Water use and physiological responses of new citrus rootstocks under drought stress conditions

BackgroundDrought stress, the most prevalent abiotic stress, has a significant effect on citrus production worldwide. The differential mechanisms to overcome the drought stress has been reported in citrus rootstock genotypes. This study evaluated nine citrus rootstock genotypes, including indigenous rough lemon variants, for drought tolerance. The genotypes were subjected to well-watered, drought stress, and re-watering conditions to assess morphological, physiological, and biochemical responses. High-throughput imaging techniques were employed to non-destructively assess chlorophyll fluorescence, digital leaf area, and plant tissue water content during drought stress.ResultsFor rapid and accurate screening of rootstocks, phenomics and physio-biochemical tools were used to know morpho-physiological responses to drought. Citrus rootstock genotype X639 demonstrated superior performance under drought stress conditions. It maintained the highest growth in terms of relative shoot increment (8.09%), number of leaves (79.00), and specific leaf area (62.45 cm2 g−1). X639 also excelled in root morphological parameters, including root length, projected area, diameter, surface area, volume, and number of tips, forks, and crossings. Trifoliate hybrids X639 and Troyer citrange exhibited larger stomata (54.73 and 43.82 µm2) compared to mono-foliate species, with minimal impact of drought on stomatal pore area. X639 maintained the highest relative water content, membrane and chlorophyll stability indices, leaf gas exchange parameters, and antioxidant enzyme activity. RLC-1 and RLC-4 genotypes showed pronounced accumulation of leaf proline and antioxidant enzymes during drought, contributing to better recovery after re-watering.ConclusionIn this study, Cleopatra mandarin, Grambhiri, and RLC-2 were identified as drought-susceptible rootstocks based on their responses. Rootstock genotypes X639 and RLC-4 proven a superior drought-tolerant genotypes. Their robust root system enables efficient water uptake and the maintenance of water relations during drought stress. The drought tolerance of X639 was evidenced by its ability to maintain plant tissue moisture, membrane and chlorophyll stability, and higher photosystem II efficiency. High-throughput imaging techniques have proven effective in rapidly assessing and differentiating drought-tolerant and drought-susceptible citrus rootstocks based on their photosystem- II efficiency, leaf area, and tissue water content during induced drought stress. These findings will contribute to the selection and development of drought-tolerant citrus rootstocks to improve citrus production under water-limited conditions.

به‌منظور بررسی اثر تنش خشکی روی برخی ویژگی‌های فیزیولوژیکی دو رقم ارزن علوفه‌ای آزمایشی به‌صورت فاکتوریل در قالب طرح بلوک کامل تصادفی با سه تکرار در مزرعه تحقیقاتی دانشگاه شهید چمران اهواز انجام شد. عامل اول دو رقم ارزن علوفه‌ای‌ شامل نوتریفید و پیشاهنگ و عامل دوم تنش خشکی در چهار سطح شامل تأمین 100درصد نیاز آبی به‌عنوان شاهد، 75، 50، 25 درصد نیاز آبی بود. مقدار آب آبیاری در هر تیمار بر مبنای 50، 100، 150 و 200 میلی‌متر تبخیر از تشتک تبخیر کلاس A محاسبه شد. بیشترین عملکرد ماده خشک در رقم نوتریفید در شرایط شاهد و کمترین عملکرد ماده خشک در رقم پیشاهنگ در 25 درصد تأمین نیاز آبی به‌دست آمد. میزان پرولین و نفوذپذیری نسبی غشاء در هر دو رقم طی تنش همواره بیشتر از شاهد بود و با افزایش سطح تنش خشکی میزان پرولین افزایش یافت. بیشترین میزان نفوذپذیری نسبی غشا در رقم پیشاهنگ در 25 درصد تأمین رطوبت و کمترین میزان نفوذپذیری نسبی غشاء در رقم نوتریفید در شاهد به‌دست آمد. با افزایش سطح تنش محتوای نسبی آب برگ، عملکرد ماده خشک، پتانسیل اسمزی، هدایت روزنه‌ای، بیشینه کارآیی فتوسنتزی فتوسیستم ΙΙ (Fv/Fm)، فرود فتوشیمیایی (qP) و عملکرد کوآنتومی فتوسیستم دو کاهش یافتند. عملکرد ماده خشک همبستگی مثبت و معنی‌دار با هدایت روزنه‌ای، محتوای نسبی آب برگ، شاخص کلروفیل (عدد SPAD)، عملکرد کوآنتومی فتوسیستم ΙΙ و Fv/Fm داشت. ارزن نوتریفید نسبت به رقم پیشاهنگ هم در شرایط غیر تنش و هم در شرایط تنش از کارایی مصرف آب بهتری برخوردار بود و به‌نظر می‌رسد این رقم در شرایط محدودیت آب آبیاری بتواند از تولید علوفه مناسبی برخوردار باشد.

