Fabrício Ávila Rodrigues’s research while affiliated with Federal University of Minas Gerais and other places

The hormone ethylene (ET) plays multiple roles in plant growth and development. However, its involvement in the maize– Exserohilum turcicum interaction must be better elucidated. This study investigated the role of ET in the infection process of E. turcicum on maize leaves at the physiological (leaf gas exchange and chlorophyll a fluorescence parameters and concentrations of photosynthetic pigments) and biochemical [concentrations of malondialdehyde (MDA), hydrogen peroxide (H 2 O 2 ) and superoxide anion radical] levels. Plants were sprayed with water (control), ET or aminooxyacetic acid (AOA) (an inhibitor of ET production) and challenged or not with E. turcicum . ET was not detected in the infected leaves of ET‐ or AOA‐sprayed plants compared to noninfected leaves exposed to ET. The symptoms of northern corn leaf blight were very well developed in the leaves of ET‐sprayed plants. Moreover, the greatest disease severity was closely associated with higher concentrations of MDA and H 2 O 2 in the leaf tissues, indicating intense lipid peroxidation. On top of that, the photosynthetic apparatus was significantly impaired considering the lower values for net carbon assimilation rate, stomatal conductance, transpiration rate and maximal photosystem II quantum yield. In conclusion, the exogenous supply of ET to maize leaves was of pivotal importance in favouring the infection process of E. turcicum in maize leaves.

This study hypothesized that eucalypt plants from a clone susceptible to bacterial blight, caused by the bacterium Erwinia psidii, could display greater damage to their photosynthetic capacity in contrast to plants from a resistant one. This hypothesis was tested by combining the measurements of leaf gas exchange and chlorophyll (Chl) a fluorescence parameters on leaves infected by E. psidii. Symptoms of bacterial blight were more expressive on the leaves of plants from the susceptible clone at 15 days after inoculation. At this time, the photosynthetic machinery (e.g. impairments in energy dissipation and photoprotection) was profoundly damaged due to infection by E. psidii. By contrast, disease symptoms were absent on the leaves of plants from the resistant clone and the values for leaf gas exchange and Chl a fluorescence parameters were quite similar between non-inoculated and inoculated leaves. In conclusion, plants from the susceptible clone had their photosynthetic apparatus extensively damaged during infection by E. psidii. Factors related to the innate resistance of plants from the resistant clone hampered the infection process of E. psidii. Consequently, impairments in photosynthesis were not noticed based on the techniques used for its evaluation.

Background and aims Rice is an important crop worldwide and brown spot, caused by the fungus Bipolaris oryzae, has caused great yield losses. This study tested the hypothesis that rice plants sprayed with β-aminobutyric acid (BABA) or γ-aminobutyric acid (GABA) could have their resistance against brown spot increased. Methods Plants were sprayed with BABA (100 mM) or GABA (100 mM) before fungal inoculation. The control treatment was water-sprayed plants. The photosynthetic performance and the action of defense and antioxidant enzymes was investigated. Results Brown spot progressed much faster in the leaves of water- and GABA-sprayed plants than in the leaves of BABA-sprayed plants. Reduced values for net CO2 assimilation rate, stomatal conductance to water vapor, and transpiration linked to a lower concentration of photosynthetic pigments (chlorophyll a + b and carotenoids) were obtained for infected leaves of water- and GABA-sprayed plants compared to infected BABA-sprayed ones. The Chl a fluorescence parameters (variable-to-maximum Chl a fluorescence ratio, photochemical yield, yield for dissipation by down-regulation, and yield for non-regulated dissipation) were less impacted in the leaves of BABA-sprayed plants than for GABA-sprayed ones. For BABA-sprayed plants, greater superoxide dismutase (SOD) activity helped to lower the superoxide anion production. Chitinase (CHI), β-1,3-glucanase (GLU), peroxidase (POX), phenylalanine ammonia-lyase (PAL), and lipoxygenase activities were greater for infected BABA-sprayed plants than for infected GABA-sprayed ones. Conclusion The use of BABA ensured the preservation of the photosynthetic apparatus of infected leaves and potentiated CHI, GLU, PAL, POX, and SOD activities to alleviate the harmful effect of infection by B. oryzae.

