Academic literature on the topic 'Reproductive frost tolerance'

FROST RESISTANCE 2 (FR2) genes of wheat are C-Repeat Binding Factor (CBF) genes with two major alleles known for both Fr-A2 (‘T’ and ‘S’) and Fr-B2 (‘WT’ and ‘DEL’). VERNALIZATION 1 (VRN1) genes have a regulatory role on CBF genes, with known epistatic interactions between Vrn-A1 and Fr-A2 for tolerance to freezing temperatures during vegetative growth. VRN1 genes were also known to affect days to heading and grain yield. Therefore, FR2 genes might also affect these traits. A wide range of cultivars was characterised for VRN1, Fr-A2 and Fr-B2 genes. A third allele of Fr-A2 was found in cvv Excalibur and Axe. The winter cultivar Norstar, which was known to have a high level of frost tolerance during vegetative growth, had the combination Vrn-A1w + Fr-A2T + Fr-B2WT, as did a spring landrace from Afghanistan that was known to have superior tolerance to frost during reproductive development. No Australian spring cultivar was found with this combination, but it could be selected from crosses between adapted cultivars. This would enable the role of VRN1 and FR2 alleles in reproductive frost tolerance to be evaluated in an adapted background. Using large, existing, plant-breeding datasets, the T allele of Fr-A2 delayed heading relative to the S allele, and the WT allele of Fr-B2 delayed heading relative to the DEL allele, but only in combination with particular alleles of the VRN1 genes. Fr-B2 affected grain yield, with the highest grain yields for spring lines produced by Fr-B2DEL in combination with the spring allele of Vrn-B1.

The United Nations Food and Agriculture Organisation (FAO) forecasts a 34% increase in the world population by 2050. As a consequence, the productivity of important staple crops such as cereals needs to be boosted by an estimated 43%. This growth in cereal productivity will need to occur in a world with a changing climate, where more frequent weather extremes will impact on grain productivity. Improving cereal productivity will, therefore, not only be a matter of increasing yield potential of current germplasm, but also of improving yield stability through enhanced tolerance to abiotic stresses. Successful reproductive development in cereals is essential for grain productivity and environmental constraints (drought, cold, frost, heat and waterlogging) that are associated with climate change are likely to have severe effects on yield stability of cereal crops. Currently, genetic gains conferring improved abiotic stress tolerance in cereals is hampered by the lack of reliable screening methods, availability of suitable germplasm and poor knowledge about the physiological and molecular underpinnings of abiotic stress tolerance traits.

Extreme cold events can damage plant tissues, altering growth and reproduction. Soil fungi may help plants tolerate environmental stressors, but the role these microbes play during episodes of severe cold warrants further examination. Using the bunchgrass Elymus canadensis L., we tested how inoculation with mycorrhizal fungi alters plant tolerance to freezing temperatures (tested at –8 °C and –16 °C). We found that, regardless of mycorrhizal inoculation, E. canadensis exposed to –16 °C exhibited greater tissue damage, less tiller growth, and fewer reproductive tillers than plants exposed to the control or –8 °C conditions. Plants exposed to –8 °C and –16 °C displayed greater levels of visible damage compared with the control plants. Mycorrhizae reduced damage to tillers in the –8 °C treatment, but had less effect on tiller damage in the control or –16 °C treatments. Inoculation with arbuscular mycorrhizal fungi limited the tiller number for E. canadensis, but only at the control temperature, suggesting that mycorrhizae may impose costs on E. canadensis under benign thermal conditions. Our study demonstrates that extreme temperatures can affect multiple components of growth in E. canadensis, and that the costs and benefits of arbuscular mycorrhizal fungi, where found, depend upon the thermal environment. Our findings reinforce the overarching importance of historically rare, but increasingly common, environmental extremes in shaping the growth of plants.

Mutation induction has played an integral role in the improvement of most commercially important crop species but has not been successfully applied to tree species because of their long reproductive cycles which hinder the use of the traditional seed-treatment approaches. Treatment of pollen with a chemical mutagen prior to pollination will, theoretically, allow stable, heterozygous mutant trees to be produced in a relatively short time and might facilitate mutagenesis of tree species. As the first step in testing this hypothesis, a controlled-pollination trial with chemically treated pollen was conducted in Eucalyptus globulus ssp. globulus (Labill.). Assessment of fruit, seed and seedlings from more than 500 pollinations associated mutagenic treatment of pollen with a significant reduction in seed set. Non-significant increases in capsule (fruit) abortion, the inhibition of seed germination and the incidence of aberration in seedlings were also noted. We argue that pollen treatment may be a useful means of producing Eucalyptus mutants with variation in flowering time, salinity and frost tolerance, lignification and other traits of scientific and economic importance.