Experiments were conducted to determine the role of epicuticular wax cover on the rate of water loss of sorghum plants. Relative Water Content (RWC), water potential ( ), transpiration rate, stomatal conductance and stomatal density were measured in 3 near-isogenic lines of sorghum variety ROKY62, bloom (BmBm), sparse-bloom (hh) and bloomless (bmbm) under different water conditions. Under drought conditions, bloomless sorghum exhibited more negative?? values than the bloom type, -1.70 Mpa as compared to -1.43 Mpa for the bloomless and bloom lines, respectively. Under normal water conditions, similar trend was observed in? , where the values were -1.62 and -1.21 Mpa for the bloomless and bloom lines, respectively. Data indicated that there is a positive relationship between wax cover and the internal water content of plants. The bloomless plants had higher stomatal conductance and transpiration rates than the bloom or sparse-bloom plants. Microscopic examinations revealed higher stomatal densities on the flag leaf than on the third leaf down in all 3 isogenic lines. We conclude that wax cover on sorghum leaves reduces the transpirational water loss and prevents a rapid decrease in plant water potential

Introduction: Water shortage is the most important factor affecting crop production in the world. The deficit irrigation is a way to reduce water consumption in farming. The Partial Root- zone Drying (PRD) irrigation is a new improvement in deficit irrigation in which the half of the root zone is irrigated alternatively in scheduled irrigation events. In the fixed partial root zone drying (FPRD) the irrigation is fixed to one side of the root zone in the growing season. Maize is a drought sensitive crop. In maize, secondary traits related to drought resistance are considered in producing tolerate cultivars. Materials and Methods: An experiment was conducted in order to investigate the effects of regulated deficit irrigation, variable partial root zone drying (PRD) and fixed partial root zone drying (FPRD) on the yield, physiological and photosynthetic parameters of forage maize (KSC 704) during the growing seasons of 2014 in Mashhad region. A factorial experiment based on randomized complete block design with four replications was carried out. The treatments included the full irrigation (FI) and the deficit irrigations (regulated deficit irrigation (DI) and the replacements of 80 % (DI80) and 60 % (DI60) of total water requirement, fixed PRD (FPRD) at 100% (FPRD100), 80% (FPRD80) and 60%(FPRD60) of water requirement, and variable PRD at 100% (PRD100), 80% (PRD80) and 60% (PRD60) of water requirement). Drip irrigation tapes were placed between plant rows. In the full irrigation and regulated deficit irrigation treatments, the plants were irrigated from two sides for every irrigation. In the PRD, one of two neighboring tapes was alternatively used for irrigation. In FPRD, a drip tape was used for two plant rows and irrigation was fixed to one side of the root. The irrigation interval was 3 days for all treatments. Dry and fresh forage yield, leaf area index (LAI), stomatal conductance, leaf relative water content (RWC) and chlorophyll content were measured. Results and Discussions: All the measured traits were affected by the deficit irrigation. The highest fresh forage yield (72099 kg/ha) was produced by the full irrigation treatment. The statistical comparison showed that there was no significant difference between regulated deficit irrigation and PRD method for the fresh forage yield. But the FPRD treatment reduced the fresh forage yield. There was no significant difference between the fresh forage yield of FI and PRD80 treatments. The dry forage yield was affected by the different irrigation methods, irrigation levels and the interaction effects of the treatments (p

