Sônia Maria de Lima Salgado

Espécies Ativas de Oxigênio na Resposta de Defesa de Plantas a Patógenos

Oxidative burst is a very quick plant defense response after pathogen recognition, leading to hypersensitive reaction (HR). This response is due to generation of reactive oxygen species (ROS), such as H2O2 , O2-, and OH-. Several roles in plant defense have been proposed for ROS. Hidrogen peroxide (H2O2), apart from being directly toxic to pathogens, is also involved in cell wall strengthening, since it is necessary for lignin biosynthesis. Hidrogen peroxide acts as a second messenger, being responsible for the activation of the benzoic acid 2-hydrolase, enzyme responsible for benzoic acid conversion to salycilic acid. Oxidative burst is not only confined to the macroscopic site of HR, since secondary bursts can occur in distant tissues, causing micro-HRs and leading to systemic acquired resistance (SAR), which is mediated by salycilic acid as a signal. Therefore, occurrence of both HR and SAR are dependent on signaling cascades derived from oxidative burst, as an early event in plant response against pathogen invasion.

Effect of extracts from citric biomass, rusted coffee leaves and coffee berry husks on Phoma costarricencis of coffee plants

Phoma leaf spot, caused by Phoma costarricensis poses a serious threat to coffee (Coffea arabica) production, especially in the highlands of the state of Minas Gerais, Brazil. Extracts of citric biomass, coffee berry husks and coffee leaves severely affected by rust caused by Hemileia vastatrix, were evaluated against P. costarricensis. In an in vitro assay, aqueous extracts of rusted leaves and berry husks plus the commercial extracts based on citric biomass named Ecolife® and Agromil® were tested at various dilutions on the mycelial growth inhibition of P. costarricensis. In vivo, coffee seedlings maintained in glasshouse, were sprayed with these extracts seven days before inoculation of P. costarricensis. Only extracts from citric biomass had inhibitory effects on the fungus. In vivo, Ecolife® (5 ml/l), Agromil® (5 g/l) and the aqueous extract of rusted coffee leaves (dilution 1:6) reduced Phoma leaf spot. Both, Ecolife® and the extract of rusted coffee leaves were significantly more effective in reducing the area under the lesion progress curve when applied at lower doses, indicating a possible effect on the induction of resistance.

Eclosão e mortalidade de Meloidogyne exigua em extratos e em produtos naturais

The hatching and mortality of Meloidogyne exigua second-stage juveniles (J2) were evaluated after 24 h in aqueous extracts of Bixa orellana, Cinnamomum zeylanicum, Petroselium crispum, Piper nigrum, Syzygium aromaticum, Zingiber officinale whey of milk, hidroponic solution, sodium chloride (NaCl) and saccharose aqueous solution, yeast and probiotic (Controlmix®) solutions. The whey of milk, C. zeylanicum, yeast and sodium chloride (NaCl) solutions caused 100% mortality of J2 (P<0,05). Extracts of S. aromaticum and Controlmix® probiotic caused more than 50% mortality of J2 (P<0,05). Hatching was evaluated by placing eggs of M. exigua in those different extracts and products for 16 days. The area under the curve of hatching progress, evaluated at 48 h intervals, showed that all extracts and products caused inhibition as compared to water (P<0,01), except for saccharose and hidroponic solutions. Whey of milk, probiotic, C. zeylanicum and S. aromaticum accounted for greater inhibition, among all the tested extracts and products (P<0,01). As shown, whey of milk and C. zeylanicum extract also caused 100% mortality of J2.

Efeito de nutrientes combinados com indutores de resistência na proteção contra a vassoura-de-bruxa no cacaueiro

Na busca por novos indutores de resistencia contra a vassoura-de-bruxa no cacaueiro avaliou-se o efeito de varios nutrientes, acibenzolar-S-metil (ASM) e a combinacao desses nutrientes com ASM. Os produtos e as misturas foram pulverizados 30 dias antes da inoculacao nas mudas do clone SIC-23. Foram utilizados os produtos comerciais Supa-potassio®(silicato de potassio), Hortifos® PK (fosfito de potassio) e Broadacre® Mn (sulfato de manganes), testados nas dosagens 2,5 mL; 5,0 mL; 10 mL/L de agua, isoladamente ou combinados com ASM (0,2g/L). O experimento foi conduzido no delineamento de blocos ao acaso, no esquema fatorial, com quatro repeticoes de doze plantas/parcela. A incidencia da doenca foi avaliada 60 dias apos a inoculacao. Somente o ASM promoveu controle significativo da vassoura-de-bruxa. Os nutrientes aplicados isoladamente nao apresentaram efeito na severidade da doenca. Por outro lado, o efeito protetor do ASM desapareceu quando este foi misturado ao Supa-potassio®, na dose de 5 ou 10 mL/L.