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RESUMO A mancha parda (Bipolaris oryzae) é uma das mais importantes doenças foliares do arroz. Nesse estudo, alguns componentes de resistência e algumas variáveis bioquímicas amplamente conhecidas como mecanismos de defesa de plantas contra patógenos foram avaliadas em genótipos de arroz classificados, segundo SOSBAI, como moderadamente suscetível, moderadamente resistente e resistente, buscando entender epidemiológica e bioquimicamente como ocorre a variação na resistência dos diferentes genótipos. Sete cultivares de arroz foram inoculadas com 1 × 104 conídios mL-1 de B. oryzae nas quais foram avaliados os seguintes componentes de resistência: eficiência relativa de infecção (ERI); número final de lesão (NFL); comprimento final de lesão (CFL); taxa de expansão de lesão (r) e a severidade final (SF). Além disso, também foram avaliadas variáveis bioquímicas, como atividade das enzimas superóxido dismutase (SOD), catalase (CAT), peroxidase (POX), quitinase (QUI) e fenilalanina amônia-liase (FAL). Os resultados demonstram diferenças significativas entre as cultivares para os componentes de resistência, bem como nas atividades enzimáticas. Todos os genótipos testados foram suscetíveis a B. oryzae, variando quanto ao nível de resistência parcial a mancha parda. As variáveis de r e CFL apresentaram maior correlação com a SF indicando serem as variáveis que mais influenciam a intensidade final da doença em cada genótipo. Os genótipos com maior resistência parcial a mancha parda apresentaram alterações caracterizadas como antecipação, potencialização e prorrogação da atividade das enzimas QUI, FAL, CAT e POX.

Tan spot caused by Pyrenophora tritici‐repentis is a disease present in all wheat‐producing countries and silicon (Si) treatment of wheat plants has been shown to increase plant resistance to tan spot. In this study, the effect of phenylpropanoid metabolism on resistance to tan spot was evaluated and some phenolic compounds that accumulated in response to P. tritici‐repentis attack were identified. Furthermore, the effect of Si on phenylalanine ammonia‐lyase (PAL) activity and phenolic compound accumulation were determined in situ. Antifungal activity of differentially accumulated phenolic compounds was also evaluated in in vitro tests. Results showed that the increase in concentration of phenolic compounds was greatest at the onset of infection, and that some compounds showed fungitoxic effects including fungal tip swelling, granulation of germ tube and hyphae, and hyphal hyperbranching. Silicon‐induced reduction in both lesion size and tan spot disease progression were associated with activation of phenylpropanoid metabolism. PAL activity and accumulation of antifungal phenolic compounds were greater in pathogen‐inoculated plants supplied with Si. In these plants, fluorescence indicative of accumulation of phenolic compounds occurred early in epidermal cells and its intensity increased during the evaluation period, showing higher numbers of fluorescent cells around infected cells. Thus, the combined responses of cell fluorescence at sites of infection, increased PAL activity and accumulation of phenols indicate that Si strengthened wheat defence responses to infection by P. tritici‐repentis, reducing the severity of tan spot.

Tan spot caused by Pyrenophora tritici-repentis is the main foliar diseases of wheat in Brazil. The effect of silicon (Si) on the components of resistance of a susceptible (Fundacep Horizonte) and a moderately resistant (Quartzo) wheat cultivar was studied in a controlled environment. Silicon was supplied as calcium silicate in the soil 30 days before sowing. At the booting stage, a conidial suspension of the fungus was sprayed onto the flag leaves of potted plants, which were incubated under moist conditions for 48 h. Afterwards, inoculated leaves were assessed for: incubation period (IP), infection efficiency (IE), area under lesion size curve (AULSC), lesion size (LS), severity (SEV) and area under severity curve (AUSC). Foliar Si concentrations were quantified at the end of the evaluations. Si supply to plants increased leaf Si concentration in 233% for Fundacep Horizonte (from 4.8 to 16.0 g kg−1 of dry matter) and 211% for Quartzo (from 5.3 to 16.5 g kg−1 of dry matter). In the Si + treatments, IP was longer by 24 and 17 h, IE declined by 53.5 and 65.5%, LS (at 264 h after inoculation) by 4.6 mm (from 9.5 to 4.9 mm) and 5.9 mm (from 8.2 to 2.3 mm), and SEV by 53% (from 54.4 to 18.8%) and 88% (from 47.7 to 5.5%) respectively, for the Fundacep Horizonte and Quartzo cultivars. The Si x cultivar interaction was not significant for AULSC and AUSC, and these variables were reduced by 55.8 and 80.8%, respectively, in plants supplied with Si. In conclusion, Si enhanced the resistance of wheat plants to tan spot development by affecting several resistance components, regardless of the resistance level of the cultivar. However, the greatest reduction in tan spot development by Si supply was observed when using a moderately resistant cultivar.