PDF HTML阅读 XML下载 导出引用 引用提醒 4种茶菊对干旱胁迫的形态和生理响应 DOI: 10.5846/stxb201401220164 作者: 作者单位: 山西农业大学林学院,山西农业大学林学院,山西农业大学林学院,山西农业大学林学院,山西农业大学林学院,山西农业大学林学院,山西农业大学林学院;山西省农业科学院高粱研究所,山西农业大学林学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家"十二五"科技支撑计划课题(2013BAD01B07); 山西省攻关项目(20120311015-2); 山西农业大学中青年学科带头人及学术骨干计划项目(XG201213) Varied morphological and physiological responses to drought stress among four tea Chrysanthemum cultivars Author: Affiliation: College of Forestry,Shanxi Agricultural University,Taigu,College of Forestry,Shanxi Agricultural University,Taigu,College of Forestry,Shanxi Agricultural University,Taigu,College of Forestry,Shanxi Agricultural University,Taigu,College of Forestry,Shanxi Agricultural University,Taigu,College of Forestry,Shanxi Agricultural University,Taigu,College of Forestry,Shanxi Agricultural University,Taigu;China;Institute for Sorghum Research,Shanxi Academy of Agricultural Sciences,Yuci;China,College of Forestry,Shanxi Agricultural University,Taigu;China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以4种茶菊幼苗为材料,采用盆栽控水法,研究了不同强度干旱胁迫下茶菊形态、生理生化及光合生长的响应特性,并对其进行耐旱性评价。结果显示,随着干旱胁迫程度的增强,各茶菊幼苗叶片数增量、叶面积、生物量、叶片相对含水量、净光合速率(Pn)、蒸腾速率(Tr)和气孔导度(Gs)降低;根冠比、丙二醛(MDA)含量、脯氨酸(Pro)含量、可溶性蛋白(SPC)含量和叶绿素(Chl)含量增加;胞间CO2(Ci)浓度先降后升;乳荷、黄滁龙株高增量持续降低,而玉人面、繁白露株高增量先升后降;玉人面叶超氧化物歧化酶活性(SOD)呈先升后降趋势,其它3个品种则持续升高。运用隶属函数法对抗旱能力进行综合评定,不同茶菊品种耐旱性由高到低为乳荷> 黄滁龙> 繁白露> 玉人面。 Abstract:Drought is a serious stress factor, limiting crop yield and restricting the expansion of production area. Breeding and commercialization of drought-resistant varieties is an important approach to alleviate the negative impact. Tea Chrysanthemum with its multiple health benefit has shown a great potential for the improvement of people's living standards. Current research activities have been centered on cultivation techniques, product processing, and chemical analysis. However, there is only limited information on varietal differences in response to drought stress and its mechanisms. In this study, four tea Chrysanthemum cultivars were used to investigate morphological, physiological, and photosynthetic characteristics of seedlings in pot experiments with varied relative water content (RWC) in the soil (control, RWC at 85%-90%; light stress, RWC at 65%-70%; medium stress, RWC at 45%-50%; sever stress, RWC at 25%-30%) in order to unveil varietal differences and possible mechanisms of drought resistance. Multiple indicator variables were analyzed by the method of membership function to evaluate synthetic drought resistance. These variables provide a theoretical basis for the cultivation and breeding of water-saving drought-resistant varieties.Results showed that, following the increased severity of drought stress, the growth of four tea Chrysanthemum cultivars was inhibited as parameters for the leaf increment, leaf area, and biomass were decreased, while the root to shoot ratio increased to enhance the soil moisture utilization. Following the decrease of leaf relative water content, the content of malonic dialdehyde (MDA) was increased, while the content of praline (Pro) and soluble protein (SPC) was increased to maintain the cell turgor content. The activities of superoxide dismutase (SOD) were enhanced to protect cell membranes from damages. Under the increased levels of drought stress, chlorophyll (Chl) content was significantly increased, and net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) were significantly reduced. The intercellular CO2 concentration (Ci) initially decreased and then increased, indicating that the reduced photosynthetic rate of plants under drought conditions was related to stomatal and non-stomatal factors. In the meantime, following the increased levels of drought stress, differences in morphology, biochemical and photosynthetic characters among four tea Chrysanthemum cultivars were observed. The leaf relative water content of Ruhe, Huangchulong, and Fanbailu were higher than in Yurenmian. The biomass yield and Pro content were higher and MDA content was lower in Ruhe, and it significantly differed from the rest of varieties. The membership function method was used to calculate the synthetic drought resistance. Ruhe was the most drought resistant, followed by Huangchulong, then Fanbailu, and finally Yurenmian, suggesting that Ruhe should be considered first for water-saving cultivation. 参考文献 相似文献 引证文献