Epidemics of coffee leaf rust (CLR), caused by the biotrophic fungus Hemileia vastatrix, contribute to lower production of fruit berries. This study aimed to determine the potential of Mantus® [nitrogen (1%) and copper (20%) complexed with a plant-derived pool of polyphenols (10%) and referred to as copper-polyphenols compound (CPC) hereafter] to hamper the infection process of H. vastatrix in coffee leaves. A 3 × 2 factorial experiment was arranged in a completely randomized design with four replications (one plant) per evaluation time. The factors studied were plants sprayed with water (control), CPC (1 mL/L), and fungicide (dicopper chloride trihydroxide) that were non-inoculated or inoculated with H. vastatrix. Some components of coffee resistance against infection by H. vastatrix [incubation period (IP, in days), latent period (LP, in days), intensity of fungal sporulation (IFS), area of uredosporic sori (AUS), number of uredosporic sori (NUS) per cm2 of leaf, and production of urediniospores (PU) per cm2 of leaf] and impairments in photosynthesis [quantification of the parameter maximum photochemical efficiency of photosystem II (Fv/Fm) and the pool of photosynthetic pigments] were determined in the plants of each treatment. In the in vitro assay, urediniospores germination was significantly reduced by 59 and 99% for the CPC and fungicide treatments, respectively, compared to the control treatment. Urediniospores did not germinate after exposure to 2.5, 5, 10, and 15 mL of CPC/L. The CLR severity (92-99% from 22 to 35 days after inoculation) and the area under coffee leaf rust progress curve (98 to 99%) were significantly lower for plants from CPC and fungicide treatments compared to plants from the control treatment. The IP significantly increased by 46 and 53% for CPC and fungicide treatments, respectively, compared to the control treatment. The LP and the IFS were significantly higher by 40% and lower by 55%, respectively, for CPC treatment compared to the control treatment. For the CPC treatment, significant decreases of 28 and 45% were obtained for the AUS and the NUS, respectively, compared to the control treatment. The PU was significantly lower by 96 and 99% for CPC and fungicide treatments, respectively, compared to the control treatment. At the physiological level, the CPC-sprayed and infected plants displayed a better photosynthetic performance based on the greatest values for Fv/Fm linked to the preservation of chlorophyll a+b and carotenoids concentrations compared to water-sprayed and infected ones. In conclusion, the CPC showed great potential to affect the infection process of H. vastatrix, considering that some components of coffee resistance were greatly affected. It is noteworthy in this context that besides the effect of Cu from the CPC against the germination of urediniospores from H. vastatrix, defense reactions could be boosted in coffee leaves to hamper the colonization of leaf tissues by fungal hyphae. Considering a field coffee-growing scenario, using CPC could contribute to lowering the CLR epidemic rate and be considered in an integrated disease management program.

Root-knot, caused by Meloidogyne javanica, is a serious disease on tomato. This study aimed to investigate the potential of using Lentinula edodes and Pleurotus eryngii to boost the resistance of tomato roots against infection by M. javanica. Tomato plants were grown in different conditions: substrate made of a mixture of soil with sand (SS) and infested with M. javanica; substrate made of a mixture of SS with mushroom (SSM) and colonized by L. edodes; SSM colonized by L. edodes and infested with M. javanica; SSM colonized by P. eryngii; and SSM colonized by P. eryngii and infested with M. javanica. Root samples were examined at 0, 4, 10, and 20 days after growing the tomato plants to determine the fresh weight of roots, activities of phenylalanine ammonia-lyase (PAL), chitinase (CHI), and β-1,3-glucanase (GLU), as well as the concentration of phenolics. There was no significant difference in PAL activity nor in the concentration of phenolics regardless of treatments and sampling time. Activities of CHI and GLU were greater for plants grown on SSM colonized by either L. edodes or P. eryngii regardless of the presence of M. javanica. Mushroom substrates enhance tomato plant defenses against root-knot nematodes by increasing CHI and GLU activities, suggesting potential for both direct antagonistic effects and indirect stimulation of plant resistance mechanisms. Key words alternative disease control; defense-related enzymes; host defense reactions; induced resistance

The sour passion fruit (Passiflora edulis Sims) is a very profitable crop, and yield losses due to severe scab epidemics have been a major concern for growers. Scab, caused by fungi from the complex Cladosporium cladosporioides, is very difficult to control. This study aimed to study the events of penetration, colonization, and sporulation of C. passiflorae on the leaves of sour passion fruit plants using light and scanning electron microscopies. The circular lesions of water-soaked appearance and gray color on leaves occurred at 72 hours post-inoculation (hpi). As the lesions expanded, they coalesced and exhibited a brown color surrounded by brown haloes at 96 hpi. At 108 hpi, intense fungal sporulation of gray color was noticed in the necrotic lesions. Conidia started to germinate on the abaxial leaf surface at 24 hpi. The germ tubes were formed in one of the conidial cells from 24 to 48 hpi. The germ tubes grew only over the abaxial leaf surface. Occasionally, the germ tubes grew toward the stomata without evidence of appressoria formation. At 72 hpi, germ tubes penetrated mainly through the stomata and fungal hyphae were noticed in the abaxial epidermal cells and at the substomatal chamber. Fungal hyphae colonized the mesophyll, at first only the cells of the spongy parenchyma. At 84 hpi, the mesophyll cells of the palisade parenchyma were massively colonized by hyphae of C. passiflorae. After colonizing the mesophyll cells, fungal hyphae grew toward epidermal cells in the adaxial leaf surface from which conidiophores emerged. Fungal hyphae massively colonized the leaf tissues at 108 hpi resulting in greater disintegration. Intense formation of conidiophores on the abaxial leaf surface, mainly close to the veins, was observed at 108 hpi and conidia were abundantly produced. Together, these results will undoubtedly contribute to developing more efficient control strategies of scab especially directing the spraying of fungicides to the abaxial leaf surface.

