Scielo RSS <![CDATA[Tropical Plant Pathology]]> vol. 39 num. 4 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[<b>Potential of ethyl acetate fractions of <i>Stryphnodendron adstringens</i> shells and fruit extracts of <i>Caesalpinia ferrea</i> to control bacterial leaf speck and on the potentiation of defense enzymes in tomato</b>]]> Considering the importance of bacterial leaf speck (Pseudomonas syringae pv. tomato) in reducing tomato yield and difficulties in disease control, this study investigated the effects of fractions of shells extract of Stryphnodendron adstringens (Sa) and fruit extract of Caesalpinia ferrea (Cf) compared to Acibenzolar-S-Methyl (ASM) on reducing bacterial leaf speck symptoms and on the potentiation of the activities of defense enzymes. The number of lesions per plant (NLP) was significantly lower in plants treated with the ethyl acetate fraction (EAF) of S. adstringens (Sa) and ASM compared to other treatments (EAF of Cf, n-butanol fractions of Sa and Cf, aqueous fractions of Sa and Cf and sterile distilled water). The bacteria were inhibited by the EAF of Sa and EAF of Cf and n-butanol fractions of Sa and Cf according to the bioautography assay. Saponins and tannins were the two major compounds found in these fractions based on the phytochemical analysis. Peroxidase (POX), polyphenoloxidase (PPO), β-1,3-glucanase (GLU) and phenylalanine ammonia-lyase (PAL) activities were determined on the leaves of plants treated with EAF Sa, ASM and sterile distilled water. Both POX and PAL activities were higher at 3 and 6 days after inoculation (dai), while the PPO and GLU activities were higher from 9 to 12 dai. It is suggested that saponins increased tomato resistance to P. s. pv. tomato because no antimicrobial activity against the bacteria was observed. In conclusion, the EAF Sa was very efficient in reducing bacterial leaf speck symptoms in conditions where the POX, PPO, PAL and GLU activities played a pivotal role in increasing tomato resistance to the disease. <![CDATA[<b>The CD1/CD2 marker for specific detection of <i>Colletotrichum lindemuthianum</i> is an iron transporter pseudogene</b>]]> Colletotrichum lindemuthianum, the causal agent of anthracnose in common bean (Phaseolus vulgaris), is one of the most yield-limiting factors worldwide. Anthracnose affects the quality of pods by inducing black, sunken cankers and can also affect petioles, leaf veins and stems where it induces the typical anthracnose sunken lesions. A few years ago, a duplex PCR method that combines amplification of an ITS rDNA segment (CY1/CY2) together with an uncharacterized RAPD-derived amplicon (CD1/CD2) was developed for specific detection of C. lindemuthianum. This study shows that the CD1/CD2 marker corresponds to a portion of an iron permease (Ftr1) pseudogene in the vicinity of the gene encoding for a polyhydroxyproline-rich protein in Colletotrichum. Discrimination with Colletotrichum orbiculare is due to a 15 nt deletion in the CY1 annealing region. The potential of using this genomic region for phylogenetic analysis of the C. orbiculare species complex and detection of their related species is discussed. <![CDATA[<b>Observations on the gall rust fungus <i>Prospodium transformans</i>, a potential biocontrol agent of <i>Tecoma stans</i> var. <i>stans</i> (Bignoniaceae) in South Africa</b>]]> Tecoma stans var. stans, a tree originating from the Americas, is emerging as an invasive weed in South Africa. A microcyclic gall inducing rust fungus, Prospodium transformans, has been investigated as a biological control agent against this plant. Development of germinating teliospores and symptoms on host plants are described, and the optimum temperature for teliospore germination was found to be 18-22ºC. Inoculations of plants grown from seed originating from South Africa and various localities in Mexico and Texas (USA) indicate that there are likely races specific to morphological variants of this widespread and highly variable plant species. Despite readily inducing galls on plants grown under quarantine glasshouse conditions in South Africa, this rust fungus failed to establish in the field upon release. It is suggested that the origin of the form of this plant, which has become invasive in South Africa, needs to be identified to source the correct race of P. transformans for release in South Africa. <![CDATA[<b>Field resistance of potato cultivars to foliar early blight and its relationship with foliage maturity and tuber skin types</b>]]> Three field experiments were carried out to assess the level of resistance of several cultivars to early blight (EB) and to examine the association between host resistance and either foliage maturity or tuber skin types. A total of 26 cultivars were used in Exps. 1 and 2, and 24 in Exp. 3. Plants were inoculated with isolates of Alternaria grandis at 31 days after planting. EB severity was quantified in each plot every seven days. The approach to determine the resistance levels of potato cultivars was based on multivariate analysis techniques. The tested cultivars responded as either resistant, moderately resistant, moderately susceptible or susceptible to EB. Most of the cultivars were classified as susceptible or moderately susceptible to EB. Resistant cultivars were mid-season, mid-late or late maturity. None of the susceptible cultivars were later maturity (mid-late or late maturity). In most cases, susceptible cultivars were earlier maturity (early or mid-early maturity). Most resistant cultivars had rough, mid-rough or smooth skin. None of the susceptible cultivars had rough skin. In most cases, susceptible or moderately susceptible cultivars had smooth skin. Obtaining potato cultivars that are resistant to this destructive disease will help reduce production costs and the need for costly fungicides. <![CDATA[<b>Resistance to <i>Phytophthora infestans</i> in <i>Solanum tuberosum</i> landraces in Southern Chile</b>]]> The objective of this work was to evaluate the resistance of 30 Chilean potato landraces to natural infection by Phytophthora infestans during two growing seasons in Southern Chile. Control cultivars were 'Désirée', which has moderate susceptibility to late blight, and 'Karú', which is characterized by moderate resistance to the disease. The response of the potato landraces to late blight infection was assessed weekly by scoring the percentage of foliage destruction during the growing season. Subsequently, the relative area under the disease progress