Methods for the Selection of Low-Temperature Tolerant Mutants of Chrysanthemum morifolium Ramat. by Using Irradiated Cell Suspension Cultures

In order to improve mutant selection procedures, 5000 plantlets were regenerated in three different harvests (flush A, B and C) from X-irradiated (15 and 20 Gy) and non-irradiated cell suspensions of Chrysanthemum morifolium cv. ‘Parliament’. After screening under suboptimal energy condition (12°C greenhouse temperature, winter low-light), a total of 95 early flowering plants were selected. These plants flowered at least as early as a low-temperature tolerant (LTT) mutant E₂, used as a reference. The percentage of early flowering variants was highest among plants obtained from calli, X-irradiated with 15 Gy and regenerating relatively late (flush B). It appeared that the applied selection method (e.q. harvest) had a large impact on the number of early plants obtained.     

Effect of temperature on gametophytic selection in a <Emphasis Type="Italic">Phalaenopsis</Emphasis> F<Subscript>1</Subscript> population

Gametophytic selection has potential to increase the efficiency of breeding for temperature tolerance. Here, we describe orchid seedlings after application of low and high temperatures during gametophytic development. In addition to phenotypic traits, amplified fragment length polymorphism (AFLP) markers were used to determine the genetic variability in seedlings. Two hybrid Phalaenopsis were cross-pollinated and exposed to 30°C day/25°C night for 3 days for a warm pollination or 15°C day/10°C night for 7 days as a cold pollination treatment. The plants were returned to the greenhouse after pollination and green capsules were collected after 150 days. Protocorms obtained from these treatments were evaluated 72 days after initial plating for germination and size on a thermogradient table ranging from 10 to 30°C. Seedlings were then evaluated 1 year after initial plating. The mean number of roots per seedling (4.2) was greater for plantlets that derived from the cold pollination treatment compared to those from warm pollination (3.6). Weight of the seedlings, number of roots and the average root length were significantly affected by the interaction between pollination treatment and germination temperature. The weight, number of leaves, and average root length were significantly affected by the interaction between pollination treatment and incubator/growth chamber. The results indicated that seedlings derived from warm pollination were more vigorous under warm growing conditions and those derived from cold pollination were more vigorous under cold growing conditions. Genetic variation among 16 F₁ seedlings randomly selected from various temperature treatments was analyzed. A dendrogram based on 651 loci resulted in three major groups and one subgroup. The groups and subgroup revealed common selection pressure during the gametophytic stage. The AFLP data support genetic differentiation of Phalaenopsis hybrids pollinated under different temperatures.     

Microspore Embryogenesis Induced by Low Gamma Dose Irradiation in Apple

Flower buds and extracted anthers of two apple genotypes, ‘Golden Delicious’— a previously known non-androgenic genotype — and ‘Topred’— a known androgenic genotype —, were irradiated by gamma-rays at doses ranging from 5 to 20 Gy, after 0 to 5 weeks of cold pre-treatment (3 °C). When the extracted anthers were irradiated, both microspore embryogenesis and callogenesis were limited for the two genotypes. For ‘Golden Delicious’, androgenic embryogenesis was induced from the flower buds irradiated at 10 to 20 Gy and after 3 to 5 weeks of cold pre-treatment. For ‘Topred’, androgenic embryogenesis was slightly improved after flower bud irradiation at 5 to 10 Gy following cold pre-treatment from 0 to 3 weeks; it was limited after 5 weeks of cold pre-treatment.     

Putrescine Increases Floral Retention, Pod Set and Seed Yield in Cold Stressed Chickpea

Chickpea (Cicer arietinum L.) is sensitive to cold stress (<8 °C) at its reproductive phase that results in flower abortion, poor pod set and thus reduced yield. Early maturing genotypes are especially more sensitive. In this crop, the metabolic causes underlying cold injury that are imperative to induce cold tolerance are not known. In the present study, the endogenous levels of putrescine (diamine), spermidine (triamine) and spermine (tetramine) were examined in early maturing chickpea genotype ICCV 96029, subjected to chilling temperatures of field (12–15/4–6 °C; average maximum and minimum temperature respectively), at flowering or early podding stage. These were compared with controls growing in warmer conditions (28/12 °C) of the glasshouse. The polyamine levels increased six to nine times because of stress. Relatively, putrescine (PUT) elevation was the highest but short-lived and its decrease appeared to match with the onset of flower and pod abscission in stressed plants. Compared with controls, chilling injury, observed as electrolyte leakage (EL), increased by 60 % while cellular respiration declined by 68 % in stressed plants. Exogenous application of 10 mm PUT to stressed plants reduced the EL by 29 % and elevated the cellular respiration by 40 %. PUT application at flowering stage resulted in increase of 30, 31, 23 and 25 % in floral retention, pod set, pod retention and fertile pods respectively. At the early podding stage, PUT treatment increased the seed yield per plant, seed number per 100 pods and individual seed weight by 50, 17 and 19 % respectively. The number of single-seeded pods per plant increased from 4.4 in stressed plants to 12.2 in PUT-treated plants while the number of double-seeded pods reduced from 6.2 to 4.3. The number of infertile pods declined from 8.2 in stressed plants to 3.1 in PUT-treated plants.     

