Chilling Tolerance, Cold Hardening and Freezing Tolerance of Low-temperature-tolerant Mutants of Dendranthema × grandiflorum (Ramat.) Kitamura

Two low-temperature-tolerant mutants of the Dendranthema × grandiflorum (Ramat.) Kitamura cultivar ‘Puck’ derived from an x-radiated tissue culture system were compared, as vegetatively growing plants, to ‘Puck’ ssfor several physiological properties under low-temperature conditions. So far, the low-temperature tolerance of the mutants has been defined as the capacity to flower earlier under low temperature conditions (8—15°C) the wild type. All three lines were not chilling sensitive in the vegetative state and were able to acclimatize and to develop freezing tolerance. Differences between ‘Puck’ and the mutants were found but could not be related to the low-temperature tolerance of the mutants in the generative phase. Levels of the amino acid proline increased during the hardening process, reaching the highest level in the cultivar ‘Puck’. No evidence could be obtained that proline is causally involved in the cold-hardening process. Freezing-induced membrane injury was found to decrease with cold hardening (0—28 days) but the two mutants did not show a greater capacity to acclimatize and cold harden than the original cultivar ‘Puck’.     

Seed storage potential of population varieties and hybrid varieties and their breeding components in rye (Secale cereale L.)*

Seeds of population varieties, hybrid varieties, cytogenetic male sterility (CMS) single cross lines and CMS inbred lines of rye (Secale cereale L.) were stored to determine the respective rates of germination loss with a view to their storage potential. The seeds were stored under controlled conditions at a seed moisture content of 14% and a temperature of 30°C for periods of up to 80 days. The storage potential decreased in the order: hybrid varieties > population varieties > CMS single cross lines > CMS inbred lines. However, the rates of germination loss showed no differences within the respective categories. The inferences drawn for seed storage potential hold for seed vigour potential.     

Marker‐assisted breeding for improvement of anaerobic germination in japonica rice (Oryza sativa)

Direct seeding is increasingly being practiced in rice cultivation areas because it saves labour and reduces cost of production and management. In this study, four japonica‐type breeding lines were developed from a cross of a japonica cultivar and an AG‐tolerant donor, KHO, using marker‐assisted selection. Validation of the target genes AG1 and AG2 in the selected lines was examined by PCR analysis and the background recovery rate by the recurrent parent was confirmed by genotyping using a 6K SNP chip. Compared to the recurrent, the survival rates of the selected lines were improved in a range from 33% to 115% in three conditions; in particular, the survival rate was increased in more than twice that of the recurrent parent under the hypoxic condition. The main agronomic trait, yield and quality‐related traits were similar to those of the recurrent parent. The use of these lines will contribute to the expansion of the cultivation area due to the proven economic benefits of direct seeding in Korea.     

The potential of selection and breeding for improved salt tolerance in lucerne (Medicago sativa L.)

Summary Four cultivars of Medicago sativa L. were subjected to selection for improved salt tolerance using a salinized solution culture technique at 250 mM NaCl. Selections were made after two weeks growth, based upon seedling shoot length differences. High (shoot lengths 14–31 mm) and low (7–12 mm) selection lines were established. Unselected shoot lengths ranged from 0–11 mm. Selection intensities ranged from 0.17% to 0.22% for the high selection lines, and from 0.30% to 1.05% for the low selection lines.Eleven selected plants from cv. CUF 101, and 10 from Local Syria were grown on and polycrossed. A sample of progeny seed from each was grown at 8 NaCl concentrations in solution cultures. Selected line seedlings produced shoots at 225, 250, 260, and 275 mM NaCl, whereas unselected material failed to grow above 225 mM NaCl. A second cycle of selection at 280 mM NaCl with these two cultivars achieved selection intensities of 0.21% and 0.45% for high and low selection lines, respectively. Selected lines grew and produced shoots at 300 mM NaCl.Seedlings derived from 1st and 2nd selection cycles and unselected control material were grown for 6 weeks at 0, 150, 175, and 200 mM NaCl in a sand culture experiment. The high selection line produced significantly greater shoot fresh weight, dry weight, and % live shoot weight than the unselected control material. Clearly selection as practised here can isolate individual seedlings having enhanced genetically based tolerance to NaCl, which is manifest in mature plants derived from polycrossing those selected individuals.     

