Somaclonal variation and improvement in chilling tolerance in rice: changes in chilling-induced electrolyte leakage

Excised leaves of four rice varieties, ‘Facagro 57’, ‘Facagro 76’, ‘Kirundo 3’, ‘Kirundo 9’, were chilled for six days at 10/5°C day/night, along with 11 somaclonal families arising from three of these varieties, which had been selected over four generations for improved chilling tolerance. At the end of the chilling treatment, electrolyte leakage from leaf pieces was followed for 12 h and compared with an unchilled control. With unchilled leaves, no varietal differences nor a rise in leakage over time were observed. Chilling induced higher leakages in all varieties, except in ‘Kirundo 3’ at the time of first measurement, and a continuous rise over time was found in all varieties. Varietal differences were detected, ‘Kirundo 3’ being the least affected, followed by ‘Kirundo 9’ and ‘Facagro 76’, and finally ‘Facagro 57’, which coincides with their ranking for chilling tolerance established through chilling survival tests. The leakages were generally lower in the somaclonal families than in the variety they originated from in ‘Kirundo 9’ and ‘Facagro 76’, while the opposite was observed in ‘Kirundo 3’. The significance and usefulness of electrolyte leakage measurement for chilling tolerance screening, and the potentials of somaclonal variation for chilling tolerance improvement are discussed.     

Studies on the flooding tolerance of soybean seed: varietal differences

Summary To evaluate seed tolerance of soybean seed to flooding, a screening method by soaking seeds at 25°C for 4 days has been established. Of 730 varieties tested, many from South America, India and Southeast Asia appeared highly tolerant to pre-germination flooding. Seed flooding tolerance correlated with seed coat color. Seeds with black colored coat exhibited high tolerance, and some varieties with black seed coat germinated well even after 10 days soaking at 25°C. All yellow seeds failed completely to germinate after 8 days of soaking.     

Glycinebetaine Improves Chilling Tolerance in Hybrid Maize

Plant growth and development is hampered by various environmental stresses including chilling. We investigated the possibility of improving chilling tolerance in hybrid maize by glycinebetaine (GB) seed treatments. Maize hybrid (Hycorn 8288) seeds were soaked in 50, 100 and 150 mg l^?1 (p.p.m.) aerated solution of GB for 24 h and were dried back. Treated and untreated seeds were sown at 27 °C (optimal temperature) and at 15 °C (chilling stress) under controlled conditions. Germination and seedling growth was significantly hindered under chilling stress. Moreover, chilling stress significantly reduced the starch metabolism and relative water contents (RWC), and increased the membrane electrolyte leakage. However, activities of antioxidants (catalase, superoxide dismutase and ascorbate peroxidase) were increased under stress conditions. Seed treatments with GB improved the germination rate, root and shoot length, seedling fresh and dry weights, leaf and root scores, RWC, soluble sugars, α‐amylase activity and antioxidants significantly compared with untreated seeds under optimal and stress conditions. Induction of chilling tolerance was attributed to maintenance of high tissue water contents, reduced membrane electrolyte leakage, and higher antioxidant activities and carbohydrate metabolism. Seed treatment with 100 mg l^?1 GB was the best treatment for improving the performance of hybrid maize under normal and stress conditions compared with control and other levels used.     

Heat tolerance in food legumes as evaluated by cell membrane thermostability and chlorophyll fluorescence techniques

Summary The genotypic variation for heat tolerance in chickpea, groundnut, pigeonpea, and soya bean was evaluated by testing membrane stability and photosystem (PSII) function in leaves at high temperatures. The legumes could be ranked from heat-tolerant to sensitive in the order: groundnut, soya bean, pigeonpea and chickpea. The damage to cell membranes (as reflected by an increased leakage of electrolytes) and PS II (as reflected by a decrease in the ratio of variable to maximum fluorescence) was less, and recovery from heat stress was faster in groundnut than in other crops. Prior exposure of plants to 35°C for 24h led to a reduced leakage of electrolytes at high temperatures in all crops but the differences among legumes were consistent. Substantial genotypic variation for heat tolerance was found in all legumes. Membrane injury was negatively associated with specific leaf weight in groundnut (r=–0.69^**) and soya bean (r=–0.56^**) but not in the pulses. Electrolyte leakage and fluorescence ratio were negatively correlated in all legumes. The potential use of electrolyte leakage and fluorescence tests as screening procedures for breeding heat-tolerant legumes is discussed.Abbreviations RI relative injury - Fo initial fluorescence - Fm maximum fluorescence - Fv variable fluorescence - PS II photosystem II - PAR photosynthetically active radiation     

