Physiological Response to Heat Stress During Seedling and Anthesis Stage in Tomato Genotypes Differing in Heat Tolerance

Tomato cultivars differ in their sensitivity to heat stress, and the sensitivity depends on the developmental stage of the plants. It is less known how heat stress affects tomato at the anthesis stage in terms of leaf physiology and fruit set and whether the ability of tomato to tolerate heat at different developmental stages is linked. To investigate photosynthetic gas exchange characteristics, carbohydrate content and fruit set during heat stress, a thermo‐tolerant cultivar (‘LA1994’) and a thermo‐sensitive cultivar (‘Aromata’) were studied at the seedling and anthesis stage. The photosynthetic parameters, maximum quantum efficiency of photosystem II (F_v/F_m), chlorophyll content, carbohydrate content and fruit set were determined in plants grown at 26/18 °C (control) and 36/28 °C (heat stress). The physiological responses including net photosynthetic rate (P_N), chlorophyll content and F_v/F_m decreased in ‘Aromata’ at both developmental stages during heat stress, whereas they were unaltered in ‘LA1994’ during heat stress as compared to the respective control. This was accompanied by lower contents of glucose and fructose in mature leaves of ‘Aromata’ at the seedling stage under heat stress. In contrast, the glucose content increased while the fructose content was unaltered in mature leaves of ‘LA1994’ at the seedling stage under heat stress. High temperature induced a similar change in carbohydrate content in the young leaves of both cultivars at anthesis. The fructose and sucrose content were unaffected in the mature leaves of ‘Aromata’ but significantly increased in ‘LA1994’ under heat stress at anthesis. The heat stress treatment decreased pollen viability and inhibited fruit set due to flower wilting and abnormal abscission in ‘Aromata’, whereas fruit set was not inhibited in ‘LA1994’. A decrease in chlorophyll content, photosynthesis and carbohydrate content in the mature leaves of tomato could be related to fruit set failure at high temperature. The results show that physiological responses to heat stress at the seedling stage correspond with the responses at the anthesis stage, demonstrating that screening for heat stress sensitivity can be carried out in young plants.     

Characterizing Submergence Survival Strategy in Rice Via Chlorophyll Fluorescence

Rice plants cope with flash floods using either an ‘escape strategy’ involving rapid shoot elongation or a ‘quiescence strategy’ involving survival underwater with minimal activity. To clarify the differences in the response of leaf photosynthesis properties to conditions during and after submergence, two rice cultivars were compared: a non‐shoot‐elongating cultivar IR 67520‐B‐14‐1‐3‐2‐2 (IR67520) and a shoot‐elongating cultivar IR72442‐6B‐3‐2‐1‐1 (IR72442). Twenty‐three‐day‐old seedlings were submerged in 80‐cm‐deep water for 14 days. During submergence, the chlorophyll contents of the upper fully expanded leaf (5th leaf) and newly developed leaf later (6th leaf) and the maximal quantum yield of photosystem II (F_v/F_m) of the fifth leaf decreased earlier in IR72442 than in IR67520. In the submerged sixth leaf, F_v/F_m was higher in IR72442 than in IR67520 at early measurement. Although F_v/F_m of the sixth leaf in submerged IR67520 increased substantially from 2 days post‐submergence, IR72442 decreased because of leaf chlorosis. Therefore, a non‐shoot‐elongating cultivar coped with submergence by inhibiting photodamage and maintaining high chlorophyll content in the leaves. The shoot‐elongating cultivar was able to maintain the photosynthetic capacity of the newly developed leaf during submergence by prompt reduction of chlorophyll and chlorophyll fluorescence in the leaf that developed before submergence.     

The relationship between water status and chlorophyll a fluorescence in grapes (Vitis spp.)