Chlorophyll Fluorescence‐Based Studies of Frost Damage and the Tolerance for Cold‐Induced Photoinhibition in Freezing Tolerance Analysis of Triticale (×Triticosecale Wittmack)

Freezing tolerance of 60 breeding lines of winter hexaploid triticale (×Triticosecale Wittmack) was studied in the field‐laboratory experiment. The experiment was repeated over three winters. The survey was also carried out in plants grown and cold‐acclimated in the laboratory. In both the experiments, plant survival analysis and chlorophyll fluorescence‐based studies on energy flows in photosystem II (PSII) (JIP‐test) after freezing of detached leaves were performed. In the laboratory experiment, the temperature of 50 % electrolyte leakage from leaves and the resistance against cold‐induced photoinhibition were additionally investigated. In the case of plants’ cold‐acclimated in the field, determination of the freezing tolerance of PSII gave similar results as the determination of freezing tolerance of whole plants. Both traits were strongly affected by genotype–environmental interactions, but these effects were less visible for PSII characteristics. In the laboratory experiments, a strong correlation between freezing tolerance and the tolerance for cold‐induced photoinhibition of photosynthesis was observed. The possibility of the use of chlorophyll fluorescence‐based techniques for the determination of freezing tolerance in triticale is discussed.     

QTLs for black-point resistance in wheat and the identification of potential markers for use in breeding programmes

Quantitative trait loci (QTLs) for black‐point resistance have been mapped in two doubled haploid‐derived wheat populations, each thought to contain unrelated sources of resistance. In the ‘Sunco’בTasman’‐derived population, QTLs were located on chromosomes 1D, 2B, 3D, 4A, 5A and 7A with each QTL explaining between 4 and 15% of the observed phenotypic variance. QTLs were contributed by both parents. In the ‘Cascades’בAUS1408’‐derived population, QTLs from ‘Cascades’ were identified on chromosomes 2A, 2D and 7A with each QTL explaining between 12 and 18% of the phenotypic variance. Several markers were identified which are promising candidates for use in marker‐assisted selection programmes. If one, two or three of these markers would have been used to select for black‐point resistance in the ‘Sunco’בTasman’ population, then with one marker 34 of 39 resistant lines, with two markers 23 of 32 and with three markers 17 of 32 would have been selected. At the same time, 67 false positives obtained by selecting with one marker are reduced to 24 by selection with two markers and to 11 by selection with three markers. Similarly, if one, two or three markers are used to select for black‐point resistance in the ‘Cascades’בAUS1408’ populations, then with one marker 25 of 31 resistant lines, with two markers 26 of 31 and with three markers 10 of 31 are selected. At the same time, 14 false positives are obtained with one marker are reduced to six by selection with two markers and no false positives are selected using three markers.     

Phenotypic evaluation of floral and flowering traits with relevance for hybrid breeding in wheat (Triticum aestivum L.)

Hybrid breeding is a promising approach to increase the yield potential in wheat (Triticum aestivum L.). The profitability of wheat hybrids highly depends on a cost‐efficient system for hybrid seed production for which an adequate outcrossing in the male pool is of utmost importance. Employing a set of 51 elite winter wheat lines, we developed and evaluated phenotyping methods for floral and flowering traits with relevance for improved cross‐pollination. We observed significant genotypic variances and high heritabilities for most traits, including important traits like pollen mass and anther extrusion. Our results suggest the utility of the developed phenotyping approaches for applied plant breeding and the potential of the traits to assist in the design of the male ideotype for increased cross‐fertilization.     

