Fitopatologia - Artigos
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Item In vitro production of conidia of Alternaria solani(Tropical Plant Pathology, 2010-07) Rodrigues, Tatiana T. M. S.; Maffia, Luiz A.; Dhingra, Onkar D.; Mizubuti, Eduardo S. G.Sporulation of Alternaria solani can be scarce and is often reduced when the fungus is cultivated in vitro. A series of experiments were conducted to assess the effects of moisture, mycelial wounding, light quality and photoperiod, and culture media on conidial production. A procedure to induce sporulation based on mycelial wounding and dehydration was adapted and validated. Best results were obtained when fungal colonies were grown in V8 medium at 25ºC in the dark with agitation for seven days; the mycelium mass was ground, poured into potato dextrose agar (pH 6.5) in plates, and incubated at 25 ± 2ºC under near ultraviolet light and 12 h-photoperiod. The procedure was validated with 30 isolates of A. solani from different hosts, sampling locations, ages, and storage conditions. Conidial production, germination, and infectivity were quantified. Seventy-five percent of the isolates sporulated and the lowest germination rate was 68%. Inoculations of conidial suspension of all isolates resulted in lesions on tomato and potato plants. The effect of subculturing on A. solani sporulation was also assessed. After six subcultures, every seven days, there was no reduction in sporulation of colonies that were induced with the protocol.Item Reappraisal of the black mildews (Meliolales) on Hevea brasiliensis(Tropical Plant Pathology, 2014-01) Pinho, Danilo B.; Honorato Junior, Jaime; Firmino, André L.; Hora Junior, Braz T.; Mizubuti, Eduardo S. G.; Pereira, Olinto L.The rubber tree (Hevea brasiliensis) is host to several fungal species, including Irenopsis heveae as described by Hansford in 1961, which causes black mildew on leaves. One specimen of Irenopsis heveae from the state of Espírito Santo and two from the state of Pará were analyzed and showed some morphological differences. Some structures are similar to morphological characteristics as described and illustrated by Vincens in 1915 for Meliola heveae. Morphological comparisons with the type specimen of I. heveae and the alignment of the nucleotide sequences of the 28S rDNA region, however, indicate that the three samples belong to the same species. According to these data M. heveae and I. heveae are heterotypic synonyms with M. heveae being the older name. As the name I. heveae is already occupied by Hansford, Irenopsis vincensii is proposed as new name for the black mildew on H. brasiliensis. This is the first contribution of molecular sequence data for this species.Item Green synthesis of silver nanoparticles using tomato leaf extract and their entrapment in chitosan nanoparticles to control bacterial wilt(Journal of the Science of Food and Agriculture, 2019) Santiago, Thaís R.; Bonatto, Cínthia C.; Rossato, Maurício; Lopes, Cláudio A. P.; Lopes, Carlos A.; Mizubuti, Eduardo S. G.; Silva, Luciano P.Silver nanoparticles (AgNPs), partipt-BRcularly those entrapped in polymeric nanosystems, have arisen as options for managing plant bacterial diseases. Among the biopolymers useful for the entrapment of AgNPs, chitosan is promising because of its low cost, good biocompatibility, antimicrobial properties and biodegradability. The present study aimed: (i) to greenly‐synthesize AgNPs using different concentrations of aqueous extract of tomato leaves followed by entrapment of AgNPs with chitosan (CH‐AgNPs); (ii) to characterize the optical, structural and biological properties of the nanosystems produced; (iii) to evaluate the antimicrobial activitiept-BRs of AgNPs and nanomaterials; and (iv) to assess the effectiveness of AgNPs and nanomaterials for controlling tomato bacterial wilt caused by Ralstonia solanacearum. Spherical and oval AgNPs had incipient colloidal instability, although the concentration of the tomato leaf extract influenced both size (< 87 nm) and the polydispersity index. Nanomaterials (< 271 nm in size) were characterized by a highly stable matrix of chitosan containing polydisperse AgNPs. Free AgNPs and CH‐AgNPs were stable for up to 30 days, with no significant alteration in physicochemical parameters. The AgNPs and nanomaterials had antibacterial activity and decreased bacterial growth at micromolar