Left Injury Research Articles

Dynamics of Jasmonate Metabolism upon Flowering and across Leaf Stress Responses in Arabidopsis thaliana.

The jasmonic acid (JA) signaling pathway plays important roles in adaptation of plants to environmental cues and in specific steps of their development, particularly in reproduction. Recent advances in metabolic studies have highlighted intricate mechanisms that govern enzymatic conversions within the jasmonate family. Here we analyzed jasmonate profile changes upon Arabidopsis thaliana flower development and investigated the contribution of catabolic pathways that were known to turnover the active hormonal compound jasmonoyl-isoleucine (JA-Ile) upon leaf stress. We report a rapid decline of JA-Ile upon flower opening, concomitant with the massive accumulation of its most oxidized catabolite, 12COOH-JA-Ile. Detailed genetic analysis identified CYP94C1 as the major player in this process. CYP94C1 is one out of three characterized cytochrome P450 enzymes that define an oxidative JA-Ile turnover pathway, besides a second, hydrolytic pathway represented by the amido-hydrolases IAR3 and ILL6. Expression studies combined with reporter gene analysis revealed the dominant expression of CYP94C1 in mature anthers, consistent with the established role of JA signaling in male fertility. Significant CYP94B1 expression was also evidenced in stamen filaments, but surprisingly, CYP94B1 deficiency was not associated with significant changes in JA profiles. Finally, we compared global flower JA profiles with those previously reported in leaves reacting to mechanical wounding or submitted to infection by the necrotrophic fungus Botrytis cinerea. These comparisons revealed distinct dynamics of JA accumulation and conversions in these three biological systems. Leaf injury boosts a strong and transient JA and JA-Ile accumulation that evolves rapidly into a profile dominated by ω-oxidized and/or Ile-conjugated derivatives. In contrast, B. cinerea-infected leaves contain mostly unconjugated jasmonates, about half of this content being ω-oxidized. Finally, developing flowers present an intermediate situation where young flower buds show detectable jasmonate oxidation (probably originating from stamen metabolism) which becomes exacerbated upon flower opening. Our data illustrate that in spite conserved enzymatic routes, the jasmonate metabolic grid shows considerable flexibility and dynamically equilibrates into specific blends in different physiological situations.

Evaluation of European corn borer Ostrinia nubilalis (Lepidoptera: Crambidae) larval movement and survival in structured and seed blend refuge plantings

Blending Bacillus thuringiensis (Bt) corn and non-Bt corn seeds in the same bag is a convenient and easier compliance solution to satisfy refuge regulations. However, there has been considerable debate and concern about larval movement of the target insects in a seed blend because of its potential effect on the development of resistance. Reported here are studies to determine the larval movement of European corn borers, Ostrinia nubilalis (Hübner), in a seed blend compared to a structured refuge and their effects on survival, feeding injury and larval fitness. Also evaluated is the relative performance of a purple-seeded corn hybrid as a surrogate host plant for tracking gene flow. Seed blend and structured refuge arrangements of Agrisure GT/CB/LL Bt corn expressing Cry1Ab and isoline plants were evaluated at two locations in 2013 and 2014 by manually infesting refuge plants with first and second generation corn borer larvae. The majority of leaf and stalk injury was recorded on the refuge plant, which amounted to 66–83% of the total tunnel length. In both refuge arrangements, plant injury and the number of larvae recovered significantly decreased on neighboring plants with increasing distance away from the refuge plant in the same row. The relative decline in injury was much more pronounced in the seed blend, with neighbor Bt plants experiencing very minor tunneling or no injury at all due to the high dose trait. Eighty-nine percent fewer live larvae were also found on neighbor Bt plants in the seed blend compared to those found in the structured refuge plots. Larvae that moved to Bt plants as well as older instars that were manually placed on Bt plants failed to complete development. Comparison of the number of tunnels and larvae recovered per refuge plant indicated that the seed blend may not produce as many susceptible individuals as those produced in a structured refuge arrangement. Although the purple-seeded hybrid showed lower levels of ear and stalk injury, it could serve as an appropriate surrogate refuge plant to track gene flow.