Crop breeding for salt tolerance in the era of molecular markers and marker‐assisted selection

Crop salt tolerance (ST) is a complex trait affected by numerous genetic and non‐genetic factors, and its improvement via conventional breeding has been slow. Recent advancements in biotechnology have led to the development of more efficient selection tools to substitute phenotype‐based selection systems. Molecular markers associated with genes or quantitative trait loci (QTLs) affecting important traits are identified, which could be used as indirect selection criteria to improve breeding efficiency via marker‐assisted selection (MAS). While the use of MAS for manipulating simple traits has been streamlined in many plant breeding programmes, MAS for improving complex traits seems to be at infancy stage. Numerous QTLs have been reported for ST in different crop species; however, few commercial cultivars or breeding lines with improved ST have been developed via MAS. We review genes and QTLs identified with positive effects on ST in different plant species and discuss the prospects for developing crop ST via MAS. With the current advances in marker technology and a better handling of genotype by environment interaction effects, the utility of MAS for breeding for ST will gain momentum.     

Physiological and biochemical adaptive traits support the specific breeding of alfalfa (Medicago sativa) for severely drought-stressed or moisture-favourable environments

The adaptation of alfalfa to moisture-favourable and drought-prone environments and its underlying mechanisms have not been thoroughly investigated despite their crucial importance to maximize the crop breeding progress. The main aim of this study was to support breeding strategies by exploring the relationship of leaf morphophysiological traits assessed in three growth chamber experiments with the adaptive response of five cultivars (Mamuntanas; Demnat 203; Erfoud 1; Prosementi; SARDI 10) that showed large genotype × environment interaction (GEI) across 10 drought-prone to moisture-favourable Mediterranean environments. Changes in shoot and root metabolite profiles across moisture-contrasting conditions were assessed for two cultivars with contrasting adaptation pattern. The cultivar specifically adapted to drought-prone environments (Mamuntanas), compared with that specifically adapted to moisture-favourable environments (Demnat 203), displayed: (i) lower leaf wilting under drought stress; (ii) delayed leaf senescence under stress, assessed as limited chlorophyll reduction either in vivo from upper to central leaves or in vitro from control to polyethylene glycol-treated leaflets, (iii) greater leaf tolerance to desiccation, measured in vitro as less pronounced reduction of leaf dry weight from control to polyethylene glycol-treated leaflets, (iv) smaller leaves, (v) lower early root and shoot growth and (vi) lower leaf stomata density. The other cultivars exhibited different combinations and/or intermediate values of these traits. The metabolite profiles of Mamuntanas and Demnat 203 differed more in shoots than in roots. Mamuntanas accumulated more amino acids than Demnat 203 under moisture-favourable and drought conditions. The distinct and partly incompatible combination of traits featuring the cultivars that maximized the crop yield in favourable or drought-prone conditions (Mamuntanas and Demnat 203) improves our understanding of traits contributing to large GEI across moisture-contrasting environments and support the breeding for specific adaptation to either condition. We identified a few inexpensive morphophysiological traits that could be used for early selection targeting drought-prone environments.     

Screening for and heritability of flood-tolerance in the Florida (CP) sugarcane breeding population

Summary An experiment screening for flood-tolerance and estimating the heritability of flood-tolerance was conducted on 160 sugarcane clones in the Canal Point, Florida, USA sugarcane breeding population. Clones were grown in two environments, a drained control and a continuous, five-month flood. The test ran for two crop years, plant-cane and first ratoon. A wide range of production was observed, with some clones dying out after the first year. Several clones had two-year mean cane production in flood that was 70% of their production in control. Heritabilities calculated by parent-offspring regression ranged from 0.29 to 0.51.     

Genetic gains for yield after two back-crosses of the interspecific hybrid Libusta (Coffea canephora P. × C. liberica Bull. Ex Hiern) to C. canephora P.

The Libusta (Coffea canephora P. × C. liberica B.) programme initiated in the seventies in Côte d'Ivoire aims at improving the quality of coffee grown in low altitudes, with a yield comparable to current commercial C. canephora clones. The second generation of back‐crosses to the C. canephora (CAN) parent, BC2, are now likely to be commercially exploited as far as yield is concerned. The best BC2 progeny yielded 1386 kg of green coffee/ha/y, averaged over five harvest years. On average, the genetic gain for yield from BC1 to BC2 reached 22%. In a factorial mating design, no interaction was observed between BC1 and CAN parents, while both main effects were highly significant. This explained that observed genetic gains and further genetic gains may be achieved with appropriate strategies.     

