An apparent decline of fungicide performance for the control of soybean rust in Brazil has been reported but the rate at which it has occurred has not been formally quantified. Control efficacy and yield response to three fungicides applied as single active ingredients (a.i.)—azoxystrobin (AZOX), cyproconazole (CYPR), and tebuconazole (TEBU)—and four applied as mixtures—AZOX+CYPR, picoxystrobin + CYPR, pyraclostrobin + epoxiconazole, and trifloxystrobin + prothioconazole (TRIF+PROT)—were summarized using network meta-analytic models fitted to mean severity and yield data from 250 trials (10-year period). The effect of year was tested on both variables in a meta-regression model. Overall control efficacy ranged from 56 to 84%; the three single-a.i. fungicides performed the poorest (56 to 62%). Yield increase for single-a.i. fungicides was as low as 30% but ranged from 47 to 65% for the premixes. Significant declines in both variables were detected for all fungicides except TRIF+PROT. For TEBU, control efficacy (yield response) declined the most: 78% (18%) to 54% (8%) from 2004–05 to 2013–14. The recent surge of resistant populations of Phakopsora pachyrhizi to both demethylation inhibitor and quinone outside inhibitor fungicides is likely the driving force behind a significant decline after 4 years of fungicide use.

25The wheat blast disease has been a serious constraint for wheat production in Latin America 26 since the late 1980s. We used a population genomics analysis including 95 genome 27 sequences of the wheat blast pathogen Pyricularia graminis-tritici (Pygt) and other 28Pyricularia species to show that Pygt is a distinct, highly diverse pathogen species with a 29 broad host range. We assayed 11 neutral SSR loci in 526 Pygt isolates sampled from wheat 30 and other grasses distributed across the wheat-growing region of Brazil to estimate gene 31 flow, assess the importance of sexual reproduction, and compare the genetic structures of 32Pygt populations infecting wheat and nearby grasses. Our results suggest a mixed 33 reproductive system that includes sexual recombination as well as high levels of gene flow 34 among regions, including evidence for higher gene flow from grass-infecting populations and 35 into wheat-infecting populations than vice versa. The most common virulence groups were 36 shared between the grass-and wheat-infecting Pygt populations, providing additional 37 evidence for movement of Pygt between wheat fields and nearby grasses. Analyses of 38 fruiting body formation found that proto-perithecia and perithecia developed on senescing 39 stems of wheat and other grass hosts, suggesting that sexual reproduction occurs mainly 40 during the saprotrophic phase of the disease cycle on dead residues. Phalaris canariensis 41 (canarygrass) supported the fullest development of perithecia, suggesting it is a promising 42 candidate for identifying the teleomorph in the field. Based on these findings, we formulated 43 a more detailed disease cycle for wheat blast that includes an important role for grasses 44 growing near wheat fields. Our findings strongly suggest that widely grown pasture grasses 45 function as a major reservoir of wheat blast inoculum and provide a temporal and spatial 46 bridge that connects wheat fields across Brazil. 47. CC-BY-NC-ND 4.0 International license It is made available under a (which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint . http://dx.doi.org/10.1101/203455 doi: bioRxiv preprint first posted online Oct. 16, 2017; 3 Author summary (200 words) 48 After the first wheat blast epidemic occurred in 1985 in Paraná, Brazil, the disease 49 spread to Bolivia, Argentina, and Paraguay, and was introduced into Bangladesh in 2016 50 followed by India in 2017. Wheat blast is caused by Pyricularia graminis-tritici (Pygt), a 51 highly diverse pathogen species related to the rice blast fungus P. oryzae, but with an 52 independent origin and a broader host range. We conducted a large scale contemporary 53 sampling of Pygt from symptomatic wheat and other grass species across Brazil and analyzed 54 the genetic structure of Pygt populations. Pygt populations on both wheat and other grasses 55 had high genotypic and virulence diversity, a genetic structure consistent with a ...

RESUMOPalavras-chave adicionais: Magnaporthe oryzae, Pyricularia grisea, ImageJ, severidade, epidemia.A qu a ntifica çã o correta da bru sone ca u sa da pelo fu ngo Magnaporthe oryzae em espigas de trigo (Triticum aestivum) é um componente importa nte pa ra o entendimento do desenvolvimento dessa doença com vistas ao seu controle. A quantificação visual baseada em uma esca la diagramática pode ser uma tarefa prática e eficiente que já tem demonstrado utilidade em diversos patossistemas, inclusive doenças da espiga do trigo como a mancha das glu mas e fusariose. Espigas apresentando diferentes valores de severidade da doença foram coletadas em u ma lavou ra com o objetivo de ela borar u ma escala diagramática para quantificar a severidade da brusone em espigas de trigo. As espigas foram fotografa das e a severidade da bru sone foi Maciel, J.L.N.; Danelli, A.L.D.; Boretto, C.; Forcelini, C.A. Escala diagramática para avaliação de brusone na espiga de trigo. Summa Phytopathologica, v.39, n.3, p.162-166, 2013. determinada usando os recursos do programa computacional ImageJ. Uma escala diagramática foi elaborada com os seguintes valores de severidade de doença: 3,7; 7,5; 21,4; 30,5; 43,8; 57,3; 68,1; 86,0; e 100,0%. Uma espiga assintomática foi adicionada à escala. A validação da escala foi realizada por oito pessoas que estimaram a severidade da brusone em imagens digitalizadas de 40 espigas de trigo. A precisão e a a cu rá cia da s a va lia ções va ria ra m de a cordo com o a va lia dor (0,82

