Oxidative stress indicators as selection tools for salt tolerance

Oxidative stress indicators, malondialdehyde (MDA) accumulation and chlorophyll retention, were tested as tools for salt‐tolerance screening in Chloris gayana (Kunth), a forage grass exhibiting inter‐ and intra‐cultivar variability in the response to salt stress. Three types of experimental system were compared, salt shock, gradual salt treatment and leaf segments floated on control and saline solutions. Results followed the same trend in the three systems, but leaf segments or gradually salinized plants are the most convenient. Lower mean MDA and higher mean chlorophyll content were found under salinity in cv. ‘Katambora’, which is considered, from previous field trials, to be more salt tolerant than cv. ‘Boma’. Nevertheless, chlorophyll content did not give consistent results in other tests and it is not recommended for selection purposes. Within cv. ‘Boma’, clones rating higher in a salt tolerance evaluation under greenhouse conditions had lower MDA content under salinity and lower mean MDA ratios between salt‐treated and control samples. The survival of 80‘Boma’ plants under increasing NaCl concentration was assessed and MDA was measured in the leaves of very plant before the final NaCl level was reached, to assess whether it was predictive of survival capability. MDA values were significantly lower in the group surviving longer, thus, a selection based on low MDA values would have enriched the original population with more tolerant individuals.     

QTL mapping for heading date,leaf area and chlorophyll content under cold and drought stress in two related recombinant inbred line populations (Japonica rice) and meta‐analysis

Rice is highly susceptible to drought and cold. The goal of this study was to identify the QTLs affecting the rice heading date (HD), leaf area (LA) and chlorophyll content (CC) under cold and drought stress. A total of twenty‐nine and thirty‐eight additive QTLs were detected from two crosses of ‘Dongnong422’/‘Kongyu131’ and ‘Xiaobaijingzi’/‘Kongyu131’, respectively. qHD1‐7‐1, qHD1‐7‐2, qHD1‐2‐1, qLA1‐7‐1, qLA1‐6‐3 and qCC1‐7‐1 show adaptive effects under cold treatment, while qHD2‐2‐3, qHD2‐2‐2, qLA2‐7‐3 and qCC2‐5‐1 were important for explaining the genetic mechanism during drought tolerance. Additionally, nine and five additive × environment interaction QTLs were detected for two RILs, respectively. RIL26 and RIL73 were two lines that are associated with cold and drought for HD. 339 QTLs related to HD, CC and LA of rice from database and our research were projected onto the genetic map. Nine cloned genes and nineteen homologous candidate genes related to HD, CC, cold tolerance and drought tolerance were mapped by meta‐analysis. These results lay the foundation for the fine mapping of QTLs related to HD, LA and CC for marker‐assisted selection.     

Genetic transformation of lipid transfer protein encoding gene in <Emphasis Type="Italic">Phalaenopsis amabilis</Emphasis> to enhance cold resistance

Embryogenic callus of Phalaenopsis amabilis derived from leaf tissue was cocultivated with Agrobacterium tumefaciens strain LBA4404 harboring a plant cloning vector. The vector carried the lipid transfer protein (LTP) encoding gene cloned from cold tolerant Brazilian upland rice cv. IAPAR 9. The highest transformation efficiency (12.16%) was obtained when 1–2 mm calli were infected and cocultivated with 0.4 (OD₆₀₀) A. tumefaciens for 20 min. Transgene integration of kan-resistant plants was confirmed through polymerase chain reaction analysis and Southern hybridization. Four hundred seventy transgenic plants, each derived from an independent protocorm-like body, were obtained. The expression of rice cold-inducible LTP gene in transgenic P. amabilis improved its adaptive responses to cold stress. The examination of transgenic plants revealed that enhanced cold tolerance was most likely due to the increased accumulation of several compatible solutes such as total soluble sugars, proline, antioxidant superoxide dismutase, decreased accumulation of malondialdehyde, and maintained electrolytes within the membrane compared with controls.     