Methods for Selection of Low-Temperature Tolerant Mutants of Chrysanthemum morifolium Ramat. Using Irradiated Cell Suspension Cultures III. Comparison of Mutants Selected with or without Preselection in vitro at Low-Temperature

One hundred variants of Chrysanthemum morifolium cv. ‘Parliament’, selected on a single plant basis for early flowering at low temperature, were tested on a clonal basis. These variants originated from irradiated or non-irradiated microcalli subjected to a one-step greenhouse selection procedure, or, a two-step selection procedure (preselection in vitro at 6°C followed by selection in the greenhouse). Clones originating from irradiated calli flowered significantly earlier than the controls. Most of the low-temperature tolerant (LTT) mutants were found among plants obtained by the one-step selection procedure. Variants originating from slowly regenerating calli yielded more LTT mutants as compared to those of fast(er) regenerating calli. We therefore conclude that, irradiation and subsequent selection of plants from slowly regenerating calli considerably increases the efficiency of selecting LTT mutants. The expected advantage of a preselection in vitro at low-temperature could not be confirmed.     

Methods for evaluation of soybean chilling tolerance at the reproductive stage under artificial climatic conditions

Several evaluation methods for soybean chilling tolerance at the reproductive stage were examined under artificial climatic conditions. Comparisons were made on plants in control and treated plots using three cultivars differing in the level of chilling tolerance. In all methods, plants were grown at 22/17°C (day/night) until first flowering, and then transferred to growth chambers at 24/17°C for control and 15/15°C for chilling treatment, respectively. A method, in which plants were grown at 20/16°C after 4 weeks of the different temperature treatments, proved comparable to the conventional one, in which chilling tolerance at the flowering stage is evaluated using natural and artificial conditions. Another method, in which the plants in chilling treatment plots were grown at 15°C until maturity, also proved usable to evaluate genotypic differences in chilling tolerance independently of maturity time.     

Effects of day-length and temperature on floral structure and fertility restoration in a season-dependent male-sterile Solanum villosum Mill. mutant

Solanum villosum is an important African leafy vegetable whose yield is limited mainly by competition from early and excess fruit-set. Induced male-sterility is a potential tool to reduce this competition and enhance yields. This study was conducted to investigate the influence of photoperiod and temperature on the floral dynamics of a season-dependent male-sterile mutant. The mutant, named T-5, has flowers which are sepaloid, mostly stamenless, indeterminate and partially restored in winter, late-spring, summer and autumn, respectively. Floral organ restoration was found to be largely independent of photoperiod conditions. Day/night temperatures of 25/25 and 30/20°C were found to favour restoration of the floral organ but most flowers were stamenless and infertile. High night temperature favoured the formation of indeterminate flowers both in the growth chamber (30°C) and in the greenhouse (>25°C). On the other hand, low growth chamber (10°C) and greenhouse (<15°C) night temperature favoured the formation of sepaloid flowers. The optimum temperatures for floral structure and fertility restoration were between 20°C and 25°C (day) and 15–20°C (night). Propagation of T-5 mutant can thus be achieved by growing in regions or seasons with such temperature ranges. Under temperatures unfavourable for fruit-set, leaf productivity is expected to be high.     