Evaluation of thifluzamide 24% sc fungicide against early blight disease in tomato (Lycopersicum Esculentum)

Field experiments were conducted during season of 2015 and 2016 at experimental research farm of Institute of Pesticide Formulation Technology, Gurgaon, India. Thifluzamide 24% SC @ 600ml/ha and 500 ml/ha was evaluated for two seasons against early blight of tomato variety Pusa Ruby. Thifluzamide 24% SC at all the doses including the highest dose did not show any sort of phytotoxicity symptoms Viz., leaf injury on tips/surface, necrosis, wilting, epinasty, hyponasty and vein clearing etc., on the crop during the testing period hence found non phytotoxic to the crop during both seasons. Since there was no significant difference in Thifluzamide 24% SC @ 600ml/ha and 500 ml/ha. Thifluzamide 24% SC @ 500 ml/ha is suggested for the control of the early Blight disease of Tomato crop. The highest yield was recorded in Thifluzamide 24% SC @ 600 ml/ha seed followed by Thifluzamide 24% SC @ 500 ml/ha during both seasons. Lowest yield recorded in untreated control.

Tolfenpyrad 15% EC, A New Pyrazole Insecticide, Against Sucking Pests of Okra and Its Impact on Natural Enemies

Okra is infested by various sucking insect pests among which jassids (Amrasca biguttula biguttula), aphids (Aphis gossypii), and whiteflies (Bemisia tabaci) are the major ones. Tolfenpyrad, belonging to the pyrazole class of insecticides is used against Hemiptera, Coleoptera, Diptera, Lepidoptera, Thysanoptera and Acarina. In this study tolfenpyrad 15% EC @ 125 and 150g a.i./ha showed better performance against sucking pest complex of okra. The observations on the phytotoxicity symptoms (viz., leaf injury, wilting, vein clearing, necrosis, epinasty and hyponasty etc.), if any, with tolfenpyrad 15% EC (300g a.i/ha) are also included. It is concluded that tolfenpyrad @ 125 and 150g a.i./ha might be recommended for okra and it is also safer to natural enemies.

Resistance to the spotted stem borer Chilo partellus (Swinhoe) and pink stem borer Sesamia inferens walker in maize

Two hundred twelve maize inbred lines were screened against Chilo partellus (Swinhoe) and Sesamia inferens Walker during rainy and post rainy seasons, 2012, respectively, under artificial infestation in field conditions. Based on the leaf injury rating (LIR) scale (1–9), 110 inbred lines with LIR < 3.0 along with resistant and susceptible check were re-screened against C. partellus during rainy season 2013 in augmented design under artificial infestation. Of the 212 inbred lines, 34 genotypes with LIR < 3.0 were re-screened along with three checks in replicated randomized block design during post rainy season 2013, against S. inferens under artificial infestation. The six genotypes viz., PFSRS2, AEBYC5341-1, P390AM/CMLC4F230-B-2, AEBCYC534-3-1, CML384X176F3- 100-9 and P63C2-BBB-17B were found to be the least susceptible to C. partellus, and 29 genotypes were categorized as moderately susceptible. Of the 34 inbred lines screened against S. inferens, six inbred lines namely WNZPBTL 9 (3.2), WNZPBTL 8 (3.5), CML 338 (3.6), WNZ EXOTIC POOL DC2 (3.1), CML 424 (3.2), WNZPBTL 91 (3.4) recorded LIR less than resistant check CM 500 (3.8) and 15 inbred lines were considered as moderately susceptible. These maize inbred lines could be utilized as sources of resistance against C. partellus and S. inferens.