The purpose of this study was to explore the utility of chlorophyll fluorescence to non-destructively monitor water status in plant tissue, specifically water loss in grapes (Vitis spp.) destined for wine production. An automated remote-sensing (ARS), pulse amplitude modulation (PAM) fluorometer prototype, capable of scanning a large surface area, was used to monitor chlorophyll fluorescence from ‘L’Acadie’ (LAc) and ‘Thompson Seedless’-type (TS) grape clusters during postharvest dehydration. Increasing mass loss (%) in grapes correlated with increasing soluble solids (SS) content and decreasing osmotic potential (Ψ_s) (p < 0.001). All of the primary fluorescence parameters monitored (F₀, F_m, F_v and F_v/F_m) had a strong curvilinear relationship (p < 0.001) with grape mass loss. In both cultivars, F₀ increased during the later stages of dehydration, likely as a result of increased disorder within the thylakoid membranes and/or a reduction in energy transfer between LHCII and PSII. F_m, F_v and F_v/F_m declined, likely due to several factors that are known to inhibit photosynthesis and the primary charge recombination during osmotic stress. Chlorophyll degradation during dehydration was a major factor influencing cultivar differences in the fluorescence relationships. An inflection point in the F₀ value at ≈20–25% mass loss appeared to correspond with an inflection point in the decreasing glucose:fructose ratio. The relationship between chlorophyll fluorescence and water loss, SS, Ψ_s and potentially other indicators of metabolic change, could lead to practical applications of this technology in the slow dehydration of grapes and other fruits used to make high value wines.     

Use of chlorophyll fluorescence to evaluate the cold acclimation and freezing tolerance of winter and spring oats

The efficiency of the excitation capture by open Photosystem II (PSII) reaction centres was measured by the F_v/F_m ratios in a collection of winter and spring oats in order to assess the effects of hardening and freezing on the functionality of PSII and also the suitability of a chlorophyll fluorescence‐based method to screen oat cultivars for frost tolerance. A significant reversible decrease in F_v/F_m was found in all genotypes during acclimation to low, non‐freezing temperatures. F_v/F_m analysis appears to be an attractive test for the evaluation of frost tolerance in oats, being rapid, non‐invasive and capable of monitoring a trait related to a crucial stage in the acquisition of frost tolerance. It is more sensitive and precise than other standard methods and highly correlated with field‐evaluated frost damage. The measurements made during recovery 1 or 2 days after stress when the visual symptoms are not yet expressed, were especially advantageous because of the large variability in genotype response. The r‐values (close to 0.8) were reduced due to the non‐standard behaviour of the winter cultivar ‘Aintree’. The cold acclimation response of this genotype has been analysed in detail and the limits of artificial freezing tests are discussed.     

氮、钾水平对小麦花后旗叶光合特性的影响

在大田栽培条件下,以冬小麦（Triticum aestivum L.）弱筋品种宁麦9号和中筋品种扬麦10号为材料,研究了不同氮、钾施肥水平下花后旗叶叶绿素含量（SPAD）、净光合速率（P_n）和荧光参数的变化特征及其与开花期叶片氮、钾营养的关系。结果表明,与不施氮、钾的对照（N0K0）相比,施氮、钾肥增加小麦开花后旗叶SPAD和P_n,提高PSⅡ最大光量子产量（F_v /F_m）、潜在光化学活性（F_v /F_o）、有效光量子产量（F_v’/F_m’）和实际光量子产量（Φ_PSⅡ）等叶绿素荧光参数,其中氮肥效应高于钾肥。除SPAD外,扬麦10号的Pn及叶绿素荧光参数（F_v /F_m、F_v /F_o、F_v’ /F_m’和Φ_PSⅡ）均高于宁麦9号。相关分析表明,F_v /F_m、F_v /F_o、F_v’/F_m’和Φ_PSⅡ等叶绿素荧光参数受开花期叶片氮/钾比的显著影响,是施氮、钾肥提高净光合速率的主要生理原因,较高的光能转化特性是满足扬麦10号较高能量需求的生理基础。     

1,2,4-三氯苯对2个不同耐性水稻品种光合特性与产量的影响

为明确不同类型水稻品种的响应规律,为水稻高产稳产、安全生产提供依据。在盆栽土培条件下,研究了5种1,2,4-三氯苯(TCB)浓度(0、10、20、40、80 mg kg^-1土)对2个水稻品种(宁粳1号,敏感;扬辐粳8号,耐性)灌浆期剑叶光合特性与产量的影响。结果表明,TCB的影响品种间差异显著。低浓度TCB (10 mg kg^-1)下,扬辐粳8号的株高、鲜重和产量显著增加,叶绿素含量、净光合速率、胞间CO₂浓度、蒸腾速率和q_N略有升高,但与对照的差异不显著,而F_v/F_m和F_v/F_o略有下降;宁粳1号的净光合速率、胞间CO₂浓度、蒸腾速率、Φ_PSII、F_v/F_m、F_v/F_o、q_p和产量略有下降,气孔导度显著降低。在20 mg kg^-1 TCB处理下,宁粳1号的光合参数、产量、株高、地上部和地下部鲜重均显著降低,而扬辐粳8号略有降低,表现出较强耐性;在中高浓度TCB (40 mg kg^-1,80 mg kg^-1)处理下,2个水稻品种的光合特性、株高、鲜重和产量均受显著抑制,且以宁粳1号的降幅较大。TCB对水稻光合特性与产量的影响不仅与其浓度有关,且存在显著品种差异,耐性水稻品种表现出低浓度TCB处理对其株高、鲜重、叶绿素含量、光合特性及其产量有一定的促进作用,在中高浓度TCB处理时表现出较强的耐性,受胁迫程度小     