Deployment of cold tolerance loci from Oryza sativa ssp. Japonica cv. ‘Nipponbare’ in a high‐yielding Indica rice cultivar ‘93‐11’

Cold tolerance is a complex trait, and QTL pyramiding is required for rice breeding. In this study, a total of seven QTLs for cold tolerance in the Japonica rice variety ‘Nipponbare’ were identified in an F_2:3 population. A stably inherited major QTL, called qCTS11, was detected in the region adjacent to the centromere of chromosome 11. In a near‐isogenic line population, the QTL was further dissected into two linked loci, qCTS11.1 and qCTS11.2. Both of the homozygous alleles of qCTS11.1 and qCTS11.2 from ‘Nipponbare’ showed major positive effects on cold tolerance. Through pyramiding the linked QTLs in the cold‐sensitive Indica rice cultivar ‘93‐11’, we have developed a new elite, high‐yielding Indica variety with cold tolerance.     

Leaf greenness measurements to evaluate water stressed genotypes in Vitis vinifera

Summary The leaf greenness (measured by a portable chlorophyll meter SPAD-501) has been used to differentiate table grape genotypes (Vitis vinifera) in water stress condition. The SPAD and chlorophyll values are lower in the stressed treatment after 2 weeks from the onset of stress. Linear response model has been observed between the chlorophyll content and the SPAD readings. The leaf greenness (SPAD readings) of apical and expanded leaves seems an easy indicator, which might be used for screening grape genotypes (Vitis vinifera) for drougth tolerance.     

Methods for Selection of Low-Temperature Tolerant Mutants of Chrysanthemum morifolium Ramat. Using Irradiated Cell Suspension Cultures II. Preselection in vitro under Low-Temperature Stress

The effect of in vitro cold treatment (+6°C, 90 days) on selection of low-temperature tolerant (LTT) mutants was investigated using X-irradiated (15 Gy and 20 Gy) and non-irradiated cell suspensions of Chrysanthemum morifolium cv. ‘Parliament’. Low temperature reduced significantly the number of regenerating calli, especially in the irradiated cultures. After the end of the cold stress 684, 197 and 54 plants were obtained from the 0 Gy, 15 Gy and 20 Gy treated cultures, respectively. Testing these plants in the greenhouse (+12 °C, winter low-light) most of the early flowering variants were selected from the 15 Gy population.     

Salt (NaCl)‐Induced Modulation in some Key Physio‐Biochemical Attributes in Okra (Abelmoschus esculentus L.)

Salt (NaCl)‐induced regulation of some key physio‐biochemical characteristics in two okra (Abelmoschus esculentus L.) cultivars (Nirali and Posa Sawni) was examined under greenhouse conditions. Plants of both cultivars were subjected for 30 days to sand culture salinized with four salt levels [0 (control), 50, 100 and 150 mm NaCl] in Hoagland’s nutrient solution. Salt stress significantly reduced the shoot and root fresh weights, transpiration rate, chlorophyll b content, net CO₂ assimilation (A), transpiration rate (E), while enhanced leaf and root Na⁺ and Cl^– concentrations in both cultivars. In contrast, chlorophyll a content, stomatal conductance (g_s), leaf internal CO₂ (C_i), C_i/C_a ratio, water‐use efficiency (A/E) and fluorescence characteristics such as photochemical quenching (qP), non‐photochemical quenching (NPQ), efficiency of PS‐II (F_v/F_m), proline contents, and leaf and root K⁺, Ca^{2 +} and N contents remained almost unaffected in both lines due to salt stress. The efficiency of PSII (F_v/F_m), A, chlorophyll b, root fresh weight and root N were higher in relatively salt tolerant cv. Nirali, whereas leaf Na⁺ and root Cl^– were higher in cv. Posa Sawni. The relatively more reduction in growth in the cv. Posa Sawni was found to be associated with higher accumulation of Na⁺ in its leaves and Cl^– in roots.     