Deacclimation response is an important part of reproductive success in woody perennials because late winter or early spring thaws followed by hard freezes can cause severe injury to dehardened flower buds. There is a need to develop more spring-frost tolerant cultivars for the blueberry (Vaccinium L.) industry. The identification of later or slower deacclimating genotypes could be useful in breeding for more spring-frost tolerant cultivars. This study was undertaken to investigate cold hardiness and deacclimation kinetics under field conditions for 12 Vaccinium (section Cyanococcus A. Gray) genotypes (the cultivars Bluecrop, Duke, Legacy, Little Giant, Magnolia, Northcountry, Northsky, Ozarkblue, Pearl River, Tifblue, and Weymouth; and a population of V. constablaei Gray) with different germplasm compositions and expected mid-winter bud hardiness levels. Examination of bud cold hardiness (BCH) vs. weeks of deacclimation over a 7-week period in 2 consecutive years (2002 and 2003) revealed clear genotypic differences in cold hardiness and timing and rate of deacclimation. Among cultivars, `Legacy' was the least cold hardy at initial evaluation, even less so than `Tifblue'. Regarding deacclimation kinetics, the weekly intervals with the largest losses (i.e., high rates of deacclimation) also varied among genotypes. For `Duke', the largest losses in BCH were detected at weeks 2 and 3, making it the earliest deacclimator. For `Bluecrop', `Ozarkblue', `Weymouth', `Tifblue', and `Legacy', the greatest losses in BCH were observed at weeks 3 and 4. For `Little Giant', `Magnolia', `Northcountry', `Northsky', and `Pearl River', losses in BCH were greatest at weeks 4 and 5, while for V. constablaei, losses were greatest at weeks 6 and 7, making it the latest deacclimator. Deacclimation kinetics were not correlated with mid-winter hardiness or chilling requirements in any fixed pattern. On the other hand, a strong positive correlation was found between BCH and stage of bud opening (r = 0.84). A comparison of timing of deacclimation with germplasm composition indicated that V. constablaei was particularly late to deacclimate. `Little Giant', a 50:50 hybrid of V. constablaei and V. ashei Reade, was nearly as late to deacclimate as the 100% V. constablaei selections. Thus, V. constablaei may be useful in breeding programs to contribute genes for late deacclimation, which should translate into greater spring frost tolerance, in addition to genes for mid-winter hardiness.

Predictions from climate simulation models suggest that by 2050 mean temperatures on the Loess Plateau of China will increase by 2.5 to 3.75°C, while those in the cropping region of south-west Australia will increase by 1.25 to 1.75°C. By 2050, rainfall is not expected to change on the Loess Plateau of China, while in south-west Australia rainfall is predicted to decrease by 20 to 60 mm. The frequency of heat waves and dry spells is predicted to increase in both regions. The implications of rising temperatures are an acceleration of crop phenology and a reduction in crop yields, greater risk of reproductive failure from extreme temperatures, and greater risk of crop failure. The reduction in yield from increased phenological development can be countered by selecting longer-season cultivars and taking advantage of warmer minimum temperatures and reduced frost risk to plant earlier than with current temperatures. Breeding for tolerance of extreme temperatures will be necessary to counter the increased frequency of extreme temperatures, while a greater emphasis on breeding for increased drought resistance and precipitation-use efficiency will lessen the impact of reduced rainfall. Management options likely to be adopted in south-west Australia include the introduction of drought-tolerant perennial fodder species and shifting cropping to higher-rainfall areas. On the Loess Plateau of China, food security is paramount so that an increased area of heat-tolerant and high-yielding maize, mulching with residues and plastic film, better weed and pest control and strategic use of supplemental irrigation to improve rainfall-use efficiency are likely to be adopted.