The toxicity of aluminum (Al) in acidic soils impairs plant growth, however silicon (Si) can attenuate this toxic effect. Here we investigate the short-term effects of Si as an attenuator of Al toxicity in popcorn (Zea mays) root tips. The presence of Al reduced the root growth rate. However, Si alleviated the inhibition of root elongation. Furthermore, Si reduced the Al concentration in the roots, indicating its ability to bind to Al in the nutrient solution through the hydroxyaluminosilicate complex, and consequently reducing the absorption of this toxic metal by the plants. The morphoanatomical analysis of the roots revealed that Si attenuated the alterations induced by Al, such as the increase in the radial diameter of the root tip, desquamation of the root apex cells and disorganization of the epidermal cells. These changes suggest that Si benefits the morphology of roots exposed to Al. The addition of Si resulted in increases in the root tip concentrations of fructose, sucrose, total amino acids and nitrate. Aditionally, Si-treated plants exhibited a lower lipid peroxidation and higher cell wall peroxidase activity. These results highlight the beneficial potential of Si fertilization as a strategy to improve crop development in acidic soils and mitigate the effects of Al toxicity.

Infection of coffee leaves by the biotrophic fungus Hemileia vastatrix results in intense plant defoliation and lower fruit berries production. Resistant cultivars and fungicide spray (contact and/or systemic) help to reduce the impact of coffee leaf rust (CLR) on coffee production. New alternatives for CLR management are needed to reduce fungicides spray and the emergence of populations from H. vastatrix resistant to them. In this study, it was hypothesized that β-aminobutyric acid (BABA) could boost the defense of coffee leaves against infection by H. vastatrix. In the in vitro assay, urediniospores germination was significantly reduced from 58 to 94% as the concentrations of BABA increased from 100 to 500 mM. Fungal sporulation and uredinia were much less intense on the leaves of BABA-sprayed plants compared to the ones obtained from water-sprayed plants at 22 and 30 days after inoculation. The area under coffee leaf rust progress curve and intensity of fungal sporulation were significantly lower by 76 and 88%, respectively, for BABA-sprayed plants compared to water-sprayed plants. The BABA-sprayed plants infected by H. vastatrix showed better photosynthetic performance, greater concentrations of chlorophyll a + b and carotenoids, higher activity of defense-related enzymes (chitinase and phenylalanine ammonia-lyase), and a more robust antioxidative metabolism (higher activities of ascorbate peroxidase, catalase, glutathione reductase, and superoxide dismutase) compared to water-sprayed and infected ones. Higher concentration of superoxide anion radical on BABA-sprayed and infected leaves intensified the defense against infection by H. vastatrix besides having a possible fungistatic effect against the fungus. In conclusion, BABA besides affecting the germination of urediniospores from H. vastatrix helped them to cope more efficiently against infection by H. vastatrix and can become an alternative for CLR control.

Asian rust, caused by the fungus Phakopsora pachyrhizi, is one of the most destructive diseases affecting soybean production. Foliar fertilization as a strategy to maintain higher amounts of nutrients, besides promoting better plant growth, may potentiate some biochemical pathways for defense reactions against pathogens. This study hypothesized that soybean plants sprayed with a foliar fertilizer containing nutrients (copper, potassium, zinc, and sulfur) and silicon [Sikon Fert® and referred to as induced resistance (IR) stimulus] could raise their basal level of resistance to cope with infection by P. pachyrhizi more efficiently. Plants were sprayed with water (control) or with IR stimulus and non-inoculated or inoculated with P. pachyrhizi. The urediniospores germination was significantly reduced from 57 to 100% after exposure to IR stimulus rates ranging from 0.5 to 10 mL/L compared to the control treatment. For inoculated plants, foliar concentrations of sulfur, copper, and zinc were significantly higher by 40, 490, and 13%, respectively, for IR stimulus treatment compared to the control treatment. The area under disease progress curve significantly decreased by 58% for IR stimulus-sprayed plants compared to plants from the control treatment. Infected and IR stimulus-sprayed plants had their photosynthetic apparatus preserved (significant increases for photochemical yield and electron transport rate values at 7 and 11 days after inoculation (dai) and significantly lower values for yield for non-regulated dissipation and yield for dissipation by down-regulation at 7 and 11 dai, respectively) along with great concentrations of chlorophyll a+b and carotenoids than infected plants from the control treatment. Lower concentrations of malondialdehyde and reactive oxygen species (hydrogen peroxide and anion superoxide) indicated less cellular damage imposed by fungal infection and greater activities of defense-related enzymes [chitinase, β-1,3-glucanase, phenylalanine ammonia-lyase (PAL), peroxidase (POX), polyphenoloxidase (PPO), and lipoxygenase] and more lignin production allowed the IR-stimulus sprayed plants to hamp the infection by P. pachyrhizi more efficiently. In conclusion, the reduction in Asian rust symptoms in soybean plants gained by spraying them with the IR stimulus was a collective contribution of a better nutritional status (higher foliar concentrations of copper, zinc, sulfur, and silicon), less cellular damage, and the interplay of PAL, POX, and PPO activities for more lignin production. Taken together, these findings open the way to explore the possibility of using this IR stimulus in field conditions to reduce the yield losses caused by Asian rust outbreaks in soybean.