Genetic Resources for Salt Tolerance in the Wild Progenitors of Wheat (Triticum dicoccoides) and Barley (Hordeum spontaneum) in Israel

Salt tolerance was tested in the progenitors of cultivated cereals, wild barley (Hordeum spontaneum) and wild emmer wheat (Triticum dicoccoides) from Israel. Plants from five selected populations of H. spontaneum from the Mediterranean Coastal Plain and northern Negev desert, were grown on 250 and 350 mM of NaCl. Likewise, five populations of T. dicoccoides from the eastern Samaria steppes, Mt. Hermon and Mt. Carmel, were grown on 175 and 250 mM of NaCl. Here we report on superior genotypes of H. spontaneum, ripening at 350 mM NaCl (= 60 % sea water), and of T. dicoccoides ripening at 250 mM (— 40 % sea water). We are proceeding now with both genetical and physiological studies aimed at chromosomally-locating salt tolerant genes and unravelling the mechanism(s) of salt resistance in these wild cereals.     

Development and validation of gene-based markers for shrunken2-Reference allele and their utilization in marker-assisted sweet corn (Zea mays Sachharata) breeding programme

The recessive shrunken2-Reference (sh2-Ref) allele is traditionally used in sweet corn cultivar development worldwide. However, non-availability of suitable gene-based marker(s) for sh2-Ref has considerably delayed its utilization in molecular breeding. Here, 7,320 bp sequence of Sh2 gene among five wild- and six sh2-Ref-based inbreds was analysed by employing 13 overlapping primers. SNP583 (A in wild and G in mutant) and SNP755 (T in wild and C in mutant) in 5’UTR, and SNP5112 (C in wild and T in mutant) in intron-12 clearly differentiated dominant (Sh2) and recessive (sh2-Ref) allele. These SNPs were used to develop four gene-based PCR markers. The newly developed markers were validated in six F₂ populations segregating for sh2-Ref allele, and 230 diverse inbreds of normal and sweet corn types. These markers were further used in genotyping of BC₁F₁ populations leading to successful selection of sh2-Ref allele in the marker-assisted breeding. Globally, this assumes great significance in molecular breeding of sweet corn.     

Genetic variation in F<Subscript>2</Subscript> populations and their potential in the improvement of grain yield in tef (<Emphasis Type="Italic">Eragrostis tef</Emphasis>)

Tef is a staple cereal of Ethiopia in high demand by consumers. In order to cope up with this high consumer demand, productivity per unit of land must increase through the development and use of high-yielding varieties. To this effect, the National Tef Research Project has long been striving towards the development of high yielding varieties through direct selection from germplasm and concentrating favourable alleles through hybridization and selection, despite the tedious crossing technique. The objective of this study was to assess the degree of genetic variation in F₂ populations of tef as a basis for improving grain yield. F₂ populations from 12 crosses and their parents were grown at the Debre Zeit Agricultural Research Center, Ethiopia, and assessment was made on eight traits on individual plant basis. Eleven of the 12 crosses showed substantial genetic variation for grain yield and its components, indicating the potential for improvement through selection. Moreover, grain yield, plant weight and yield related traits showed moderate to high heritability values (17–80%). In all the crosses, tiller number, panicle weight, yield per panicle and panicle length showed significant (P ≤ 0.05) and positive association with grain yield. Considering the degree of genetic variation and heritability values, emphasis should be given to selected crosses in an effort to developing high-yielding tef varieties.     

Spatial variability of salt-affected soils in the middle Ebro Valley (Spain) and implications in plant breeding for increased productivity

