RESUMO Dentre as doenças fúngicas, a mancha marrom de Alternaria (MMA) é a doença mais importante para tangor “Murcott”, causando desfolha, mancha e queda de frutos e, com isso, acarretando muitos prejuízos. Nesse trabalho foi avaliada a eficiência de trifloxistrobina e tebuconazol, em formulação comercial, combinados com pirimetanil, em duas dosagens, e combinado com cobre solúvel em água, comparado com oxicloreto de cobre, no controle da MMA em pomar de tangor ‘Murcott’, com 15 anos de plantio, em Estiva Gerbi/SP. Os tratamentos foram constituídos pela mistura de tanque de trifloxistrobina e tebuconazole a 0,80 L ha-1 com os seguintes fungicidas (L ou kg de produto comercial 2000 L-1): T1- pirimetanil (1,0); T2- pirimetanil (1,5); T3- sulfato de cobre solúvel (1,0); T4- oxicloreto de cobre (3,60). Foi adotado o delineamento de Split-block, em subparcelas, com três repetições de dez plantas na linha entre as duas linhas adjacentes. Os fungicidas foram aplicados mediante turbopulverizador FM Copling, sendo empregada uma vazão de 100 mL (m3) -1. No total foram realizadas 17 aplicações de fungicidas, em intervalos que variaram de 12 a 15 dias. As avaliações consistiram na determinação dos níveis de severidade dos sintomas nos frutos, determinados em três épocas (S1, S2 e S3) a determinação do número de cicatrizes nos frutos, quando realizada a colheita. Verificou-se que os tratamentos constituídos pelas combinações de trifloxistrobina e tebuconazole e pirimetanil, em duas dosagens, foram eficientes no controle do patógeno, assemelhando-se aos resultados do tratamento padrão, representados pela combinação de trifloxistrobina e tebuconazole com oxicloreto de cobre.

ABSTRACT Among fungal diseases, Alternaria brown spot (ABS) is the most important disease for “Murcott” tangors, causing leaf drop, spots, fruit drop and consequently heavy losses. The present study evaluated the efficiency of two levels of trifloxystrobin and tebuconazole, in commercial formulation, combined with pyrimethanil or water-soluble copper, in comparison with copper oxychloride, on ABS control in a 15-year-cultivation “Murcott” tangor orchard in Estiva Gerbi, Sao Paulo State, Brazil. Treatments were composed of the tank mixture of trifloxystrobin and tebuconazole at 0.80 L ha-1 with the following fungicides (L or kg commercial product 2000 L-1): T1 - pyrimethanil (1.0); T2 - pyrimethanil (2.0); T3 - soluble copper sulfur (1.0); T4 - copper oxychloride (3.60). Split-block design was adopted, in subplots, with three replicates containing ten plants on the row between two adjacent rows. Fungicides were applied with an FM Copling turbo sprayer, at a flow of 100 mL (m3) -1. In total 17 fungicide applications were performed at intervals varying between 12 and 15 days. Evaluations consisted of determining the severity levels of symptoms on fruits in three periods (S1, S2 and S3) and the number of injuries on fruits at harvest. Treatments combining trifloxystrobin and tebuconazole with pyrimethanil, in two levels, were efficient in controlling the pathogen, similarly to the results of the standard treatment, represented by the combination of trifloxystrobin and tebuconazole with copper oxychloride.

ABSTRACT. Triazole fungicides have not been effective for managing the wheat blast disease in Brazil. A broad analysis across six geographical populations of Pyricularia graminis-tritici in central-southern Brazil indicated a high level of resistance to triazole fungicides. Since P. graminis-tritici is also associated with others poaceous species, here, we analyzed whether triazole-resistant isolates of the blast pathogen could be recovered from other poaceous hosts that are invasive of sprayed wheat fields. In addition to P. graminis-tritici (Pygt), we also evaluated the levels of sensitivity of three other grass-associated blast pathogens, which included P. grisea (Pg), P. pennisetigena (Pp), and P. urashimae (Pu). Resistance to the triazole fungicides tebuconazole and epoxiconazole was assessed phenotypically based on EC50 values and molecularly by analysis of the presence of mutations in the CYP51A gene, which encodes for the target enzyme 14-alpha-demethylase. We detected triazole-resistant Pyricularia spp. (Pg, Pp, Pu and Pygt) that is associated with Avena sativa, Cenchrus echinatus, Chloris distichophylla, Cynodon sp., Digitaria horizontalis, D. sanguinalis, Panicum maximum or Urochloa spp. The major outcome from our study was the evidence that invasive poaceous species from wheat fields could be an important source of triazole resistant fungal inoculum for the initial phases of the wheat blast epidemics.

RESUMO O fungo Rhizoctonia solani grupo de anastomose AG-1 IA emergiu como patógeno importante associado à queima foliar, podridão do coleto e morte de pastagens do gênero Urochloa (braquiária) na América do Sul. Neste estudo objetivou-se determinar se a adaptação de R. solani AG-1 IA à Urochloa spp. na Colômbia promoveu diferenças fenotípicas de agressividade a hospedeiros distintos. Testou-se a hipótese de que as populações do patógeno adaptadas à Urochloa não são hospedeiro-especializadas e, desta forma, não estão geneticamente isoladas, mantendo assim ampla gama de hospedeiros, incluindo as fabáceas feijão caupi e soja. Determinou-se, também, se dois grupos de isolados obtidos de populações de R. solani AG-1 IA amostradas de Urochloa na Colômbia tinham potencial adaptativo para emergir como patógeno do milho. Além do nível de agressividade da doença em diferentes hospedeiros, determinou-se os componentes de evolutibilidade como o coeficiente de variância genotípica (IG), de variância ambiental (IE) e a herdabilidade (h2). Concluiu-se que: i) A adaptação de R. solani AG-1 IA à Urochloa spp. não promoveu diferenças fenotípicas de agressividade em hospedeiros distintos e, desta forma, o patógeno mantêm ampla gama de hospedeiros; ii) A população de R. solani AG-1 IA de Urochloa híbrido Mulato da Colômbia tem potencial adaptativo para emergir como patógeno do milho.

Palavras-chave The fungus Rhizoctonia solani anastomosis group AG-1 IA has emerged as an important pathogen associated with foliar blight, collar rot and death of Urochloa (Brachiaria) forage pastures in South America. This study aimed to determine whether the adaptation of R. solani AG-1 IA to Urochloa spp. in Colombia promoted phenotypic differences in aggressiveness to distinct hosts. Our hypothesis was that the pathogen populations adapted to Urochloa spp. are not host-specialized and hence are not genetically isolated, thereby maintaining a broad host range, including the fabaceous plants cowpea and soybeans. We also determined whether two groups of isolates from populations of R. solani AG-1 IA sampled from Urochloa in Colombia have adaptive potential to emerge as maize pathogens. Besides the levels of disease severity in different hosts, we also determined the components of evolvability, such as the coefficient of genotypic variance (IG), the environmental variance (IE) and the heritability (h2). We concluded that: i) The adaptation of R. solani AG-1 IA to Urochloa spp. did not cause any phenotypic differences in aggressiveness to distinct hosts and therefore the pathogen maintains a broad host range. ii) The population of R. solani AG-1 IA from Urochloa hybrid Mulato in Colombia has adaptive potential to emerge as a maize pathogen.