The effect of dehydration and rehydration at pre and post-flowering stages on the water relations, gas exchange characteristics (stomata conductance, photosynthesis and Fv/Fm (quantum efficiency) ratio), pigment compositions (chlorophyll and carotenoid contents) and water use efficiency on maize (cv Melkassa-2) and sorghum (cv Macia) were investigated with the objectives of understanding the physiological basis of drought resistance mechanisms and investigating whether there were differential responses in some of the physiological traits of drought resistance and recovery upon rehydration of maize and sorghum. The study was carried out in a controlled environment growth chamber under constant environmental conditions (12/12 h day/night, 28-32/17°C day/night temperature, 60-80% RH and PPFD of 1200-1400 μ mol m-2s-1). Both species showed reduced gs (stomatal conductance) in response to dehydration to reduce water loss over a range of relative water contents during both developmental stages. In maize, stomata appeared to be closed earlier and completely, while partial stomatal closure at relatively higher relative water contents appeared to have occurred in sorghum. gs recovery occurred following pre-flowering rehydration to the control level in both species only. The response of all other gas exchange characteristics (Pn and Fv/Fm) and water use efficiency followed similar trends to that of gs both in maize and sorghum at pre and post-flowering dehydration and rehydration. Dehydration also led to a decrease in Fv/Fm ratios as compared to the control plants in both species. Both species, however, exhibited similar rates of Fv/Fm ratios during pre and post-flowering dehydration. Fv/Fm ratios appeared to be affected more during post than pre-flowering dehydration in both species. Fv/Fm ratios of both species were recovered following pre-flowering rehydration but only maize recovered from post-flowering rehydration. Key words: Chlorophyll, carotenoid, dehydration, electrolyte leakage, rehydration, stomatal conductance.

Wheat is an important cereal crop, which is adversely affected by water deficit stress. The effect of induced stress can be reduced by the application of salicylic acid (SA). With the objective to combat drought stress in wheat, an experiment was conducted in greenhouse under hydroponic conditions. The treatments consisted of (a) no drought (DD0 = 0 MPa), mild drought (DD1 = -0.40 MPa) and severe drought (DD2 = -0.60 MPa) by applying PEG-8000, (b) two contrasting wheat varieties Barani-17 (drought tolerant) and Anaj-17 (drought-sensitive), and (c) foliar treatments of salicylic acid (0, 50 mM, 75 mM, and 100 mM). Evaluation of wheat plants regarding biochemical, physiological, and morphological attributes were rendered after harvesting of plants. Statistically, maximum shoot and root fresh and dry weights (18.77, 11.15 and 1.99, 1.81 g, respectively) were recorded in cultivar Barani-17 under no drought condition with the application of SA (100 mM). While, minimum shoot and root fresh and dry weights (6.65, 3.14 and 0.73, 0.61 g, respectively) were recorded in cultivar Anaj-2017 under mild drought stress without SA application. The maximum shoot length (68.0 cm) was observed in cultivar Barani-2017 under no drought condition with the application of SA (100 mM). While, maximum root length (59.67 cm) was recorded in cultivar Anaj-17 under moderate drought stress without application of SA. Further, minimum shoot length (28.67 cm) was recorded in Anaj-17 under moderate drought stress without SA application. Minimum root length (38.67 cm) was recorded in cultivar Barani-17 under no drought condition without SA application. Furthermore, maximum physio-biochemical traits, including membrane stability index (MSI), chlorophyl content, photosynthetic rates, stomatal conductance, antioxidant enzymatic activities and relative water content (RWC) were found highest in cultivar Barani-17 under no drought stress and SA application at 100 mM. However, minimum values of these traits were recorded in cultivar Anaj-17 under severe drought stress without SA application. Our results also demonstrated that under severe drought, application of SA at 100 mM significantly increased leaf nitrogen (N), phosphrus (P) and potassium (K) contents and cultivar Barani-17 demonstrated significantly higher values than Anaj-17. The obtained results also indicated that the cultivation of wheat under drought stress conditions noticeably declines the morphological, physiological, and biochemical attributes of the plants. However, the exogenous application of SA had a positive impact on wheat crop for enhancing its productivity.