concentrations after 48 h. Morphological changes in R. solanacearum cells were observed after treatment with CH‐AgNPs. The application of CH‐AgNPs at 256 µmol L−1 reduced the incidence of bacterial wilt in a partially resistant tomato genotype but not in the susceptible line. Greenly‐synthesized chitosan‐derived nanomaterials containing AgNPs produced with leaf extracts from their own species appear to comprise a promising and sustainable alternative in an integrated management approach aiming to reduce the yield losses caused by bacterial wilt. © 2019 Society of Chemical IndustryItem Fusarium wilt of banana: current knowledge on epidemiology and research needs toward sustainable disease management(Frontiers in Plant Science, 2018-10) Heck, Daniel; Dita, Miguel; Barquero, Marcia; Mizubuti, Eduardo S. G.; Staver, Charles P.Banana production is seriously threatened by Fusarium wilt (FW), a disease caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc). In the mid-twentieth century FW, also known as “Panama disease”, wiped out the Gros Michel banana industry in Central America. The devastation caused by Foc race 1 was mitigated by a shift to resistant Cavendish cultivars, which are currently the source of 99% of banana exports. However, a new strain of Foc, the tropical race 4 (TR4), attacks Cavendish clones and a diverse range of other banana varieties. Foc TR4 has been restricted to East and parts of Southeast Asia for more than 20 years, but since 2010 the disease has spread westward into five additional countries in Southeast and South Asia (Vietnam, Laos, Myanmar, India, and Pakistan) and at the transcontinental level into the Middle East (Oman, Jordan, Lebanon, and Israel) and Africa (Mozambique). The spread of Foc TR4 is of great concern due to the limited knowledge about key aspects of disease epidemiology and the lack of effective management models, including resistant varieties and soil management approaches. In this review we summarize the current knowledge on the epidemiology of FW of banana, highlighting knowledge gaps in pathogen survival and dispersal, factors driving disease intensity, soil and plant microbiome and the dynamics of the disease. Comparisons with FW in other crops were also made to indicate possible differences and commonalities. Our current understanding of the role of main biotic and abiotic factors on disease intensity is reviewed, highlighting research needs and futures directions. Finally, a set of practices and their impact on disease intensity are discussed and proposed as an integrative management approach that could eventually be used by a range of users, including plant protection organizations, researchers, extension workers and growers.Item Epidemiological aspects of cowpea bacterial blight(Tropical Plant Pathology, 2015-02) Lima-Primo, Hyanameyka E. de; Oliveira, José Rogério de; Mizubuti, Eduardo S. G.; Nechet, Kátia de L.; Halfeld-Vieira, Bernardo de A.; Souza, Giovanni R. deCowpea bacterial blight, caused by Xanthomonas axonopodis pv. vignicola (Xav), can severely reduce the yields of cowpea in tropical regions. Despite its destructiveness, research on the epidemiology of bacterial blight is scarce in Brazil. The objectives of this study were to quantify the effect of the Xav inoculum concentration and of the duration of leaf wetness periods on disease severity, in addition to assessing bacterial transmissibility by seed and to identify indicator plants that might be used for simple diagnostic tests. In experiments conducted in greenhouse and field conditions, cowpea plants were inoculated with 105, 106 and 107 CFU (colony forming units) of Xav/mL, and seeds harvested from field plots were used to determine the transmissibility of the bacteria. Under greenhouse conditions, plants were subjected to leaf wetness duration periods of 0, 4, 8, 12, 16, 20 and 24 h after inoculation. In another experiment, soybean, common bean and wild poinsettia were inoculated with Xav. It was observed that plants inoculated with a concentration of 107 UFC/mL and subjected to 12 h of leaf wetness had higher disease severity. There was transmission of Xav to the seeds in all inoculum concentrations used. Hypersensitivity reaction was observed in wild poinsettia less than 24 h after inoculation.Item Cultural and Aggressiveness Variability of Cercospora coffeicola(Journal of Phytopathology, 2012-10) Souza, André