Nutrients distribution in diseased coffee leaf tissue

Knowing the structure and distribution of nutrients in plant tissues can clarify some mechanisms of pathogen attack in plants and plant defense against infection, thus helping management strategies. The aim of this study was verify differences in distribution of mineral nutrients in coffee leaf tissues around foliar lesions of bacterial blight of coffee, blister spot, cercospora leaf, phoma leaf spot and coffee leaf rust. Fragments of leaf tissue surrounding the lesions were dehydrated in silica gel, carbon covered and subjected to X-ray microanalysis (MAX). Thirty-three chemical elements were detected in leaf tissue; however, there was variation in potassium and calcium contents surrounding the lesions. The highest potassium content was found in asymptomatic tissues surrounding the lesions, decreasing toward the transition zone and reaching minimum content in symptomatic tissues. The highest calcium content was found in symptomatic tissues, decreasing toward the transition zone and reaching minimum content in asymptomatic tissues. Therefore, MAX can be used to analyze the composition and distribution of nutrients in plant tissues and, if associated with mineral nutrition, it may help understand host-pathogen relationships and plant disease management.

Silicon in plant disease control

All essential nutrients can affect the incidence and severity of plant diseases. Although silicon (Si) is not considered as an essential nutrient for plants, it stands out for its potential to decrease disease intensity in many crops. The mechanism of Si action in plant resistance is still unclear. Si deposition in plant cell walls raised the hypothesis of a possible physical barrier to pathogen penetration. However, the increased activity of phenolic compounds, polyphenol oxidases and peroxidases in plants treated with Si demonstrates the involvement of this element in the induction of plant defense responses. The studies examined in this review address the role of Si in disease control and the possible mechanisms involved in the mode of Si action in disease resistance in plants.

Impact of nutritional deficiency on Yellow Sigatoka of banana

The objective of this work was to assess the incidence of Yellow Sigatoka in banana plants cultivated with deficiencies of nitrogen, phosphorus, potassium, calcium, magnesium, sulfur or boron. The experimental design was a randomized complete block with 8 treatments, 4 repetitions and 1 plant per repetition. The treatments were supplied in solution culture and consisted of all the nutrients (control) or nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulphur (S) or boron (B) deficiency. Leaves 1 and 2 were inoculated on the abaxial surface with a suspension of conidia and assessed every 5 days to with a total of 5 assessments. The average number of lesions were integrated for the area under the disease progress curve (AUDPC). The greatest AUDPC occurred in plants deficient in K, N, P, S, or Mg. Plants deficient in N, P, K, Ca, Mg, S or B had lower leaf contents of these nutrients and showed morphological changes expressed in visual deficiency symptoms. Thus, banana plants deficient in K, N, P, S or Mg had a greater incidence of Yellow Sigatoka, compared with plants with full nutrients and plants deficient Ca or B.

Influência do etileno na regulação do florescimento de Coffea arabica L.

Coffee is one of the most valuable exported agricultural product worldwide as well as the second most traded commodity after oil. This crop represents a source of employment and considerably accounts for the revenue of the country, besides its undeniable importance for local and world socioeconomical scenery. The quality of the coffee drink is directly related to the fruit ripening stage, which is found in different stages at harvesting due to the sequential flowering, increasing costs with the production and generating a lower-quality beverage. The asynchronous flowering of the coffee tree comes from the uneven development of buds, which can be influenced by environmental factors, taking into account that the anthesis takes place after a water deficit period, followed by precipitation. Changes in the hormone balance have been observed after water deficit and rehydration cycles, and such oscillation on the water status of the plant increased the level of ethylene in some species. This finding led to the association between the requirements at the flowering stage of the coffee tree and the involvement of the ethylene in promoting anthesis. The application of 1- MCP (ethylene action inhibitor) triggered the anthesis in coffee trees. And, in coffee seedlings in greenhouse conditions after a period of water shortage followed by irrigation, the profile of gene expression of the biosynthesis route and signaling of ethylene are changed in leaves and roots. The increased levels of the ethylene precursor (ACC) in roots throughout the dry season and the transportation of this compound into shoots may be the signal to trigger the anthesis in coffee tree after rehydration. Thus, in order to better understand the role of the ethylene in regulation of flowering, we analyzed the effects of the exogenous application of 1-MCP in different physiological characteristics and in the expression of genes related to the ethylene biosynthesis and signaling pathways in coffee leaves and bud from plants under field conditions. The evaluations and tissue sampling were carried out in different times treatments implementation: T1 – control, T2 – 1-MCP+Break-Thru, and T3 – Break-Thru. There was influence of 1-MCP and Break-Thru in gas exchange parameters and of 1-MCP contributed to the increase in relative water content. RT-qPCR analyses showed a different behavior in relation to the profile of gene expression in leaves and buds analyzed in the present study (CaACS1 – like, CaACO1 – like, CaACO4 – like, CaETR4 – like) and the expression levels were changed a few hours (2h) after applying the products. However, there was flowering only in plants treated with 1-MCP, in the absence of rain and irrigation.