The aim of the research reported in this thesis was to identify genetic variation for Reproductive Frost Tolerance (RFT) in barley, characterise the genetic basis of the observed tolerance and devise and execute a strategy to incorporate the tolerance into germplasm adapted to Australian production environments. Effects of wheat chromosome regions syntenous to the barley RFT loci were also investigated. A field based screening nursery was developed to characterise barley germplasm for RFT. A diverse collection of international barley germplasm was screened for RFT to identify barley genotypes exhibiting better levels of RFT than what was available in Australian cultivated germplasm. Three lines were identified as having an increased level of RFT and populations derived from these three lines were used to QTL map RFT traits. One QTL was common between the three populations and a second QTL was common between 2 of the populations. These two loci were found to control a reduction in Frost Induced Sterility (FIS) and frost induced grain damage. One of the barley QTL spanned the vernalisation response gene and vegetative frost tolerance locus vrn-H1/Fr-H1. The syntenous genomic regions in hexaploid wheat were investigated to determine if they had an effect on RFT. Two sets of wheat germplasm containing variation for winter/spring alleles of vrn-A1, vrn-B1 and vrn-D1 loci revealed that no measurable differences in RFT were associated with these loci in wheat. Targeted populations were developed from selected tolerant and intolerant genotypes. The location of the RFT locus on chromosome 5HL in barley was refined further by developing molecular markers within the QTL region. A population phenotyped for RFT using a frost simulation chamber revealed that the RFT locus on chromosome 5HL was distal to the major phenology gene vrn-H1 segregating in the population. A breeding strategy was devised to rapidly incorporate the two RFT loci into Australian adapted barley that utilised specific germplasm, newly developed FIS phenotyping methods, molecular markers and doubled haploid technology. A recurrent parent was selected based on adaptation to regions that experience frequent damaging frost events. Germplasm derived from this breeding strategy was screened with diversity array technology markers to determine the effect of donor introgression segment size on yield in target environments. The resulting germplasm from the fast track breeding strategy was evaluated for RFT using field and controlled environment frost tolerance screening methods. The adaptation of the developed germplasm was assessed by conducting yield trials in the environments where frost is a major risk to production in southern Australia. The performance of this germplasm under a range of frost events provided a better understanding of the conditions in which this source of tolerance is effective. The results of this thesis highlighted challenges associated with RFT breeding in barley and wheat. The systematic way in which this work was approached through the development of screening methods, identification of genetic variation, genetic analysis and devising a breeding strategy to incorporate the tolerance into adapted germplasm provides a good example of how a cereal crop can be rapidly improved for a quantitative trait such as RFT.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2010

In Australia, cereal crops such as wheat and barley are planted in autumn with the majority of the growing season occurring over winter. This results in occasional exposure of cold sensitive reproduction organs of the florets to frost events (-2 to -4°C) that sporadically occur in winter and early spring. Direct frost damage to cereal reproductive tissues can cause up to 85% yield losses and is estimated to cause 10% reduction in long-term yield in Australia. Two loci (2H and 5H) controlling frost tolerance at the reproductive stage were identified in Amagi Nijo × WI2585 and Galleon × Haruna Nijo DH populations, with alleles inherited from the Japanese parents associated with tolerance. The 5H locus (Fr-5H) position is close to the Triticeae homoeoloci influencing vernalization response (Vrn-1) and vegetative frost tolerance (Fr-1), while no frost tolerance effects had previously been reported in the region of the 2H locus (Fr-2H) in cereals. In the current study, the 2H and 5H chromosome regions controlling frost tolerance were also found to control developmental traits (e.g. flowering time), suggesting that developmental effects could directly or indirectly determine frost tolerance at one or both loci. However, preliminary data suggest that none of the developmental traits were consistently associated with tolerance. Using rice-barley co-linearity, the flowering time effect on 2HL (we named Flt-2L) was delimited to a 1.3 cM genetic interval in barley where it co-segregated with flowering time, spike compactness, plant height and an APETALA2-like gene. The AP2 gene represents a plausible candidate for Flt-2L because members of the AP2 gene family have been shown to control flowering time in maize, rice and wheat. Further analysis showed that the 2H frost tolerance effect can be genetically separated from Flt-2L by recombination. Thus frost tolerance at this locus appears to be controlled by a tolerance per se mechanism and is not as a result of flowering time differences (frost escape). Therefore, tolerance is unlikely to be due to a pleiotropic effect of Flt-2L. Floret sterility levels obtained using a frost simulation chamber distinguished the parents and F₂ derived individuals carrying contrasting alleles at the 2H tolerance locus. The use of an ice nucleator facilitated uniform freezing on the surfaces of the spikes and leaves, and was used to demonstrate that the 2H effect likely depends on freezing and not chilling. Future activities will include using rice-barley co-linearity to isolate the gene(s) responsible for frost tolerance at the 2H and 5H loci. The emerging physical maps of barley and wheat and the genome sequence of Brachypodium will accelerate the positional cloning. Candidate genes will be functionally analyzed using both forward and reverse genetic approaches. Markers linked to the genes controlling tolerance will be given to breeders to assess the value of the tolerance alleles in the field.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2009