Use of somaclonal variation and in vitro selection for chilling tolerance improvement in rice

Embryo-derived calli of four rice varieties cultivated at high altitude in Burundi — Facagro 57, Facagro 76, Kirundo 3 and Kirundo 9 — were submitted to different temperature regimes. The percentage of regenerating calli greatly varied depending on variety, length of culture and callus temperature treatment. The reduction of regeneration percentages induced by low temperature was more pronounced in the more sensitive varieties. Regenerated plants (R0) and their progenies in R1, R2 and R3 were cold-screened together with control plants. In all varieties, significantly higher survival rates were obtained in R3 with in vitro plants than with control plants. Such chilling tolerance improvement was not obtained following a massal selection applied during 3 successive generations onto the control plants. In vitro plants regenerated from calli cultivated either at 25 °C, either at 4 °C, were cultivated at different altitudes in Burundi during two successive generations. For most observed traits, the in vitro plants were characterized by lower means, larger variation and higher maximum values than the control plants. The most chilling-tolerant somaclonal families were most usually characterized by extensive differences in fatty acid composition, chilling-induced electrolyte leakage and chlorophyll fluorescence, compared to the varieties they derived from. This revised version was published online in July 2006 with corrections to the Cover Date.     

低温胁迫下籽用西瓜幼苗生理变化与耐冷性的研究

以三叶一心期的籽用西瓜幼苗为材料,采用10℃低温胁迫的方法,研究了黑籽瓜兰州大片(wb10)和红籽瓜巢湖红(wb7)随着处理天数的延长幼苗的耐冷性、光合特性、生理特性的变化规律,以探讨籽用西瓜耐低温的生理机制,从而为籽用西瓜的引种栽培和抗寒品种选育提供理论依据。结果表明:不同品种籽用西瓜幼苗的叶绿素含量、Pn、Tr、Gs、Ci随低温胁迫时间的延长而逐渐降低;Pro、MDA、相对电导率随低温胁迫时间的延长而升高。两品种的冷害指数存在一定差异,耐冷性表现为wb10>wb7。低温胁迫下,耐冷性较强的wb10幼苗叶片中的叶绿素含量、Pn、Tr、Gs、Ci均高于耐冷性较弱的wb7,而耐冷性较强的wb10幼苗叶片中MDA含量、脯氨酸含量、相对电导率均低于wb7。综合试验中各项指标认为,耐冷性与品种的来源、类型及在低温下植株的冷害指数、光合特性和细胞膜稳定性有关。     

水稻品种对几种逆境的多重耐性及与ABA的关系

从一些耐旱和耐冷品种中筛选出几个具多重耐性的品种,其中大黄谷耐渗透胁迫和盐胁迫,芝麻糯耐盐和冷胁迫,桂溪和湘中籼2号耐渗透胁迫,也较耐冷胁迫.以大黄谷、芝麻糯和桂溪为材料,研究了多重耐性与ABA积累的关系.在渗透胁迫、盐胁迫和冷胁迫下,各水稻品种内源游离ABA含量迅速积累,耐性品种积累的ABA量都较敏感品种高,     

宁夏设施番茄主栽品种芽期和苗期抗寒性评价

以9个不同番茄品种在低温下的发芽特性及苗期的冷害指数,综合评估其耐冷性,以期为生产上筛选抗寒性强的品种提供依据。试验结果,表明“嘉粉8346”和“爱吉168”均表现为耐低温较强的品种。     