Glycinebetaine Improved Photosynthesis in Canola under Salt Stress: Evaluation of Chlorophyll Fluorescence Parameters as Potential Indicators

Salinity is a widespread soil problem limiting productivity of oilseed crops worldwide. Reduction in growth generally associated with decline in photosynthesis. Accumulation of osmo‐protectants such as glycinebetaine (GB) permits the plant to cope with salt stress. This study was aimed to understand the mechanism by which exogenous GB application improves photosynthetic capacity and salt tolerance in two diverse lines of canola differing in salt tolerance using chlorophyll fluorescence technique. Glycinebetaine was applied as foliarly or through rooting medium to two canola lines Dunkeld and Cyclone that were grown under non‐saline or saline conditions. Root‐applied GB caused adverse effects whereas foliar application of GB was effective in improving growth of canola cultivars. However, the response of salt‐tolerant cultivar Dunkeld was stronger than that of salt sensitive Cyclone. Foliar application of GB improved accumulation of proline and plant water status. Application of GB enhanced the photosynthetic CO₂ fixation, stomatal conductance (g_s) and water‐use efficiency. The tolerant lines Dunkeld had more responsive to GB application. Chlorophyll fluorescence measurements (F_o, F_m, F_v, F_o/F_m, F_v/F_o and F_v/F_m ratios) revealed that salt stress reduced energy trapping efficiency by damaging oxygen evolving complex, over reduction of Q_A resulting in occurrence of chronic photoinhibition. However, exogenous GB protected the oxygen evolving centre of PSII and maintains activity of PSII. Although root‐applied GB adversely affected the growth of canola plants, it did not have any adverse effect on PSII photochemistry. Moreover, fluorescence parameters could provide a rapid means for determining salt tolerance in canola and could be a rapid and sensitive test to identify genotypes highly tolerant to salt stress.     

高温胁迫对水稻灌浆结实期叶绿素荧光、抗活性氧活力和稻米品质的影响

选用西农优30和富优1号两个水稻品种, 在灌浆结实期利用人工气候室进行高温处理, 测定叶绿素含量、叶绿素荧光参数、抗活性氧活力的动态及成熟稻米的营养品质。结果表明, 高温胁迫下水稻叶片叶绿素含量降低, 叶绿素荧光参数初始荧光(F_o)明显上升, PS II的潜在活性(F_v/F_o)和PS II的最大光能转化效率(F_v/F_m)均低于对照, 呈下降趋势; 灌浆结实后期F_v/F_o和F_v/F_m的下降速率最快; 灌浆结实后期抗氧化活力低于对照。同时, 高温胁迫下的成熟稻米总淀粉及直链淀粉含量降低, 蛋白质含量升高, 垩白度上升而千粒重下降。高温胁迫下光合作用的原初反应被抑制, 抗活性氧活力降低, 水稻叶片功能期缩短, 可能是稻米品质降低的重要原因。     

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.     

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.     

强光高温同时作用下不同小麦品种的光合特性

以小麦品种藁城8901、豫麦49、郑麦9405、周18为试材,用强光(1 900 μmol m^-2 s^-1)、高温(35℃)同时处理材料3 h,研究了高光强和高温共同合胁迫对小麦旗叶光合作用和叶绿素荧光特性的影响。结果表明,正常生长条件下,郑麦9405和周18的光饱和速率、饱和光强均高于藁城8901和豫麦49,郑麦9405的表观量子效率也最高。强光高温处理使藁城8901、豫麦49和周18的光合速率(P_n)、蒸腾速率(T_r)、气孔导度(G_s)、胞间CO₂浓度(C_i)较对照大幅下降;郑麦9405的P_n、G_s也出现了下降,但降幅最小,P_n仍保持11.6 μmol CO₂ m^-2 s^-1,T_r较对照略有上升;4种基因型小麦的Ci未较对照明显变化;与对照相比,4个材料的最大光量子效率(F_v/F_m)、开放的光系统II反应中心的激发能捕获效率(F_v’/F_m’)、作用光下光系统II的实际量子效率(Ф_PSII)、光化学猝灭系数(q_P)均下降,而非光化学猝灭系数(NPQ)大幅上升;其中郑麦9405的各项荧光参数均较高。研究表明,小麦旗叶对强光高温的适应性存在品种间差异,郑麦9405的耐强光高温特性优于其他3品种;强光高温下较高的蒸腾速率和较大的NPQ可能是郑麦9405维持光合机构功能的重要原因。     

