Índice SPAD e trocas gasosas ao longo do dia para diferenciação de cana-de-açúcar sob deficiência hídrica

The sugarcane (Saccharum spp.) is a globally important not only for sugar production but also for the production of bioenergy crop. The drought is one of the most important environmental factors limiting the global production of sugarcane. Due to the irregularity rainfall, growers have some dependence of irrigation to maintain production targets. However, the water irrigation is limited and must be rationally utilized not only to reduce wastage, but also to reduce the costs of production and maintenance of productivity. The study and development of tolerant varieties to water stress is crucial for production in areas where water is scarce or limited. It is found, in some cultures, the concentration of chlorophyll and the greening of leaves correlate with tolerance to water stress, but these variables are influenced by different environmental conditions, such as irradiance, air temperature and leaf water conditions, that occur in a large variation during the day. The study aimed to evaluate the influence of water stress and time of assessment on reading the SPAD index on sugarcane. The experiment was conducted in a greenhouse, where RB867515 and RB855453 varieties were evaluated, by water stress or not water stress, in relation to SPAD index, total chlorophyll content, leaf temperature, leaf water potential (ψw), CO2 rate assimilation, maximum quantum efficiency of photosystem II (Fv/Fm), photosynthetic active radiation, temperature and humidity on +1 leaf in four times of the day (7, 10, 13 and 16 hours). Thus, we found the variation of SPAD index during the day, that showed a decreasing tendency over the hours, and it was verified that the total chlorophyll content extracted ranging in the same way. Overall, the most significant results of physiological parameters, except for stomatal conductance, for the maximum quantum efficiency of photosystem II (Fv/Fm) and for the water use efficiency ...A cana-de-açúcar (Saccharum spp.) é uma cultura globalmente importante não só para a produção de açúcar como também para a produção de bioenergia. A seca é um dos fatores ambientais mais importantes que limita a produção mundial de cana-de-açúcar. Devido à natureza irregular das chuvas, os produtores têm certa dependência da irrigação para manter as metas de produção. Entretanto, a água para irrigação é limitada, e deve ser utilizada racionalmente, não só para reduzir o desperdício, mas também pela redução dos custos de produção e manutenção de produtividade. O desenvolvimento e estudo de variedades tolerantes ao estresse hídrico é crucial para a produção em áreas onde a água é escassa ou limitada. É verificado, em algumas culturas, que a concentração de clorofila e o esverdeamento das folhas se correlacionam com tolerância à deficiência de água, porém essas variáveis recebem influência de diferentes condições ambientais,rever tais como irradiância, temperatura do ar e condições hídricas da folha, que normalmente ocorrem grandes variações durante o dia. O trabalho teve como objetivo avaliar a influência do estresse hídrico e do horário de avaliação sobre a leitura do índice SPAD e das trocas gasosas em cana-de-açúcar. O experimento foi conduzido em casa de vegetação, onde foram avaliadas as variedades RB867515 e RB855453, sob ou não deficiência hídrica em relação a índice SPAD, conteúdo de clorofila total, temperatura foliar, potencial hídrico foliar (ψw), taxa de assimilação de CO2, máxima eficiência fotoquímica do fotossistema II (Fv/Fm), radiação fotossinteticamente ativa, temperatura e umidade do ar na folha +1 em quatro horários do dia (7, 10, 13 e 16h). Para tanto, constatou-se a variação do índice SPAD durante o dia, obtendo uma tendência decrescente com o passar das horas, tendo o conteúdo de ..

Sugarcane tolerance to ratoon eradication with glyphosate determined by physiological responses