G. C.; Maffia, Luiz A.; Mizubuti, Eduardo S. G.Although brown eye spot of coffee, caused by Cercospora coffeicola, is important for coffee production in Brazil, there is a general lack of knowledge regarding the disease. In this study, we evaluated the variability of both the cultural and aggressiveness traits of 60 isolates from coffee plants grown under conventional and organic systems in three regions of Minas Gerais State, Brazil. Variability among the isolates was detected with regard to all of the traits and was unrelated to an effect of either the region or cropping system. Mycelial growth, cercosporin production and sporulation were assessed in the laboratory. Of the 60 isolates, 27 did not sporulate at 25°C; the mycelial growth of all of the isolates and cercosporin production by 18 of the isolates linearly increased as the temperature rose from 18 to 26°C. We inoculated six selected isolates on plants of two coffee cultivars (ÔCatuaı ́ Vermelho IAC44Õ and ÔCatucaı ́ Vermelho 785-15Õ) and evaluated the incubation period (IP), latent period (LP) and disease severity. All three of these traits were affected by temperature postinoculation and KCl amendment. The significant correlations were as follows: IP and LP in both cultivars; severity and leaf fall in both cultivars; and cercosporin production in vitro and severity values in ÔCatucaı ́ Vermelho 785-15Õ. In conclusion, we found that (i) C. coffeicola is highly variable for both cultural and aggressiveness traits; (ii) laboratory and glasshouse experiments were suitable to assess the pathogen variability; (iii) research protocols should account for the effect of environmental factors, such as temperature and KCl, on the traits evaluated; and (iv) these protocols should include the assessment of the IP instead of the LP, as both are correlated, and the IP is easier to evaluate.Item Genetic structure of the population of Alternaria solani in Brazil(Journal of Phytopathology, 2011-04) Lourenço Jr, Valdir; Rodrigues, Tatiana T. M. S.; Campos, Antonio M. D.; Bragança, Carlos A. D.; Scheuermann, Klaus K.; Reis, Ailton; Brommonschenkel, Sérgio H.; Maffia, Luiz A.; Mizubuti, Eduardo S. G.Understanding the genetic structure of the population of Alternaria solani (AS) is an important component of epidemiological studies of early blight, a severe disease that affects potato (Po) and tomato (To) worldwide. Up to 150 isolates obtained from both hosts were analysed with RAPD and AFLP markers to estimate the amount and distribution of genetic variability of AS in Brazil. Using RAPD, gene diversity (h=0.20) and scaled indices of diversity of Shannon (H′=0.66) and Stoddart and Taylor’s (G=0.31) for the Po population were higher than those of the To (h=0.07, H′=0.34, G=0.17). For AFLP, the statistics for the Po (h=0.17, H′=0.86, G=0.49) and To (h= 0.17, H′=0.85, G=0.36) populations were similar. For each RAPD and AFLP locus, the allele frequency for the overall population ranged from 0.006 to 0.988, and 0.007 to 0.993, respectively. Genetic differentiation was high (GST=0.41 and θ=0.59) and moderately high (GST=0.23 and θ=0.37) when estimated with RAPD and AFLP, respectively. Based on cluster analyses, there was strong evidence of association of pathogen haplotypes with host species. The null hypothesis of random association of alleles was rejected in the analysis of both RAPD (IA=13.1, P<0.001) and AFLP (IA=2.2, P<0.001) markers. The average number of migrants was estimated to be around one and two individuals per generation, using RAPD and AFLP, respectively. There was no correlation between genetic distance and geographical origin of AS haplotypes for RAPD (r=−0.07, P=0.84) and AFLP (r=−0.03, P=0.70). The AS population is clonal with high genetic variability, and there is genetic differentiation between the populations that affect To and Po.Item Biological control of eucalyptus bacterial wilt with rhizobacteria(Biological Control, 2015-01) Santiago, Thais R.; Rossato, Mauricio; Romeiro, Reginaldo S.; Mizubuti, Eduardo S. G.; Grabowski, CristhianThe antagonistic potential of 298 rhizobacteria obtained from the rhizosphere and rhizoplane of tomato and eucalyptus plants was assessed for the control of bacterial wilt of eucalyptus caused by Ralstonia solanacearum. Several tests were performed using tomato plants as a screening system to select efficient rhizobacteria. Different