This study was conducted to evaluate the physiological indices in relation to screening of rapeseed genotypes for drought tolerance, and to study seed yield and seed yield components under early and late season drought stress. Six rapeseed genotypes were evaluated under non-stressed and water deficit conditions during rosette and seed filling stages. The experiments were conducted in East Azarbaijan Agricultural and Natural Resources Research and Education Center, Iran for 2 years (2010-2011 and 2012-2013). According to the results, canopy temperature (Tc) was increased, stomatal conductance (Kl) and relative water content (RWC) were decreased significantly by drought stress during the rosette and seed filling stages. Correlations among the aforementioned physiological traits at seed filling stage with each other and with seed yield were significant. It seems that these physiological traits can reflect the drought effects in rapeseed genotypes. Among the genotypes, significant differences were observed for Kl at seed filling and RWC at rosette stages. While, Okapi and Licord having the highest seed yield, presented the highest Kl during seed filling and RWC at rosette stages. Therefore, Tc, Kl and RWC can be used to screen rapeseed genotypes for tolerance to drought stress. Drought stress during the seed filling stage significantly decreased plant height, the number of siliques per plant, 1,000-seeds weight and seed yield. Results of path analysis indicated that plant height and yield components indicated positive direct effect on seed yield. Plant height had the highest direct effects on seed yield. Among the genotypes, Okapi and Licord were more suitable for cultivation in normal and drought conditions.

Drought is an important environmental factor that severely restricts crop production. The high-affinity nitrate transporter partner protein OsNAR2.1 plays an essential role in nitrate absorption and translocation in rice. Our results suggest that OsNAR2.1 expression is markedly induced by water deficit. After drought stress conditions and irrigation, compared with wild-type (WT), the survival rate was significantly improved in OsNAR2.1 over-expression lines and decreased in OsNAR2.1 RNAi lines. The survival rate of Wuyunjing7 (WYJ), OsNRT2.1 over-expression lines and OsNRT2.3a over-expression lines was not significantly different. Compared with WT, overexpression of OsNAR2.1 could significantly increase nitrogen uptake in rice, and OsNAR2.1 RNAi could significantly reduce nitrogen uptake. Under drought conditions, the expression of OsNAC10, OsSNAC1, OsDREB2a, and OsAP37 was significantly reduced in OsNAR2.1 RNAi lines and increased substantially in OsNAR2.1 over-expression lines. Also, the chlorophyll content, relative water content, photosynthetic rate and water use efficiency were decreased considerably in OsNAR2.1 RNAi lines and increased significantly in OsNAR2.1 over-expression lines under drought conditions. Finally, compared to WT, grain yield increased by about 9.1 and 26.6%, in OsNAR2.1 over-expression lines under full and limited irrigation conditions, respectively. These results indicate that OsNAR2.1 regulates the response to drought stress in rice and increases drought tolerance.