In vitro pollen germination and tube growth of tomato (Lycopersicon esculentum Mill.) and its relation with plant growth

Summary In vitro pollen germination at 10°C, 14°C and 22°C of four groups of two pure line tomato varieties was compared with their plant growth at 19°C D/10°C N under controlled environmental conditions. Generally, pollen germination was slow at 10°C but after 6 h the percentage of germination was similar to that at 22°C. Maximum germination was obtained at 14°C already after 4 h. The longest pollen tubes occurred at 22°C. The two varieties within each group differed significantly from each other for percentage of pollen germination. For one group, this difference was greater at 10°C than at 22°C. The varieties in two groups also differed significantly for pollen tube growth. These differences in pollen tube growth rate were greater at 22°C than at 10°C. There was no clear relationship between pollen germination, pollen tube growth and plant growth in any of the four pairs of varieties. The results are discussed with regard to the possibility of pollen selection at low temperature in order to improve the efficiency of breeding for growth at low temperature.     

Evaluation of seedling cold tolerance in rice cultivars: a comparison of visual ratings and quantitative indicators of physiological changes

Rice (Oryza sativa L.) is sensitive to prolonged exposure to low temperature, which at the seedling stage can result in significant chilling injury and mortality. The objective of this study was to quantify physiological and biochemical changes in rice seedlings undergoing chilling stress and compare those changes with visual evaluation of tolerance. Seedlings from the cultivars M-202 (tolerant) and IR50 (sensitive) were subjected to 9°C for 14 days in a controlled environment chamber. Leaf tissues were harvested at various time points for determination of electrolyte leakage, proline, malondialdehyde, ascorbic acid and reduced glutathione. Significant differences between M-202 and IR50 were detected in electrolyte leakage, proline, and ascorbic acid starting at 7 days with IR50 exhibiting higher levels of these indicators. Most IR50 seedlings were dead at 14 days. A set of fifty rice accessions including M-202 and IR50 was evaluated at 10 days of cold treatment to examine the correlation of visual ratings with the physiological indices. Visual ratings were most highly correlated with electrolyte leakage and least correlated with proline content. Based on visual ratings and the physiological indices, we identified several cultivars that outperformed M-202 in cold tolerance while IR50 had the lowest tolerance of the cultivars tested.     

Chilling Tolerance in Hybrid Maize Induced by Seed Priming with Salicylic Acid

The optimum temperature for maize germination is between 25 and 28 °C. Poor and erratic germination at suboptimal temperature is the most important hindrance in its early sowing. This study was conducted to induce chilling tolerance in hybrid maize (Zea mays L.) by seed priming with salicylic acid (SA) and to unravel the background biochemical basis. For seed priming, maize hybrid (Hycorn 8288) seeds were soaked in 50, 100 and 150 ppm (mg l^?1) aerated solutions of SA for 24 h and were dried back. Treated and untreated seeds were sown at 27 °C (optimal temperature) and at 15 °C (chilling stress) under controlled conditions. Performance of maize seedlings was hampered under chilling stress. But seed priming with SA improved the seedling emergence, root and shoot length, seedling fresh and dry weights, and leaf and root score considerably compared with control both at optimal and chilling temperatures. However, priming in 50 mg l^?1 SA solution was more effective, followed by priming in 100 mg l^?1 SA solution. Seed priming with SA improved the chilling tolerance in hybrid maize mainly by the activation of antioxidants (including catalase, superoxide dismutase and ascorbate peroxidase). Moreover, maintenance of high tissue water contents and reduced membrane permeability also contributed towards chilling tolerance.     