curve (AUDPCr) was calculated. A wide response variation was observed among the landraces during the occurrence of late blight. The comparative analysis of the AUDPCr showed that three landraces achieved high resistance to the disease (low AUDPCr values). These were UCT-34Cor (0.05), UCT-26Ach (0.06) and UCT-27Mu (0.10). Most of the potato landraces were classified into the range moderately resistant to moderately susceptible. The estimated values of heritabilities of the means were moderate to high for the joint analysis of the two years tested (0.65). The wide range of AUDPCr observed within potato landraces suggests the presence of partial resistance in response to the complex virulence pattern of the P. infestans populations present in Southern Chile. <![CDATA[<b>Specific boundaries between the causal agents of the soybean stem canker</b>]]> Pathogens within the Diaporthe complex cause seed decay, stem blight and stem canker on soybean, representing a serious threat for this crop species. We herein utilize worldwide sequence data retrieved from Genbank in order to assess the species boundaries between the soybean stem canker causal agents, and define whether or not they should be regarded as members of the same biological species. These studies were complemented with compatibility tests, in order to validate our findings from a biological standpoint. Species delimitation assays supported the occurrence of a speciation event between D. caulivora and D. phaseolourm var. meridionalis. A speciation hypothesis between D. aspalathi and D. phaseolourm var. meridionalis was also supported, based on three reciprocally monophyletic substitutions at locus EF1-α. Compatibility tests further validated species delimitation assays indicating that D. caulivora has developed barriers to gene exchange with D. phaseolorum var. meridionalis. Clarification of the specific boundaries of the SSC pathogens and related entities will be an important asset to future research in soybean pathology, epidemiology and breeding. <![CDATA[<b><i>Colletotrichum theobromicola</i></b><b> causes defoliation, stem girdling and death of mini-cuttings of eucalyptus in Brazil</b>]]> Eucalyptus plantations cover approximately 5.1 million hectares of Brazil, an area that will likely increase given the demand for natural products from planted forests. In recent years, anthracnose diseases have been frequently found on eucalyptus in Brazilian nurseries. In 2012, rooted mini-cuttings of clones of E. urophylla x E. grandis ("urograndis") exhibiting leaf spot and stem girdling symptoms were collected from nurseries in the Brazilian states of Pará and Minas Gerais, and cultures of Colletotrichum were obtained from the lesions. The isolates were initially identified to species of the C. gloeosporioides species complex, according to searches of the Q-bank Fungi database with the DNA sequences of their internal transcribed spacer (ITS) regions. Subsequent phylogenetic analysis of the β-tubulin (TUB2) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) regions, combined with morphological characterization, allowed us to conclude that the fungus belongs to C. theobromicola. Conidial suspension sprayed on "urograndis" clone plants induced similar symptoms as those found under natural conditions. Re-isolation of the fungus from symptomatic plants fulfilled the Koch´s postulate. To our knowledge, this is the first report of C. theobromicola in Brazil. <![CDATA[<b>Additional species of <i>Aspergillus</i> causing bole rot disease in <i>Agave sisalana</i></b>]]> The production of sisal in Bahia, Brazil, has been declining due to the occurrence of a disease know as bole rot. Aspergillus niger was regarded as the only causal agent. In this study A. brasiliensis and A. tubingensis, in addition to Aspergillus niger, identified on the basis of morphological and molecular analyses, were shown to cause bole rot of sisal. Their pathogenicity was confirmed but their significance for the epidemiology of the disease in the field remains unclear. <![CDATA[<b>Resistance in <i>Capsicum</i> spp. to anthracnose affected by different stages of fruit development during pre- and post-harvest</b>]]> This study aimed to investigate the reaction of unripe and ripe fruits of Capsicum spp. accessions to Colletotrichum gloeosporioides during the pre- and post-harvest periods, and to identify sources of resistance for use in plant breeding programs. Thirty-seven Capsicum spp. accessions of the Universidade Estadual do Norte Fluminense Darcy Ribeiro were evaluated. They were cultivated in a greenhouse and arranged in a completely randomized design with five replications. Twenty fruits from each accession were inoculated at two stages (unripe and ripe) in two different environments (fruits inoculated in the plant and detached fruit inoculated under laboratory conditions). The symptoms were assessed every 24 hours between the 1st and 8th days after inoculation. There were highly significant differences in the values of the area under the disease progress curve and in severity, considering all sources of individual variation and their interactions. Values of low and moderate correlation were observed for inoculation of unripe and ripe fruit in both environments. These results indicate the existence of distinct genes responsible for resistance at different stages of fruit development. Complete lack of symptoms was registered only for accessions UENF 1718 and UENF 1797 (C. baccatum var. pendulum). <![CDATA[<b>Episomal detection of <i>Banana streak OL virus</i> in single and mixed infection with <i>Cucumber mosaic virus</i> in banana 'Nanicão Jangada'</b>]]> Banana streak virus (BSV) and Cucumber mosaic virus (CMV) are commonly found in all banana growing-areas of the world. These viruses cause diseases that lead to yield reduction and constrain plant breeding and distribution of Musa germplasm. Most of the diagnostic methods targeting BSV can generate dubious results because of the considerable genetic and serological diversity among BSV isolates and the presence of integrated BSV sequences in the banana plant. Both viruses are usually detected in single and mixed infections in banana plantations in the north region of Paraná state using DAS-ELISA and PCR. A rolling-circle amplification protocol tested in this study allowed specific detection and identification of an episomal BSV isolate infecting Nanicão Jangada cultivar, thus confirming the occurrence of Banana streak OL virus in Brazil.