Variations in the biology of spotted stem borer, Chilo partellus (Swinhoe) and its damage to maize genotypes

Laboratory studies were undertaken to evaluate variations in important biological characters of three populations of Chilo partellus (Swinhoe). These were reared for 8 (P1), 3 (P2) and 1 (P3) generations and their response under field conditions to maize cultivars viz. PMH 1, JH 3459 and CML 67 evaluated. It was observed that the incubation, larval and pupal periods were highest in P1, intermediate in P2 and lowest in P3. The hatchability of eggs, pupation, pupal weight, adult longevity and fecundity were highest in P3, intermediate in P2 and lowest in P1. The leaf injury rating at 10, 20 and 25 days after egg release was significantly more for P3 (4.3, 6.0 and 7.2, respectively) than that for P2 (4.5, 5.5 and 6.5, respectively) and P1 (3.7, 4.6 and 5.4, respectively). The deadheart formation at 25 days after egg release was also significantly more in P3 (39.99%) than that of P2 (26.66%) and P1 (9.99%).

Fluoride in soil and plant

Fluorine is unique chemical element which occurs naturally, but is not an essential nutrient for plants. Fluoride toxicity can arise due to excessive fluoride intake from a variety of natural or manmade sources. Fluoride is phytotoxic to most plants. Plants which are sensitive for fluorine exposure even low concentrations of fluorine can cause leave damage and a decline in growth. All vegetation contains some fluoride absorbed from soil and water. The highest levels of F in field-grown vegetables are found up to 40 mg kg -1 fresh weight although fluoride is relatively immobile and is not easily leached in soil because most of the fluoride was not readily soluble or exchangeable. Also, high concentrations of fluoride primarily associated with the soil colloid or clay fraction can increase fluoride levels in soil solution, increasing uptake via the plant root. In soils more than 90 percent of the natural fluoride ranging from 20 to 1,000 μg g -1 is insoluble, or tightly bound to soil particles. The excess accumulation of fluorides in vegetation leads to visible leaf injury, damage to fruits, changes in the yield. The amount of fluoride taken up by plants depending on the type of plant, the nature of the soil, and the amount and form of fluoride in the soil should be controlled. Conclusively, fluoride is possible and long-term pollution effects on plant growth through accumulation of the fluoride retained in the soil.

Effects of spectral distribution and photosynthetic photon flux density for overnight LED light irradiation on tomato seedling growth and leaf injury

We investigated the effects of spectral distribution and photosynthetic photon flux density (PPFD) for overnight light irradiation supplied by light-emitting diodes (LEDs) on the growth and degree of continuous light (CL)-induced leaf injury of tomato seedlings in a growth-chamber experiment. Over a 14-day treatment period, all plants were irradiated daily for 12h with white LED light at 300μmolm−2s−1 PPFD. During each 12-h nighttime interval, all plants except for the controls were irradiated with white LED light at 150 or 300μmolm−2s−1, or alternatively with blue, orange, or red LED light at 150μmolm−2s−1. Plants irradiated overnight exhibited injuries, with their visually rated severity of injury increased as the PPFD of nighttime white light was increased. In plants irradiated overnight at 150μmolm−2s−1, a higher degree of injury was experienced under blue light than under orange and red light. Overnight white-light irradiation at 150μmolm−2s−1 PPFD promoted dry matter production compared with the no-irradiation control, but no further increase was observed at a PPFD of 300μmolm−2s−1. Among different spectra, blue light was less effective than orange light at promoting dry matter production when white light was supplied during the day. Thus, both spectral distribution and PPFD of overnight LED light irradiation were demonstrated to affect tomato seedling growth and degree of injury.

