This study used both microscopic and biochemical analyses to investigate the possible defense responses induced by acibenzolar-S-methyl (ASM) and potassium phosphite (Phi) in mango plants inoculated with Ceratocystis fimbriata. Disease development was evaluated in the stems of inoculated mango plants and these were examined using fluorescence and light microscopy. High-performance liquid chromatography (HPLC) was used to quantify secondary metabolites in the stem sections. Spraying the plants with ASM and Phi reduced internal necrosis and disease development. The ASM and Phi induced many microscopic defense responses in the stem tissues against C. fimbriata infection. HPLC analysis revealed that the concentrations of two alkaloids (theobromine and 7-methylxanthine) and 10 phenolic compounds (catechin, epicatechin, epigallocatechin, gallic acid, myricetin, p-coumaric acid, p-hydroxybenzoic acid, phloridzin, sinapinic acid, and salicylhydroxamic acid) were higher in the stem tissues of plants sprayed with ASM or Phi than in inoculated control treatment. The concentrations of phenolic compounds were higher in the stem tissues of inoculated plants than in noninoculated plants, while the inverse was observed for alkaloids. Higher concentrations of secondary metabolites in the stem tissues were detected in the early stages of fungal infection, especially in plants treated with inducers. Taken together, the results from the present study clearly support the concept that the phenylpropanoid pathway in the stem tissues of mango plants infected by C. fimbriata can be induced by ASM and Phi.

Mango wilt, caused by Ceratocystis fimbriata, is one of the most important diseases affecting mango yields in Brazil. Information regarding the infection process of C. fimbriata in the stem tissues of mango from different cultivars and the basis of host resistance to the pathogen is rare in the literature. Thus, the objective of the study was to investigate how infection by two isolates of C. fimbriata can be affected by mango cultivar-specific mechanisms of resistance. Disease progress on the inoculated stem tissues of the mango cultivars was evaluated and stem sections were obtained from the site of inoculation and prepared for histopathological observations using light microscopy. The factors mango cultivars and C. fimbriata isolates and their interaction were significant for all measures of disease development. Plants from the cultivars Espada, Haden and Palmer inoculated with isolates of C. fimbriata were more susceptible, whereas plants from the cultivars Tommy and Ub a were moderately resistant and resistant, respectively. Histopathologically, fungal isolates apparently massively colonized the stem tissues of plants from the susceptible cultivars Espada, Haden and Palmer, starting from the collenchyma and moving in the direction of the cortical parenchyma, xylem vessels and pith parenchyma. By contrast, on stem tissues of plants from the resistant cultivars Tommy Atkins and Ub a, most of the cells reacted to C. fimbriata infection by accumulating amorphous material. The results from the present study strongly indicated the importance of phenolic compounds for mango cultivar resistance against infection by Brazilian C. fimbriata isolates.

This study was designed to characterize and describe host cell responses of stem tissue to mango wilt disease caused by the fungus Ceratocystis fimbriata in Brazil. Disease progress was followed, through time, in inoculated stems for two cultivars, 'Ubá' (field resistant) and 'Haden' (field susceptible). Stem sections from inoculated areas were examined using fluorescence light microscopy and transmission and scanning electron microscopy, coupled with energy-dispersive X-ray microanalysis. Tissues from Ubá colonized by C. fimbriata had stronger autofluorescence than those from Haden. The X-ray microanalysis revealed that the tissues of Ubá had higher levels of insoluble sulfur and calcium than those of Haden. Scanning electron microscopy revealed that fungal hyphae, chlamydospores (aleurioconidia), and perithecia-like structures of C. fimbriata were more abundant in Haden relative to Ubá. At the ultrastructural level, pathogen hyphae had grown into the degraded walls of parenchyma, fiber cells, and xylem vessels in the tissue of Haden. However, in Ubá, plant cell walls were rarely degraded and hyphae were often surrounded by dense, amorphous granular materials and hyphae appeared to have died. Taken together, the results of this study characterize the susceptible and resistant basal cell responses of mango stem tissue to infection by C. fimbriata.

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Mango wilt is one of the most important diseases affecting mango production, yet the physiological mechanisms underlying host responses to this fungal infection are poorly known. The disease attenuation displayed by some mango cultivars might be related to higher antioxidant capacities in leaves. To test this hypothesis, the activities of a range of enzymes (e.g. superoxide dismutase and catalase) and metabolites (e.g. ascorbate and glutathione) involved in the antioxidant system, as well as some markers for oxidative stress (e.g. hydrogen peroxide and malondialdehyde equivalents), were evaluated for 30 days after the inoculation of mango plants with Ceratocystis fimbriata. Tommy Atkins plants displayed higher values for the upward, downward and radial fungal colonization of the stem tissues than Ub a plants.In contrast to the working hypothesis, Tommy Atkins plants exhibited more prominent increases in enzyme activities and metabolite concentrations related to oxidative stress responses. These increases were minimal, if any, in Ub a plants. These results suggest that Tommy Atkins plants are less effective at restraining fungal spread through vascular tissues and thus trigger leaf antioxidant defences to cope with the developing stress.