Crescimento de cultivares de café em resposta a doses contrastantes de zinco

Providing zinc to coffee plants interferes with the growth, development and productivity, and coffee varieties differ in their responses to nutrient availability in soil. This study aimed to identify the differential tolerance of cultivars of Coffea arabica to the lack of Zn, verify how does the partition of zinc contents occur in the plant organs in low and high supply of it and indicate easy measure characteristics of the plant well correlated with tolerance to low zinc supply. Nursery plants of 11 cultivars of C. arabica were grown for eight months in nutritive solution with concentrations of 0,0 and 6,0 mmol L-1 Zn. Stem diameter, plant height, number of primary branches, root volume, leaf number, leaf area and dry weight were determined. There is variability in the response of the coffee cultivars to the supply of Zn, and among the cultivars studied San Ramon, IPR- 102 and Rubi were the most tolerant to the restriction in Zn supply, whereas the ‘São Bernardo’ was the less tolerant to low Zn dose. In adequate or high supply this nutrient accumulates in roots and stems, which can serve as the nutrient reserve organs. In conditions of lack of the nutrient the appical leaves are the preferred accumulation organ. The total dry weight accumulation proved to be the characteristic of greater relative importance in the discrimination of the varieties studied.O fornecimento de zinco interfere no crescimento, desenvolvimento e produtividade do cafeeiro e as cultivares de café diferem em suas respostas à disponibilidade do nutriente no solo. Objetivou-se, neste trabalho,identificar a tolerância diferencial de cultivares de Coffea arabica à deficiência de zinco, verificar como se dá a partição do nutriente nos órgãos da planta sob baixo e alto suprimento e discriminar que características de crescimento passíveis de serem avaliadas precocemente se correlacionam à tolerância ao baixo suprimento do nutriente. Mudas de 11 cultivares de cafeeiro foram cultivadas por oito meses em solução nutritiva nas concentrações de 0,0 e 6,0 μmol L 1 de Zn. Determinaram-se diâmetro do caule, altura de planta, número de ramos plagiotrópicos, volume de raiz, número de folhas, área foliar e produção de massa seca. Conclui-se que há variabilidade de resposta de cultivares de cafeeiro ao suprimento de zinco, sendo as cultivares San Ramon, IPR-102 e Rubi, dentre as estudadas, as mais tolerantes à restrição no seu fornecimento e a cultivar São Bernardo a menos tolerante à baixas doses de Zn. Em condições de suprimento adequado ou elevado de zinco esse se acumula em raízes e caules, que podem servir como órgãos de reserva do nutriente, enquanto que em condições de deficiência há maiores concentrações em folhas apicais. A produção de massa total é a característica de maior importância relativa na discriminação das cultivares quanto à resposta ao suprimento do nutriente

Physiological response of Conilon coffee clone sensitive to drought grafted onto tolerant rootstock

O objetivo deste trabalho foi determinar alterações fisiológicas e de tolerância à seca em clones de café Conilon (Coffea canephora) contrastantes quanto à sensibilidade ao deficit hídrico. Foram avaliadas as enxertias recíprocas entre os clones 109A, sensível ao deficit hídrico, e 120, tolerante – 120/109A, 120/120, 109A/120, 109A/109A –, além de seus respectivos pés-francos. As plantas foram cultivadas em vasos de 12 L em casa de vegetação. Após seis meses, metade das plantas foi submetida ao deficit hídrico por meio da suspensão da irrigação, até que as folhas atingissem o potencial hídrico de antemanhã de -3,0 MPa. Quando o clone 120 foi usado como porta-enxerto, as plantas apresentaram sistema radicular mais profundo, mas com menor massa, retardaram por mais tempo a desidratação celular das folhas e apresentaram maior eficiência no uso da água. Sob seca severa, os teores de amido e sacarose decresceram em todos os tratamentos, enquanto os teores de glicose, frutose, aminoácidos totais e prolina aumentaram, particularmente nos tratamentos 109A pé-franco, 109A/109A e 120/109A. Essas plantas apresentaram menor eficiência no uso da água. O acúmulo de solutos não foi associado à tolerância à seca. O uso de porta-enxertos tolerantes à seca contribui para a maior tolerância das plantas ao deficit hídrico.The objective of this work was to determine alterations in physiology and those due to drought tolerance on Conilon coffee (Coffea canephora) contrasting clones regarding the sensitivity to hydric stress. The reciprocal grafting between clones 109A, drought sensitive, and 120, drought tolerant, – 120/109A, 120/120, 109A/120, 109A/109A – along with their ungrafted control plants (109A and 120) were evaluated. Plants were cultivated in 12-L vases in greenhouse. Six months after grafting, half of the plants was subjected to water deficit, by suspending irrigation until leaves reached the hydric potential of -3,0 MPa. When clone 120 was used as rootstock, plants presented deeper roots, although with lower root-biomass, higher ability to postpone leaf dehydration and higher instantaneous water-use efficiency (WUE). Under severe drought, starch and sucrose contents decreased similarly, regardless of the treatment, whereas leaf concentrations of glucose, fructose, total amino acids and proline were higher in non-grafted 109A, 109A/109A, and 120/109A plants. These plants showed the lowest WUE values. Solute accumulation was not primarily related to drought tolerance. The use of drought tolerant rootstocks improves to drought tolerance in coffee