QTLs for chlorophyll and chlorophyll fluorescence parameters in barley under post-flowering drought

Drought is one of the major factors limiting barley yields in many developing countries worldwide. The identification of molecular markers linked to genes controlling drought tolerance in barley is one way to improve breeding efficiency. In this study, we analyzed the quantitative trait loci (QTL) controlling chlorophyll content and chlorophyll fluorescence in 194 recombinant inbred lines (RILs) developed from the cross between the cultivar ‘Arta’ and Hordeum spontaneum 41-1. Five traits, chlorophyll content, and four chlorophyll fluorescence parameters, namely initial fluorescence (F_o), maximum fluorescence (F_m), variable fluorescence (F_v), and maximum quantum efficiency of PSII (F_v/F_m) which are related to the activity of the photosynthetic apparatus, were measured under well-watered and drought stress conditions at post-flowering stage. QTL analysis identified a total of nine and five genomic regions, under well-watered and drought stress conditions, respectively, that were significantly associated with the expression of the five target traits at post-flowering stage. No common QTL was detected except one for chlorophyll content, which was identified in both growth conditions, demonstrating that the genetic control of the expression of the traits related to photosynthesis differed under different water conditions. A QTL for F_v/F_m, which is related to the drought tolerance of photosynthesis was identified on chromosome 2H at 116 cM in the linkage map under drought stress. This QTL alone explained more than 15% of phenotypic variance of maximum quantum yield of PSII, and was also associated with the expression of four other traits. In addition, another QTL for F_v/F_m was also located on the same chromosome (2H) but at 135.7 cM explaining around 9% of the phenotypic variance under drought conditions. The result presented here suggest that two major loci, located on chromosome 2H, are involved in the development of functional chloroplast at post-flowering stage for drought tolerance of photosynthesis in barley under drought stress. If validated in other populations, chlorophyll fluorescence parameters could be used as selection criteria for drought tolerance.     

Heterosis in CMS hybrids of cotton for photosynthetic and chlorophyll fluorescence parameters

Summary The characterization of photosynthetic, chlorophyll fluorescence parameters and yield and yield components was compared between two newly developed CMS cotton hybrids (H1, H2) and their parents, as well as currently planted hybrid and conventional cultivars (C1, artificially produced hybrid CCRI 29 and C2, conventional cultivar CCRI 12) under the field condition. The results showed that P_n, F_v/F_m, Φ_PSII and qP of hybrids was significantly higher than that of C1 and C2. Furthermore, heterosis was found on photosynthetic parameters in hybrids over their parents at the first four growth stages, while only heterosis over mean of parents (HOMP) was detected in chlorophyll fluorescence parameters. It was clearly shown that one male-sterile line M2 was higher than the hybrids in F_v/F_m, Φ_PSII and qP over all growth stages. Significantly positive correlations (P < 0.01) were found between LAI or Yield and P_n, C_s, T_r, F_v/F_m, Φ_PSII, or qP, while significantly negative correlations between C_i and LAI or Yield, and no significance between qN and Chl a, C_s and qP were found. It was concluded that CMS hybrid cottons showed better potential to maintain relatively higher photosynthetic ability during the growth, which contributes to the increased lint yield.     

