Plasma Membrane Alterations in Callus Tissues of Tuber-bearing Solanum Species during Cold Acclimation

Plasma membrane alterations in two tuber-bearing potato species during a 20-day cold acclimation period were investigated. Leaf-callus tissues of the frost-resistant Solanum acaule Hawkes `Oka 3878' and the frost-susceptible, commonly grown Solanum tuberosum `Red Pontiac,' were used. The former is a species that can be hardened after subjecting to the low temperature, and the latter does not harden. Samples for the electron microscopy were prepared from callus cultures after hardening at 2 C in the dark for 0, 5, 10, 15, and 20 days. After 20 days acclimation, S. acaule increased in frost hardiness from −6 to − 9 C (killing temperature), whereas frost hardiness of S. tuberosum remained unchanged (killed at −3 C). Actually, after 15 days acclimation, a −9 C frost hardiness level in S. acaule callus cultures had been achieved.     

Glycoalkaloids and acclimation capacity of hybrids between <Emphasis Type="Italic">Solanum tuberosum</Emphasis> and the incongruent hardy species <Emphasis Type="Italic">Solanum commersonii</Emphasis>

F₁ and backcross hybrids between sexually incompatible species Solanum commersonii and Solanum tuberosum were characterized for glycoalkaloid content and capacity to cold acclimate. Glycoalkaloid (GA) analysis revealed that F₁ triploids and BC₁ pentaploids contained the glycoalkaloids of both parents. In BC₂ (near) tetraploids the situation was different, in that some hybrids produced the GAs of both parents, whereas others contained only the GAs of S. tuberosum. This suggested that the GAs from S. commersonii may be lost rapidly, and that they may have a simple genetic control. The total tuber GA content of BC₁ and BC₂ groups averaged quite acceptable levels (165.9 mg/kg in BC₁ and 192.8 mg/kg in BC₂), with six genotypes having a GA content <200 mg/kg fresh weight. The F₁ triploid hybrids expressed a capacity to cold acclimate similar to S. commersonii, whereas BC₁ and BC₂ genotypes generally displayed an acclimation capacity higher than the sensitive parent but lower than S. commersonii. However, one BC₁ and two BC₂ genotypes with an acclimation capacity as high as S. commersonii were identified. The polar lipid fatty acid composition in S. commersonii and its hybrid derivatives showed that, following acclimation, there was a significant increase in 18:3. Correlation analysis between the capacity to cold acclimate and the increase in 18:3 was significant, suggesting that the increase in 18:3 can be used as a biochemical marker for the assisted selection of cold-acclimating genotypes in segregating populations.Communicated by G. Wenzel     

Inheritance of the photoperiodically induced cold acclimation response in Cornus sericea L., red-osier dogwood

Summary Cold acclimation responses of latitudinal ecotypes of Cornus sericea L. (C. stolonifera Michx.) and F₁, F₂ and BC₁ hybrid progenies were measured under natural photoperiod conditions in St. Paul, MN and artificially shortened photoperiods in the glass-house. The 65 °N and 62 °N ecotypes (Alaska and Northwest Territories, respectively) were characterized by a short night length for hardiness induction, the 42 °N ecotype (Utah A and B) by a long night length for hardiness induction, while the F₁ was intermediate to the parents. Results from reciprocal crosses indicated there was no significant unilateral maternal influence on cold acclimation. Acclimation responses of the F₂ were highly variable but generally ranged between the parental extremes. However, three individuals from the 42 ° × 62 °N crosses exhibited greater cold resistance than the northern parent on two successive freezing test dates. F₂ plants were also found with less freezing resistance than the southern parent. Backcrosses to the southern parent produced progeny with acclimation patterns resembling that of the southern parent and were significantly less hardy than the F₂ in early freezing tests.Scientific Journal Series Paper No. 12,075 of the Minnesota Agricultural Experiment Station     

Effect of frost nights and day and night temperature during dormancy induction on frost hardiness, tolerance to cold storage and bud burst in seedlings of Norway spruce

For trees, the ability to obtain and maintain sufficient levels of frost hardiness in late autumn, winter and spring is crucial. We report that temperatures during dormancy induction influence bud set, frost hardiness, tolerance to cold storage, timing of bud burst and spring frost hardiness in seedlings of Norway spruce (Picea abies (L.) Karst.). Bud set occurred later in 12°C than in 21°C, and later in cool nights (7°C) than in constant temperature. One weekly frost night (−2.5°C) improved frost hardiness. Cool nights reduced frost hardiness early, but improved hardiness later during cold acclimation. Buds and stems were slightly hardier in 21°C than in 12°C, while needles were clearly hardier in 12°C. Cold daytime temperature, cool nights and one weekly frost night improved cold storability (0.7°C). Seedlings receiving high daytime temperatures burst buds later, and were less injured by light frost some days after bud burst.     

