Daniel Rufino Amaral

Fosfito de potássio na indução de resistência a Verticillium dahliae Kleb., em mudas de cacaueiro (Theobroma cacao L.)

Ha varios relatos da utilizacao de fosfitos no controle de doencas de plantas, por meio de acao direta, antifungica e indireta por inducao de resistencia. Essa atuacao como indutor e questionada, nao sendo encontradas, em muitos desses trabalhos, evidencias de respostas de defesa ativadas pelos sais de fosfito. Com o presente trabalho, objetivou-se estudar o efeito de doses (0,62; 1,25; 2,5 e 5 mL.L-1 de agua) de fosfito de potassio na inducao de resistencia em mudas de cacaueiro a V. dahliae, alem de investigar os possiveis mecanismos envolvidos na resposta de defesa. Foram realizados experimentos no Laboratorio de Fisiologia do Parasitismo e casa-de-vegetacao do Departamento de Fitopatologia UFLA. A aplicacao foliar do fosfito foi realizada 7 dias antes das inoculacoes e as avaliacoes de severidade foram realizadas aos 20, 30, 40, 50 e 60 dias apos a inoculacao. Foi realizado tambem um experimento para verificar o efeito toxico direto e outro para avaliar a atividade das enzimas peroxidases e polifenoloxidases e a concentracao de lignina. O tratamento com o fosfito de potassio (1,25 mL.L-1 de agua) proporcionou 10% de reducao na area abaixo da curva de progresso da severidade da murcha-de-Verticillium (AACPD), 60 dias apos aplicacao foliar, nao diferindo de nenhuma das doses, nem da testemunha. Todas as doses utilizadas apresentaram efeito fungitoxico, inibindo a germinacao de V. dahliae. A aplicacao do fosfito de potassio (1,25 mL.L-1 de agua) nao induziu aumento na atividade das enzimas peroxidases e polifenoloxidases em relacao a testemunha. Plantas tratadas com esse produto apresentaram um pequeno incremento na concentracao de lignina, nao apresentando diferenca significativa da testemunha absoluta.

Ativação de defesa em cacaueiro contra a murcha-de-verticílio por extratos naturais e acibenzolar-S-metil

The objective of this work was to assess the potential of fungal and plant extracts on the reduction of Verticillium wilt of cocoa, the activities of the enzymes peroxidase and polyphenoloxidase, as well as the lignin content. Seedlings of cocoa were sprayed with the mycelial filtrate of Rhizopus sp. (FMR), chitosan from Rhizopus sp. (QMR) and Trichoderma sp. (QMT), extracts of fresh and dry passion fruit peel, methanolic extract from dry passion fruit peel (MMS) and acibenzolar-S-methyl (ASM - 0.2 mg mL-1) and, inoculed with Verticillium dahliae, seven days later. ASM reduced the cocoa Verticillium wilt in 38.0%. The extract FMR, QMT, MMS and QMR presented as well reductions of 22.8, 20.1, 19.2 and 15.7%, respectively, in comparison with the control. Plants sprayed with ASM or FMR followed by inoculation presented increase of peroxidase activity at the 8th day after spraying, compared to the respective controls, with peak at the 18th day after spraying. ASM and FMR increased polyphenoloxidase activity at the 4th day after spraying. Higher lignin concentrations were obtained in plants treated with FMR and FMR following by inoculation. FMR may constitute a potential resistance inducer for the management of the Verticillium wilt of cocoa.

Purification of two substances from bulbs of onion ( Allium cepa L.) with nematicidal activity against Meloidogyne exigua Goeldi

To contribute to the development of a new method for Meloidogyne exigua Goeldi control, a nematode widely disseminated through Brazilian coffee fields, this work aimed to purify the nematicidal substances produced by onion (Allium cepa L.). Thus, the methanolic extract of onion bulbs was concentrated under reduced pressure and submitted to a purification process guided by in vitro assays with second-stage juveniles (J2) of M. exigua. After several steps, two nematicidal substances that seemed to be interconverting when in solution were isolated. When exposed to 500 ppm aqueous solutions of substances 1 and 2, 55 and 38% of the J2, respectively, were dead after 24 h. Very preliminary nuclear magnetic resonance spectroscopy studies suggested that these substances correspond to a pair of carbohydrates.

Silicato de potássio na proteção do cafeeiro contra Cercospora coffeicola

The objective of this work was to study the effect of potassium silicate doses in greenhouse and field conditions, for the protection of coffee seedlings against Cercospora coffeicola, and to evaluate the effect of potassium silicate on the activities of peroxidase, polyphenoloxidase and on the content of lignin, carotenoids and chlorophyll a and b. Potassium silicate was tested in greenhouse at doses 0.75, 1.5, 3.0 and 6.0 mL/L of water. In these conditions, the dose of 1.5 mL/L provided greater protection against brown eye spot on coffee seedlings, this dose having been chosen for the field trial and biochemical determinations. In the field, potassium silicate provided protection of 31% in relation to the control, while the fungicide mixture of the epoxiconazole + pyraclostrobin provided 61% of protection. Part of this protection conferred by potassium silicate can be explained by the increase in the activities of peroxidases, polifenoloxidases and the higher accumulation of lignin.

Effect of plant and fungous metabolites on Meloidogyne exigua

As nematodes cause great damage to Brazilian coffee production, effective methods to control these parasites are necessary. In a previous work Allium cepa L., Cajanus cajan (L.) Mill., Crotalaria juncea L., Ficus elastica Roxb., Ruta graveolens L., Stylosanthes guianensis Aubl., Leucaena leucocephala (Lam.) Dewit., Brachiaria decumbens Stapf., Catharanthus roseus G. Don, Tagetes minuta L., Ricinus communis L. and Coffea arabica L. produced active substances against Meloidogyne exigua Goeldi, a nematode widely disseminated through Brazilian coffee fields. Thus, aqueous extracts of such plants, collected in a different season from that of the previous work, as well as crude metabolites produced in liquid medium by Fusarium moniliforme Shelden and Cylindrocarpon magnusianum (Sacc.) Woll., were submitted to in vitro assays with M. exigua second-stage juveniles (J2). All plants and fungi produced active substances against J2. Therefore, their metabolites were applied to six-month-old coffee plants inoculated with M. exigua. After 90 days in a greenhouse, those samples obtained from A. cepa, L. leucocephala, R. graveolens and F. moniliforme inhibited the production of galls and eggs by M. exigua, demonstrating potential to control such parasite.

Efeito de extratos vegetais de plantas do Cerrado para controle de pinta-preta em tomateiro

A “Mancha de Alternaria” causada pelo fungo Alternaria solani é uma das principais e mais frequentes doenças que incidem na cultura do tomate. Manifesta-se nas hastes, caule e principalmente nas folhas, e em alta severidade. Causa desfolha e também pode provocar infecções nos frutos, tornando-os impróprios para comercialização. Para controle da doença, os defensivos sintéticos ainda são os mais utilizados. Visando a diminuição da toxicidade ao meio ambiente e à saúde humana, surge a busca pela utilização de produtos alternativos para o controle de doenças. O objetivo do trabalho foi avaliar o efeito de extratos vegetais para o controle de Alternaria solani na cultura do tomateiro: in vivo e in vitro. O experimento foi conduzido em duas etapas: 1in vivo (em casa de vegetação em sistema hidropônico) e 2in vitro (em laboratório). Os Kobayashi, B.F.; Amaral, D.R. Efeito de extratos vegetais de plantas do Cerrado para controle de pinta-preta em tomateiro. Summa Phytopathologica, v.44, n.2, p.189-192, 2018.