Blast, caused by Pyricularia grisea, is one of the most important diseases of wheat. The effects of silicon (Si) on this wheat disease were studied. Plants of wheat cultivars Aliança and BH-1146 were grown in plastic pots containing Si-deficient soil amended with either calcium silicate (+Si) or calcium carbonate (−Si). The content of Si in leaf tissue was significantly increased by 14.8% for the +Si treatment. There were no significant differences between Si treatments for calcium content, so variations in Si only accounted for the observed differences in the level of blast resistance. The incubation period was significantly increased, on average, by 28.2% for the +Si treatment. The area under blast progress curve and the number of lesions per cm 2 of leaf area significantly decreased by 31 and 45%, respectively, for the +Si treatment. There was no significant effect of Si on final disease severity. The concentration of total soluble phenolics observed in both cultivars supplied with Si did not apparently play any role in the increased blast resistance. The highest content of lignin-thioglycolic acid derivatives was found in plants from both cultivars with Si during the time period evaluated. Chitinase activity was high at the intermediate stages of fungal infection in both cultivars supplied with Si. Peroxidase activity was found to be high at the late stage of fungal infection for both cultivars supplied with Si and seemed to play a role in enhancing wheat blast resistance. Polyphenoloxidase activity also apparently had no effect on resistance for any of the treatments. These overall results revealed the potential of Si to decrease wheat susceptibility to blast.

G Gisele isele P Pereira ereira D Domiciano omiciano, , F Fabrıcio abrício A Avila vila R Rodrigues odrigues, , F Francisco rancisco X Xavier avier R Ribeiro ibeiro V Vale ale, , M Maria aria S Santina antina X Xavier avier F Filha ilha, , W Wiler iler R Ribas ibas M Moreira oreira, , C Camila amila C Cristina ristina L Lage age A Abstract Spot blotch, caused by the fungus Bipolaris sorokiniana, is one of the most important diseases on wheat. The effects of silicon (Si) on this wheat disease were studied. Plants of wheat cultivars BR-18 and BRS-208 were grown in plastic pots containing Si-deficient soil amended with either calcium silicate (+Si) or calcium carbonate ()Si). The content of Si in leaf tissue was significantly increased by 90.5% for the +Si treatment. There was no significant difference between Si treatments for calcium content, so variations in Si accounted for differences in the level of resistance to spot blotch. The incubation period was significantly increased by 40% for the +Si treatment. The area under spot blotch progress curve, number of lesions per cm 2 of leaf area, and real disease severity significantly decreased by 62, 36 and 43.5% in +Si treatment. There was no significant effect of Si on lesion size. The role played by total soluble phenolics in the increased resistance to spot blotch of plants from both cultivars supplied with Si was not clear. Plants from cultivar BR-18 supplied with Si showed the highest values for concentration of lignin-thioglycolic acid derivatives during the most advanced stages of fungus infection. Chitinase activity was high at the most advanced stages of fungus infection on leaves from both cultivars supplied with Si and may have had an effect on fungus growth based on the reduction of the components of resistance evaluated. Peroxidase activity was found to be high only at 96 h after inoculation of both cultivars supplied with Si. Polyphenoloxidase activity had no apparent effect on resistance regardless of Si treatments. Results revealed that supplying Si to wheat plants can increase resistance against spot blotch.

A cercosporiose do pimentão, causada pelo fungo Cercospora capsici, é uma importante doença que ocorre em condições tropicais. Devido à inexistência de métodos padronizados para quantificação desta doença em campo, uma escala diagramática com os níveis de 1,5; 3,5; 8,0; 16,5; 31,0 e 50% de área foliar lesionada foi elaborada e testada para a acurácia, a precisão e a reprodutibilidade das estimativas de severidade da cercosporiose do pimentão, sem e com a sua utilização. Na validação da escala diagramática, 50 folhas com diferentes níveis de severidade da doença, mensurados previamente com o programa AutoCAD®, foram avaliadas por 13 avaliadores, sem e com a utilização da escala diagramática. Foram realizadas duas avaliações com utilização da escala, com intervalo de sete dias, onde seqüências diferentes das mesmas folhas foram estimadas visualmente pelos mesmos avaliadores. A acurácia e a precisão de cada avaliador foi determinada por regressão linear simples, entre a severidade real e a estimada. Sem a escala, oito avaliadores superestimaram significativamente a severidade da doença. Com a escala, os avaliadores obtiveram melhores níveis de acurácia e precisão, embora quatro tendessem a superestimar a severidade, com os erros absolutos concentrando-se abaixo de 10%. Os avaliadores apresentaram boa repetibilidade e elevada reprodutibilidade das estimativas com a utilização da escala, o mesmo não sendo verificado sem a utilização desta. A escala diagramática proposta mostrou-se adequada para avaliação da severidade da cercosporiose do pimentão.