Apple leaf spot (ALS) caused by Colletotrichum spp. is a major disease of apple (Malus domestica) in Southern Brazil. The epidemiology of this disease was studied in experiments carried out in the counties of Passo Fundo and Vacaria, State of Rio Grande do Sul, from February 1998 to October 2000. The disease was found in all the six apple orchards sampled in the growing seasons of 1997/98 and 1998/99. The fungus isolates associated with ALS fit the characteristics of C. gloeosporioides (75%), C. acutatum (8%), and Colletotrichum sp. (17%). The pathogen overwintered in dormant buds and twigs but not in dropped leaves or fruit mummies. Two sprays of copper oxychloride (at 0.3%) reduced the fungus initial inoculum by 65-84.6% in buds and 85.6-93.7% in twigs, but had no effect on the early season progress of the disease. Disease severity increased proportionally to elevation of temperature from 14 to 26-28 °C. At 34 °C, however, infection was completely inhibited. The duration of leaf wetness required for infection ranged from two hours at 30 °C to 32 h at 16 °C. The relationship of temperature (T) and leaf wetness (W) to disease severity (Y) was represented by the model equation Y = 0.00145[((T-13)1.78)((34.01-T )1.09)] * 25/[1+14 exp(-0.137W)], R² = 0.73 and P < 0.0001. Currently, this information is being used to manage the disease and to validate a forecast system for ALS.

Application volume, adjuvants that act on the drop surface tension and droplet spectrum are the main factors affecting leaf surface coverage and the spray penetration droplets inside the canopy of the soybean crop, which may have an impact on fungicide efficiency, since those used in the handling of Asian-rust, including those that are absorbed by the plant, present a small displacement from the point of deposition. Thus, it was sought to determine the impacts on the use of the organosilicone surfactant compared to the changes in the spray volumes. For that, five spray volumes and the combination of two adjuvants were compared in randomized blocks with a factorial arrangement 5x2. Reductions in volume negatively impacted the number of drops cm-2 affecting the leaf surface cover which did not exceed 13% in the lower third, in the absence of the surfactant. Also, the reduction in the volume provided decreases in the control of Asian-rust, and the use of surfactant minimized the negative impacts of the disease, reflecting on the index of the leaf area which varied up to 6.5 times on changes in the spray volume, and up to 2.8 times against the use of the surfactant in relation to the mineral oil isolated. Grain yield was negatively affected as reductions in the spray volumes, occurred with less impact when the surfactant was used. Thus, coverage of the leaf surface and the number of drops cm-2 along the plant profile respond to the addition of the surfactant and to the increase of the spray volume, having relation with the control of soybean Asian-rust, and affecting the leaf area index and productivity.

Em experimentos com o cultivar de trigo Embrapa 16 conduzidos em Passo Fundo e Não-Me-Toque nas safras de 1999 e 2000 houve uma relação inversa entre a incidência foliar da ferrugem da folha do trigo, a severidade, o número de pústulas por centímetro quadrado e a área abaixo da curva de progresso da doença com o rendimento de grãos, e uma relação direta entre a refletância da radiação solar, na faixa de 810 nm, com o rendimento de grãos. A refletância da radiação solar na faixa permitiu estimar o rendimento de grãos do trigo, a severidade da doença e o número de pústulas cm-2. As equações da função de dano com maior R² obtidas pela análise de regressão permitem o cálculo do limiar de dano econômico (LDE) em diferentes estádios fenológicos da cultura. O LDE pode servir de critério indicador do momento para o controle da ferrugem da folha do trigo. Os danos causados pela doença atingiram um máximo de 43%, com uma média de 40 %.

No abstract

A resistência sistêmica adquirida (SAR = systemic acquired resistance) é um importante mecanismo de resistência a doenças em plantas. Neste estudo, a ação do acibenzolar-S-metil (ASM), derivado benzotidiazólico ativador de resistência em plantas foi avaliada sobre a brotação de tubérculos de batata (Solanum tuberosum) e quanto à ação deste na indução de resistência à canela-preta, incitada por Pectobacterium carotovorum subsp. atrosepticum atípica (Pcaa), nas cultivares Asterix, Baronesa e Monalisa. Nas doses, 60, 120, 150, 200 e 250 mg i.a. l -1, o produto não inibiu o número de brotos. Contudo, em concentrações mais elevadas influenciou o comprimento destes. Em casa de vegetação, nas concentrações de 60 e 120 mg i.a. l -1 ASM, tanto no tratamento de tubérculos quanto no de aspersão nas plantas, a cultivar Asterix, respondeu ao tratamento do ASM, conferindo-lhe resistência à canela preta. Na cultivar Baronesa, a resposta ao ASM ocorreu somente no tratamento de tubérculos, e, para a cultivar Monalisa, não houve resposta ao ASM. Verifica-se, neste estudo, que houve ação do ASM sobre a indução de resistência e que este foi específico para determinadas cultivares de batata.