Trocas gasosas e injúrias foliares visíveis em plantas jovens de Astronium graveolens Jacq. fumigadas com ozônio

Astronium graveolens Jacq. é uma espécie arbórea de grande ocorrência na floresta atlântica de encosta e do interior do Estado de São Paulo. Como as concentrações de ozônio (O3) no Estado de São Paulo são fitotóxicas, decidiu-se avaliar algumas respostas fisiológicas e bioquímicas da espécie ao O3 devido sua importância em programas de recuperação de áreas degradadas. Plantas jovens foram mantidas em câmaras fechadas, uma com ar filtrado (AF) e outra com ar filtrado enriquecido com O3 (AF + O3, 100 ppb, 4 h dia-1, 7 dias, n = 9). As injúrias foliares foram avaliadas diariamente e ao final da fumigação foram determinadas a assimilação de carbono (A), condutância estomática (gs), transpiração (E), concentração interna de CO2 (Ci), assimilação máxima de carbono (Amax), peroxidação de lipídios (PL) e permeabilidade relativa de eletrólitos (PRE). O O3 induziu o surgimento de injúrias foliares e reduziu A, gs, E e Amax, porém não alterou Ci, PL e PRE. A espécie é medianamente sensível ao O3. Experimentos de longa duração devem ser realizados para verificar se a redução nas trocas gasosas pode prejudicar o crescimento a ponto de reduzir sua aplicação em programas de reflorestamento.

Economic evaluation of biorational and conventional insecticides for the control of maize stem borer Chilo partellus (Swinhoe) in Zea mays

Maize borer, Chilo partellus (Swinhoe) is the chief limiting factor for higher corn production. Field trials to assess the efficacy of different insecticides against C. partellus were carried in district Ropar, Punjab. It was observed that significantly lesser leaf injury incidence was recorded in biorational treatment T1: chlorantriniliprole 18.5 SC (3.43 &amp; 4.23) in comparison to broad spectrum conventional insecticide treatment T3: Deltamethrin 2.8 EC (4.63&amp; 5.36) and T4 :Farmer’s practice 4.43 and 6.93. Whereas in plots with parasitoid application (T2), the leaf injury incidence was recorded to be 6.56 &amp; 7.86 during 2012 and 2013, respectively. Though T2 was statistically superior to control, however it was not at par with insecticide treatments. Furthermore similar trend was observed for dead hearts reduction in different treatments. It was recorded to be 3.16 and 3.90, 3.33 and 3.96, 3.53 and 3.96 in insecticide treatment plots T1, T3 and T4 respectively. The economic returns on the basis of marketable grain yield in insecticide treated plots was more in T1 followed by T3 and T4 (51.99, 49.58 and 48.51) in comparison to control (40.44) and biological control plots (46.75). Therefore experimental data revealed overall superiority of biorational pesticide in comparison to conventional insecticides for reduction in pest damage and economic returns. Hence the option of biorational for the control of maize stem borer not only justify safety to environment but also offers effective control of borer population in maize ecosystem due to its distinct chemical class and unique mode of action.

Effects of acute O3 stress on PSII and PSI photochemistry of sensitive and resistant snap bean genotypes (Phaseolus vulgaris L.), probed by prompt chlorophyll “a” fluorescence and 820 nm modulated reflectance

The response of PSII and PSI photochemistry to acute ozone (O3) stress was tested in a “model plant system”, namely the O3 sensitive (S156) and O3 resistant (R123) genotype pairs of Phaseolus vulgaris L., during a phenological phase of higher O3 sensitivity (pod formation). The modulation of the photosynthetic activity during O3 stress was analysed by measuring gas exchanges, Prompt Fluorescence (PF, JIP-test) and 820 nm Modulated Reflectance (MR), a novel techniques which specifically detects the changes in the redox state of P700 and plastocyanin. The results showed that, coherently with genotypic-specific O3 sensitivity, the response of the two snap bean genotypes differed for the intensity and time of onset of the considered physiological changes. In fact, despite leaf injury and gas exchanges reduction appeared concurrently in both genotypes, S156 showed a PSII down regulation already after the first day of fumigation (DOF), and an enhancement of Cyclic Electron Flow of PSI after the second DOF, whereas R123 showed only slight adjustments until the third DOF, when the activity of both photosystems was down-regulated. Despite these differences, it is possible to distinguish in both genotypes an early O3 response of the photochemical apparatus, involving PSII only, and a following response, in which PSI activity and content are also modulated. The measurement of the MR signal, performed simultaneously with the PF measurements and the JIP-test analysis, has allowed a better understanding of the role that PSI plays in the O3 stress response of the S156/R123 model plant system.