Protective Effects of Polyamines against Oxidative Stress Induced by Water and Cold Stress in Chickpea

Chickpea (Cicer arietinum L.) yields are drastically reduced by water and cold stress that occur individually or simultaneously in northern region of India. The comparative effects of both the stresses were investigated at the metabolic level by examining the endogenous status of polyamines (PAS), active oxygen species and antioxidants. Chickpea plants (15‐day old) growing hydroponically under controlled conditions (light/ dark; 24/21 °C, 16/8 h; irradiance 250 μmol m^?2 s^?1) were subjected to water deficit stress (Ψ_s of ?0.2 to ?1.0 MPa) and cold stress (5–25 °C) for 4 days. LD₅₀ in terms of root growth rate (RGR), electrolyte leakage and triphenyl tetrazolium chloride (TTC) reduction activity was observed at ?0.6 MPa and 10 °C for water and cold stress, respectively. In a subsequent experiment, 15‐day‐old plants were exposed to these stress levels under the above‐mentioned growth conditions for 7 days and analysed for various parameters. In cold‐stressed plants (CS), putrescine (PUT) was observed to be relatively higher while water‐stressed plants (WS) had more of spermidine (SPD). Spermine (SPM) levels increased more rapidly in WS and declined on the fourth day of stress while in CS, a gradual increase occurred that decreased on the seventh day. The accumulation of PAs was short‐lived under the combined presence of both the stresses. Hydrogen peroxide elevated abruptly in WS and remained higher than CS while the latter showed a marked increase in malondialdehyde content. Ascorbic acid increased sharply in WS that decreased on the fourth day while CS showed a relatively gradual increase that reached its maximum on the fourth day and declined subsequently. Glutathione was significantly higher in CS plants in comparison with WS and CS + WS plants. The activity levels of superoxide dismutase were higher up to 4 days and declined subsequently while those of WS stayed higher till the last day of stress. Ascorbate peroxidase levels were significantly higher in CS plants while catalase activity was comparatively more in WS. Exogenous application of PAs reduced the level of hydrogen peroxide, malondialdehyde content and raised the level of antioxidants. Put caused 44 and 32 % increase in RGR in CS and WS, respectively, while SPD resulted in 110 and 25 % enhancement in WS and CS, respectively. Under combination of stresses, RGR increased by 21, 53 and 10 % by Put, SPD and SPM, respectively. The effects of PAs could be reversed largely by their biosynthetic inhibitors. α‐difluoromethylornithine (a biosynthetic inhibitor of putrescine) caused more damage to CS while cyclohexylamine (inhibitor of SPD and SPM biosynthesis) was more inhibitory in WS.     

Induction of mutations for heat tolerance in potato by using in vitro culture and radiation

Heat tolerant mutants were obtained in two commercial potato cultivars, `Kufri Jyoti' and `Kufri Chandramukhi' through in vitro mutagenesis of in vitro propagated plantlets. Gamma-irradiated (20 and 40 Gy) shoots were micropropagated for three cycles (M₁V₃). A large number of the micropropagated shoots produced microtubers at 28 ^°C. Microtubers induced at high temperature had distorted shape but showed normal germination in field. Under stress conditions of high temperature, the frequency of chlorophyll variants increased in the gamma irradiation-derived material, however, nearly 40% of the plants had normal leaf tissue, whereas control plants showed completely damaged leaves. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interspecific cross of Brassica oleracea var. alboglabra and B. napus : effects of growth condition and silique age on the efficiency of hybrid production, and inheritance of erucic acid in the self-pollinated backcross generation

Interspecific hybrids were produced from reciprocal crosses between Brassica napus (2n = 38, AACC) and B. oleracea var. alboglabra (2n = 18, CC) to introgress the zero-erucic acid alleles from B. napus into B. oleracea. The ovule culture embryo rescue technique was applied for production of F₁ plants. The effects of silique age, as measured by days after pollination (DAP), and growth condition (temperature) on the efficiency of this technique was investigated. The greatest numbers of hybrids per pollination were produced under 20°/15°C (day/night) at 16 DAP for B. oleracea (♀) × B. napus crosses, while under 15°/10°C at 14 DAP for B. napus (♀) × B. oleracea crosses. Application of the ovule culture technique also increased the efficiency of BC₁ (F₁ × B. oleracea) hybrid production by 10-fold over in vivo seed set. The segregation of erucic acid alleles in the self-pollinated backcross generation, i.e. in BC₁S₁ seeds, revealed that the gametes of the F₁ and BC₁ plants carrying a greater number of A-genome chromosomes were more viable. This resulted in a significantly greater number of intermediate and a smaller number of high-erucic acid BC₁S₁ seeds.     

Genetic analysis of cold tolerance during vegetative growth in tomato, Lycopersicon esculentum Mill.

