Alexei de Campos Dianese

Management of wheat blast with synthetic fungicides, partial resistance and silicate and phosphite minerals

Field trials conducted on a yellow-red latossol (pH 6.0), replicated in 2010 and 2011, sought to examine the effect of silicon, phosphite minerals, synthetic fungicides and genetic resistance for wheat blast management (Magnaporthe grisea) in Central Brazil. Disease intensity was measured on cvs. BRS 264 and BR18 subjected to the following Si treatments: pre-plant furrow application of Ca & Mg silicate (300 kg ha-1); post-plant scattered application of Ca & Mg silicate on top of the soil (1 ton ha-1); multiple foliar SiO2 applications (30 g l-1); and non-treated control. Blast incidence and severity were scored. Further experiments were conducted on cv. BR-264, for examination of the effect of potassium phosphite and synthetic fungicides on wheat blast intensity, with the following treatments: K2HPO3 (1ml l-1); epoxinazole + pyraclostrobin (700 ml ha-1); tebuconazole (600 ml ha-1); tebuconazole + trifloxystrobin (750 ml ha-1); and non-treated control. In 2010, disease intensity was lower than in 2011. In the silicate experiments, disease was significantly lower when plants were treated with foliar or furrow silicate. Si applications significantly reduced disease in BRS-264. While BR-18 consistently demonstrated lower disease levels, cv. BRS-264 generally responded more markedly to silicon applications. In the phosphite/fungicide experiment of 2010, all treatments reduced disease when compared with the control, and in 2011 phosphite efficiency was not significantly different from some fungicide treatments. Synthetic fungicides demonstrated an average blast control of 55% by severity values. Yields were increased in the phosphite-treated plots (by 9–80%), in the Si treatments (by 26–92%), and more so, and more consistently, with synthetic fungicides (by 90–121%). Combined results of all field studies, carried out under environmental conditions highly conducive to disease, indicated that control of wheat blast necessitates the joint integration of several alternatives for efficient disease management.

Avaliação do efeito de fosfitos na redução da varíola (Asperisporium caricae) do mamoeiro (Carica papaya)

The control of black spot of papaya is necessary, therefore, the objective of this study was to evaluate the effect of foliar applications of phosphites (K, Ca, Mg and Cu) on papaya black spot. Two phosphites and the fungicide Fosetyl-Al were tested on a field trial with papaya plants naturally infected by the pathogen. Ten phosphites and the fungicide Fosetyl-Al were tested in a greenhouse trial, also with plants naturally infected by A. caricae. In both, field and greenhouse trials, the phosphite treatments reduced black spot severity.

Papaya (Carica papaya) foot rot (Phytophthora palmivora) reduction due to phosphites

Papaya (Carica papaya) foot rot (Phytophthora palmivora) reduction due to phosphites This study showed that two weekly sprays of phosphite [A (40 % P2O5 + 20 % K2O, 150 mL commercial product. hL-1), B (40 % P2O5 + 20 % K2O, 250 mL), C (10 % P2O5 + 6 % Ca, 400 mL), D (20 % P2O5 + 20 % K2O, 200 mL), E (40 % P2O5 + 6 % Mg, 150 mL), F (30 % P2O5 + 20 % K2O, 175 mL), G (20 % P2O5 + 20 % K2O, 200 mL) ] for three consecutive weeks before pathogen inoculation reduced disease severity. A podridao do pe, causada por Phytophthora palmivora Butler, e uma das principais doencas mamoeiro (Carica papaya L.). Os fosfitos constituem uma alternativa para o controle de Phytophthora em plantas, pois inibem o patogeno ou induzem na hospedeira a producao de substâncias e compostos que agem no processo de defesa contra a infeccao. A determinacao de metodos eficientes de controle da doenca menos agressivos ao ambiente e necessaria. Neste estudo objetivou-se determinar o efeito de aplicacoes de fosfitos sobre a severidade da doenca. Os testes foram realizados em casa de vegetacao com plantas de ‘Tailândia Roxao’ (2 meses de idade). O patogeno (PP-24) foi multiplicado em meio seletivo (200 ml suco de tomate temperado ‘Superbom’, 18 g agar, 3 g CaCO3, 800 mL agua destilada, 10 mg pimaricina, 250 mg ampicilina, 10 mg rifampicina, 30 mg rosa de bengala). Os tratamentos aplicados estao apresentados na tabela 1. Os produtos foram aplicados nas folhas via pulverizacao (pulverizador manual – 500 mL) ate o ponto de escorrimento. A inoculacao do patogeno ocorreu 48 h apos a ultima pulverizacao, inserindo-se palitos colonizados pelo fungo na base do caule das plantas. Seguiu-se um delineamento em blocos ao acaso (9 tratamentos; 4 repeticoes de 5 plantas). A severidade da doenca foi avaliada diariamente utilizando-se a seguinte escala: (0) sem sintomas; (1) ate 50% de murcha; (2) de 51 a 100% de murcha; (3) – planta morta. Os dados foram submetidos a analise de variância com repeticao de medidas, e, as medias comparadas pelo teste de Tukey (P < 5 %). Com uma aplicacao semanal (Tabela 1), somente o tratamento com o fosfito C (10 % P2O5 + 6 % Ca – 400 mL.hL -1) diferiu significativamente da testemunha. Ja, com duas aplicacoes semanais, todos os tratamentos com fosfito diferiram da testemunha, sendo que, neste caso, o tratamento com fosfito B (40 % P2O5 + 20 % K2O 150 mL.hL-1), foi o que mais reduziu a doenca.