The main purpose of this research is to provide a theoretical foundation for the screening of drought-resistant soybean varieties and to establish an efficient method to detect the PSII actual photochemical quantum yields efficiently. Three soybean varieties were compared in this experiment after 15 d when they were planted in a greenhouse. These varieties were then exposed to light drought stress (LD) and serious drought stress (SD) conditions. With five times’ measurement, chlorophyll fluorescence and soil-plant analysis development considered as the main basis for this study. Several parameters in SD conditions significantly reduced, such as net photosynthetic rates (Pn), stomatal conductance (Gs), PSII primary light energy conversion efficiency (Fv/FM), PSII actual photochemical quantum yields [Y(II)], photochemical quenching coefficient (qP) and non-photochemical quenching coefficient (qN). The soybeans in the seedling stage adapted to the inhibitory effect of drought stress on photosynthesis through stomatal limitation. Under serious drought stress, non-stomatal limitation damaged the plant photosynthetic system. The amplitudes of Pn and Y(II) of drought-resistant Qihuang 35 were lower than those of the two other varieties. Based on the data of this study, a new method had been developed to detect Y (II) which reflected the photosynthetic capacity of plant, R=0.85989, u=0.048803 when using multiple linear regression, and R=0.84285, u=0.054739 when using partial least square regression. Keywords: soybean seedling, drought stress, photosynthetic parameters, chlorophyll fluorescence parameters, chlorophyll fluorescence images DOI: 10.25165/j.ijabe.20181102.3390 Citation: Wang W S, Wang C, Pan D Y, Zhang Y K, Luo B, Ji J W. Effects of drought stress on photosynthesis and chlorophyll fluorescence images of soybean (Glycine max) seedlings. Int J Agric & Biol Eng, 2018; 11(2): 196–201.

Understanding the genetic basis of traits of economic importance under drought stressed and well-watered conditions is important in enhancing genetic gains in dry beans (Phaseolus vulgaris L.). This research aims to: (i) identify markers associated with agronomic and physiological traits for drought tolerance and (ii) identify drought-related putative candidate genes within the mapped genomic regions. An andean and middle-american diversity panel (AMDP) comprising of 185 genotypes was screened in the field under drought stressed and well-watered conditions for two successive seasons. Agronomic and physiological traits, viz., days to 50% flowering (DFW), plant height (PH), days to physiological maturity (DPM), grain yield (GYD), 100-seed weight (SW), leaf temperature (LT), leaf chlorophyll content (LCC) and stomatal conductance (SC) were phenotyped. Principal component and association analysis were conducted using the filtered 9370 Diversity Arrays Technology sequencing (DArTseq) markers. The mean PH, GYD, SW, DPM, LCC and SC of the panel was reduced by 12.1, 29.6, 10.3, 12.6, 28.5 and 62.0%, respectively under drought stressed conditions. Population structure analysis revealed two sub-populations, which corresponded to the andean and middle-american gene pools. Markers explained 0.08–0.10, 0.22–0.23, 0.29–0.32, 0.43–0.44, 0.65–0.66 and 0.69–0.70 of the total phenotypic variability (R2) for SC, LT, PH, GYD, SW and DFW, respectively under drought stressed conditions. For well-watered conditions, R2 varied from 0.08 (LT) to 0.70 (DPM). Overall, 68 significant (p < 10−03) marker-trait associations (MTAs) and 22 putative candidate genes were identified across drought stressed and well-watered conditions. Most of the identified genes had known biological functions related to regulating the response to drought stress. The findings provide new insights into the genetic architecture of drought stress tolerance in common bean. The findings also provide potential candidate SNPs and putative genes that can be utilized in gene discovery and marker-assisted breeding for drought tolerance after validation.

Drought stress severely affects the physio-biochemical processes and yield of nutritious crops like vegetable soybean (Glycine max L. Merrill), threatening global food security and emphasising the need for effective strategies to improve drought tolerance. This study, conducted under controlled conditions in a greenhouse, investigates the effects of three selenium application methods (seed priming, foliar spray, and soil application) on photosynthesis efficiency, relative water content (RWC), hydrogen peroxide (H2O2), antioxidative responses, and yield traits of two vegetable soybean cultivars, UVE14 (drought-tolerant) and UVE17 (drought-susceptible), under drought stress. Among the three Se application methods, soil application was the most effective in improving drought tolerance and yield performance in both cultivars. In UVE17 (drought-susceptible), soil application significantly increased the number of seeds per plant (SPP) and the number of pods per plant (PPP), while in UVE14 (drought-tolerant) SPP increased. Selenium foliar spray and seed priming treatments did not increase yield in drought-stressed UVE14, suggesting that they are unlikely to further enhance tolerance in drought-tolerant cultivars. For UVE17 under drought conditions, selenium soil application improved key physio-biochemical indicators of drought tolerance, including photosynthesis efficiency (total performance of photosystems I and II, total chlorophyll content, and stomatal conductance), water retention (RWC), and carotenoid content. These improved physio-biochemical responses directly impacted yield outcomes. Notably, RWC and total chlorophyll content at the pod-filling stage in drought-stressed UVE17 were positively correlated with an increase in PPP under selenium soil application. Selenium soil application stands out as the most effective method for enhancing drought tolerance in vegetable soybean, presenting a promising and practical solution for enhanced crop production under climate change.