QTL analysis of flooding tolerance in soybean at an early vegetative growth stage

Soybean cultivars are sensitive to flooding stress and their seed yields are substantially reduced in response to the stress. This study was conducted to investigate the genetic basis of flooding tolerance at an early vegetative growth stage. Sixty recombinant inbred lines derived from a cross between a relatively tolerant cv. ‘Misuzudaizu’ and a sensitive cv. ‘Moshidou Gong 503’ were grown in pots in a vinyl plastic greenhouse in 2002 and 2003. At the two‐leaf stage, half of the pots were waterlogged by water placed in plastic containers and adjusted to 5 cm above the soil surface. After 3 weeks of treatment, the pots were returned to the greenhouse and grown until maturity. Flooding tolerance was evaluated by dividing the seed weight of the treated plants by that of the control plants. Quantitative trait loci (QTL) analysis using 360 genetic markers revealed three QTLs for flooding tolerance, ft1 to ft3 in 2002. The ft1 (molecular linkage group C2) was reproducible and an additional four QTLs, ft4 to ft7, were found in 2003. The ft1 had a high LOD score in both years (15.41 and 7.57) and accounted for 49.2% and 30.5% of the total variance, respectively. A large QTL for days to flowering was consistently observed across treatments and years at a similar position to ft1. Comparing the relative location with markers, the maturity gene probably corresponds to E1. Late maturity may have conferred a longer growth period for recovery from flooding stress.     

Long‐Term Field Drought Affects Leaf Protein Pattern and Chloroplast Ultrastructure of Winter Wheat in a Cultivar‐Specific Manner

Recurrent drought periods of varying duration often cause extensive crop damage and affect wheat production in Southern Europe. This study compares biochemical and ultrastructural responses of four wheat (Triticum aestivum L.) cultivars to long‐term field drought, and their contribution to final grain yield. Gel electrophoresis and immunoblotting analyses combined with transmission electron microscopy and grain yield evaluation were employed to assess drought susceptibility of the wheat cultivars. Two of them behaved as drought‐tolerant, the other two presented as drought sensitive. Enhanced degradation of Rubisco large subunit (RLS), Rubisco small subunit (RSS) and Rubisco activase (RA) accompanied by an increased protease activity and reduced levels of heat shock proteins (HSP70) and dehydrins (DHNs) were associated with drought sensitivity. Drought tolerance coincided with relatively stable or increased HSP70 and DHN contents, and unchanged/higher levels of RLS, RSS and RA. Sensitive cultivars were more vulnerable to ultrastructural damages, showing obvious degradation of chloroplast membrane systems and depletion of leaf starch reserves. These drought responses affected yield potential, as tolerant cultivars gave higher yield under intense drought. Thus, our results provide additional insights into the complexity of plant drought responses, identifying multiple interacting traits that may serve as indirect selection criteria for wheat drought tolerance.     

低温锻炼诱导葡萄幼苗的耐热性过程中sHSP17.6在叶片中的亚细胞定位

为了探讨热激蛋白在低温锻炼诱导的耐热性形成过程中的保护功能,进一步分析葡萄幼苗对温度逆境产生交叉适应性的细胞学机制,试验以葡萄(vitis vinifera L.cv.Jingxiu)幼苗为试材,采用胶体金免疫电镜定位技术,定位观察了小分子热激蛋白17.6(sHSP17.6)在葡萄叶片中的亚细胞分布情况,结果表明,低温锻炼预处理可增强其在高温胁迫条件下的表达水平,细胞核和叶绿体中代表sHSP17.6的免疫金颗粒密度比相应的对照细胞明显增多,尤其是胁迫处理3 h时.这一结果为sHSP17.6参与低温锻炼诱导的耐热性提供了更直观的细胞学证据.     

Vigour/tolerance trade‐off in cultivated sunflower (Helianthus annuus) response to salinity stress is linked to leaf elemental composition

Developing more stress‐tolerant crops will require greater knowledge of the physiological basis of stress tolerance. Here, we explore how biomass declines in response to salinity relate to leaf traits across 20 genotypes of cultivated sunflower (Helianthus annuus). Plant growth, leaf physiological traits and leaf elemental composition were assessed after 21 days of salinity treatments (0, 50, 100, 150 or 200 mM NaCl) in a greenhouse study. There was a trade‐off in performance such that vigorous genotypes, those with higher biomass at 0 mM NaCl, had both a larger absolute decrease and proportional decrease in biomass due to increased salinity. More vigorous genotypes at control were less tolerant to salinity. Contrary to expectation, genotypes with a low increase in leaf Na and decrease in K:Na were not better at maintaining biomass with increasing salinity. Rather, genotypes with a greater reduction in leaf S and K content were better at maintaining biomass at increased salinity. While we found an overall trade‐off between sunflower vigour and salt tolerance, some genotypes were more tolerant than expected. Further analysis of the traits and mechanisms underlying this trade‐off may allow us to breed these into high‐vigour genotypes in order to increase their salt tolerance.     

