Nadson de Carvalho Pontes

Xanthomonas perforans and X. gardneri associated with bacterial leaf spot on weeds in Brazilian tomato fields

Plants of Nicandra physaloides, Solanum americanum and Euphorbia heterophylla with leaf lesions have been found naturally grown among tomato plants in commercial fields in Brazil. Tomato bacterial spot was occurring in these fields. Xanthomonad-like isolates were obtained from affected weed leaf samples. These isolates were species identified using BOX-PCR and specific primers. Isolates from N. physaloides and S. americanum were identified as Xanthomonas perforans and that of E. heterophylla were identified as X. gardneri. Each of them was able to artificially infect and cause symptoms on the three weed species and tomato plants.

Intervals and Number of Applications of Acibenzolar-S-Methyl for the Control of Bacterial Spot on Processing Tomato

Acibenzolar-S-methyl (ASM) is a plant activator that triggers systemic acquired resistance that is labeled for use in Brazil for managing tomato bacterial spot. The aim of this study was to define the optimum relationship between interval and number of applications of ASM for the most efficacious control of bacterial spot on processing tomato. Four intervals between applications (4, 7, 10, and 14 days) and four application frequencies (4, 6, 8, and 10 applications) were evaluated in five trials performed between 2010 and 2011 in Brasília, Distrito Federal, and in Morrinhos, in the state of Goiás. Copper hydroxide (CH) was applied after ASM applications to complete 13 applications per growing season. Two check treatments were added: standard CH weekly applications and untreated. The following variables were evaluated: severity of bacterial spot, yield, percentage of ripe and rotten fruit, soluble solids content, and the benefit/cost ratio. Disease severity varied between treatments in three trials and yield varied in two trials. A greater number of applications resulted in a reduction of bacterial spot, and the ideal interval between applications was between 8 to 10 days. However, there was a reduction in yield with 10 ASM applications. The temporal effect of ASM applications on bacterial spot severity was evaluated under greenhouse conditions. Reduction in disease severity was observed up to 6 days following ASM application. Additionally, the weekly treatment of seven applications of ASM followed by six applications of CH was compared with a standard program of CH under commercial production conditions in Itaberaí, Goiás, where bacterial spot occurred naturally. The program with ASM and CH resulted in significantly less foliar disease severity than the standard program, which did not result in yield gains. In addition, no differences were detected between the two programs for soluble solids content, industrial yield, plant height, and percentage of ripe and rotten fruit.

First Report of Myrothecium roridum Causing Myrothecium Leaf Spot on Begonia in Brazil

Begonia (Begonia elatior) cultivars are among the most commercialized ornamental potted plants in Brazil. Since 2012, a high incidence of plants with leaf spots has been found in greenhouses of São Paulo State, for the first time in Jacareí Municipality (23°15′58.45′′ S; 46°2′32.24′′ W). The symptoms, initially small and circular, evolve into irregularly shaped spots with a light brown color. Dark sporodochia surrounded by white hyphal tufts develop in older lesions. Symptoms were consistent with those of Myrothecium leaf spot observed on other ornamental plants such as gardenia, gloxinias, impatiens, and begonias in North America (Daughtrey et al. 1995). Isolations from these lesions on potato dextrose agar (PDA) produced white, floccose, concentric-ringed colonies with irregular shapes of dark green-to-black sporodochia. Conidiophores presented 2 to 4 branches at each node while phialides were hyaline, cylindrical, in whorls of 3 to 5, and measured 13 to 16 × 2.0 μm. Conidia were hyaline, one-celled, rod-shaped with rounded ends, and measured 5 to 7.5 × 2.0 μm. These characteristics are consistent with the morphology of Myrothecium roridum Tode (Tulloch 1972). 1/2 Sequencing of the internal transcribed spacer regions ITS1, 5.8S rDNA, and ITS2 of one Myrothecium isolate was performed using ITS5 (5′-GGAAGTAAAAGTCGTAACAAGG-3′) and ITS4 (5′TCCTCCGCTTATTGATATGC-3′) primers (White et al. 1990) and compared with sequences in the GenBank database. The resulting 563-bp amplicon (Accession No. KJ494661) was 99% identical to the other M. roridum sequences present on GenBank (JF343832 and KJ174523.1). The strain was deposited in the Mycological Reference Collection of the University of Brasília (Accession No. KJ4946612246). To confirm pathogenicity, 10 begonia plants were inoculated, placing mycelial plugs on begonia leaves, from which five were previously injured with a needle tip. Plants were maintained for 7 days at 28°C at relative humidity above 80%. Ten control plants received only PDA disks. Symptoms were observed on all inoculated plants after 7 days, while control plants remained symptomless. M. roridum was consistently reisolated from symptomatic tissues, fulfilling Koch’s postulates. This is the first report of Myrothecium leaf spot caused by M. roridum on begonias in Brazil. This pathogen has been previously reported on begonias in North America (Daughtrey et al. 1995). Begonia represents a popular ornamental plant in Brazil and damage to the foliage reduces its marketability; therefore, early and correct diagnosis is necessary to take control measures and reduce production losses. References: Section: Daughtrey, M. G., et al. 1995. Page 19 in: Compendium of Flowering Potted Plant Diseases. APS Press, St. Paul, MN. Tulloch, M. 1972. Mycol. Pap. 130:1. White, T. J., et al. 1990. Page 315 in: PCR Protocols: A Guide to Methods and Applications . M. A. Innis , et al., eds. Academic Press, San Diego, CA.

