ABSTRACT: The selection of wheat genotypes according to their drought tolerance is essential to off-season cultivation. The objective of this work was to characterize wheat genotypes through yield and components, morphological characteristics under water stress, and irrigated water use efficiency in the Cerrado region in Brazil. Genotypes were planted during the winters of 2016 and 2017 since there is no precipitation during this season and water levels can be measured. They were then submitted to four water regimes: WR1, WR2, WR3, and WR4, representing 100 %, 83 %, 50 %, and 30 % of evapotranspiration replacement. The following variables were evaluated: peduncle length (PL), number of ears m−2 (NE m−2), hectoliter weight (HW), thousand grain weight (TGW), drought resistance index (DRI), irrigated water use efficiency (IWUE) and yield. Most variables showed correlation with yield and can be a useful tool for breeding programs. PL and HW were best correlated with yield. BRS 264 (irrigated biotype) was productive in treatments receiving the greatest number of irrigation treatments. Given that WR1 registered the highest water level, it was not expected that the rainfed biotype (BR18) would show a higher yield than an irrigated biotype (BRS254). BRS404 (rainfed biotype) was the most productive under moderate stress treatment (WR3). Aliança (rainfed biotype) showed a higher yield under severe stress. Rainfed biotypes presented a higher DRI than the irrigated ones. These genotypes can be used as a reference in breeding programs under each water regime in which their performance was outstanding. None of the variables studied contributed to the selection of the most efficient wheat genotypes in the IWUE.

Resumo: O objetivo deste trabalho foi avaliar a influência do remineralizador de solo finos de mica xisto (FMS) na fisiologia, na produtividade e na qualidade de grãos de soja (Glycine max) em diferentes regimes hídricos (RHs), no Cerrado brasileiro. O experimento foi conduzido em condições de campo durante dois anos, tendo-se utilizado quatro RHs e três tratamentos: mica xisto, adubação convencional e controle. Em 2017 e 2018, foram avaliados os seguintes RHs: RH1, RH2, RH3 e RH4, que correspondiam ao valor médio de 100, 65, 44 e 28% da reposição da evapotranspiração da cultura, respectivamente. A fotossíntese, a condutância estomática, a transpiração, a concentração interna de CO2, o rendimento quântico efetivo do fotossistema II (FSII) (Fv’/Fm’), o rendimento quântico (FSII) (ᶲFSII) e a taxa de transporte de elétrons reduziram em função do avanço da fase fenológica da soja e da redução do RH. A qualidade dos grãos foi afetada apenas pelo RH. O mica xisto foi estatisticamente semelhante à adubação convencional e ao controle em 2017 e 2018. A produtividade reduziu devido à antecipação da idade fenológica da soja e do RH, mas não houve diferenças entre os três tratamentos em 2017 e 2018. A redução da produtividade da soja é atribuída ao fechamento estomático, à perda da capacidade fotoprotetora e aos danos ao maquinário fotossintético causados pela seca.

Abstract: The objective of this work was to evaluate the influence of the soil remineralizer fine-graded mica schist (FMS) on soybean (Glycine max) physiology, yield, and grain quality under different water regimes (WRs) in the Brazilian Cerrado. The experiment was conducted under field conditions for two years, using four WRs and three treatments: mica schist, conventional fertilization, and control. In 2017 and 2018, the following WRs were evaluated: WR1, WR2, WR3, and WR4, corresponding to a mean value of 100, 65, 44, and 28% of crop evapotranspiration replacement, respectively. Photosynthesis, stomatal conductance, transpiration, internal CO2 concentration, effective quantum yield of photosystem II (PSII) (Fv’/Fm’), quantum yield (PSII) (ᶲFSII), and electron transport rate reduced as a function of the advanced phenological stage of soybean and the reduction in WR. Grain quality was only affected by the WR. The mica schist was statistically similar to conventional fertilization and the control in 2017 and 2018. Yield decreased due to the anticipation of soybean phenological age and WR, but there were no differences between the three treatments in 2017 and 2018. The reduction in soybean yield is attributed to stomatal closure, loss of photoprotective capacity, and damage to the photosynthetic machinery caused by drought.

