Marlos Alves Bezerra

Crescimento e níveis de solutos orgânicos e inorgânicos em cultivares de Vigna unguiculata submetidos à salinidade

Os efeitos da salinidade no crescimento e nos teores de solutos orgânicos e inorgânicos foram analisados em sete cultivares de Vigna unguiculata. As plantas foram cultivadas em solucao nutritiva sem NaCl (controle) e com NaCl a 75 mM (estresse salino), em casa de vegetacao. Apos 14 dias da semeadura, adicionou-se 25 mM de sal diariamente, durante tres dias, perfazendo o total de 75 mM. A coleta foi realizada no 33o dia. A salinidade reduziu a materia seca de todos os cultivares, sendo Pitiuba e Vita 5 os menos afetados e TVU o que sofreu maior reducao. A suculencia foliar e o indice de esclerofilia foram concordantes com o grau de tolerância, aumentando significativamente, em funcao da salinidade, apenas nos cultivares com menores reducoes nas materias secas. Contrariamente, a relacao raiz/parte aerea teve maior aumento nos cultivares mais afetados. Os teores de Na+ e Cl- foliares aumentaram em resposta ao estresse salino, sendo o Na+ acumulado em niveis maiores nos cultivares mais afetados, especialmente no TVU. Os niveis de K+ foliar, que se mostraram mais elevados que os de Na+ e Cl-, foram poucos afetados pela salinidade, de modo que a relacao Na+/K+ aumentou mais nos cultivares mais afetados e, possivelmente, se constituiu num fator importante para a maior reducao em seus crescimentos. As variacoes nos teores de prolina, carboidratos soluveis e N-aminossoluveis em resposta a salinidade indicam uma falta de proporcionalidade entre seus niveis e o grau de tolerância a salinidade nos cultivares de feijao-de-corda estudados.

Antioxidant-enzymatic system of two sorghum genotypes differing in salt tolerance

Two forage sorghum genotypes were studied: CSF18 (salt-sensitive) and CSF20 (salt-tolerant). Shoot growth reduction as a result of salt stress was stronger in the salt sensitive genotype compared to the salt tolerant one. When the two genotypes were subjected to salt stress (75 mM NaCl) no significant change in lipid peroxidation was observed. However, salt stress induced increases in superoxide dismutase and catalase activities in both genotypes. These salt-induced increases were higher in the salt-tolerant genotype. Peroxidase activity was differentially affected by salt stress in the two genotypes. The activities of these peroxidases were decreased by salt stress in the salt-sensitive genotype and increased in the salt-tolerant genotype. In addition, the activity ratio between the superoxide dismutase and the H2O2-scavenging enzymes was higher in the salt-sensitive genotype. The results obtained support the hypothesis that the higher efficiency of the antioxidant-enzymatic system of the CSF20 genotype could be considered as one of the factors responsible for its tolerance to salt stress. Therefore, it is suggested that the ratio between superoxide dismutase and H2O2-scavenging enzyme activities could be used as a working hypothesis for a biochemical marker for salt tolerance in sorghum.

Produtividade do feijão-de-corda e acúmulo de sais no solo em função da fração de lixiviação e da salinidade da água de irrigação

The study had the objective to evaluate the effect of water salinity and the leaching fraction (LF) on soil salt accumulation and on the yield of grains of cowpea plants. A completely randomized block design, with four treatments and five repetitions, was adopted. The treatments studied were: 1 - well water with ECw of 0.8 dS m-1 (without LF); 2 - saline water with ECw of 5.0 dS m-1 (without LF); 3 - saline water with ECw of 5.0 dS m-1 with LF of 0.14, and 4 - saline water with ECw of 5.0 dS m-1 with LF of 0.28. The following parameters were evaluated: soil salt accumulation, vegetative plant growth, yield, gas exchange and leaf ion contents (Na+, Ca+2, K+, and Cl-). The saline water application provoked salt accumulation in the soil profile, but this effect was partially reverted by the increase of the leaching fraction. Salinity reduced plant yield, but it did not affect its quality. The reduction in plant yield was related, at least in part, to decrease in net assimilation of carbon during flowering and fruit development due to osmotic effects and to accumulation of potentially toxic ions (Na+ and Cl-). In general, the increase in leaching fraction did not reduce the effect of the salinity on plant development.