Evaluating the role of seed priming in improving drought tolerance of pigmented and non‐pigmented rice

This study was conducted to evaluate the influence of seed priming on drought tolerance of pigmented and non‐pigmented rice. Seeds of pigmented (cv. Heug Jinju Byeo) and non‐pigmented (cv. Anjoong) rice were soaked in water (hydropriming) or solution of CaCl₂ (osmopriming). Seeds were sown in soil‐filled pots retained at 70 (well‐watered) and 35% (drought) water‐holding capacity. Drought stress caused erratic and poor stand establishment and decreased the growth of both rice types. More decrease in plant height and leaf area under drought stress was noted in pigmented rice, whereas decrease in root length and seedling dry weight, under drought, was more obvious in non‐pigmented rice. Pigmented rice maintained more tissue water and photosynthesis and had more polyphenols, flavonoids and antioxidant activity than non‐pigmented rice. Seed priming was effective in improving stand establishment, growth, polyphenols, flavonoids and antioxidant activity; however, extent of improvement was more in pigmented rice under drought. In conclusion, drought caused erratic germination and suppressed plant growth in both rice types. However, pigmented rice had better drought tolerance owing to uniform emergence, and better physiological and morphological plasticity. Seed priming was quite helpful in improving the performance of both rice types under drought and well‐watered conditions.     

Aluminium tolerance in lentil (Lens culinaris Medik.) with monogenic inheritance pattern

The objectives of this study were to determine genetics of Al tolerance and whether the Al tolerance observed is governed by the same gene. The lines ‘L‐7903’ and ‘L‐4602’ have been developed through breeding programme as Al‐tolerant lines. These lines showed maximum root regrowth and minimum accumulation of Al and callose as compared to sensitive genotypes (‘BM‐4’ and ‘L‐4147’). Al tolerance in the parents, F₁, F₂ and backcross generations was estimated using the regrowth of the primary root after staining and scoring of fluorescent signals. The F₁ hybrids responded similarly to the tolerant parents, indicating dominance of Al tolerance over sensitivity. The segregation ratios obtained for Al tolerance and sensitivity in the F₂ and backcross generations were 3 : 1 and 1 : 1, respectively. Test of allelism confirmed the same gene was conferring Al tolerance in both genotypes (‘L‐7903’ and ‘L‐4602’) as the F₁ was also tolerant and no segregation of tolerant : sensitive was recorded. These results indicated that Al tolerance is a monogenic dominant trait that can be easily transferred to agronomic bases through backcross breeding technique.     

Fine mapping the QTL qFS‐chr.23, using a CSIL

In an earlier advanced‐backcross quantitative trait locus (QTL) analysis of an interspecific cross of Gossypium hirsutum cv. ‘Xinluzhong 36’(‘XLZH36’) and G. barbadense cv. ‘Xinhai 21’(‘XH21’), a QTL for fibre strength in the chromosome segment introgression line IL23‐09 was analysed. Single marker analysis revealed that the markers on chro.23 were associated with fibre strength. Using composite interval mapping with the F₂ population (1296 plants), a QTL for fibre strength was detected on chro. 23. The QTL explained 8.9% and 15.9% of phenotypic variances in the F₂ and F_2 : 3 generations, respectively. Substitution mapping suggested that the QTL was located at a physical distance of 23.4 kb between the markers BNL1414 and the single nucleotide polymorphism (SNP) locus D09_43776813 C‐G. We designated this QTL as qFS‐chr.23 (quantitative trait locus for fibre strength on chro.23). This work provides a valuable genetic resource for the breeding of high fibre quality in cotton and will facilitate future efforts for map‐based cloning.     