Bioefficacy of wild plant extract for biological control of insect pests of Bt cotton

Wild plant fruit extract such as hinganbet, Balanites roxburghii , ritthaa/soap nut, Sapindus trifoliatus , shikekaaee, Acacia concinna , Neem, Azadirachta indica , Karanj, Pongamia pinnata and vekhand, Acorus calamus L. were evaluated to screen their efficiency for the control of sucking pests of Bt cotton during Kharif 2009 to 2012 at Cotton Improvement Project, Mahatma Phule Krishi Vidyapeeth, Rahuri. All the organic pesticide treatments were superior over untreated control. Among the evaluated organic pesticides the treatment with 5 per cent hingan bet extract @ 2 litre per hectare was observed to be effective in reducing pest population in which aphids, jassids, thrips and whiteflies of 22.68, 8.16, 14.53 and 10.97 per three leaves, respectively, were recorded with the seed cotton yield of 20.77 quintal per hectare. However, this treatment was statistically at par with 5 per cent ritthaa extract @ 2 litre per hectare. The treatment with 5 per cent ritthaa extract recorded aphids, jassids, thrips and whiteflies of 23.16, 9.87, 15.34 and 12.65 per three leaves, respectively, with the seed cotton yield of 20.09 quintal per hectare. The treatment with 5 per cent NSE @ 2 litre per hectare recorded 28.96, 12.61, 17.71 and 15.18 aphids, jassids, thrips and whiteflies per three leaves, respectively, with the seed cotton yield of 12.31 quintal per hectare. The phytotoxicity studies on leaf injury on tips and leaf surface, wilting, vein necrosis, epinasty and hyponasty showed that there was no phytotoxic effect of the evaluated pesticides on cotton crop at the evaluated doses. The counts on natural enemies in the treatments with hinganbet and ritthaa extract were more or less similar to those recorded in untreated control. This clearly indicated that there was no adverse effects on natural enemies due to spraying of hinganbet and ritthhaa extract at evaluated doses.

Recovery of tomato (Solanum lycopersicum L.) leaves from continuous light induced injury

Continuous light (CL) causes leaf injuries in tomato plants, but very little has been done to study the nature of recovery from these leaf injuries. To facilitate this, tomato plants (Solanum lycopersicum L. cv. ‘Aromata’) were first exposed to CL for 11 days in order to study the development of the leaf injuries. Afterwards, the plants were exposed to a photoperiodic treatment with a dark period of eight hours to study the nature of recovery of the leaves. Plants were grown in two photoperiodic treatments in climate chambers; a control treatment with a 16/8h light/dark and a CL treatment with 24h light. The two treatments had different light intensities to maintain a similar daily light integral (15molm−2d−1). The temperature and humidity were adjusted to maintain a similar vapor pressure deficit (VPD) of 1kPa in the two treatments. After 11 days of CL, 12% of the total leaflet area appeared light green in spots on the leaf surface aligned with lower total leaf chlorophyll content. The light green spots partially reversed while the leaf chlorophyll content increased to similar levels as seen in control leaves after 11 days of recovery. The CL significantly reduced the stomatal conductance (gs) and net photosynthesis (PN) and altered the carbohydrate content in the leaves. These negative effects of CL were also rapidly restored to the control levels when the plants were returned to the 16h photoperiodic conditions. The results demonstrate that, though leaf discoloration is only partially recovered, tomato plants can be grown for 11 days in CL conditions with the development of chlorotic discoloration of the leaves covering 12% of the leaf surface and rapidly recover physiological processes affected by CL by shortening the photoperiod to 16h.

Continuous light increases growth, daily carbon gain, antioxidants, and alters carbohydrate metabolism in a cultivated and a wild tomato species.