Physiology of cashew plants grown under adverse conditions

The cashew (Anacardium occidentale L.) is an important crop for semi-arid agriculture and contributes to the social and economical development of several world regions, including the northeast of Brazil. In spite of its importance, very few studies aim to understand the effects of abiotic stresses on the development and yield of the cashew. This review covers the research on cashew ecophysiology, with emphasis on the effects of water and salt stress on its development, mineral nutrition and gas exchange processes. The results presented here were obtained at different plant growth stages and under different environmental conditions of soil and climate. The ecophysiological significance of this information is also discussed.

Morpho-physiological responses of cowpea leaves to salt stress

The effect of salt stress of known intensity and duration on morpho-physiological changes in leaves of different ages from cowpea [Vigna unguiculata (L.) Walp.] plants was studied, aiming for a better understanding of the acclimation process of the whole-plant. Seeds were sown in vermiculite and seedlings were transferred to plastic trays containing aerated nutrient solution, and kept in a greenhouse. When the first trifoliate leaf emerged the seedlings were transplanted into 3 L plastic pots containing aerated nutrient solution. Salt additions started 5 d later, and the salt-treated plants received 25 mmol L-1 per day until reaching a final concentration of 75 mmol L-1. During the experimental period primary leaves and the 1st, 2nd, and 3rd trifoliate leaves were used for measurements of net photosynthesis, leaf area, leaf succulence, specific leaf mass, ions and chlorophyll concentrations. Growth analysis of the whole-plant was performed at the end of the experimental period. Salinity did not affect net photosynthesis, but reduced dry mass production and the number of lateral branches. Leaf concentrations of Na+, Cl-, K+ and P increased in salt-stressed plants, but these responses were dependent upon stress duration and leaf age. The higher concentration of potentially toxic ions (Na+ and Cl-) in older leaves could contribute to the reduced ion accumulation in growing tissues, but the tendency of K and P accumulation in leaves appeared to be the result of reduced re-translocation, i.e., not related to plant acclimation. Salinity also increased the source/sink ratio, leaf succulence, specific leaf mass, and chlorophyll accumulation per unit of leaf area, suggesting that the observed changes could be part of an integrated mechanism of whole-plant acclimation to salt stress.

Physiological and biochemical changes occurring in dwarf-cashew seedlings subjected to salt stress

The effects of salt stress on some physiological and biochemical traits were evaluated in dwarf-cashew seedlings at the same developmental stage. Seeds were sown in trays containing vermiculite moistened with distilled water or with NaCl solutions having different electrical conductivities: 0.7, 1.8, 6.0, 9.8, 13.4, 17.4 and 20.6 dS m-1. Salinity delayed and inhibited seedling growth and development, particularly in the shoot. Concentrations of Na+ and Cl-, but not of K+, increased with increasing stress severity. With the exception of proline, concentration of organic solutes was only marginally affected by salt stress. Catalase activity in leaves increased slightly as a result of salt stress, whereas guaiacol peroxidase activity was induced only under low levels of salt. In contrast, activities of guaiacol peroxidase and ascorbate peroxidase increased dramatically in roots. Apparently, roots were better protected against oxidative damage than shoots, as judged from the decrease in lipid peroxidation in root tissues. In leaves, expression of 75 proteins, evaluated by 2D electrophoresis, was altered by salt stress: 35 of them increased their expression and three were apparently de novo synthesized. In roots, 69 proteins were modified by salt stress: 34 proteins increased their expression and two proteins appeared only in stressed seedlings. The changes in protein patterns were caused by the imposed salt stress rather than by a response to the developmental stage. Overall, these responses could play an important role in salt stress acclimation of cashew seedlings.