Breeding for resistance to begomovirus in tropic-adapted tomato genotypes

Four tomato lines introgressed from Lycopersicon chilense were compared with the commercial F₁ hybrids ‘ARO 8479’ and ‘HA 3108’, which are tolerant to Tomato yellow leaf curl virus, and the cv. ‘Campbell 28’ as a susceptible control. Resistance was evaluated by the use of grafted diseased scions as well as in a field trial where plants infected by viruliferous whiteflies and disease‐free plants were transplanted in paired rows. The new lines LD 3, LD 4, LD 5 and LD 6 showed no disease symptoms after grafting or in the field trial. Virus accumulation at 60 days after transplanting was low in the infected plants: 0.09, 0.60, 1.00 and 0.50 ng, respectively. No fruit‐set or yield losses were registered under the high temperature conditions prevalent in the trial, in which lines LD 5 and LD 6 were better adapted to tropical conditions. Viral DNA concentrations were over 1000 ng in the cvs.‘Campbell 28′,‘ARO 8479’ and ‘HA 3108’. The last two are considered tolerant as they were asymptomatic or had mild symptoms, respectively, but achieved acceptable yields in the trial. By contrast, virus had a negative effect on fruit‐set, number of fruit per plant and total yield in the cv.‘Campbell 28’.     

Histological and inheritance studies of partial resistance in the Brassica napus–Albugo candida host-pathogen interaction

Traditional and doubled haploid (DH) genotypes of oilseed Brassica spp. resistant, partially resistant, moderately susceptible, and susceptible to Albugo candida were compared for phenotypic development of host‐pathogen interaction and histology of host‐pathogen interaction. The partially resistant genotype showed pinhead‐size pustules, mainly on the upper surface of cotyledonary leaves. Relatively less mycelium was observed in the partially resistant genotype compared with the susceptible genotype. In resistant B. napus genotypes, there was neither pustule development nor any mycelial growth. In the moderately susceptible genotype, the pustules were similar to those in the partially resistant genotype in being of pinhead‐size and occasionally coalescing. However, ample mycelial growth in the mesophyll tissue in the moderately susceptible genotype was similar to that in the susceptible control B. rapa cv. ‘Torch’. The susceptible genotype B. rapa cv. ‘Torch’ also showed large coalescing pustules. In the non‐host B. juncea cv. ‘Commercial Brown’, no pustules were formed although some mycelial growth was observed beneath the epidermal cell layer and in the mesophyll cell layer of the cotyledonary leaf tissue. For inheritance studies, two partially resistant B. napus genotypes were crossed with a resistant B. napus genotype. Various generations viz., F1, F1(reciprocal), F₂, and DHs produced from the crosses were inoculated with a zoospore suspension of race 7v of A. candida. The partially resistant phenotype appeared to be controlled by a single recessive gene designated as wpr with variable expression. The simple inheritance of partial resistance has implications for disease resistance breeding against white rust, as this type of resistance can be easily incorporated into elite breeding lines through conventional and DH breeding methods.     

从非洲水稻材料中筛选耐高温种质资源

为了更好的开展抗热水稻育种工作，本研究试图从非洲地区收集的水稻种质资源中筛选耐热资源。采用最新建立的梯级温度法对来自非洲各地区的6 个水稻品种进行花期高温处理，通过不同温度下的受精率，计算耐热指数和耐热综合指数，以耐热综合指数判定材料的耐热性。结果表明，品种‘SDWG005’在不同温度下的耐热指数皆大于0.9，耐热综合指数为6.462，表现出极强的耐热性；品种‘SDWG001’在不同温度下的耐热指数大于0.5，耐热综合指数为4.163，表现出强耐热性；品种‘SDBN001’与品种‘SDSL013’在37℃下的耐热指数小于0.5，其他温度下耐热指数大于0.6，耐热综合指数分别为3.694 与3.406，表现出较耐热性。筛选得到了一个极强耐高温品种‘SDWG005’，2 个强耐高温品种‘SDWG001’与‘SDBN001’，试验显示来源于非洲的水稻中可能潜藏有宝贵的可用于育种的耐热资源和基因。