Changes in leaf gas exchange and chlorophyll a fluorescence on soybean plants supplied with silicon and infected by Cercospora sojina

Frogeye spot, caused by Cercospora sojina, is one of the major diseases causing yield losses in soybean. Considering the potential of silicon (Si) to attenuate the physiological impairments imposed by pathogens infection, this study investigated its effect on leaf gas exchange and chlorophyll (Chl) a fluorescence parameters as well as on the concentrations of photosynthetic pigments and carbohydrate pools on soybean plants from cultivars Bossier and Conquista (susceptible and resistant to frogeye spot, respectively) grown in hydroponic culture containing 0 or 2 mM Si (−Si and +Si plants, respectively) that were noninoculated or inoculated with C. sojina. Plants from cultivar Bossier were more susceptible to frogeye spot compared to cultivar Conquista regardless of Si supply. Frogeye spot severity increased by Si supply regardless of the cultivar. There were no changes in the physiological parameters for noninoculated +Si plants. Even though the susceptibility of plants from cultivar Bossier to frogeye spot increased by Si supply, they showed lower values for the leaf gas exchange parameters, photochemical efficiency and concentration of photosynthetic pigments. The impairments imposed by C. sojina infection on the physiology of plants from cultivar Conquista were governed chiefly by reductions in stomatal conductance regardless of Si supply. The increase in hexose concentration for inoculated plants of the two cultivars was associated with their resistance to frogeye spot. Considering that the increased susceptibility of +Si plants from cultivar Conquista did not result in physiological impairments, it is plausible to rule out that the lower photosynthetic efficiency of plants from cultivar Bossier occurred due to a sharp reduction in the photosynthetically active leaf tissue

Effects of long-term soil drought on photosynthesis and carbohydrate metabolism in mature robusta coffee (Coffea canephora Pierre var. kouillou) leaves

Four clones of robusta coffee representing drought-tolerant (14 and 120) and drought-sensitive (46 and 109A) genotypes were submitted to a slowly imposed water deficit. Sampling and measurements were performed when predawn leaf water potential (Ψpd) approximately −2.0 and −3.0 MPa was reached. Regardless of the clone evaluated, drought led to sharper decreases in stomatal conductance than in photosynthesis, which was accompanied by significant declines in internal to ambient CO2 concentration ratio. Little or no effect of drought on chlorophyll a fluorescence parameters was observed. Regardless of the stress intensity, starch decreased remarkably. This was not accompanied by significant changes in concentration of soluble sugars, with the exception of clone 120 in which a rise in sucrose and hexose concentrations was found when Ψpd reached −3.0 MPa. At Ψpd = −2.0 MPa, activity of acid invertase increased only in clone 120; at Ψpd = −3.0 MPa, it increased in clones 14, 46 and 120, while activity of sucrose synthase declined, but only in clone 109A. Drought-induced decrease in ADP-glucose pyrophosphorylase activity was found only in clones 14 and 46, irrespective of stress intensity. At Ψpd = −3.0 MPa, maximal extractable and activation state of sucrose-phosphate synthase (SPS) decreased in all clones with the exception of clone 120, in which SPS activity was maintained in parallel to a rising activity of fructose-1,6-bisphosphatase. Changes in SPS activity could neither be explained by the CO2 decrease linked to stomatal closure nor by differences in leaf water status

Germination and biochemical changes in 'Formosa' papaya seeds treated with plant hormones