小麦叶片氮含量与荧光动力学参数的关系

通过分析不同氮素水平下不同品种小麦上部叶片氮含量和荧光参数随生育进程的变化模式及小麦叶片氮含量与荧光参数的相关关系,提出小麦叶片氮含量的预测方程。结果表明,小麦不同叶位叶片氮含量和荧光参数Fv/Fm、Fv/Fo均随施氮量的增加呈上升趋势。从孕穗到成熟,F_v/F_m和F_v/F_o表现为先上升后下降的趋势。小麦各叶位叶片氮含量与荧光参数F_m、F_v、F_v/F_m、F_v/F_o、F_s和Fo’都呈极显著正相关,且顶部2张叶片的相关性最好。不同小麦品种顶2叶氮含量分别与F_v/F_o和F_v/F_m呈良好的幂函数关系,平均决定系数分别达0.66和0.61。对于低、中、高蛋白质含量的小麦品种类型,可以利用统一的回归方程来描述顶部2张叶片氮含量随F_v/F_o的变化模式。     

New sources of resistance for stripe rust in barley

Eight spring barley accessions from the gene bank in Gatersleben, Germany, and 10 cultivars were tested for stripe rust resistance. Tests were performed at the seedling stage in the growth chamber and as adult plants in the field. All accessions and six cultivars were scored as resistant against race 24 under all test conditions, with very few plants as exceptions, while the susceptible control cultivars ‘Karat’ and ‘Certina’, and four other cultivars were attacked in all cases. Differences between accessions and between cultivars were detected after infection with isolates from ‘Trumpf’ and ‘Bigo’ (seedling tests only). Infection structures within seedling leaves without pustules and for the first time within leaves of adult plants from the field were analysed by fluorescence microscopy. With this method additional genetic Differences in the resistance reaction could be detected which could not to be seen in the resistance test. Crosses between the accessions and the susceptible cultivar ‘Karat’ led to segregating F₂ progenies. The percentage of resistant plants varied between the accessions. This also indicates a different genetic basis of resistance in the accessions. The infection structures observed by fluorescence microscopy stopped earlier in leaves of the two accessions HOR 8979 and HOR 8991 than in leaves of other accessions in all the tests. These accessions were the only ones with more than 50% resistant plants in all F₂ tests. In general, the accessions from the gene bank can be used as new resistance sources against stripe rust.     

Effects of Shading on Chlorophyll Content,Chlorophyll Fluorescence and Photosynthesis of Subterranean Clover

A field‐experiment (2004/2005 and 2005/2006 seasons) was conducted in the coastal plain of south‐eastern Sicily (37°03′N, 15°18′E, 15 m a.s.l.), on a Calcixerollic Xerochrepts soil, aimed at quantifying the effect of shading on chlorophyll (Chl) content, Chl fluorescence, photosynthesis and growth of subterranean clover. Four levels of photosynthetically active radiation reduction (from 0 % to 90 %) were tested on Trifolium brachycalycinum cv. ‘Clare’ and Trifolium subterraneum ecotype ‘Ragalna’. In both species shading progressively increased F_v/F_m, internal CO₂ concentration, diffusive leaf resistance and specific leaf area (up to 8 %, 34 %, 18 % and 68 %, respectively), and decreased Chl content, T_max, photosynthetic rate and plant dry weight (up to 9 %, 24 %, 79 % and 39 %, respectively). As plants aged, characteristic bell‐shaped trends were evident for photosynthetic parameters, with F_v/F_m increasing up until the onset of flowering, and thereafter declining. This implies that F_v/F_m may be a useful indicator of earliness in subterranean clover genotypes. The aboveground dry biomass response to shading was both genotype‐ and season‐dependent, but was predictable from the measurement of relative leaf Chl content. Moreover, our results suggest that an improvement in the interaction between host‐rhizobium may represent a major potential breeding target for enhancing subterranean clover tolerance to shading.     

不同生育期水稻耐冷性的鉴定及耐冷性差异的生理机制

以粳稻9516、H45、武育粳、转PEPC基因水稻、Kitaake、苏沪香粳，籼稻扬稻6号、香籼、IR64，培矮64S以及杂交稻粤优938、汕优63、X07S/紫徽100、两优培九等14个水稻品种为材料，分别鉴定了芽期（胚根1 cm, 胚芽0.5 cm）、苗期（三叶）和孕穗期的耐冷性，同时选取南京对水稻播种敏感的自然低温条件，进行低温鉴定。结果表明，芽期存活率、苗期的枯死率和孕穗期结实率均为可靠的水稻耐冷性鉴定指标。进一步从叶片的光合速率、PSⅡ光化学效率（F_v/F_m）、脂肪酸组分、活性氧指标(丙二醛,过氧化氢和超氧阴离子和抗氧化物质(抗坏血酸和谷胱甘肽)的变化等方面，研究耐冷性不同的水稻的耐冷生理机制。表明耐冷的水稻品种武育粳含较多的不饱和脂肪酸，在低温逆境下，膜的流动性愈大，低温对其伤害愈小；对杂交稻汕优63而言，其叶内抵御逆境的保护系统抗坏血酸和谷胱甘肽的循环被较大地激活，特别是谷胱甘肽再生的高速运转，与不耐冷的品种香籼相比，汕优63叶内的过氧化物质累积较少，其耐冷性表现中等。看来水稻叶片维持高的脂肪酸不饱和指数和谷胱甘肽的周转循环能力是水稻耐冷的重要特征。     