Crescimento, partição de matéria seca e retenção de Na+, K+ e Cl- em dois genótipos de sorgo irrigados com águas salinas

SUMMARY : GROWTH, DRY MASS PARTITIONING, AND Na + , K + , AND Cl - RETENTION BY TWO SORGHUM GENOTYPES IRRIGATEDWITH SALINE WATER The mechanisms for salt tolerance are complex and depend upon physiological andanatomical changes occurring in the whole-plant. This research aimed at evaluating ionretention, vegetative growth, and dry matter partitioning by two forage sorghum genotypes[Sorghum Bicolor (L.) Moench] irrigated with saline water. Selected seeds were sown inplastic pots containing 12 kg a sandy Argisol and grown under greenhouse conditions. Theexperiment was in completely randomized with treatments arranged in a 2 x 5 factorialdesign, consisting of two genotypes (CSF 18, sensitive and CSF 20, tolerant) and five levelsof increasing salinity (0.5, 2.0 , 4.0, 6.0 and 8.0 dS m -1 ), with four replicates. The treatments(salinity water) application began five days after seeds emergence. On the forty-fourth dayafter the salt water applications began plants were harvested and evaluated for the followingcharacteristics: dry mass production, dry mass partitioning, root distribution into pots,and Na

Influência do acúmulo e distribuição de íons sobre a aclimatação de plantas de sorgo e feijão-de-corda, ao estresse salino

In this paper the influence of accumulation and distribution of ions in plant shoots on acclimation to salt stress of cowpea and sorghum plants was studied. The plants were subjected to two treatments: control (nutrient solution without addition of NaCl) and saline (nutrient solution containing 75 mM of NaCl). Sorghum showed a higher tolerance to salt stress in comparison to cowpea, mainly after the 10th day of stress. Cowpea showed higher shoot ion accumulation than sorghum, which behaved as a plant with good capacity of ion exclusion. The higher accumulation of potentially toxic ions in cowpea leaves contributed to the increase in leaf succulence. Although the exclusion or retention of ions observed in stressed plants of sorghum had produced a certain degree of leaf dehydration, it seemed to be a much more efficient mechanism of stress acclimation than the excessive accumulation of ions in leaf tissues of cowpea plants.

Physiologic responses of precocious dwarf cashew at different levels of salinity.

Salinity is an abiotic stress that alters the plant development, limiting plant production. At the present experiment, it was evaluated the effect of salt stress on osmotic potential, content of organic and inorganic solutes, gas exchanges (photosynthesis, transpiration and stomatal conductance) and production of precocious dwarf cashew (Anacardium occidentale L.). For this, the experiment was carried out at Embrapa Agroindustria Tropical experimental station, in Pacajus, Ceara, Brazil, during the months of August to December. The plants were subjected to increasing levels of salinity using irrigation water with electrical conductivity (EC w ) of 0.5 (control), 4.0, 8.0 and 12.0 dS m -1 . The data were collected monthly and subjected to statistic analyses. Although the electrical conductivity of soil saturation extract (EC se ) increased with salinity, there were no significant differences between treatments for osmotic potential, gas exchange and levels of organic and inorganic solutes. With the exception of leaf osmotic potential and gas exchange, all the others parameters studied varied along the experiment in function of the phenophisiological stage of the plant, presenting greater values in the fructification period. So, the salinity stress was not enough to cause significant changes in growth and productivity of the plants.

Ocorrência endofítica de Lasiodiplodia theobromae em tecidos de cajueiro e sua transmissão por propágulos

Lasiodiplodia theobromae, agent of gummosis and black branch dieback of cashew, is the most important disease of cashew crop in semi-arid regions of northeastern Brazil. This pathogen is a well known fungus in many host plants as capable of colonizing their tissues without showing disease symptoms. This feature ensures great epidemiologic importance as considering tactics for disease avoidance. The occurrence of cashew gummosis in geographically isolated areas reinforces the seed and scion borne pathogen hypothesis. The objectives of this study were to determine the ability of L. theobromae to survive in cashew tissues without showing symptoms and to evaluate plant propagating materials (seed and scion) as source of primary inoculum. The presence of the fungus at different distances from the canker throughout the stem in both ascendant and descendent direction was determined by plating infected tissue samples. In another study, transplanting materials were produced by using rootstocks from seeds sampled either from healthy and gummosis-infected plants and grafted with scions also from healthy and gummosis-infected plants, making a four set of treatments. These plants were transplanted into a commercial cashew farm located in Pio IX, County, Piaui State, highly conducive for disease outbreak. L. theobromae was isolated from up to 80 cm distance from canker in both directions. Greater gummosis incidence was observed in plots initiated by rootstock and scion originated from diseased plants. These findings showed the endophytic behavior of L. theobromae in cashew tissues and the importance of rootstock seed as a source of primary inoculum.