This study aimed to investigate the effects of growth regulators on germination rates and biochemical compound concentrations in Carica papaya L. seeds ('Formosa' group). The seeds were harvested from fruits at maturation stages 3 and 5 (50 and 75% yellow fruit skin, respectively). The effects of 2-chloroethylphosphonic acid (CEPA), KNO3 and gibberellic acid (GA3) on seed germination, germination index speed, soluble sugars, starch, lipids, soluble proteins and total proteins of the papaya seeds were evaluated. The seeds from stage 5 showed a higher rate of germination 30 days after sowing than did the seeds from stage 3. Treatment with CEPA decreased seed germination, apparently due to decreased starch mobilization; the opposite response was observed following KNO3 treatment. GA3, alone or in combination with KNO3, stimulated an increase in lipid mobilization. In general, with the exception of CEPA, all growth regulators tested were effective in overcoming seed dormancy, and KNO3 was the most effective. The seeds from stage 3 fruits treated with KNO3 or KNO3 + GA3 had higher rates of germination at 14 days

Photosynthesis impairments and excitation energy dissipation on wheat plants supplied with silicon and infected with Pyricularia oryzae

Considering the effect of silicon (Si) in reducing the blast symptoms on wheat in a scenario where the losses in the photosynthetic capacity of the infected plants is lowered, this study investigated the ability of using the incident light, the chloroplastidic pigments (chlorophylls and carotenoids) alterations and the possible role of carotenoids on the process of light dissipation on wheat plants non-supplied (-Si) or supplied (+Si) with Si and inoculated or not with Pyricularia oryzae. For + Si plants, blast severity was reduced compared to -Si plants. Reductions in the concentration of photosynthetic pigments (total chlorophyll, violanxanthin + antheraxanthin + zeaxanthin, β-carotene and lutein) were greater for inoculated -Si plants than for inoculated + Si ones. The α-carotene concentration increased for inoculated -Si and +Si plants in comparison to non-inoculated plants limiting, therefore, lutein production. Higher functional damage to the photosystem II (PSII) was noticed for inoculated -Si plants with reductions in the values of maximum quantum quenching, photochemical yield of PSII and electron transport rate, but higher values for quenching non-photochemical. This finding also contributed to reductions in the values of light saturated rate photosynthesis and light saturation point for -Si plants which was attenuated for inoculated + Si plants. Increase in dark respiration values occurred for inoculated plants than for non-inoculated ones. The Si supply to wheat plants, besides reducing blast severity, contributed to their better photosynthetic performance. Moreover, inoculated + Si plants coped with drastic losses of light energy dissipation processes (fluorescence and heat) by increasing the concentration of carotenoids which helped to maintain the structural and functional viability of the photosynthetic machinery minimizing, therefore, lipid peroxidation and the production of reactive oxygen species

Picolinic acid spray stimulates the antioxidative metabolism and minimizes impairments on photosynthesis on wheat leaves infected by Pyricularia oryzae

Fungal pathogens produce toxins that are important for their pathogenesis and/or aggressiveness towards their hosts. Picolinic acid (PA), a non‐host selective toxin, causes lesions on rice leaves resembling those originated from Pyricularia oryzae infection. Considering that non‐host selective toxins can be useful for plant diseases control, this study investigated whether the foliar spray with PA on wheat (Triticum aestivum L.) plants, in a non‐phytotoxic concentration, could increase their resistance to blast, stimulate the anti‐oxidative metabolism, and minimize alterations in photosynthesis. The PA spray at concentrations greater than 0.1 mg ml−1 caused foliar lesions, compromised the photosynthesis and was linked with greater accumulation of hydrogen peroxide (H2O2) and superoxide anion radical (O2•−). Fungal mycelial growth, conidia production and germination decreased by PA at 0.3 mg ml−1. Blast severity was significantly reduced by 59 and 23%, respectively, at 72 and 96 h after inoculation for plants sprayed with PA (0.1 mg ml−1) at 24 h before fungal inoculation compared to non‐sprayed plants. Reduction on blast symptoms was linked with increases on ascorbate peroxidase (EC 1.11.1.11), catalase (EC 1.11.1.6), glutathione peroxidase (EC 1.11.1.9), glutathione reductase (EC 1.8.1.7), glutathione‐S‐transferase (EC 2.5.1.18), peroxidase (EC 1.11.1.7), and superoxide dismutase (EC 1.15.1.1) activities, lower H2O2 and O2•− accumulation, reduced malondialdehyde production as well as less impairments to the photosynthetic apparatus. A more efficient antioxidative metabolism that rapidly scavenges the reactive oxygen species generated during P. oryzae infection, without dramatically decreasing the photosynthetic performance, was a remarkable effect obtained with PA spray