Single and Interactive Effects of Temperature and Light Quality on Four Canola Cultivars

Combined effects of temperature and light quality on plants have received little attention. We investigated the single and interactive effects of temperature and light quality on growth and physiological characteristics of four canola (Brassica napus) cultivars – Clearfield 46A76 (cv₁), Clearfield 45H72 (cv₂), Roundup Ready 45H24 (cv₃) and Roundup Ready 45H21 (cv₄). Plants were grown under lower (24°/20 °C) and higher (30°/26 °C) temperature regimes at low red/far‐red (R/FR), normal R/FR and high R/FR light ratios in environment‐controlled growth chambers (16 h light/8 h dark). Higher temperature reduced stem height and diameter; leaf number and area; dry matter of all plant parts; and specific leaf weight, but increased leaf area ratio; and chlorophyll (Chl) fluorescence (Y). Low R/FR increased stem height; Y; and ethylene, but decreased stem diameter; F_v/F_m; Chl a; Chl b; and carotenoids. Among cultivars, plants from cv₄ were tallest with thickest stems and greatest dry matter. None of the main factors affected gas exchange. Higher temperature at high R/FR caused cv₃ to be shortest, whereas lower temperature at low R/FR caused cv₄ to be tallest. We conclude that heat and other stress factors will adversely affect sensitive crops, but tolerant genotypes should perform well under future climate.     

Inheritance of resistance to Fusarium wilt (race 2) in chickpea

The inheritance of resistance to Fusarium wilt (race 2) of chickpea was studied in a set of three crosses, i.e. ‘WR315’בC104’ (resistant × susceptible), ‘WR315’בK850’ (resistant × tolerant) and ‘K850’בGW5/7’ (tolerant × tolerant) in order to investigate the number of genes involved, their complementation and to find out whether resistant segregants are possible in a cross between two tolerant cultivars. Tests of F₁, F₂ and F₃ generations of these crosses under controlled conditions at ICRISAT, Patancheru, India, indicated involvement of three loci (two recessive and one dominant alleles). The homozygous recessive form at the first two loci conferred resistance whereas susceptibility occurred when the first two loci were in the dominant form. A dominant allele at the third locus can complement the dominant alleles at the other two loci to confer tolerance. Occurrence of resistant segregants in a cross between two tolerant cultivars was observed.     

The Alleviating Effect of Elevated CO2 on Heat Stress Susceptibility of Two Wheat (Triticum aestivum L.) Cultivars

This study analysed the alleviating effect of elevated CO₂ on stress‐induced decreases in photosynthesis and changes in carbohydrate metabolism in two wheat cultivars (Triticum aestivum L.) of different origin. The plants were grown in ambient (400 μl l^?1) and elevated (800 μl l^?1) CO₂ with a day/night temperature of 15/10 °C. At the growth stages of tillering, booting and anthesis, the plants were subjected to heat stress of 40 °C for three continuous days. Photosynthetic parameters, maximum quantum efficiency of photosystem II (PSII) photochemistry (F_v/F_m) and contents of pigments and carbohydrates in leaves were analysed before and during the stress treatments as well as after 1 day of recovery. Heat stress reduced P_N and F_v/F_m in both wheat cultivars, but plants grown in elevated CO₂ maintained higher P_N and F_v/F_m in comparison with plants grown in ambient CO₂. Heat stress reduced leaf chlorophyll contents and increased leaf sucrose contents in both cultivars grown at ambient and elevated CO₂. The content of hexoses in the leaves increased mainly in the tolerant cultivar in response to the combination of elevated CO₂ and heat stress. The results show that heat stress tolerance in wheat is related to cultivar origin, the phenological stage of the plants and can be alleviated by elevated CO₂. This confirms the complex interrelation between environmental factors and genotypic traits that influence crop performance under various climatic stresses.