The genetic basis of cold tolerance (CT) during vegetative growth in tomato was investigated by evaluating plants of a cold-tolerant primitive cultivar (PI120256) and a cold-sensitive breeding line (UCT5) and their reciprocal F₁, F₂, F₃, BC₁P₁ and BC₁P₂ progeny under two temperature regimes of 15/10 ^°C (cold stress) and 25/15 ^°C (control). Plants were evaluated for shoot dry weight (DW) under cold stress and by a tolerance index (TI) measured as the ratio of DW under cold stress (DW_s) to DW under control (DW_c) conditions. Shoot DW was reduced in all genotypes in response to cold stress. However, PI120256 exhibited the highest CT (TI = 90.5%) and UCT5 the lowest (TI = 38.9%). The TIs of the filial and backcross progeny were intermediate to the parents. Across generations, there was a positive correlation (r = 0.76, p < 0.01) between DW_s and DW_c indicating that growth under cold stress was influenced by plant vigor. However, the absence of a significant correlation (r=0.47, p >0.05) between DW_c and the TI and, in contrast, the presence of a significant correlation (r =0.92, p <0.01) between DW_s and the TI suggest that plant vigor was not a determining factor in the expression of CT in PI120256 and its progeny. Generation means analyses of DW_s and TI indicated that the variation among generations was genetically controlled, with additive effects accounting for most of the variation. There were no significant dominance effects, and epistatic effects were minor and involved only additive × additive interactions. The results suggest that the inherent CT of PI120256 should be useful for improving CT of commercial cultivars of tomato. This revised version was published online in August 2006 with corrections to the Cover Date.     

Plant age and in vitro or in vivo propagation considerably affect cold tolerance of Miscanthus × giganteus

The aims of the study were to determine why young Miscanthus × giganteus plants are more frost sensitive during the first winter than older plants, to compare cold tolerance of plants propagated in in vivo and in vitro conditions, and to select plants with higher cold tolerance. The study was performed in three experiments in which plants were prehardened at 12 °C for 2 weeks, hardened at 5 °C for 3 weeks and next chilled at 0 °C or ?3 °C for 3 or 14 days. Afterwards shoot regrowth from rhizomes was evaluated. In Experiment 1 frost tolerance of young plants obtained from a horticultural farm and plants that had already survived the first winter in the field was compared on the basis of LT₅₀ coefficient. In Experiment 2 frost tolerance of plants obtained in vivo and in vitro was compared. Experiment 3 was performed on four groups of plants: in vivo and in vitro obtained plants which were twice selected in cold, as well as in vivo and in vitro obtained plants which were cold treated once. Plants of all these groups were analysed with respect to their frost tolerance. They were prehardened, hardened and subjected to a temperature of 0 °C or ?3 °C for 14 days. The changes in processes accompanying cold acclimation occurring in the rhizomes or leaves of these plants were investigated. The content of abscisic acid, low-molecular antioxidants and phenolics, as well as catalase and non-specific peroxidase activities were analysed.Young commercially obtained plants were more frost sensitive than plants which had survived the first winter in the field. This effect could be caused by a small amount of storage compounds accumulated in finely divided rhizomes produced in a horticultural farm. Prehardening temperature of 12 °C caused more considerable changes in cold acclimation processes in Miscanthus rhizomes than hardening temperature of 5 °C. Plants propagated by in vitro culture were more cold tolerant but only in the first vegetative season compared to plants obtained in vivo. Plants chilled twice demonstrated a higher low-molecular antioxidant level, as well as a greater capability of phenolic accumulation compared to plants which were once cold stressed. Regardless of the recurrence of cold acclimation, ABA level was significantly increased in leaves by prehardening and in rhizomes by hardening. Each repetition of cold acclimation increased cold tolerance and shoot regeneration ability of M. × giganteus rhizomes.     

Genotypic differences in utilization of assimilate sources during maturation of wheat under chronic heat and heat shock stresses