First report of an insect pest on Passiflora tenuifila Killip (Passifloraceae)

The genus Passiflora L. has more than 400 species, most of which occur natively in tropical and subtropical regions of South America. The fruit of Passiflora tenuifila Killip, one of the native species of Brazil, has great potential for commercial use by pharmaceutical and cosmetic industries, due to its high content of phenolic compounds, which are natural antioxidants. The study was conducted in two areas located in Tocantins and in the Federal District, Brazil. The presence of globose lumps and thickening of the stems on plants of Pa. tenuifila was observed on plants in these areas. Injured samples taken from both locations were analyzed and showed the presence of larvae and pupae of a Curculionidae, which completed their life cycle in the laboratory. The adults were identified as Philonis crucifer (Brèthes) (Coleoptera: Curculionidae). In Tocantins, 100% of the plants in the trial area were infested, while in the Federal District trial the incidence of infestation was 20.3%. This is the first report of an insect on Pa. tenuifila, indicating the need to develop management strategies for this pest to be applied in commercial crops of this Passiflora species.

Variability of Fusarium spp. isolates, causal agents of the soybean sudden death syndrome

Soybean (Glycine max L.) is the most widely cultivated crop in the world and an important commodity. Besides its main role in human nutrition, this grain is also used in animal feed and production of biofuels, among other purposes. Due to these factors, soybean became important in the global economy and is the most exported agricultural product from Brazil. Fungal diseases are among the limiting factors on soybean production; sudden death syndrome, caused by Fusarium spp., has been responsible for severe losses on this crop in Brazil. Four species of Fusarium can be considered causal pathogens: F. brasiliense, F. crassistipitatum, F. tucumaniae, and F. virguliforme. The Fusarium spp. isolates characterized in this work were collected in different soybean-producing regions in Brazil. The genetic variability of these isolates was determined through the random amplified polymorphic DNA (RAPD) technique. Disease severity was evaluated on moderately resistant and susceptible soybean cultivars in greenhouse trials. RAPD analysis demonstrated a great genetic diversity among the isolates and a clear tendency to split into two main species groups, F. tucumaniae and F. brasiliense, both prevalent in Brazil. The disease severity experiments, in which soybean plants were artificially inoculated, have shown that all isolates caused significant damage to the seedling root system. In fact, the genetic diversity of isolates does not correlate with disease severity, and also does not correlate with geographic distribution.

Caracterização de genótipos de soja na região dos Cerrados quanto à reação à podridão vermelha da raiz, causada pelos fungos Fusarium tucumaniae e Fusarium brasiliense

A podridao vermelha da raiz de soja vem crescendo em importância, a cada ano, no Brasil, com aumento substancial de participacao nas perdas de produtividade. Na regiao dos Cerrados, sao escassos os dados de campo sobre a reacao de cultivares a doenca. Assim, este trabalho teve como objetivo a caracterizacao, em campo, de uma serie de genotipos de soja, quanto a resistencia a podridao vermelha da raiz, em solos naturalmente infestados. Foram testados 71 genotipos de soja, sendo 16 do ciclo de maturacao precoce, 28 do ciclo de maturacao medio e 27 do ciclo de maturacao tardio, em quatro localidades, no entorno do Distrito Federal. O delineamento experimental foi o de blocos ao acaso, com quatro repeticoes. A caracterizacao foi realizada por meio dos niveis de incidencia e severidade dos sintomas foliares. Genotipos com altos niveis de resistencia a doenca foram observados nos tres grupos de maturacao, em cultivares e linhagens em fase final de melhoramento.

New Cercospora species on Jatropha curcas in central Brazil

A new cercosporoid hyphomycete, Cercospora jatrophiphila, herein described and molecularly characterized, was found in Planaltina, DF, Brazil on Jatropha curcas (Euphorbiaceae).