Identification of sources of seedling resistance to Phytophthora capsici in Cucumis melo

The employment of genetic resistance to minimize yield losses induced by Phytophthora capsici remains unexplored in melon (Cucumis melo). A diverse collection of melon accessions was evaluated against P. capsici isolates at the seedling stage. In the first screening assay, 105 accessions were evaluated using isolate PCpe-04 obtained from cucumber (Cucumis sativus). In a second assay, 31 accessions displaying high levels of resistance in the first assay were challenged with a distinct isolate (PCpe-09 also from cucumber). In a third assay, a subset of 14 selected accessions was re-evaluated using isolates PCpe-09 and PCmo-07 (from strawberry). In the last screening, seven accessions with high levels of resistance across all assays were challenged with five isolates from representative host species [PC-Vagem (snap bean), PCp-129 (Capsicum chinense), PCp-155 (C. annuum), PCpe-09 and PCmo-07] to assess their reaction against a varied sample of P. capsici isolates. For two accessions (CNPH-093 and L040), all plants remained free of symptoms after inoculation with all five isolates. Accessions WMR-29, CNPH 084, CNPH 088 and CNPH 092 were also free of symptoms to all isolates, except PCmo-07. These large-spectrum resistance sources might be useful for breeding programs aiming to incorporate resistance against P. capsici in elite melon lines.

First report of Lasiodiplodia theobromae causing stem rot disease of begonia (Begonia x elatior hort.) in Brazil

Lasiodiplodia theobromae was found causing stem rot on commercial production of Begonia x elatior in São Paulo, Brazil. Illustrations, morphological and molecular description are provided. Based on the morphology, this fungus was recognized as L. theobromae. However, L. theobromae has high similarity with other Lasiodiplodia species, some of which are not possible to be separated by morphological characters. Molecular identification of the fungus isolated from the infected tissues was conducted. The strain from begonia clustered with other isolates of L. theobromae. This is the first report of the occurrence of L. theobromae on B. elatior.

Volume de aplicação e eficiência do controle químico da mancha bacteriana em tomateiro industrial

Hortic. bras., Brasília, v.35, n.3, July-September 2017 N Brasil, a cultura do tomate para processamento industrial vem crescendo, resultado do aumento da demanda dos derivados de tomate (Melo & Fonte, 2011). A produção brasileira nesse segmento concentra-se no estado de Goiás, onde as condições de clima, solo e topografia favorecem o cultivo (Silva-Junior et al., 2015). Nessa região, irrigam-se os cultivos de tomate para processamento por aspersão via pivôcentral, o que favorece a ocorrência de doenças que comprometem a produtividade e a qualidade dos frutos, com destaque para a mancha bacteriana (Quezado-Duval et al., 2004). Essa doença está associada a quatro espécies do gênero Xanthomonas: X. euvesicatoria, X. gardneri, X. perforans e X. vesicatoria. Nas principais regiões produtoras do Brasil, os primeiros estudos de epidemias da mancha bacteriana em tomate para processamento indicavam a prevalência da espécie X. gardneri (Quezado-Duval et al., 2004). Entretanto, segundo levantamentos mais recentes, a ocorrência de X. perforans tem aumentado e passou a prevalecer nos campos de tomate para processamento na região central do país (Araújo et al., 2016). Essas bactérias podem sobreviver em restos culturais, sementes, plantas daninhas e plantas voluntárias (Quezado-Duval & Lopes, 2010), o que dificulta a eliminação das fontes de inóculo. Até o momento, não há variedades comerciais desse segmento com níveis efetivos de resistência (Quezado-Duval et al., 2014). Assim, a ferramenta mais utilizada pelos produtores para o manejo da mancha bacteriana tem sido o controle químico. PONTES, NC; NASCIMENTO, AR; GOLYNSKI, A; MOITA, AW; MAFFIA, LA; OLIVEIRA, JR; QUEZADO-DUVAL, AM. 2017. Volume de aplicação e eficiência do controle químico da mancha bacteriana em tomateiro industrial. Horticultura Brasileira 35: 371-376. DOI http://dx.doi.org/10.1590/ S0102-053620170309