Heat stress from chronic, prolonged exposure up to 32 ^°C or heat shock from brief exposure to 33 ^°C and above alters the source of assimilates for grain growth of wheat (Triticum asetivum L.). Our objectives were to identify genotypes that resist chronic heat stress and heat shock and to determine the relative contributions of photosynthesis and stem reserves to grain filling under both conditions. Twenty-eight genotypes were grown in controlled enviroments at 20/15 and 30/25 ^°C day/night in light and darkness during maturation in the first experiment, and six genotypes were grown in light at the same temperatures and at 40/35 ^°C followed by 20/15 or 30/25 ^°C in the second experimnet. Heat susceptibility indices (HSI) were calculated from grain yields of the genotypes in both experiments. The ratio of chlorophyll variable fluorescence to maximum fluorescence (Fv/Fm), a measure of the stability of photosynthesis, and carbohydrate reserves in the stems were measured in the second experiment. Photosynthesis provided 63 and 65% of assimilates in the grain at 20/15 and 30/25 ^°C, respectively, but both stable photosynthesis in some genotypes and high content of reserves in other genotypes were associated with low susceptibility to stress. The Fv/Fm ratio was decreased by heat shock and returned to normal values intolerant genotypes when the treatment was followed by 20/15 ^°C but not 30/25 ^°C. Grain yield was highly correlated among 20/15, 30/25, and 40/35 ^°C followed by 20/15 ^°C treatments, suggesting that similar plant traits were involved. We conclude that assimilates from either stable photosynthesis or high reserve levels provided for high grain yields during heat stress. Combining the two traits could improve heat tolerance of wheat but might not be feasible if other traits are impeded. This revised version was published online in July 2006 with corrections to the Cover Date.     

Exogenous Application of Abscisic Acid Improves Cold Tolerance in Chickpea (Cicer arietinum L.)

Chickpea suffers cold stress (<10 °C) damage especially during reproductive phase resulting in the abortion of flowers and pods, poor pod set, and reduction in seed yield and seed quality. One of the ways in modifying cold tolerance involves exogenous treatment of the plants with chemicals having established role in cold tolerance. In the present study, the chickpea plants growing under optimum temperature conditions (28/12 °C, as average maximum and minimum temperature) were subjected to cold conditions of the field (10–12/2–4 °C; day/night as average maximum and minimum temperature) at the bud stage. Prior to exposure, these plants were treated exogenously with 10 μm abscisic acid (ABA) and thereafter again after 1 week of exposure. The stress injury measured in terms of increase in electrolyte leakage, decrease in 2,3,5-triphenyl tetrazolium chloride reduction %, relative leaf water content and chlorophyll content was observed to be significantly mitigated in ABA-applied plants. A greater pollen viability, pollen germination, flower retention and pod set were noticed in ABA-treated plants compared with stressed plants. The seed yield showed considerable improvement in the plants treated with ABA relative to the stressed plants that was attributed to the increase in seed weight, greater number of single seeded pods and reduction in number of infertile pods. The oxidative damage measured as thiobarbituric acid-reactive substances was lesser in ABA-treated plants that was associated with greater activities of superoxide dismutase, catalase, ascorbate peroxidase, ascorbic acid, glutathione and proline in these plants. It was concluded that cold stress effects were partly overcome by ABA treatment because of the improvement in water status of the leaves as well as the reduction in oxidative damage.     

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’.     

Impact of waterlogging and temperature on autumn growth,hardening and freezing tolerance of timothy (Phleum pratense)

Precipitation has generally increased in Norway during the last century, and climate projections indicate a further increase. The growing season has also become longer with higher temperatures, particularly in autumn. Previous studies have shown negative effects of high temperatures and, depending upon temperature conditions, contrasting effects of waterlogging on hardening capacity of timothy. We studied effects of waterlogging on seedlings of timothy (Phleum pratense, cv. Noreng) under three pre-acclimation temperatures: 3°C, 7°C, 12°C, and in autumn natural light in a phytotron at Holt, Tromsø (69°N). After temperature treatments, all plants were cold acclimated at 2°C for three weeks under continued waterlogging treatments. Freezing tolerance was determined by intact plants being frozen in pots at incremental temperature decreases in a programmable freezer. Waterlogging resulted in a higher probability of death after freezing, and a significantly reduced regrowth after three weeks at 18°C, 24 hrs light in a greenhouse. Increasing pre-acclimation temperatures also had a clear negative effect on freezing tolerance, but there was no interaction between temperatures and waterlogging. The results indicate that waterlogging may have negative implications for hardening of timothy and may contribute to reduced winter survival under the projected increase in autumn temperatures and precipitation.     