Water stress in plants affects a number of physiological processes such as photosynthetic rate, stomatal conductance as well as the operating efficiency of photosystem II (PSII) and non‐photochemical quenching (NPQ). Photochemical reflectance index (PRI) is reported to be sensitive to changes in xanthophyll cycle which occur during stress and could possibly be used to monitor changes in the parameters mentioned before. Therefore, the aim of this study was to evaluate the use of PRI as an early water stress indicator. Water stress treatment was imposed in a greenhouse tomato crop. CO2 assimilation, stomatal conductance, light‐adapted and dark‐adapted fluorescence as well as PRI and relative water content (RWCs%) of the rooting medium were repeatedly measured. The same measurements were also performed on well‐irrigated plants that acted as a reference. The experiment was repeated in four consecutive weeks. Results showed a strong correlation between RWCs% and photosynthetic rate, stomatal conductance, NPQ and operating efficiency of PSII but not with PRI when the whole dataset was considered. Nevertheless, more detailed analysis revealed that PRI gave a good correlation when light levels were above 700 µmol m−2 s−1. Therefore, the use of PRI as a water stress indicator cannot be independent of the ambient light conditions.

Seven citrus rootstocks of commercial importance in Florida were evaluated for their tolerance to Phytophthora root rot. Six-month-old seedlings were planted in soil artificially infested with chlamydospores at 0, 0.5, 1, 5, and 10 propagules of Phytophthora parasitica per cm 3 of soil. For all rootstocks, at 6 wk after inoculation there was little increase in disease rating with an increase in inoculum density above 1 propagule/cm 3 . Disease severity at the higher inoculum densities was significantly greater for the susceptible rootstocks (sour orange, Ridge Pineapple sweet orange, Cleopatra mandarin, and Carizzo citrange) than for the tolerant rootstocks (trifoliate orange and Swingle citrumelo) (...)

This study evaluates antioxidant responses and jasmonate regulation in Digitaria eriantha cv. Sudafricana plants inoculated (AM) and non-inoculated (non-AM) with Rhizophagus irregularis and subjected to drought, cold, or salinity. Stomatal conductance, photosynthetic efficiency, biomass production, hydrogen peroxide accumulation, lipid peroxidation, antioxidants enzymes activities, and jasmonate levels were determined. Stomatal conductance and photosynthetic efficiency decreased in AM and non-AM plants under all stress conditions. However, AM plants subjected to drought, salinity, or non-stress conditions showed significantly higher stomatal conductance values. AM plants subjected to drought or non-stress conditions increased their shoot/root biomass ratios, whereas salinity and cold caused a decrease in these ratios. Hydrogen peroxide accumulation, which was high in non-AM plant roots under all treatments, increased significantly in non-AM plant shoots under cold stress and in AM plants under non-stress and drought conditions. Lipid peroxidation increased in the roots of all plants under drought conditions. In shoots, although lipid peroxidation decreased in AM plants under non-stress and cold conditions, it increased under drought and salinity. AM plants consistently showed high catalase (CAT) and ascorbate peroxidase (APX) activity under all treatments. By contrast, the glutathione reductase (GR) and superoxide dismutase (SOD) activity of AM roots was lower than that of non-AM plants and increased in shoots. The endogenous levels of cis-12-oxophytodienoc acid (OPDA), jasmonic acid (JA), and 12-OH-JA showed a significant increase in AM plants as compared to non-AM plants. 11-OH-JA content only increased in AM plants subjected to drought. Results show that D. eriantha is sensitive to drought, salinity, and cold stresses and that inoculation with AM fungi regulates its physiology and performance under such conditions, with antioxidants and jasmonates being involved in this process.