methods for antagonist delivery and pathogen inoculation were evaluated: (1) seeds were microbiolized (soaked for 12 h in a suspension of the antagonist propagules) and germinated seedlings had their roots immersed in the pathogen inoculum suspension; (2) seedlings originated from microbiolized seeds were transplanted to soil infested with R. solanacearum and (3) roots of seedlings were immersed in a suspension of propagules of the antagonist and subsequently in a suspension of R. solanacearum. Nine isolates (UFV-11, 32, 40, 56, 62, 101, 170, 229, and 270) were selected as potential antagonists to R. solanacearum as they suppressed bacterial wilt in at least one of the methods assessed. The selected antagonists were evaluated against two isolates of R. solanacearum using in vitro and in vivo (inoculated eucalyptus) tests. Isolates UFV-56 (Bacillus thuringiensis), UFV-62 (Bacillus cereus) and a commercial formulation of several rhizobacteria (Rizolyptus®) suppressed bacterial wilt in eucalyptus protecting the plants during the early stages of development.Item Isolation and selection of Hemileia vastatrix antagonists(European Journal of Plant Pathology, 2014-04-21) Haddad, Fernando; Saraiva, Rodrigo M.; Mizubuti, Eduardo S. G.; Romeiro, Reginaldo S.; Maffia, Luiz A.Organic coffee growing is rapidly increasing in Brazil, and many diseases, especially coffee leaf rust (Hemileia vastatrix), are threatening its production. This study is a first step towards a biocontrol program for coffee rust on organically grown plants. In three organic coffee farms in the state of Minas Gerais, 393 microbial strains including 154 bacterial and 239 fungal strains were isolated from leaves, leaf debris, and soil samples, and in 6 month-old coffee plants, 17 of these isolates reduced both the infection frequency (IF) and the number of H. vastatrix urediniospores produced per leaf (UPL) by more than 70 %. The isolates were identified as eight bacteria isolates, seven Bacillus spp. and one Pseudomonas sp., and nine fungal isolates, four Fusarium spp., two Penicillium spp., one Aspergillus sp., one Acremonium sp. and one Cladosporium sp. Each fungal and bacterial isolate was applied 0, 4, 8, 12 or 16 days before and 0, 4, 8, 12 or 16 days after H. vastatrix inoculation, and the efficiency in reducing both IF and UPL was evaluated. The efficiency was higher and lasted longer when the bacterial isolates were applied before H. vastatrix inoculation. Six Bacillus (B10, B25, B143, B157, B171, B175), two Fusarium (F205, F281), and one Pseudomonas (B286) isolates are potentially efficient as biocontrol agents of H. vastatrix and will be tested using field experiments.Item High genetic variability and recombination in a begomovirus population infecting the ubiquitous weed Cleome affinis in northeastern Brazil(Archives of Virology, 2011-10-18) Silva, Sarah J. C. da; Castillo-Urquiza, Gloria P.; Hora Júnior, Braz T.; Assunção, Iraildes P.; Lima, Gaus S. A.; Pio-Ribeiro, Gilvan; Mizubuti, Eduardo S. G.; Zerbini, F. MuriloDiseases caused by begomoviruses are a serious constraint to crop production in many tropical and subtropical areas of the world, including Brazil. Begomoviruses are whitefly-transmitted, single-stranded DNA viruses that are often associated with weed plants, which may act as natural reservoirs of viruses that cause epidemics in crop plants. Cleome affinis (family Capparaceae) is an annual weed that is frequently associated with leguminous crops in Brazil. Samples of C. affinis were collected in four states in the northeast of Brazil. Analysis of 14 full-length DNA-A components revealed that only one begomovirus was present, with 91-96% identity to cleome leaf crumple virus (ClLCrV). In a phylogenetic tree, ClLCrV forms a basal group relative to all other Brazilian begomoviruses. Evidence of multiple recombination events was detected among the ClLCrV isolates, which also display a high degree of genetic variability. Despite ClLCrV being the only begomovirus found, its phylogenetic placement, high genetic variability and recombinant nature suggest that C. affinis may act as a source of novel viruses for crop plants. Alternatively, ClLCrV could be a genetically isolated begomovirus. Further studies on the biological properties of ClLCrV should help to clarify the role of C. affinis in the epidemiological scenario of Brazilian begomoviruses.