The silicon (Si) reduced tan spot ( Pyrenophora tritici-repentis ) severity up to 40%, through both biochemical defense mechanisms and histo-cytological defense responses. The activities of enzymes involved in plant defense system such as superoxide dismutase, peroxidase and chitinase showed greater activity in inoculated plants supplied with Si. Histo-cytological analysis indicated that Si potentiated the accumulation of hydrogen peroxide in the beginning of infection process. Together, these defense mechanisms resulted in the reduction of cell death at the infection sites in plants supplied with Si, which in turn showed lower disease severity. Si appears to be a promising alternative control measure for use in integrated management of tan spot.

Rice plants cultivated under 700 ppm atmospheric CO2 concentration presented a reduction in the progress and severity of the brown spot disease (Bipolaris oryzae), through the enhancement of biochemical defense mechanisms. Plants exposed to 700 ppm of CO2 had higher activity of the enzymes superoxide dismutase, catalase, ascorbate peroxidase, peroxidase, polyphenoloxidase and chitinase, and increased phenolic compounds and lignin concentration, independent of the rice cultivar. Therefore, the lower severity values of the disease were related to changes in the development of the lesions as a result of the defense responses, which were stimulated in the rice plants by the increase of CO2 concentration.

Blueberry (Vaccinium corymbosum) is a plant native to North America, and it was introduced in Brazil in the 1980s in the State of Rio Grande do Sul. Leaves of blueberry showing leaf rust symptoms were observed on a commercial blueberry field, in the municipality of Jaguarao, Rio Grande do Sul, Brazil (32°39′80.93″S, 53°23′12.44″W) ranging from January to February 2017. The disease started as small reddish-brown leaf spots, epiphyllous, gregarious, with hypophyllous yellowish pustules. With disease progression, the leaf spots enlarged, becoming vein delimited, with a reddish-purple halo. At later stages, lesions coalesced, spreading all over the plant, causing severe precocious defoliation (especially on cultivars Jewel and Snowchaser). Pustules were produced abaxially, with abundant sporulation. Urediniospores were ovoid, yellowish-orange, echinulate, 15 to 24 × 10 to 18 μm (n = 53). Telia were not found. Genomic DNA was extracted from urediniospores and used for amplification of the internal transcribed spacer regions and intervening 5.8S nrRNA gene (ITS), using the primers ITS1-F_KYO2 and ITS4. The resulting fragment (465 bp) was sequenced and deposited in GenBank (MH029898). A BLAST search revealed 99% identity with Thekopsora minima (GenBank accession no. HQ661383). Aiming at verifying the correct diagnosis, a Bayesian phylogenetic inference was performed and showed that the Brazilian sample clustered with five other strains from different countries. To fulfill Koch’s postulates, suspension of urediniospores (1 × 10³ spores/ml) was sprayed on leaves of healthy plants. Healthy plants sprayed with water served as a control. After inoculation, plants were kept inside a mist chamber at 95 to 100% relative humidity, temperature at 25°C, and 12-h photoperiod. Symptoms as small, reddish, irregular lesions appeared 7 days after inoculation, and pustules with uredospores and necrosis were observed at 21 days after inoculation. No symptoms occurred on control plants. To the best of our knowledge, this is the first report of blueberry leaf rust caused by T. minima on highbush blueberry in South America. The fungus has been reported on highbush blueberry in China, Japan, Mexico, South Africa, and the United States (Kobayashi 2007; Mostert et al. 2010; Rebollar-Alviter et al. 2011; Shands et al. 2018; Zheng et al. 2017). Although the yield losses were not measured in the present study, the severity observed at the field suggested that the intense and early defoliation significantly reduced the yield potential of the crop. Further studies are needed to properly evaluate the risk of blueberry leaf rust in commercial fields in Southern Brazil.

Physalis (Physalis peruviana L., Solanaceae) is a perennial bushy plant native to the Andes and grown throughout the world predominantly in Colombia and South Africa. The fruit have high nutritional and functional potential (Puente et al. 2011). Physalis fruit rot was observed in summer of 2013 on plants under field conditions in Capao do Leao, Rio Grande do Sul State, Brazil (31°48'26.6"S 52°30'31.0"W). The first symptoms observed on the fruit included water-soaked lesions followed by development of black dots (pycnidia), which over time covered the entire fruit surface causing a blackened appearance. Black pycnidia measuring 94.58 – 188.44 × 150.07 – 214.64 μm produced hyaline spores of both alpha conidia hyaline, cylindrical, rounded at the ends, containing one septum, and beta conidia, flexuous to hamate, hyaline, measuring 1.8 – 3.17 × 6.7 – 10.46 μm and 0.73 – 1.43 × 13.7 – 18.7 μm, respectively. On potato dextrose agar (PDA) incubated in photoperiod of 12 hours at 25±1°C colonies were grayish, cove...