Genetics and mapping of adult plant rust resistance in soybean PI 587886 and PI 587880A

Two soybean accessions, PI 587886 and PI 587880A, previously identified as having resistance to Phakospora pachyrhizi Syd. (soybean rust, SBR) were used to create two populations (POP-1 and POP-2) segregating for SBR resistance. F₂-derived F₃ (F_2:3) families from each population were grown in a naturally SBR-infected field in Paraguay to determine inheritance and map resistance genes. Over 6,000 plants from 178 families in POP-1 and over 5,000 plants from 160 families in POP-2 were evaluated at R5 for lesion type: immune reaction (IR), reddish-brown (RB), or tan (TAN) colored lesions. Based on the lesion type present, each F_2:3 family was rated as resistant, segregating or susceptible and this classification was used to infer the F₂-phenotype and genotype. For both populations, the F₂ segregation ratios fit a 1:2:1 (resistant:segregating:susceptible) ratio expected for a single gene (P > 0.05). The RB lesions occurred almost exclusively in the heterozygous class, indicating incomplete dominance under the conditions of this study. Molecular markers flanking the locations of the known resistance genes were used to map the resistance gene in both populations to the Rpp1 locus. However, evaluation of PI 587886 and PI 587880A against eight P. pachyrhizi isolates indicated that the resistance allele in these two accessions was different from Rpp1. This test also demonstrated that these accessions were resistant to at least one P. pachyrhizi isolate collected in the southern US. This is the first report of using an adult plant field-screen with natural rust pressure to map SBR resistance.     

Characteristics of Cold Acclimation and Deacclimation in Tuber-bearing Solanum Species

The effect of temperatures on cold acclimation and deacclimation in foliage tissues was studied in Solanum commersonii (Oka 4583), a tuber-bearing potato. The threshold temperature for cold acclimation was about 12 C. In a temperature range of 2 to 12 C, the increase in hardiness was dependent on the acclimating temperature; the lower the acclimating temperature, the more hardiness achieved. A day/night temperature of 2 C, regardless of photoperiod, appeared to the optimum acclimating temperature for the Solanum species studied. A subfreezing temperature hardened plants less effectively. The maximum level of hardiness could be reached after 15 days of cold acclimation. However, it took only 1 day to deacclimate the hardened plants to a preacclimation level when plants were subjected to a warm regime from cold. The degree of deacclimation was dependent on the temperature of the warm regime.     

Microsatellite markers developed from Theobroma cacao L. expressed sequence tags

Theobroma cacao L. expressed sequence tags (ESTs) were converted into useful genetic markers for fingerprinting individuals and genetic linkage mapping. Primers were designed to microsatellite‐containing ESTs. Twenty‐two T. cacao accessions, parents of various mapping populations segregating for disease resistance and crop yield characteristics, were tested. Twenty‐seven informative loci were discovered with 26 primer pairs. The number of detected alleles ranged from two to 11 and averaged 4.4 per locus. All 27 markers could be mapped into at least one of the existing F₁ or F₂ populations segregating for agronomically important traits.     

Tolerance to multiple climate stressors: a case study of Douglas‐fir drought and cold hardiness

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Alfalfa water status and cold hardiness as influenced by cold acclimation and water stress

Abstract Water stress at a nonacclimating temperature (18–20°C) increased the cold hardiness of Medicagosativa L. (alfalfa) plants. This increased cold hardiness was retained when the previously water-stressed plants were cold acclimated (2–9°C) in the absence of water stress. Water stress during cold acclimation also increased cold hardiness. Alfalfa was demonstrated to suffer injury, measured as decreased growth following freezing, at sub-lethal temperatures. During cold acclimation the turgor potential (ψ) of watered plants increased, whereas the solute potential and the water content per unit dry weight decreased. The large positive psgrdap of acclimated plants indicates that the decreased water content per unit dry weight is related to an increased proportion of tissue dry matter rather than to tissue dehydration.     