Salicylic acid alleviates chilling injury in anthurium (Anthurium andraeanum L.) flowers

We tested if salicylic acid (SA) can alleviate chilling injury in anthurium flowers (Anthurium andraeanum). Cut flowers of five cultivars, individually placed in water, were held at 4 °C and 12 °C. Symptoms of chilling injury (CI) were found in the flowers stored at 4 °C. These symptoms included desiccation of the spadix (the compound floral stalk) and a colour change of the spathe (the large floral bract) to pink and then to brown. The time to the CI symptoms depended on the cultivar. CI symptoms were accompanied by an increase in electrolyte leakage, by loss of fresh weight, and by an increase in catalase (CAT) and superoxide dismutase (SOD) activity. SA at 2.0 mM in water was applied as a 15 min dip. It delayed the CI symptoms, as well as the loss of fresh weight, the increase in electrolyte leakage, and the increase CAT and SOD activity. The data suggest that CI in this system is related to an increase in the concentrations of active oxygen species.     

Determination of Differences in Chilling Susceptibility of Two Soybean Varieties by Means of in vivo Chlorophyll Fluorescence Measurements

Chilling susceptibility of two soybean varieties, i.e. cv. Maple Arrow and cv. Evans , in the vegetative state (V 3.0) was determined by measuring in vivo chlorophyll fluorescence of leaves exposed to low positive temperatures. In the more susceptible variety Maple Arrow quite distinct deviations from the reference fluorescence data are seen at temperatures between 6.5 and 4.8°C, but not until 5.5. to 2.5°C in the variety Evans. Fluorescence characteristics, i.e. the fluorescence decrease Rfd, the appearance of low-waves, the photochemical quenching coefficient at steady-state and the initial slope of the non-photochemical quenching coefficient qNP indicate that the two varieties differ in their susceptibility by about 1-2°C at this stage of development. Our results suggest that measurement of in vivo chlorophyll fluorescence might serve as a suitable rapid monitoring method of pre-screening soybean varieties for chilling susceptibility, as required in plant breeding.     

Activation of Antioxidant System by KCl Improves the Chilling Tolerance in Hybrid Maize

As maize is a chilling-sensitive crop, low temperatures during the early stages of development can be injurious to crop growth and development. Prime mechanism behind chilling-induced damage is oxidative stress. This study was undertaken to improve the chilling tolerance in hybrid maize by seed priming with KCl. For priming, seeds of the maize hybrid Hycorn 8288 were soaked in 50, 100 and 150 mg l⁻¹ aerated solution of KCl for 24 h and then re-dried close to original weight. Primed and untreated seeds were sown at 27 °C (optimal temperature) and at 15 °C (chilling stress) under controlled conditions. Seed priming improved the performance of maize under both normal and stress conditions. It was found that the chilling tolerance in maize is well associated with the enhanced capacity of the anti-oxidative system. Priming with KCl significantly improved the chilling tolerance mainly by the activation of antioxidants including catalase, superoxide dismutase and ascorbate peroxidase enzymes. KCl treatments also improved the germination rate and time, root and shoot length, and fresh and dry weights of seedlings compared with control. Soluble sugars and α-amylase activity determined as general metabolic indicators of stress were also improved by seed priming with KCl. Other possible bases of chilling tolerance in maize included maintenance of high tissue water contents, reduced electrolyte leakage and carbohydrate metabolism. Seed treatment with 100 mg l⁻¹ KCl was the best treatment to improve the performance of hybrid maize both under normal and chilling stress conditions.     

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.     

Differential cold sensitivity of pollen grain germination in two Prunus species

Summary Pollen grains from selected cutivars of almond [Prunus dulcis (Mill.) D. A. Webb] and peach (Prunus persica Batsch L.) were exposed to a range of temperatures between 1°C and 34°C on a thermogradient plate. Pollen germination at temperatures below 9°C was conspicuously greater in almond than peach. Miximal germination percentages were attained at about 16°C (almond) and 23°C (peach). The two species did not differ in their capacity for pollen tube elongation over a broad range of temperatures. Maximal pollen tube elongation occurred at temperatures 5°C to 8°C higher than maximal pollen germination. Species affiliation appeared to be of much greater consequence than chilling requirement or bloom date of the sporophyte in predicting gametophytic response to temperature.     

