genotype, varied from 0.80-0.94 over 10 years. It was proposed that the received equations might serve as a model for frost resistance and indicate which component of frost resistance determines the survival of plants in particular ecological conditions. The component structure concept of frost resistance is suggested and possible applications of this concept are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Development of a recurrent apple breeding programme in New Zealand: a synthesis of results,and a proposed revised breeding strategy

This paper describes an apple breeding population that has been developed in New Zealand since 1990 to broaden the genetic base for cultivar breeding. The population is now in its third generation, with recurrent selection for general combining ability being the underlying approach. During the 20 years of the programme, nearly 1,000 trees have been progeny tested. An early focus on selection within open-pollinated tests has been replaced by selection within control-pollinated tests. Genetic evaluation methods along with estimates of genetic parameters (e.g. heritability, genetic correlations, and genotype-by-environment interactions), genetic gain, and genetic diversity are summarised in this paper. The third-generation crossing programme involving nearly 350 parents is almost completed and seedlings from these crosses are in the nursery. In the revised breeding strategy, three hierarchal populations are envisioned to better integrate this broad-based population with the more commercially focused cultivar breeding programme: main breeding population (MBP), elite breeding populations (EBP) and cultivar development populations (CDP). A two-subline structure and a minimum of two crosses per parent will be implemented in the MBP. EBP will focus on developing parents for breeding goals of the CDP. Forward-selected (based on estimated breeding values) candidates from the main- and elite populations will be used as parents of the CDP. Cloning of seedlings in elite populations and also in the first-stage of cultivar development, will be investigated as a tool for enhancing predictability and shortening the cycle for delivering genetic gain.     

The use of adventitious buds to prevent chimerism in mutation breeding of potato

Summary Investigations are described to reduce chimerism by means of adventitious buds. Adventitious buds were obtained from tuber slices that had been rooted by auxin. Mutagenic treatments were applied at different stages previous to the development of adventitious buds. Mutations were induced by ethyl methanesulphonate (EMS) and X-rays. The use of the adventitious-bud technique resulted in a considerable reduction of chimerism when X-rays were used, but not so with EMS. A dose of 2 krad of X-rays was optimal for the production high numbers of mutated plants. With higher doses rooting of slices and bud formation were inhibited.     

The potential of genomic‐assisted breeding to improve Fusarium head blight resistance in winter durum wheat

Durum wheat is the most important tetraploid wheat mainly used for semolina and pasta production, but is notorious for its high susceptibility to Fusarium head blight (FHB). Our objectives were to identify and characterize quantitative trait loci (QTL) in winter durum and to evaluate the potential of genomic approaches for the improvement of FHB resistance. Here, we employed an international panel of 170 winter and 14 spring durum lines, phenotyped for Fusarium culmorum resistance at five environments. Heading date, plant height and mean FHB severity showed significant genotypic variation with high heritabilities and FHB resistance was negatively correlated with both heading date and plant height. The dwarfing gene Rht‐B1 significantly affected FHB resistance and the genome‐wide association scan identified eight additional QTL affecting FHB resistance, explaining between 1% and 14% of the genotypic variation. A genome‐wide prediction approach yielded only a slightly improved predictive ability compared to marker‐assisted selection based on the four strongest QTL. In conclusion, FHB resistance in durum wheat is a highly quantitative trait and in breeding programmes may best be tackled by classical high‐throughput recurrent phenotypic selection that can be assisted by genomic prediction if marker profiles are available.     

The use of risk aversion in plant breeding; Concept and application

Summary Variance analysis is used to measure stability (inter-temporal) and adaptability (over space) components of variance with multilocation-multiyear sorghum yield data from India. Adaptability and stability were highly correlated. Only the stability component is relevant for farmers in their adoption decision. Measures of farmer's risk aversion are used to rank genotypes according to preferences which take account both of yield and stability. Since yield differences were large and risk aversion moderate, preference based rankings did not differ markedly from yield based rankings.     

Inheritance and selection of some fruit characters of apple. II. The relation between leaf and fruit pH as a basis for preselection

Summary The leaf pH of two year old apple seedlings was found to be sufficiently related to the fruit pH, measured when the seedlings were six to seven years old, to serve as a basis for pre-selection. Discarding all seedlings with an above average leaf pH (40% of the total) eliminated the majority (74%) of seedling with low-acid cum sweet fruits. The method was not effective for reducing the proportion of seedlings with high-acid cum sour fruits.