Carbohydrate Metabolism and Frost Hardiness in Pine and Spruce Seedlings Grown at Different Photoperiods and Thermoperiods

Large changes occur in carbohydrate contents of pine (Pinus silvestris L.) and spruce (Picea abies (L.) Karst.) seedlings cold-hardened by photoperiod or by combined photo- and thermo-period. The largest change is in sucrose content, which is almost doubled after six weeks short-day (6/18 h) treatment; and more than doubled (spruce) or more than tripled (pine), when also temperature is lowered (10/5°C). Development of frost hardiness is strongly correlated with the change in carbohydrate contents. At dehardening, the carbohydrate content decreases rapidly, especially in pine, and the raffinose formed during the rest period disappears within 2–4 weeks. Frost hardiness decreases in parallel. The content of soluble carbohydrates may thus play a role in frost hardiness, although it is not the only factor. Bud formation at cold acclimation is not directly correlated with the changes in carbohydrate content and hardiness.     

CO2 enrichment predisposes foliage of a eucalypt to freezing injury and reduces spring growth

Seedlings of Eucalyptus pauciflora, were grown in open-top chambers fumigated with ambient and elevated [CO₂], and were divided into two populations using 10% light transmittance screens. The aim was to separate the effects of timing of light interception, temperature and [CO₂] on plant growth. The orientation of the screens exposed plants to a similar total irradiance, but incident during either cold mornings (east-facing) or warm afternoons (west-facing). Following the first autumn freezing event elevated CO₂-grown plants had 10 times more necrotic leaf area than ambient CO₂ plants. West-facing plants had significantly greater (25% more) leaf damage and lower photochemical efficiency (F_v/F_m) in comparison with east-facing plants. Following a late spring freezing event east-facing elevated CO₂ plants suffered a greater sustained loss in F_v/F_m than west-facing elevated CO₂- and ambient CO₂-grown plants. Stomatal conductance was lower under elevated CO₂ than ambient CO₂ except during late spring, with the highest leaf temperatures occurring in west-facing plants under elevated CO₂. These higher leaf temperatures apparently interfered with cold acclimation thereby enhancing frost damage and reducing the ability to take advantage of optimal growing conditions under elevated CO₂.     

Does ice crystal formation in buds explain growth disturbances in boron-deficient Norway spruce?

Loss of apical dominance in boron-deficient trees has been suggested to be due to frost damage of terminal buds and leaders. Excessive nitrogen (N) supply can exacerbate boron (B) deficiency by the dilution-effect. N may also have direct effects on winter hardiness. We studied frost hardening of buds of Norway spruce (Picea abies L. Karst.) in healthy-looking trees and in trees with growth disturbances. The effect of B and N on frost hardiness was studied in a factorial fertilisation experiment during cold acclimation. Frost hardiness was determined by differential temperature analysis (DTA) and scoring of visual damage. In a DTA profile of apical buds with a piece of stem, low-temperature exotherm (LTE) predicted bud injury, while two of the observed high-temperature exotherms and two of the observed intermediate-temperature exotherms were non injurious. Appearance of LTE followed changes in air temperature. The risk of frost damage was not affected by fertilisation treatments or previously observed growth disturbances. However, when the bud structure was deformed by severe B deficiency, the supercooling ability disappeared. Such buds are probably killed by freezing in nature and therefore, frost damage may play a secondary role in the development of growth disturbances.     

The Role of Light in Cold Acclimation of Hedera helix L. var. Thorndale

The role of light in cold acclimation of Hedera helix L. var. Thorndale appears to differ from that reported for winter annuals. Although light greatly enhances the degree of hardiness attained, cold acclimation is not obligatorily linked to a light requirement. Photoperiods, varying from 8 to 24 hours, received during the cold acclimation period were equally effective in promoting maximum hardiness. Relatively low light intensities and short photoperiods stimulated maximum hardiness, and proportional increases in hardiness in response to increased photoperiods were demonstrated only in stems of prestarved plants. Exclusion of CO₂ and high concentrations of photosynthetic inhibitors decreased hardiness, but in no instance was hardiness reduced to the level of the dark control. The data are only compatible with a photosynthetic role of light if it is assumed that only a small portion of the total photosynthates are required to elicit maximum hardiness. Alternatively, the light stimulation which was elicited by low light intensities, short photoperiods, in the absence of CO₂, and in the presence of photosynthetic inhibitors, may be a light signal similar to a phytochrome response.     

