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Anthracnose, downy and powdery mildew are the principal fungal diseases of grapes in tropical and sub-tropical regions. The pesticide active ingredients that control downy and powdery mildew diseases provide some protection against anthracnose attack. The release of varieties with resistance alleles to downy and powdery mildew results in less pesticide use that can increase anthracnose attack. Thus, the present work aimed to evaluate anthracnose susceptibility of genotypes with resistance loci to downy and powdery mildew under Southern Brazilian conditions. Genotype susceptibility was tested, as well as the influence of the environment (location and crop season) on increased susceptibility to anthracnose infection. To accomplish the objective, a trifactorial design was established that included 20 genotypes, two locations, and two crop seasons. An- thracnose incidence and severity were evaluated under natural infection in the field. Temperature around 16 °C and relative humidity at 84 % increased susceptibility to anthracnose infection compared to temperature around 20 °C and relative humidity at 75 %. All tested genotypes with resistance alleles to downy and powdery mildew presented symptoms of anthracnose. 'Baron', 'Cabernet Cortis' and 'Calardis Blanc' showed the least susceptibility to anthracnose, whereas 'Aromera', 'Felicia', 'Gf.2004-043-0004' and 'Gf.2004-043-0021' were the most susceptible and bore symptoms of anthracnose. Other genotypes showed variable susceptibility during the evaluation period, depending on environmental conditions. Overall, all interactions among the three tested factors were highly significant. [ABSTRACT FROM AUTHOR]

The present study aimed to investigate plant defense related pathways during Plasmopara viticola infection in Vitis vinifera varieties. Plant material consisted of 'Chardonnay' (no Rpv), 'Regent' (Rpv3-1), 'Bronner' (Rpv3-3+Rpv10), 'Calardis Blanc' (Rpv3-1+Rpv3-2), and the breeding selection GF15 (Rpv1+Rpv3-1). Gene expression analysis was carried out for the varieties 'Regent', GF15, 'Bronner', and 'Chardonnay'. Hormonal quantification was performed for jasmonic acid (JA), salicylic acid (SA), abscisic acid (ABA), indole-3-acetic acid (IAA), and trans-zeatin-ribose (tZR). The samples were collected from plants cultivated in vitro inoculated with Plasmopara viticola sporangia, and collected at 0, 1-, 3-, 5-, and 7-days post inoculation (DPI) for gene expression; and 0, 3, 5, and 7 DPI for hormonal quantification. The results showed an interaction between genotype and time post inoculation in gene expression and hormonal pathways linked with pathogen recognition. Both jasmonate and salicylic acids were involved in the resistance response. The role of stilbenes acting against the pathogen at different times was also confirmed. Changes in the expression of genes linked to cell defense were observed in all evaluated genotypes; however, genotypes with R-loci responded more quickly than the variety without R-loci, activating mechanisms of cell death, resulting in symptoms of hypersensitivity. [ABSTRACT FROM AUTHOR]

Anthracnose is one of the most destructive grapevine diseases in warm and humid regions, but no efficient tools are available to quantify disease symptoms in different parts of the plant. Therefore, this study aimed to develop and validate standard area diagrams (SADs) to evaluate grapevine anthracnose on the fruit and shoot. For fruit SAD development, fruit clusters showing signs of anthracnose symptoms were sampled from five different white grape genotypes: Aromera, Bronner, GF24, Felicia and Helios. To develop the shoot SAD, plants from a population that segregated for anthracnose resistance were artificially inoculated. Fruits and shoots with characteristic symptoms were photographed, and a total of 30 and 31 images, respectively, were selected to develop each SAD. The SADs from fruit and shoots included severity ranging from 0.5 to 17.6% and from 0.8 to 45.9%, respectively. In order to verify the applicability of both SADs, random raters evaluated the images with and without the use of the SAD. Rater data were utilized for validation of both SADs using linear regression, absolute error and Lin's statistic, and repeatability was tested by inter-rate analysis. The developed SADs improved the accuracy and repeatability among the raters. In addition, diagrammatic scales for anthracnose severity on the fruit and shoot decreased absolute error and disease overestimation. In conclusion, the use of both sets of SADs improved grapevine anthracnose evaluation on the fruit and shoots. [ABSTRACT FROM AUTHOR]

The ascomycete Erysiphe necator causes powdery mildew disease of grapevine, a disastrous infection which is commonly defeated with multiple fungicide applications in viticulture. Breeding for natural resistance of quality grapes (Vitis vinifera) is thus a major aim of current efforts. The cultivar 'Regent' is resistant to powdery mildew due to an introgression from an American Vitis sp. resistance donor. To identify key regulatory elements in defense responses of 'Regent' we performed transcript analyses after challenging with E. necator inoculation in comparison with a susceptible grapevine. A set of genes selected from preliminary microarray hybridization results were investigated by RT-qPCR. The data indicate an important role of transcription factors MYB15, WRKY75, WRKY33, WRKY7, ethylene responsive transcription factors ERF2 and ERF5 as well as a CZF1/ZFAR transcripton factor in regulating the early defense when the fungus starts the interaction with its host by the formation of haustoria. [ABSTRACT FROM AUTHOR]