Barley breeding programs have empirically selected for improving grain yield and quality. The objective of this study was to quantify genetic gains in yield in 2-rowed malting barley cultivars released from 1944to 1998 in Argentina, identifying the major physiological traits responsible for them. For this purpose, a field experiment was conducted in absence of biotic and abiotic stressful factors and with lodging being prevented mechanically. Until the 1970's,potential yield was maintained nearly constant at 5.25 mg ha^-1 and since then it increased at a rate of 41 kg ha^-1 year^-1. That bi-linear trend was closely related to the trend of averaged yields obtained by farmers. The contribution made by breeding yield potential to the total yield gains achieved by farmers was estimated in c. One third. Neither time to heading nor time to maturity were systematically modified by breeding. However, the partitioning of the developmental time was modified: time to achieve both maximum number of floret primordia and length of the jointing –heading period were increased with the year of release of the cultivars. The main component associated with yield was the number of grains per m², due to variations in number of spikes per m².Total and vegetative biomass at maturity increased with the year of release of the cultivars, at a rate of 45 and 19 kg ha^-1 year^-1, while both harvest index and stem height remained virtually unmodified. Differences in biomass at heading among cultivars were related to the improvement on the abilities to capture more radiation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Identification of a major QTL for adult plant resistance to coffee leaf rust (Hemileia vastatrix) in the natural Timor hybrid (Coffea arabica x C. canephora)

Most of the commercial varieties of coffee (Coffea arabica L.) derived from the Timor hybrid (TH) have been shown to contain major genes for coffee leaf rust (CLR) resistance. To identify markers tightly linked to such genes, an F₂ mapping population derived from a cross between ‘Caturra’ (susceptible variety) and the TH‐derived DI.200 line (highly resistant) was generated. Using expressed sequence information and a bioinformatics approach, both targeted region amplified polymorphism (TRAPs) markers and simple sequence repeat (SSR) markers were identified. Phenotypic evaluations in the field and under controlled conditions confirmed the existence of one quantitative trait locus for CLR resistance. Four candidate SSR markers were associated with high CLR resistance. They spanning a region of 2.5 cM designated Q_{CLR_4} located within chromosome 4 of the international C. canephora map. The presence of this region was confirmed in a set of elite lines and commercial varieties. The Q_{CLR_4} region corresponds to a new and genetically independent S_H locus that could potentially be useful in gene pyramiding with other genes to enhance rust resistance in TH derivatives.     

The influence of photoperiod on the Vrn-H2 locus (4H) which is a major determinant of plant development and reproductive fitness traits in a facultative × winter barley (Hordeum vulgare L.) mapping population

To determine the effect of Vrn‐H2 locus on plant developmental and agronomic traits, detailed controlled environment tests involving a factorial set of vernalization and photoperiod treatments were carried out using doubled haploid lines developed from a facultative (Vrn‐H2^?) × winter (Vrn‐H2⁺) barley cross. The allele phase at the Vrn‐H2 locus influenced heading date as well as the developmental and agronomic traits. The performance of Vrn‐H2⁺ lines was significantly influenced by vernalization: reproductive fitness traits showed significant decreases without vernalization. However, the effects of alleles at the Vrn‐H2 locus extended beyond simple satisfaction of the vernalization requirement. Vrn‐H2⁺ lines showed increased reproductive fitness compared with Vrn‐H2^? lines when vernalization was followed by a long photoperiod. The responses of the two Vrn‐H2 allele classes to photoperiod duration were quite different in terms of heading date, developmental and agronomic traits. These results suggest that alleles at the Vrn‐H2 locus – and/or tightly linked gene(s) – respond primarily to the exogenous signal of vernalization (temperature), but when the vernalization requirement has been fulfilled, they also respond to photoperiod duration.     

Hardening of Some Winter Wheat (Triticum aestivum L.), Rye (Secale cereals L.), Triticale (×Triticosecale Wittmack) and Winter Barley (Hordeum vulgare L.) Cultivars During Autumn and the Final Winter Survival in Finland

Profound hardening is the prerequisite for survival of a cultivar over winter. In the present study, hardening abilities of 13 winter wheat, 10 rye, 3 triticale and 6 winter barley cultivars were determined in field samples collected during the autumns of 1990 and 1991 by measuring the amount of ion leakage from frost-treated leaf segments. The cultivars tested were selected from the Inter-Nordic Winterhardiness Project, in which Field Survival Indices were determined for a total of 23 winter wheat, 13 rye, 5 triticale and 11 winter barley cultivars in order to estimate winter survival potentials under Finnish conditions. The winter survival of the materials studied correlated well with their hardening ability assessed by using the electrolyte leakage method.