Inheritance of resistance to leaf and glume blotch caused by Septoria nodorum Berk. in winter wheat

Sixteen crosses between eight winter wheat cultivars were screened for resistance to Septoria nodorum leaf and glume blotch in the F₁ and F₄ generations using artificial inoculation in the field. The F₁ of most crosses showed dominance for susceptibility on both ear and leaf. The effects of general combining ability were of similar magnitude as the effects for specific combining ability. On the basis of the phenotypic difference of the parents, no prediction was possible about the amount and the direction of genetic variance in the segregating populations. The variation observed in this study both within and among the segregating populations suggests a quantitative inheritance pattern influencing the expression of the two traits. The components of variance between F₂ families within a population were as high as (for S. nodorum blotch on the ear) or higher (for S. nodorum blotch on the leaf) than those between populations. Therefore, strong selection within a few populations may be as effective to obtain new resistant genotypes as selection in a large number of populations. In almost all crosses, progenies were found that were more resistant than the better parent. Thus transgression breeding may be a tool to breed for higher levels of resistance to S. nodorum blotch. Highly resistant genotypes were found even in combination with two susceptible parents. The genetic source for Septoria resistance is probably broader than is generally assumed and could be used to improve S. nodorum resistance by combination breeding followed by strong selection in large populations. Received: 18 January / Accepted: 30 April 1999     

Chilling and freezing stress in live oaks (Quercus section Virentes): intra- and inter-specific variation in PS II sensitivity corresponds to latitude of origin

Sensitivity to cold and freezing differs between populations within two species of live oaks (Quercus section Virentes Nixon) corresponding to the climates from which they originate. Two populations of Quercus virginiana (originating from North Carolina and north central Florida) and two populations of the sister species, Q. oleoides, (originating from Belize and Costa Rica) were grown under controlled climate regimes simulating tropical and temperate conditions. Three experiments were conducted in order to test for differentiation in cold and freezing tolerance between the two species and between the two populations within each species. In the first experiment, divergences in response to cold were tested for by examining photosystem II (PS II) photosynthetic yield (ΔF/F _m′) and non-photochemical quenching (NPQ) of plants in both growing conditions after short-term exposure to three temperatures (6, 15 and 30°C) under moderate light (400 μmol m⁻² s⁻¹). Without cold acclimation (tropical treatment), the North Carolina population showed the highest photosynthetic yield in response to chilling temperatures (6°C). Both ecotypes of both species showed maximum ΔF/F _m′ and minimum NPQ at their daytime growth temperatures (30°C and 15°C for the tropical and temperate treatments, respectively). Under the temperate treatment where plants were allowed to acclimate to cold, the Q. virginiana populations showed greater NPQ under chilling temperatures than Q. oleoides populations, suggesting enhanced mechanisms of photoprotective energy dissipation in the more temperate species. In the second and third experiments, inter- and intra-specific differentiation in response to freezing was tested for by examining dark-adapted F _v/F _m before and after overnight freezing cycles. Without cold acclimation, the extent of post-freezing declines in F _v/F _m were dependent on the minimum freezing temperature (0, −2, −5 or −10°C) for both populations in both species. The most marked declines in F _v/F _m occurred after freezing at −10°C, measured 24 h after freezing. These declines were continuous and irreversible over the time period. The North Carolina population, however, which represents the northern range limit of Q. virginiana, showed significantly less decline in F _v/F _m than the north central Florida population, which in turn showed a lower decline in Fv/F _m than the two Q. oleoides populations from Belize and Costa Rica. In contrast, after exposure to three months of chilling temperatures (temperate treatment), the two Q. virginiana populations showed no decline in F _v/F _m after freezing at −10°C, while the two Q. oleoides populations showed declines in F _v/F _m reaching 0.2 and 0.1 for Costa Rica and Belize, respectively. Under warm growth conditions, the two species showed different F ₀ dynamics directly after freezing. The two Q. oleoides populations showed an initial rise in F ₀ 30 min after freezing, followed by a subsequent decrease, while the Q. virginiana populations showed a continuous decrease in F ₀ after freezing. The North Carolina population of Q. virginiana showed a tendency toward deciduousness in response to winter temperatures, dropping 58% of its leaves over the three month winter period compared to only 6% in the tropical treatment. In contrast, the Florida population dropped 38% of its leaves during winter. The two populations of the tropical Q. oleoides showed no change in leaf drop during the 3-months winter (10% and 12%) relative to their leaf drop over the same timecourse in the tropical treatment. These results indicate important ecotypic differences in sensitivity to freezing and cold stress between the two populations of Q. virginiana as well as between the two species, corresponding to their climates of origin.     