This study aimed to evaluate the tolerance of sugarcane cultivars to ratoon eradication under different glyphosate rates by means of physiological responses. Therefore, a trial was carried out in randomized complete blocks with 4 x 4 factorial design (cultivars x rates) totaling 16 treatments with four replicates. The cultivars IAC91-5155, IACSP93-3046, and IAC86-2480 and IAC87-3396 and the glyphosate rates 0 g ha-1; 1,920 g ha-1; 2,400 g ha-1; 2,880 g ha-1 were tested. The variables analyzed were percentage of tiller mortality, quantum efficiency of PSII (Fv/Fm) and SPAD index. The results showed that there are differences among sugarcane cultivars for tiller eradication and for physiological responses with glyphosate different rates. The rate of 2,880 g ha-1 was the most efficient in eliminating sugarcane tillers. The cultivars IAC86-2480, IAC87-3396 and IACSP93-3046 were the most sensitive and the IAC91-5155 tolerated, for a longer period of time, the damage to the photosynthetic apparatus of the ratoons caused by glyphosate desiccation. Due to different responses, different managements should be considered for eliminating ratoons of different cultivars.O presente trabalho teve como objetivo avaliar a tolerância de cultivares de cana-de-açúcar à erradicação de soqueiras com diferentes doses de glyphosate por meio de respostas fisiológicas. Para isso, um ensaio foi desenvolvido no delineamento experimental de blocos ao acaso em esquema fatorial 4 x 4 (cultivares x doses), totalizando 16 tratamentos com quatro repetições. Foram utilizados os cultivares IAC91-5155, IACSP93-3046, IAC86-2480 e IAC87-3396 tratados com as doses de glyphosate 0, 1.920, 2.400, e 2.880gha-1. As variáveis analisadas foram porcentagem de perfilhos mortos, eficiência quântica do FSII (Fv/Fm) e índice SPAD. Há diferenças entre cultivares de cana-de-açúcar quanto à eliminação de perfilhos e a respostas fisiológicas a diferentes doses de glyphosate. A dose de 2.880gha-1 foi a mais eficiente em eliminar perfilhos de cana-de-açúcar. Os cultivares IAC86-2480, IAC87-3396 e IACSP93-3046 foram os mais sensíveis, e o IAC91-5155 tolerou por mais tempo os danos promovidos no aparato fotossintético à dessecação das soqueiras pelo glyphosate. Devido às respostas diferenciadas, manejos distintos devem ser considerados para a eliminação das soqueiras de diferentes cultivares.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Increased hormetic dose of glyphosate causes oxidative stress and reduces yield in common bean

Glyphosate can alter several physiological and biochemical processes and even plant nutrient absorption. This study aimed to verify whether biochemical and non-biochemical variables of the antioxidant complex are affected by low doses, considered hormetic, of glyphosate herbicide. Two experiments were conducted in the field, one in the winter and the other in the wet season, with the early cycle common bean cultivar IAC Imperador. The experimental design was in a randomized block, consisting of applying low doses of glyphosate (0.0, 1.8, 7.2, 12, 36, 54, and 108 g a.e. ha–1) in the phenological stage V4, with four replicates. Environmental conditions, such as air temperature, interfered in the early cycle common bean response to low doses of glyphosate. Lower doses of glyphosate did not alter the gas exchange of bean plants. However, the increase in the glyphosate doses reduced the net CO2 assimilation rate, stomatal conductance, and transpiration rate while increasing the SOD and CAT activity, and MDA and proline content. In the winter season, the dose 7.2 g a.e. ha–1 increased bean productivity, while the dose 36 g a.e. ha–1 induced oxidative stress in bean plants and reduced productivity. In the wet season, doses 36 and 54 g a.e. ha–1 increased bean productivity, and the dose 108 g a.e. ha–1 decreased grain yield. Thus, the more favorable climatic conditions in the wet season enhance plant metabolism, subsequently increasing plant tolerance to higher glyphosate doses

RESPOSTAS FISIOLÓGICAS DE CULTIVARES DE CANA-DE-AÇÚCAR SUBMETIDAS À DEFICIÊNCIA HÍDRICA E A REIDRATAÇÃO

The aim of this work was to study the physiological responses of three contrasting cultivars of sugar cane subject to water stress and rewatering, The experiment was carried out in a greenhouse, where the cultivars SP83-2847, SP80-1842 and SP81-3250 were grown in pots. The first assessment was done after 85 days of planting, then two treatments were implemented, i.e. without water stress (-D) and with water stress (+D) by withholding water for 15 days and rewatering imposed for 12 days after the stress period. Cultivars SP81-3250 and SP80-1842 showed a higher decline in the Fv/Fm ratio, leaf relative water content (RWC), leaf water potential (Ψw), SPAD index and photosynthetic pigments due to water deficit. Drought caused less damage in the physiology of the variety SP83-2847, and it still showed rapid recovery during rewatering, including for the stomatal conductance (gs), so this variety had better adaptation under this condition. The traits Fv/Fm, Ψw, RWC, SPAD index and photosynthetic pigments present as potential physiological indicators in order to select tolerant sugar cane cultivars to water deficit. The trait gs is more effective in differentiating the tolerant cultivars during rewatering

