Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, is one of the most important diseases on soybean. At the moment, ASR is managed mainly with fungicides due to the absence of commercial cultivars with resistance to this disease. This study evaluated the effects of acibenzolar-Smethyl (ASM), jasmonic acid (JA), potassium silicate (PS) and calcium silicate (CS) on soybean resistance to ASR. The ASM, JA and PS were sprayed to leaves 24 h prior to inoculation with P. pachyrhizi. The CS was amended to the soil. The incubation period (time from the inoculation until symptoms development) was longer for plants growing in soil amended with CS or sprayed with ASM in comparison with plants sprayed with water (control). Plants sprayed with ASM had longer latent period (time from the inoculation until signs appearance) in comparison with the control plants. Plants sprayed with PS showed fewer uredia per cm² of leaf in relation to the control plants. The ASM and PS were the most effective treatments in reducing the ASR symptoms in contrast to the JA and CS treatments. The JA served as an inducer of susceptibility to ASR.

RESUMOEste trabalho objetivou avaliar o potencial do ácido jasmônico (AJ), quitosana desacetilada (QUI), silicato de potássio (SP), acibenzolar-S-metil (ASM), Ethefon (ET) e fosfito de potássio (FP) na redução da severidade da brusone do trigo. O fungicida tebuconazole (TE) e a água destilada (AD) foram utilizados como tratamentos controle. Plantas das cultivares BR 23, BH 1146 e BRS 208 foram pulverizadas com AJ, QUI, SP, ASM, ET, FP, TE e AD 24 h antes da inoculação com Pyricularia grisea. Avaliou-se o período de incubação (PI), a severidade e o efeito fungitóxico dos produtos no crescimento micelial de P. grisea. Para o PI, não houve diferença significativa entre os fatores cultivares e tratamentos, mas para a severidade houve interação entre esses fatores. A menor severidade da brusone para a cultivar BR 23 ocorreu com a pulverização do TE, FP e ET, os quais não diferiram estatisticamente. Para BH 1146, os tratamentos AD, QUI e ASM não diferiram estatisticamente, mas diferiram dos demais tratamentos que apresentaram menor severidade. A aplicação do TE e do FP garantiram uma menor severidade da brusone para a cultivar BRS 208. O FP propiciou uma maior redução da severidade da brusone nos dois cultivares. Os menores valores para o crescimento micelial de P. grisea ocorreram com a adição de TE e SP no meio de cultura. Os resultados desse estudo apontam para o efeito promissor do FP e do ET na potencialização da resistência do trigo à brusone, a qual mostrou ser dependente do nível de resistência basal da cultivar de trigo. Palavras-chave: Pyricularia grisea, Triticum aestivum, indução de resistência. ABSTRACT Foliar application of products on the reduction of blast severity on wheatThis study aimed to determine the potencial of jasmonic acid (JA), deacetylated chitosan (DC), potassium silicate (PS), Acibenzolar-S-Methyl (ASM), ethephon (ET), and potassium phosphate (PP) on the reduction of blast severity on wheat. The fungicide tebuconazole (TE) and distilled water (DA) were used as control treatments. Plants from the cultivars BR 23, BH 1146, and BRS 208 were sprayed with JA, DC, PS, ASM, ET, PP, TE, and DA 24 h before inoculation with Pyricularia grisea. The incubation period (IP), blast severity, and the effect of the treatments on mycelial growth of P. grisea were evaluated. For the IP, there was no significant difference among cultivars and also for the treatments, but there was interaction between these factors for severity. The lowest severity for BR 23 cultivar occurred with the spray of TE, PP, and ET, which were not significantly different among them. For BH 1146 cultivar, the treatments DA, DC, and ASM were not significantly different among them, but differed significantly from the other treatments to which were obtained the lowest severity. The spray of TE and PP gave the best reduction on severity for BRS 208 cultivar. The PP was the treatment that most reduced severity on the three cultivars tested. The lowest values for mycelial growth of P. grisea occurred upon the addition of TE and PS to the c...

The control of Asian Soybean Rust (ASR), caused by Phakopsora pachyrhizi, has been difficult due to the aggressiveness of the pathogen and the lack of resistant cultivars. The objective of this study was to evaluate the effects of spray of potassium silicate (PS) and soil amendment with calcium silicate (CS) on soybean resistance to ASR. The PS solution was sprayed to leaves 24 hours prior to fungal inoculation while CS was amended to the soil at thirty-five days before sowing. The infection process of P. pachyrhizi was investigated by scanning electron microscopy. The uredia on leaves of plants sprayed with PS were smaller and more compact than those observed on the leaves of plants grown in soil amended with CS or in soil non-amended with CS (control treatment). On leaves of plants from the control treatment, uredia produced many urediniospores at 9 days after inoculation, and the ASR severity was 15, 8 and 9%, respectively, for plants from control, PS and CS treatments. In conclusion, the spray of PS contributed to reduce the number of uredia per cm² of leaf area and both PS spray and CS resulted in lower ASR symptoms.Key words: Glycine max, biotrophic fungi, scanning electron microscopy.Silicato de potássio e silicato de cálcio na resistência da soja à infecção por Phakopsora pachyrhizi Resumo O controle da Ferrugem Asiática da Soja (FAS), causado pelo fungo Phakopsora pachyrhizi, tem sido difícil devido à agressividade do patógeno e pela falta de cultivares resistentes. O objetivo deste estudo foi avaliar os efeitos da pulverização com silicato de potássio (SP) e do suprimento de Si via silicato de cálcio (SC) no solo sobre a resistência da soja à FAS. A solução de PS foi pulverizada nas folhas 24 horas antes da inoculação, enquanto que o SC foi aplicado no solo 35 dias antes da semeadura. O processo infeccioso de P. pachyrhizi foi investigado por microscopia eletrônica de varredura. As urédias nas folhas das plantas pulverizadas com SP foram menores e mais compactas do que as observadas nas folhas das plantas cultivadas em solo contendo SC ou em solo não contendo SC (tratamento controle). Nas folhas das plantas do tratamento controle, as urédias produziram muitos uredosporos aos nove dias após inoculação e a severidade da FAS foi de 15, 8 e 9% para as plantas dos tratamentos controle, SP e SC, respectivamente. Em conclusão, a pulverização de SP contribuiu para reduzir o número de urédias cm -2 da área foliar e ambas, a pulverização com SP e a aplicação do SC, resultaram na redução dos sintomas da FAS.Palavras-chave: Glycine max, fungo biotrófico, microscopia eletrônica de varredura.