QTL mapping of chromosomal regions conferring reproductive frost tolerance in barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.)

Spring radiation frost is a major abiotic stress in southern Australia, reducing yield potential and grain quality of barley by damaging sensitive reproductive organs in the latter stages of development. Field-based screening methods were developed, and genetic variation for reproductive frost tolerance was identified. Mapping populations that were segregating for reproductive frost tolerance were screened and significant QTL identified. QTL on chromosome 2HL were identified for frost-induced floret sterility in two different populations at the same genomic location. This QTL was not associated with previously reported developmental or stress-response loci. QTL on chromosome 5HL were identified for frost-induced floret sterility and frost-induced grain damage in all three of the populations studied. The locations of QTL were coincident with previously reported vegetative frost tolerance loci close to the vrn-H1 locus. This locus on chromosome 5HL has now been associated with response to cold stress at both vegetative and reproductive developmental stages in barley. This study will allow reproductive frost tolerance to be seriously pursued as a breeding objective by facilitating a change from difficult phenotypic selection to high-throughput genotypic selection.     

Frost tolerance in winter wheat cultivars: different effects of chromosome 5A and association with microsatellite alleles

Frost tolerance of ten Bulgarian winter wheat (Triticum aestivum L.) cultivars (Milena, Pobeda, Sadovo-1, Enola, Kristal, Laska, Svilena, Russalka, No301 and Lozen) and five foreign cultivars (Mironovskaya 808, Bezostaya-1, Rannaya-12, Skorospelka-35 and Chinese Spring) was studied in two experimental seasons following natural cold acclimation and in one experiment carried out in controlled acclimation conditions. Considerable intercultivar variability in plant survival was observed after freezing at ?21 °C following sufficient cold acclimation, or at ?18 °C following insufficient or controlled acclimation. In seven cultivars, the effects of chromosome 5A on frost tolerance were investigated in their F₂ hybrids with chromosome 5A monosomic lines of cultivars with high, intermediate and low frost tolerance. The effects of chromosome 5A depended on the stress severity and the genetic background of the hybrids and varied even in cultivars of similar frost tolerance and vernalization requirements. Effects of other chromosomes besides 5A on frost tolerance were assumed. The analysis of six microsatellite loci located in the interval from centromere to Vrn-1 on of chromosomes 5AL, 5BL and 5DL showed that the major loci determining frost tolerance in Bulgarian winter wheats were Fr-A2 on chromosome 5AL, and, to a lesser extent, Fr-B1 on chromosome 5BL. A strong association of the 176 bp allele at locus wmc327 tightly linked to Fr-A2 with the elevated frost tolerance of cvs. Milena, Pobeda, Sadovo-1, Mironovskaya-808 and Bezostaya-1 was revealed. Relatively weaker association between frost tolerance and the presence of the 172 bp allele at locus Xgwm639 tightly linked to Fr-B1 was also observed.     

Prevalence of segregation distortion in diploid alfalfa and its implications for genetics and breeding applications

Segregation distortion (SD) is often observed in plant populations; its presence can affect mapping and breeding applications. To investigate the prevalence of SD in diploid alfalfa (Medicago sativa L.), we developed two unrelated segregating F₁ populations and one F₂ population. We genotyped all populations with SSR markers and assessed SD at each locus in each population. The three maps were syntenic and largely colinear with the Medicago truncatula genome sequence. We found genotypic SD for 24 and 34% of markers in the F₁ populations and 68% of markers in the F₂ population; distorted markers were identified on every linkage group. The smaller percentage of genotypic SD in the F₁ populations could be because they were non-inbred and/or due to non-fully informative markers. For the F₂ population, 60 of 90 mapped markers were distorted, and they clustered into eight segregation distortion regions (SDR). Most SDR identified in the F₁ populations were also identified in the F₂ population. Genotypic SD was primarily due to zygotic rather than allelic distortion, suggesting zygotic not gametic selection is the main cause of SD. On the F₂ linkage map, distorted markers in all SDR except two showed heterozygote excess. The severe SD in the F₂ population likely biased genetic distances among markers and possibly also marker ordering and could affect QTL mapping of agronomic traits. To reduce the effects of SD and non-fully informative markers, we suggest constructing linkage maps and conducting QTL mapping in advanced generation populations.