Scielo RSS <![CDATA[Tropical Plant Pathology]]> vol. 39 num. 5 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Regional and varietal differences in prevalence and incidence levels of <i>Bipolaris</i> species in Brazilian rice seedlots</b>]]> A total of 722 rice seed lots were collected at six production regions of Rio Grande do Sul state during three consecutive seasons (2009/10 to 2011/12). For each seed lot, 200 seeds were assessed for the presence of Bipolaris spp. using a standard seed health blotter test. Results showed that B. oryzae and B. cynodontis were found in 62.5% and 10.4% of the seed lots, respectively. Overall mean incidence of B. oryzae and B. cynodontis were 0.5% and 0.06%, respectively. For the two most sampled varieties (75% of the seed lots), IRGA 424 and Puitá INTA CL, mean incidence levels were highest and lowest, respectively. Among regions, infection risk was highest in the southeastern and lowest in the western regions of the state, especially the Fronteira Oeste. The prevalence and the incidence levels of Bipolaris oryzae reported in this study were lower than previous reports in the same region - eighty percent of the seed lots showed incidence levels below the recommended 5% inoculum threshold. In conclusion, rice seeds produced by IRGA-certified growers showed an overall good health quality with regards to B. oryzae infection, which is the main Bipolaris species associated with rice seeds in southern Brazil. <![CDATA[<b>The etiological agent of cotton ramulosis represents a single phylogenetic lineage within the <i>Colletotrichum gloeosporioides</i> species complex</b>]]> Ramulosis of cotton, caused by Colletotrichum gossypii var. cephalosporioides (CGC), is an important disease of cotton in Brazil. The main objective of this work was to test whether CGC is a phylogenetic species inside the Colletotrichum gloeosporioides species complex. A Bayesian inference phylogenetic analysis of a combined ITS and TUB2 dataset was conducted with 21 strains identified as CGC and five strains of Colletotrichum gossypii (CG), associated with cotton anthracnose, obtained from diseased plants from different regions of Brazil. All CGC strains formed a highly supported lineage inside the clade of Colletotrichum theobromicola, a member of the C. gloeosporioides species complex. CG strains formed another lineage in the same clade. These findings were supported by a second analysis conducted with three genes (ITS+TUB2+GAPDH) and a subset of five CGC and three CG strains. During pathogenicity tests, all five CGC strains tested induced typical symptoms of ramulosis on inoculated plants, including foliar necrosis, death of apical meristems and over sprouting. Plants inoculated with CG strains exhibited foliar necrotic spots two months after inoculation. These results give phylogenetic support for the placement of CGC in the C. gloeosporioides species complex, and the distinction between the ramulosis and anthracnose pathogens of cotton in Brazil. <![CDATA[<b>Evaluation of BC1 and BC2 from the crossing <i>Erianthus arundinaceus</i> with <i>Saccharum</i> for resistance to sugarcane smut caused by <i>Sporisorium scitamineum</i></b>]]> Sugarcane smut disease caused by the fungus Sporisorium scitamineum is one of the important fungal diseases affecting sugarcane yield and sucrose content around the world. Cultivar resistance is the most appropriate control method for this disease. In this study, 37 BC1 lines chosen from the crossing YC96-40 (F1 of Erianthus arundinaceus) × CP84-1198 (commercial sugarcane cultivar) and 42 BC2 lines chosen from the crossing YCE01-116 (BC1 of E. arundinaceus) × Neijiang57-416 (commercial sugarcane cultivar) were evaluated for smut resistance using artificial inoculation. The results showed that of 79 tested BC1 and BC2 lines of E. arundinaceus, 10 (12.7%) were highly to moderately resistant to smut. BC1 of E. arundinaceus had more resistant lines than BC2 of E. arundinaceus. Of the 37 tested BC1 lines of E. arundinaceus, seven (18.9%) were highly to moderately resistant, while three (7.1%) of the 42 tested BC2 lines of E. arundinaceus were highly to moderately resistant to smut. The resistant lines identified in this study could be used as sources of smut resistance in sugarcane breeding programs. <![CDATA[<b>Age-related resistance to <i>Fusarium oxysporum</i> f. sp. <i>cepae</i> and associated enzymatic changes in seedlings of <i>Allium cepa</i> and <i>A. fistulosum</i></b>]]> This research analysed the response of onion (Allium cepa) and A. fistulosum against Fusarium oxysporum f. sp. cepae (Foc) isolates and the associated changes in peroxidase, β-1,3-glucanase and chitinase activities. The response of A. cepa and A. fistulosum at different stages of seedling development were also evaluated. Several seedling tests were performed, and disease symptoms were evaluated 12-14 days after inoculation. Allium fistulosum behaved as more resistant than A. cepa cultivars by exposition to the most aggressive Foc isolates at sowing date. Increased levels of peroxidase and glucanase activities were found in the A. cepa and A. fistulosum seedlings exposed to the pathogen, and were positively correlated with disease symptoms. For chitinase activity, this correlation was found only for A. cepa. Two peroxidase isoforms were found to be specific for A. fistulosum roots after inoculation and could be involved in resistance. The inoculation at 7, 14 and 42 days after sowing showed that both host species were resistant to Foc, proving that onion susceptibility decreased promptly after germination . However, an increase in peroxidase and glucanase activities in 7-and 14-day-old inoculated seedling was detected only for A. cepa, suggesting an earlier acquisition of resistance in A. fistulosum. <![CDATA[<b>Biological