Low Temperature Effects during Seed Filling on Chickpea Genotypes (Cicer arietinum L.): Probing Mechanisms affecting Seed Reserves and Yield

Chickpea is sensitive to cold conditions (<15 °C), particularly at its reproductive phase and consequently it experiences significant decrease in the seed yield. The information about the effects of cold stress on chickpea during the seed filling phase is lacking. Moreover, the underlying metabolic reasons associated with the low temperature injury are largely unknown in the crop. Hence, the present study was undertaken with the objectives: (i) to find out the possible mechanisms leading to low temperature damage during the seed filling and (ii) to investigate the relative response of the microcarpa (Desi) and the macrocarpa (Kabuli) chickpea types along with elucidation of the possible mechanisms governing the differential cold sensitivity at this stage. At the time of initiation of the seed filling (pod size ∼1 cm), a set of plants growing under warm conditions of the glasshouse (temperature: 17/28 ± 2 °C as average night and day temperature) was subjected to cold conditions of the field (2.3/11.7 ± 2 °C as average night and day temperature), while another set was maintained under warm conditions (control). The chilling conditions resulted in the increase in electrolyte leakage, the loss of chlorophyll, the decrease in sucrose content and the reduction in water status in leaves, which occurred to a greater extent in the macrocarpa type than in the microcarpa type. The total plant weight decreased to the same level in both the chickpea types, whereas the rate and duration of the seed filling, seed size, seed weight, pods per plant and harvest index decreased greatly in the macrocarpa type. The stressed seeds of both the chickpea types experienced marked reduction in the accumulation of starch, proteins, fats, crude fibre, protein fractions (albumins, globulins, prolamins and glutelins) with a larger decrease in the macrocarpa type. The accumulation of sucrose and the activity levels of the enzymes like starch synthase, sucrose synthase and invertase decreased significantly in the seeds because of the chilling, indicating impairment in sucrose import. Minerals such as calcium, phosphorous and iron as well as several amino acids (phenylalanine, tyrosine, threonine, tryptophan, valine and histidine) were lowered significantly in the stressed seeds. These components were limited to a higher extent in the macrocarpa type indicating higher cold sensitivity of this type.     

Suitability of A European Nuclear Collection of Brassica oleracea L. Landraces to Grow at High Temperatures

Statistical models predict that global warming will have a negative impact in crop yields in the next decades. Especially vulnerable are winter crops such as kales or cabbages (Brassica oleracea L.). We evaluated the impact of high temperatures in morphological and biochemical traits of a B. oleracea core collection during early development. When grown at 30 °C, plants showed a reduction in chlorophyll content, early vigour and biomass compared with values observed on plants grown at 20 °C. Likewise, the total content of glucosinolates shows a reduction at high temperatures. The alboglabra group showed the best general performance at 30 °C for both morphological traits and glucosinolate content. Based on a cluster analysis, we selected four populations (MBG0072, MBG0464, MBG0535 and HRIGRU5555) as the most promising to be used in further breeding programs for heat tolerance.     

Germination Responses of Cañahua (Chenopodium pallidicaule Aellen) to Temperature and Sowing Depth: A Crop Growing Under Extreme Conditions

Cañahua (Chenopodium pallidicaule) is grown in the Altiplano of Bolivia and Peru, between 3810 and 4200 m a.s.l. Rural indigenous households have cultivated the cañahua as a subsistence crop for millennia. The seeds have a high content and quality of protein. We studied the relation between the following: (i) temperature and seed germination and (ii) the effect of temperature and sowing depth on seedling emergence of five cultivars and one landrace. Three experiments were conducted as follows: (i) seeds of a cultivar were germinated in Petri dishes at six temperatures (3, 5, 10, 14, 20 and 24 °C), (ii) sown at five depths (0, 5, 10, 25 and 50 mm) in a mixed peat soil substrate at three temperatures and (iii) one landrace (Lasta) and 5 cultivars (Lasta and Saihua growth habit) were sown in 6 depth (0, 5, 10, 25, 35 and 50 mm) in a sandy loam at two temperatures (5 and 15 °C). Temperature had significantly effect on the germination percentages of the plants (P < 0.001). Seeds germinated at the lowest temperature (3 °C). The estimated base temperature was close to 0 °C. A polynomial function described well the relation between time to 50% germination (t₅₀) and temperature in the interval from 3 to 24 °C resulting in a linear relationship between germination rate and temperature. Shallow sowing depth (5–25 mm) resulted in 80% germination at 15 °C. There were significant differences of emergence in relationship to burial depth (P < 0.001). Only few seedlings emerged when seeds were sown at 50 mm depth. We did not find significant differences in emergence of seedlings between Lasta and Saihua at 15 °C. Nevertheless, at 5 °C, seedlings of cañahua belonging to the Lasta growth habit form did have higher germination rate as were shown for the Kullaca cultivar and the Umacutama landrace. This may be attributed to larger seed size of these cultivars.