The shade leaves of coffee (Coffea arabica L.) apparently retain a robust photosynthetic machinery that is comparable to that of sun leaves and can fix CO2 at high rates when subjected to high light intensities. This raises the question of why the coffee plant would construct such a robust photosynthetic machinery despite the low photosynthetic rates achieved by the shade leaves at low light supply. Here, we grew coffee plants at 100% or 10% full sunlight and demonstrated that the shade leaves exhibited faster photosynthetic induction compared with their sun counterparts, in parallel with lower loss of induction states under dim light, and were well protected against short-term sudden increases in light supply (mimicking sunflecks). These findings were linked to similar photosynthetic capacities on a per mass basis (assessed under nonlimiting light), as well as similar extractable activities of some enzymes of the Calvin cycle, including Rubisco, when comparing the shade and sun leaves. On the one hand, these responses might represent an overinvestment of resources given the low photosynthetic rates of the shade leaves when light is limiting; on the other hand, such responses might be associated with a conservative behavior linked to the origin of the species as a shade-dwelling plant, allowing it to maximize the use of the energy from sunflecks and thus ultimately contributing to a positive carbon balance under conditions of intense shading.

Considerando o efeito positivo do silício (Si) na melhoria do desempenho fisiológico de várias espécies de plantas quando infectadas por patógenos, este trabalho teve como meta investigar o efeito desse elemento na capacidade fotossintética e no metabolismo antioxidativo de plantas dos cultivares de algodoeiro NuOpal e BRS Buriti, supridas ou não com Si, durante o processo infeccioso de Ramularia areola. A infecção por R. areola afetou negativamente a taxa líquida de fixação do CO2 (A), a condutância estomática (g s), a transpiração e a razão entre concentração interna e ambiente de CO2 nas plantas dos cultivares NuOpal e BRS Buriti não supridas com Si em relação às plantas supridas com esse elemento. Na presença do Si, houve aumento em A e g s além das concentrações de clorofila a, clorofila b e carotenóides nas plantas dos dois cultivares. A concentração foliar de Si aumentou, o que contribuiu para decrescer em 38% a área abaixo da curva do progresso da mancha de ramulária nas plantas supridas com Si, em relação às plantas não supridas com esse elemento. O fornecimento de Si às plantas de algodoeiro dos dois cultivares aumentou a atividade da dismutase do superóxido (SOD), da peroxidase do ascorbato (APX) e da lipoxigenase (LOX), mas houve redução na atividade da catalase (CAT) e na concentração de peróxido de hidrogênio (H2O2) e de aldeído malônico (MDA), houve ainda uma maior perda de eletrólitos. A atividade da glutationa redutase (GR) foi maior nas plantas do cultivar BRS Buriti supridas com Si, enquanto que nas plantas do cultivar NuOpal houve aumento da atividade da glutationa redutase apenas aos 21 dias após inoculação (dai). Conclui-se que a capacidade fotossintética e o sistema antioxidativo das plantas supridas com Si sofreram menor impacto durante o processo infeccioso de R. areola.

Considering the positive effect of silicon (Si) in improving the physiological performance of several plant species when infected by pathogens, this study investigated the effect of this element in the photosynthetic capacity and on the antioxidant metabolism of cotton plants from cultivars BRS NuOpal and Buriti, supplied or not with Si, during the infectious process of Ramularia areola. The infection by R. areola negatively affected the net carbon assimilation rate (A), stomatal conductance to water vapor (g s), internal-to-ambient CO2 concentration ratio and transpiration rate on plants of the two cultivars non-supplied with Si in comparison to plants supplied with this element. In the presence of Si, there was an increase in A and g s as well as on the concentrations of chlorophyll a, chlorophyll b and carotenoids in plants of both cultivars. The Si supply increased the foliar Si concentration, which contributed to decrease the area under ramularia leaf spot progress curve by 38% in comparison to plants non-supplied with this element. The Si supply to both cultivars increased the activities of superoxide dismutase and ascorbate peroxidase, but reduced catalase activity. The activity of glutathione reductase was higher on plants from cultivar BRS Buriti supplied with Si, while for the cultivar NuOpal the activity of glutathione reductase increased only after 21 days of inoculation (dai). There was reduction in the concentration of hydrogen peroxide and malondialdehyde until 15 dai and the electrolyte leakage was higher in plants supplied with Si in both cultivars. As compared to non-supplied plants, both cultivars presented increase on lipoxygenase activity when supplied with Si until 12 dai. It was concluded that the photosynthetic capacity and the antioxidative system of plants supplied with Si were less impacted during the infectious process of R. areola.