Cultivated tomato species develop leaf injury while grown in continuous light (CL). Growth, photosynthesis, carbohydrate metabolism and antioxidative enzyme activities of a cultivated (Solanum lycopersicum L. ‘Aromata’) and a wild tomato species (Solanum pimpinellifolium L.) were compared in this study aiming to analyze the species-specific differences and thermoperiod effects in responses to CL. The species were subjected to three photoperiodic treatments for 12 days in climate chambers: 16-h photoperiod with a light/dark temperature of 26/16°C (P16D10 or control); CL with a constant temperature of 23°C (P24D0); CL with a variable temperature of 26/16°C (P24D10). The results showed that both species grown in CL had higher dry matter production due to the continuous photosynthesis and a subsequent increase in carbon gain. In S. lycopersicum, the rate of photosynthesis and the maximum photochemical efficiency of photosystem II declined in CL with the development of leaf chlorosis, reduction in the leaf chlorophyll content and a higher activity of antioxidative enzymes. The normal diurnal patterns of starch and sugar were only present under control conditions. The results demonstrated that CL conditions mainly affected the photosynthetic apparatus of a cultivated species (S. lycopersicum), and to a less degree to the wild species (S. pimpinellifolium). The negative effects of the CL could be alleviated by diurnal temperature variations, but the physiological mechanisms behind these are less clear. The results also show that the genetic potential for reducing the negative effects of CL does exist in the tomato germplasm.

Biochemical and physiological processes associated with the differential ozone response in ozone-tolerant and sensitive soybean genotypes.

Biochemical and physiological traits of two soybean [Glycine max (L.) Merr.] genotypes differing in sensitivity to ozone (O3 ) were investigated to determine the possible basis for the differential response. Fiskeby III (O3 -tolerant) and Mandarin (Ottawa) (O3 -sensitive) were grown in a greenhouse with charcoal-filtered air for 4 weeks, then treated with O3 for 7 h·day(-1) in greenhouse chambers. Mandarin (Ottawa) showed significantly more leaf injury and hydrogen peroxide (H2 O2 ) and superoxide (O2 (-) ) production compared with Fiskeby III. Peroxidase activity in Mandarin (Ottawa) was 31% higher with O3 but was not significantly different in Fiskeby III. Ozone did not affect superoxide dismutase or glutathione reductase activities, or leaf concentrations of glutathione or ascorbic acid. Thus, variation in O3 response between Fiskeby III and Mandarin (Ottawa) was not explained by differences in antioxidant enzymes and metabolites tested. Ethylene emission from leaves declined in Fiskeby III following O3 exposure but not in Mandarin (Ottawa). Ozone exposure reduced quantum yield (ΦPSII ), electron transport rate (ETR) and photochemical quenching (qp ) in Mandarin (Ottawa) more than in Fiskeby III, indicating that efficiency of energy conversion of PSII and photosynthetic electron transport was altered differently in the two genotypes. Short-term exposure to O3 had minimal effects on net carbon exchange rates of both soybean cultivars. A trend toward higher stomatal conductance in Mandarin (Ottawa) suggested stomatal exclusion might contribute to differential O3 sensitivity of the two genotypes. Increased sensitivity of Mandarin (Ottawa) to O3 was associated with higher H2 O2 and O2 (-) production compared with Fiskeby III, possibly associated with genotype differences in stomatal function or regulation of ethylene during the initial phases of O3 response.

Genetics of resistance to Sesamia inferens infestation and its correlation with yield in maize

AbstractSesamia inferens (Walker) causes 25.7–78.9% losses in maize production in South and South‐East Asia. The genetic basis of host plant resistance is the prerequisite for resistance breeding. Twenty‐four populations derived from S. inferens resistant × susceptible inbreds were used to study the genetic regulation of resistance to S. inferens in maize, to determine the importance of genetic effects through generation mean analysis (GMA) and to understand correlation between resistance and yield. Resistant and susceptible inbreds differed significantly in leaf and stem injury ratings (LSIR), a measure of host plant resistance. Mean LSIR range among resistant and susceptible parents was 2.15–2.55 and 7.83–8.22, respectively. The broad‐sense heritability ranged from 0.40 to 0.71, and the mean number of effective factors ranged from 1.9 to 2.6. The resistance against S. inferens was largely governed by additive × additive (i), followed by dominance (d) and additive (a) gene effects. Significant negative correlation (−0.27 to −0.96) was observed between LSIR and yield. The findings suggest reciprocal recurrent selection for development of new inbreds with resistance followed by their involvement in hybrid development to exploit additive and non‐additive gene effects/variance.

Ozone-Induced Rice Grain Yield Loss Is Triggered via a Change in Panicle Morphology That Is Controlled by ABERRANT PANICLE ORGANIZATION 1 Gene.

Rice grain yield is predicted to decrease in the future because of an increase in tropospheric ozone concentration. However, the underlying mechanisms are unclear. Here, we investigated the responses to ozone of two rice (Oryza Sativa L.) cultivars, Sasanishiki and Habataki. Sasanishiki showed ozone-induced leaf injury, but no grain yield loss. By contrast, Habataki showed grain yield loss with minimal leaf injury. A QTL associated with grain yield loss caused by ozone was identified in Sasanishiki/Habataki chromosome segment substitution lines and included the ABERRANT PANICLE ORGANIZATION 1 (APO1) gene. The Habataki allele of the APO1 locus in a near-isogenic line also resulted in grain yield loss upon ozone exposure, suggesting APO1 involvement in ozone-induced yield loss. Only a few differences in the APO1 amino acid sequences were detected between the cultivars, but the APO1 transcript level was oppositely regulated by ozone exposure: i.e., it increased in Sasanishiki and decreased in Habataki. Interestingly, the levels of some phytohormones (jasmonic acid, jasmonoyl-L-isoleucine, and abscisic acid) known to be involved in attenuation of ozone-induced leaf injury tended to decrease in Sasanishiki but to increase in Habataki upon ozone exposure. These data indicate that ozone-induced grain yield loss in Habataki is caused by a reduction in the APO1 transcript level through an increase in the levels of phytohormones that reduce leaf damage.

Flooding tolerance in maize (Zea mays subsp. mays) F1 hybrids containing a QTL introgressed from teosinte (Zea nicaraguensis)

Worldwide climate change has increased the risk of crop yield losses caused by flooding. Here, we report the development of maize F1 hybrids containing a teosinte QTL for flooding tolerance on chromosome 4 and the evaluation of flooding tolerance under reducing soil conditions. We used F1 hybrid Mi29 × Mi47 (cultivar Yumechikara) and two versions of Yumechikara into which the QTL has been introgressed, Mi47 × IL#18 (heterozygous for the QTL) and IL#18 × BC3#90 (homozygous for the QTL). Flooding tolerance was evaluated at three treatment levels (i.e., soluble starch at 1, 0.5 or 0 g L−1) and the non-flooded control at an early growth stage (2.6- to 3.0-leaf stage) and at the 5.5-leaf stage. Tolerance was assessed by measuring leaf injury, leaf SPAD values, and shoot and root dry weight ratios (treatment/control). The F1 hybrids containing the QTL were significantly more tolerant (as evaluated by leaf injury and SPAD values) than the original F1 cultivar (Mi29 × Mi47) at both growth stages. When flooding tolerance was evaluated by shoot dry weight ratio at an early growth stage, IL#18 × BC3#90 was significantly more tolerant than Mi29 × Mi47 at the 1 and 0 g L−1 treatment levels. At the 5.5-leaf stage, there were no significant differences among the three F1 hybrids under the three treatment levels. Although plants at an early growth stage are generally more sensitive to flooding than at later stages, IL#18 × BC3#90 should overcome flooding stress at the sensitive early stage of growth.

DO3SE model applicability and O3 flux performance compared to AOT40 for an O3-sensitive tropical tree species (Psidium guajava L. 'Paluma').

Phytotoxic ozone (O3) levels have been recorded in the Metropolitan Region of São Paulo (MRSP). Flux-based critical levels for O3 through stomata have been adopted for some northern hemisphere species, showing better accuracy than with accumulated ozone exposure above a threshold of 40 ppb (AOT40). In Brazil, critical levels for vegetation protection against O3 adverse effects do not exist. The study aimed to investigate the applicability of O3 deposition model (Deposition of Ozone for Stomatal Exchange (DO3SE)) to an O3-sensitive tropical tree species (Psidium guajava L. 'Paluma') under the MRSP environmental conditions, which are very unstable, and to assess the performance of O3 flux and AOT40 in relation to O3-induced leaf injuries. Stomatal conductance (g s) parameterization for 'Paluma' was carried out and used to calculate different rate thresholds (from 0 to 5 nmol O3 m(-2) projected leaf area (PLA) s(-1)) for the phytotoxic ozone dose (POD). The model performance was assessed through the relationship between the measured and modeled g sto. Leaf injuries were analyzed and associated with POD and AOT40. The model performance was satisfactory and significant (R (2) = 0.56; P < 0.0001; root-mean-square error (RMSE) = 116). As already expected, high AOT40 values did not result in high POD values. Although high POD values do not always account for more injuries, POD0 showed better performance than did AOT40 and other different rate thresholds for POD. Further investigation is necessary to improve our model and also to check if there is a critical level of ozone in which leaf injuries arise. The conclusion is that the DO3SE model for 'Paluma' is applicable in the MRSP as well as in temperate regions and may contribute to future directives.

Effect ofGlomus aggregatumon photosynthetic function of snap bean in response to elevated ozone

SUMMARYSnap bean genotypes (Phaseolus vulgarisL.) with different ozone (O3) sensitivities (line S156: O3-sensitive; line R123: O3-tolerant) were grown for 70 days with or without inoculation of arbuscular mycorrhizal (AM) fungi under ambient (CAMB = 20 nanolitres (nl)/l and elevated (CMID = '50 nl/l andCHIG = 80 nl/l) O3. Sequential determinations (leaf injury, pigment concentration, chlorophyll fluorescence, photosynthesis, etc) were carried out during plant growth to evaluate mycorrhizal influence on the photosynthetic function of the two genotypes under elevated O3. Inoculation with AM fungi alleviated leaf injury in both genotypes and delayed time of injury manifestation (TIM) in the R123 line at the blooming stage (growth stage (GS): 61-65 (Zadoks scale, Zadokset al. 1974), 30–35 days after the onset of O3fumigation), but mycorrhizal effect was slight at the initial growth stage (GS 11–13, 0–5 days after onset of O3fumigation). Relative to the non-mycorrhizal plant, AM fungi inoculation increased the concentrations of chlorophyll (Chl) a, Chl b and carotenoids in S156 plants, regardless of O3levels, while in R123 plants a similar effect was observed only in theCAMBtreatment. At the blooming (GS 61–65) and the pod filling (GS 71–77, 45–50 days after starting O3fumigation) stages, photosynthetic rate, stomatal conductance and transpiration rate for the two genotypes decreased with elevated O3in all treatments, although the effect was reduced inCAMBandCMIDtreatments in AM-inoculated plants; however, the mycorrhizal effect was slight in theCHIGtreatment. Intercellular carbon dioxide concentration increased with elevated O3regardless of AM fungi inoculation, but it was lower in the mycorrhizal plants than in the non-mycorrhizal plants, in most cases. Furthermore, AM fungi inoculation significantly increased the maximum quantum yield of photosystem II (PS II) photochemistry (Fv/Fm) and electron transport rate in both genotypes in theCHIGtreatment. The present study indicated that in some cases, AM fungi inoculation can enhance plant tolerance to elevated O3through improving plant photosynthetic function, but the effect was reduced by serious O3stress.