RESUMOEste trabalho teve como objetivo avaliar o efeito do silício (Si) no progresso da mancha marrom, causada por Bipolaris sorokiniana, na folha bandeira de plantas de trigo. Plantas das cultivares de trigo BR-18 e BRS-208 foram crescidas em vasos contendo 0 e 0,30 g Si/kg de solo e inoculadas aos 45 dias após emergência. Avaliou-se a severidade da mancha marrom às 48, 72 e 96 horas após a inoculação das plantas e os dados obtidos foram utilizados para calcular a área abaixo da curva do progresso da mancha marrom (AACPMM). Determinouse também a concentração foliar de Si e cálcio. A concentração de Si na folha bandeira das plantas supridas com Si foi 90,5% superior do que foi obtido para as plantas não supridas com esse elemento. A severidade da mancha marrom na folha bandeira foi significativamente menor nas plantas supridas com Si em todas as épocas de avaliação. Houve redução de 58,5% na AACPMM na folha bandeira das plantas supridas com Si. Não houve diferença significativa entre os tratamentos -Si e +Si para a concentração foliar de cálcio. Não houve diferença entre as duas cultivares para a concentração foliar de Si e a AACPMM, mas a concentração foliar de cálcio foi maior para a cultivar BR-18 do que para a cultivar BRS-208. Houve correlação negativa (r = -0,59) entre a concentração foliar de Si e a AACPMM. Com os resultados obtidos nesse estudo, observou-se um efeito positivo do Si em aumentar a resistência da folha bandeira de plantas de trigo à infecção por B. sorokiniana e ao mesmo tempo garantir uma maior produção de grãos dada à importância fisiológica dessa folha, em particular. Palavras-chave: Bipolaris sorokiniana, mancha foliar, nutrição mineral, silicato. ABSTRACT Silicon on the progress of spot blotch on wheat leaf flagThis study aimed to determine the effect of silicon (Si) on the progress of spot blotch, caused by Bipolaris sorokiniana, on wheat leaf flag. Wheat plants of cultivars BR-18 and BRS-208 were grown in pots containing 0 and 0.30 g Si/kg of soil and inoculated at 45 days after emergence. Spot blotch severity was evaluated at 48, 72, and 96 hours after inoculation and data were used to calculate the area under spot blotch progress curve (AUSBPC). The Si and calcium concentrations on leaf tissue were also determined. The Si concentration on leaf flag of plants supplied with Si was 90.5% higher compared to plants non-supplied with this element. Spot blotch severity was significantly lower on leaf flags of plants supplied with Si at all evaluation times. There was a reduction of 58.5% in AUSBPC on leaf flag of plants supplied with Si. There was no significant difference between -Si and +Si treatments for calcium concentration on leaf tissue. There was no significant difference between the two cultivars for Si concentration on leaf tissue and AUSBPC, but calcium concentration on leaf tissue was higher for cultivar BR-18 than for cultivar BRS-208. The correlation between Si concentration on leaf tissue and AUSBPC was negative (r = -0.59). The results of this study showed a positive effec...

Brassicaceae family comprises plant species that are very important as vegetable crops, such as the species complex Brassica oleracea and Brassica rapa. Alternaria brassicicola and A. brassicae are among the most important pathogens of Brassicaceae causing Alternaria leaf spot disease. The occurrence and prevalence of Alternaria species causing leaf spots in brassica crops in Pernambuco was acessed, as well as the existence of a possible preference by vegetable host for these pathogens. Twenty-eight fields were surveyed in the Agreste region of Pernambuco state, in the 2005 and 2006 growing seasons. In each year, 10 Chinese cabbage, six cabbage, six cauliflower and six broccoli fields were visited. In each field, 50 leaves showing at least five lesions were randomly collected. Species identification was performed taking into account morphology of the conidia that was compared with literature data. Among the two Alternaria species found, A. brassicae was found in all Chinese cabbage fields while A. brassicicola was found in all fields of cabbage, cauliflower and broccoli. Overall, A. brassicicola was more prevalent than A. brassicae. In Chinese cabbage there was predominance of A. brassicae, with mean prevalence of 91. 0% and 96.5% in 2005 and 2006. On the other hand, in broccoli and cabbage there was high predominance of A. brassicicola, with mean prevalence between 95.1% and 99.8%. In cauliflower, although the prevalence has been of A. brassicicola, high frequency of A. brassicae was noted. The frequency of co-occurrence of both Alternaria species was very low. The results of this study reinforce the hypothesis of existence of host preference within species of Alternaria that cause leaf spots in brassica crops, especially when Chinese cabbage, broccoli and cabbage are considered. This information is critical to developing strategies for managing Alternaria leaf spots in Brassicaceae species.