Possibility of exploitation of xerophytic crops for the Brazilian semi-arid tropics

Neste trabalho discutem-se as possibilidades de domesticação de xerófitas nativas com vistas à adoção das chamadas “lavouras xerófilas” para o trópico semi-árido brasileiro. A luz de informações e conhecimentos existentes na literatura sobre os mecanismos morfofisiológicos de resistência à seca e de seus efeitos na produtividade vegetal, demonstra-se que a domesticação de xerófitas nativas é questionável. Recomendam-se a seleção e o melhoramento de espécies cultivadas que já possuem algumas características de adaptabilidade à seca, bem como o desenvolvimento de pesquisas que possibilitem estabelecer praticas de manejo das culturas, do solo e da água, que sejam mais adequadas às condições do trópico semi-árido brasileiro.This paper discusses the possibility of domesticating wild xerophytes for the purpose of exploiting them as xerophytic crops in the Brazilian semi-arid tropics. Based on information and knowledge existent in the literature on the morphophysiological mechanisms of drought resistance and their effect on plant productivity, it is demonstrated that wild xerophyte domestication is questionable. Selection and breeding of known crops that already have some drought adaptation mechanism as well as the development of research designed to establish crop, soil and water management practices suitable for the semi-and tropics are recommended

Efeitos do H2O2 no crescimento e acúmulo de solutos em plantas de milho sob estresse salino Effects of H2O2 on the growth and solutes accumulation in maize plants under salt stress

Este trabalho teve como objetivo estudar os efeitos da aplicação foliar de H2O2 no crescimento e nos teores de solutos orgânicos e inorgânicos de plantas de milho desenvolvidas sob condições salinas. O experimento foi conduzido em casa de vegetação, sob condições hidropônicas. Oito dias após a semeadura, as plântulas foram pulverizadas com água destilada (controle) ou solução aquosa de H2O2 na concentração de 10 mM e, 48 h após o início da pulverização, foram submetidas ao tratamento com NaCl a 80 mM. Foram realizadas duas coletas, com 96 e 240 h do início da pulverização. O delineamento experimental foi o inteiramente casualizado, em um arranjo fatorial 2 (NaCl a 0 ou 80 mM) x 2 (H2O2 a 0 ou 10 mM), com cinco repetições. Os dados de cada tempo de coleta (96 h ou 240 h) foram submetidos à análise de variância (ANOVA) e as médias comparadas pelo teste de Tukey (P The aim of this study was to evaluate the effects of foliar application of H2O2 on plant growth and on the levels of organic and inorganic solutes in maize plants under salt stress. The experiments were conducted in a greenhouse under hydroponic conditions. Eight days after sowing, the seedlings were sprayed with a 10 mM H2O2 solution or with distilled water (as a control). Forty-eight hours after the beginning of spraying, they were subjected to treatment with NaCl at 80 mM. Two harvests were carried out: 96 and 240 hours after the start of spraying. The experimental design was completely randomized following a factorial arrangment 2 (NaCl at 0 or 80 mM) x 2 (H2O2 at 0 or 10 mM), with five replicates. The data for each harvest time (96 or 240 h) were submitted to analysis of variance (ANOVA) and the means were compared through Tukey's test (P < 0.05).The results showed that foliar application of H2O2 produced acclimation of the plants to salt stress, decreasing the deleterious effects of salinity on the growth of the maize. This effect can be attributed, at least partially, to a larger build up of proteins, and soluble carbohydrates and NO3- as well as lower levels of Cl- and Na+ in the foliage

Efeito da nutrição de nitrato na tolerância de plantas de sorgo sudão à salinidade Effect of nitrate nutrition on tolerance of sudangrass plants to salinity

O objetivo deste trabalho foi estudar o efeito da nutrição de NO3- no crescimento, nas trocas gasosas e no acúmulo de solutos inorgânicos e orgânicos em plantas de sorgo sudão submetidas à salinidade. As plantas foram cultivadas em meio hidropônico e mantidas em casa de vegetação. O delineamento experimental foi o inteiramente casualizado, em esquema fatorial 2 (NO3- a 0,5 mM ou 8,0 mM) x 2 (NaCl a 0 mM ou 100 mM), com cinco repetições. Os dados foram submetidos à análise de variância e as médias comparadas pelo teste de Tukey a 5% de significância. A salinidade reduziu a área foliar e a massa seca da parte aérea e das raízes, sendo as plantas nutridas com NO3- a 8,0 mM menos afetadas que aquelas com NO3- a 0,5 mM. A condutância estomática, a fotossíntese, a transpiração e a relação entre a concentração interna e externa de CO2 foram aumentadas pela melhor nutrição de NO3-. Os teores de Na+ e Cl- foram significativamente aumentados pela salinidade em folhas e em raízes e os de K+ foram reduzidos apenas nas raízes. Apesar disso, as plantas nutridas com NO3- a 8,0 mM apresentaram os menores teores de Na+ e Cl- nas folhas sob estresse salino. A salinidade aumentou os teores de prolina e N-aminossolúveis e a maior concentração de NO3- no meio favoreceu o acúmulo desses solutos nas raízes de plantas estressadas. Uma adequada nutrição com NO3- foi capaz de reduzir os efeitos deletérios da salinidade nas plantas de sorgo sudão.<br>This work aimed to study the effect of NO3- nutrition on growth, on gas exchange and on inorganic and organic solutes accumulation of sudangrass plants subjected to salinity. Plants were grown in hydroponic medium and kept in a greenhouse. The experiment was a completely randomized design, following a factorial arrangement of 2 (NO3- at 0,5 mM or 8,0 mM) x 2 (NaCl at 0 mM or 100 mM), with five replications. All data were subjected to analysis of variance and the means were compared by Tukey's test at 5% of significance. Salinity reduced leaf area and dry weight of shoots and roots. However, plants growing in the 8.0 mM NO3- increased more than those growing in 0.5 mM. The stomatal conductance, photosynthesis, transpiration and the relationship between internal and external concentration of CO2 were increased by better nutrition NO3-. Na+ and Cl- contents were significantly increased by salinity in leaves and roots and the K+ content was reduced only in the roots. Nevertheless, plants fed with 8.0 mM NO3- had the lowest contents of Na+ and Cl- in leaves under salt stress. Salinity increased proline and amino acid contents and the higher NO3- concentration promoted the accumulation of these solutes in roots of stressed plants. Proper nutrition for NO3- was able to reduce deleterious effects of salinity in sudangrass plants

Salt tolerance is unrelated to carbohydrate metabolism in cowpea cultivars

Under salinity stress, plants commonly accumulate carbohydrates for osmotic adjustment to balance the excess accumulated ions and to protect biomolecules. We selected two cowpea cultivars with contrasting response to salinity, Pitiúba (salt-tolerant) and TVu (salt-sensitive), to investigate whether the salt tolerance could be associated with changes in carbohydrate accumulation and metabolism in leaves and roots during a long-term experiment. Two salt treatments (0 and 75 mM NaCl) were applied to 10-day-old plants grown in nutrient solution for 24 days. Despite some changes in carbohydrate accumulation and carbohydrate metabolism enzymes induced by salt stress, no consistent alterations in carbohydrates could be found in leaves or roots in this study. Therefore, we suggest that tolerance to salt stress is largely unrelated to carbohydrate accumulation in cowpea