PEG模拟干旱胁迫下不同大麻品种萌发期抗旱性评价

萌发期是大麻生长周期中的一个关键时期,此期的干旱对大麻生长及产量有着重要的影响。本研究选用云麻1号等10个大麻品种为实验材料,采用PEG-6000模拟干旱胁迫的方法,对大麻萌发期的抗旱性进行分析和评价。通过高渗透压下初步筛选出萌发性和抗旱性较好的5个大麻品种。在不同PEG浓度下大麻萌发期抗旱性评价中发现,低浓度PEG溶液能促进大麻种子萌发,随着PEG浓度的增加,大麻种子萌发受到的抑制作用越大,当PEG浓度为20%时,不同品种的萌发指标差异显著,可以在此浓度下,进行抗旱性大麻品种(系)的筛选鉴定。通过隶属函数法综合评价发现,云南的3个大麻品种表现出较强的抗旱性,其中云晚6号萌发期的抗旱性最强。     

Flooding tolerance of spelt (Triticum spelta L.) compared to wheat (Triticum aestivum L.) – A physiological and genetic approach

In marginal, agroclimatic zones, yield is often affected by flooding, but the effect is much less for winter spelt (Triticum spelta L.) than for winter wheat (Triticum aestivum L.). This study evaluates the reaction of a wheat x spelt population (F₅ RILs of Forno x Oberkulmer) to flooding stress in the early phase of germination. Lines with greater tolerance to 48 h flooding just after imbibition showed less electrolyte leakage (r = -0.79) indicating greater membrane integrity and better survival. Five QTL explaining 40.6% of the phenotypic variance for survival to flooding were found, and localized on the chromosomes 2B, 3B,5A, and 7S. The tolerance to 48 h flooding four days after sowing was best correlated with the mean germination time (r = 0.8), indicating that the plants with a fast coleoptile growth during flooding are less susceptible to flooding. Ten QTL were found for seedling growth index after flooding explaining 35.5% of the phenotypic variance. They were localized on chromosomes 2A, 2B, 2D, 3A, 4B, 5A, 5B, 6A, and 7S. Standard varieties of spelt and wheat showed the same tolerance characteristics. The possibility to use marker assisted selection for flooding tolerance is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Selection for fast germination in rapeseed (Brassica napus L. and B. Campestris L.)

Summary Eleven populations of Brassica napus L. and twelve populations of B. campestris L. were subjected to three cycles of selection for fast germination at 2°C and at 25°C. The seeds from the selected populations, and unselected control populations grown in the same environment as the selected populations, were examined for germination behaviour at 2°C and 25°C, and for growth behaviour at 10°C. The populations in both species responded differently in terms of germination behaviour to selection for fast germination. In most of the populations that did respond positively to selection, selection practised at 2°C was superior to selection at 25°C in improving percent germination at 2°C, and was as good as the selection at 25°C in improving germination rate at the higher temperature. Selection for fast germination had no effect on growth characteristics of B. napus and B. campestris populations grown at 10°C. Thus, selection for fast germination at one low temperature may lead to improvement in germination characteristics over a range of temperatures, but will not necessarily lead to improved growth performance of the selected populations.     

晚稻品种种子萌发期耐酸性比较研究

为了给酸化稻田适宜晚稻品种选择提供参考,通过室内发芽试验考察了25个晚稻品种（品系）在6个pH梯度下的发芽率、发芽势和单苗鲜重,比较研究了其种子萌发期耐酸性差异。结果表明：（1）品种间发芽率、发芽势、单苗鲜重差异很大,其中3号、7号、10号、15号品种较高,18号、19号、21号、22号品种较低;（2）6号、11号、12号、13号、14号、16号、19号、21号、23号、24号、25号品种的发芽率、发芽势和单苗鲜重在6个pH梯度处理下变化幅度较大,被初步判定为酸性敏感型品种;（3）2号、3号、5号、10号、15号、17号品种的发芽率、发芽势和单苗鲜重在6个pH梯度处理下变化幅度较小,被初步判定为酸性迟钝型品种。种子萌发期耐酸性比较,可为初步筛选酸化稻田适宜水稻品种提供重要参考。