control of <i>Fusarium oxysporum</i> f. sp. <i>phaseoli</i> by <i>Trichoderma harzianum</i> and its use for common bean seed treatment</b>]]> Biological control of seed-borne pathogens has shown to enhance germination and physiological quality of seeds. The objectives of this study were to evaluate the in vitro antagonistic effect of five Trichoderma harzianum isolates (CEN287, CEN288, CEN289, CEN290, and CEN316) against Fusarium oxysporum f. sp. phaseoli (Foxy) and test its potential use in seed treatment. Initially, pathogen and antagonists were grown in paired cultures at 25ºC, from which samples were assessed using scanning electron microscopy (SEM). Then, clean or Foxy-infected seeds were treated with conidial suspension of the antagonists. Percent of Foxy-infected seeds and normal seedlings were evaluated at seven and nine days of incubation, respectively. All but one Trichoderma isolate (CEN290) inhibited Foxy mycelial growth. SEM analysis revealed that only one Trichoderma isolate (CEN287) showed parasitic interaction with Foxy. Two isolates (CEN287 and CEN316) significantly reduced the Foxy incidence and enhanced seed germination, though less effective than the fungicide mixture (carboxin + thiram). A principal component analysis indicated the importance of volatile metabolites in reducing Foxy incidence on common bean seeds. CEN287 Trichoderma harzianum isolate formed a single group due to its increase in germination rate of Foxyinfected seeds. <![CDATA[<b>Effects of UV-B radiation on <i>Lecanicillium</i> spp., biological control agents of the coffee leaf rust pathogen</b>]]> Coffee leaf rust is the main disease of coffee and its causal agent is naturally hyperparasited by Lecanicillium lecanii, indicating its potential for biocontrol. Ultraviolet-B (UV-B) radiation is an important factor that interferes on application of biocontrol agents, and Lecanicillium can be affected by UV-B. The objective of this work was to evaluate the effects of UV-B on Lecanicillium isolates and on its capacity to colonize rust lesions. There were variations among Lecanicillium strains in sensitivity to UV-B radiation, causing inactivation and delayed spore germination. The most tolerant strain (CCMA-1143) had LD50=1.63 kJ/m² of UV-B. The incidence and colonization of Lecanicillium on coffee leaf rust lesions were influenced by the dose of UV-B radiation, and were increased when the isolate CCMA-1143 was sprayed on rust lesions. The effects of UV-B should be considered on efficacy studies for the development of biopesticides. <![CDATA[<b>Supression of seed borne <i>Cladosporium herbarum</i> on common bean seed by <i>Trichoderma harzianum</i> and promotion of seedling development</b>]]> Trichoderma harzianum isolates have been broadly used for biocontrol of plant diseases caused by fungi. Cladosporium herbarum is a common saprophyte and seed borne fungus, which is easy to manipulate under controlled conditions. It was chosen as a model to test the effectivity of seed treatments with T. harzianum. Common bean seeds (cv. Pérola) contaminated with C. herbarum were treated with conidial suspension (CS) and autoclaved filtrate (AF) of five isolates of T. harzianum and subsequently submitted to health and germination tests. The proportion of normal seedlings formed, the length of roots, hypocotyls and leaves, and total plantlet length, total plantlet biomass, root mass ratio (RMR), stem mass ratio (SMR), leaf mass ratio (LMR), aerial part/root system ratio (AP/RS) and leaf area were also evaluated. Isolates CEN289 and CEN290 (CS and AF) provided 66 to 77% of supression of C. herbarum on seeds and a higher number of normal seedlings as compared with control. It also yielded a higher total biomass of plantlets. Moreover treatment with isolates CEN289 and CEN290 increased root and stem length in the experiments with CS. Such results indicate the potential of T. harzianum for seed treatment and suggest that it should be further tested as control for seed borne fungal diseases and as a plant growth promoter. The better performance found for CEN289 and CEN290 confirms the variability in terms of biocontrol activity among strains of T. harzianum. <![CDATA[<b><i>Teratosphaeria pseudoeucalypti</i></b><b> on eucalyptus in Brazil</b>]]> A new foliar disease caused by Teratosphaeria pseudoeucalypti on eucalyptus (E. globulus, E. urophylla x E. globulus and E. nitens x E. globulus) in Brazil is described . The disease is characterized by leaf spots of variable sizes and shapes, resulting in leaf blight and premature defoliation. Based on the morphological characteristics and multilocus phylogenetic analysis of the EF-1α, β-T and ITS-2 gene regions of five isolates, the fungus was identified as T. pseudoeucalypti. This is the first report of this pathogen outside Australia and a method for sporulation in culture is described. <![CDATA[<b>Biological control of tomato bacterial spot by seed microbiolization</b>]]> Six plant growth promoting rhizobacteria isolates - two Streptomyces (DFs1296 and DFs1315), three Bacillus (DFs1414, DFs1420 and DFs1423) and one Pseudomonas (DFs1421) - were used to microbiolize tomato seeds for the control of bacterial spot caused by Xanthomonas gardneri. Three assays were conducted in a completely randomized design with six replications. In each assay, X. gardneri suspensions (10(8)CFUmL-1) were spray-inoculated on the leaves. In the first and second assays, three and four leaves, respectively, were assessed for disease severity. In the third assay, three leaves per plant were assessed for the number of lesions per leaf, leaf area and dry weight. Results showed that one of the Bacillus sp. isolate (DFs1420) consistently provided the greatest relative reduction (48%) of tomato bacterial spot severity.