Respostas fisiológicas de cultivares de cana-de-açúcar submetidas à deficiência hídrica e a reidratação

The aim of this work was to study the physiological responses of three contrasting cultivars of sugar cane subject to water stress and rewatering, The experiment was carried out in a greenhouse, where the cultivars SP83-2847, SP80-1842 and SP81-3250 were grown in pots. The first assessment was done after 85 days of planting, then two treatments were implemented, i.e. without water stress (-D) and with water stress (+D) by withholding water for 15 days and rewatering imposed for 12 days after the stress period. Cultivars SP81-3250 and SP80-1842 showed a higher decline in the F-v/F-m ratio, leaf relative water content (RWC), leaf water potential (Psi(w)), SPAD index and photosynthetic pigments due to water deficit. Drought caused less damage in the physiology of the variety SP83-2847, and it still showed rapid recovery during rewatering, including for the stomatal conductance (gs), so this variety had better adaptation under this condition. The traits F-v/F-m, Psi(w), RWC, SPAD index and photosynthetic pigments present as potential physiological indicators in order to select tolerant sugar cane cultivars to water deficit. The trait gs is more effective in differentiating the tolerant cultivars during rewatering.O objetivo desse trabalho foi estudar as respostas fisiológicas de cultivares de cana-de-açúcar com características contrastantes quanto à tolerância à seca submetidas à deficiência hídrica e a reidratação. O experimento foi conduzido em casa de vegetação, onde as cultivares SP83-2847, SP80-1842 e SP81-3250 foram cultivadas em vasos, Após 85 dias do plantio, foi realizada a primeira avaliação, em seguida foram implementados dois tratamentos, sem deficiência (-D) e com deficiência (+D) por suspensão da rega por 15 dias e posterior reidratação por 12 dias. Nas cultivares SP81-3250 e SP80-1842 foram observadas maiores reduções em Fv/Fm, no teor relativo de água na folha (TRA), no potencial hídrico da folha (Ψw), no índice SPAD e nos teores dos pigmentos fotossintéticos quando submetidas à deficiência hídrica. Devido aos menores danos fisiológicos causados pela deficiência hídrica na cultivar SP83-2847, e ainda ter apresentado melhor recuperação durante a reidratação, inclusive da condutância estomática (gs), caracterizando esta cultivar com boa aclimatação sob deficiência hídrica

Physiological changes associated with antioxidant enzymes in response to sugarcane tolerance to water deficit and rehydration

Water deficit is the main limiting factor for sugarcane yield worldwide. Under this stress, the crop develops adaptive mechanisms that participate in maintaining the plants’ water status. A better understanding of these mechanisms may contribute to differentiating tolerant cultivars to be used in genetic improvement programs. Therefore, this study aimed to assess the physiological responses of sugarcane cultivars subjected to water deficit and rehydration. Cultivars RB92579, SP81-3250, SP83-2847 and IAC91-5155 were grown in pots in a greenhouse. These plants were physiologically and biochemically evaluated at three intervals: 0 (before stress), 15 (water deficit) and 27 days (rehydration) after the onset of treatment (DAT) at 85 days after planting. Cultivars RB92579 and SP81-3250 had greater reductions in stem height, number of green leaves, leaf area, relative water content, leaf water potential (Ψw), leaf temperature, stomatal conductance (gs), maximum photochemical efficiency of photosystem II (Fv/Fm), SPAD index and photosynthetic pigments, and inhibited catalase enzyme activity when subjected to water stress. Furthermore, SP81-3250 showed no recovery after rehydration. Water deficit also increased the levels of proline and the enzymes superoxide dismutase and ascorbate peroxidase in all cultivars. We also found increased carbohydrates under stress, except in the cultivar SP81-3250, which had a reduced content. Due to the minor damage caused by drought in the physiology and biochemistry of cultivars SP83-2847 and IAC91-5155, they have higher potential for tolerance and can acclimate to drought. Consequently, oxidative stress can be largely avoided in the chloroplasts of these cultivars by maintaining the balance of antioxidant enzyme activity, photosynthetic efficiency, stomatal control and water status.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq