Monitoramento da população de Phytophthora infestans na região da Zona da Mata de Minas Gerais de 1998 a 2000

Abstract

Foram caracterizados 212 isolados de Phytophthora infestans obtidos de 51 lavouras de tomate (Lycopersicon esculentum)e batata (Solanum tuberosum), em sete municípios da Zona da Mata, MG. Todos os isolados tiveram o grupo de compatibilidade determinado; 96 isolados foram caracterizados para a isoenzima glucose 6-fosfato-isomerase (Gpi); 71 isolados foram analisados quanto à resistência ao metalaxyl; e determinou-se o espectro de virulência de 46 isolados. Todos os 212 isolados testados foram classificados como do grupo A1 de compatibilidade. A maioria dos isolados testados para Gpi (95) apresentou o fenótipo 86/100, típico da linhagem clonal US-1. Apenas um isolado apresentou o fenótipo 100/100 para Gpi. Quanto à resistência ao metalaxyl, em 1998 a freqüência de isolados sensíveis, intermediários e resistentes foi de 40%, 40% e 20%, respectivamente, e em 2000 de 3,2%; 61,3% e 35,5%, respectivamente. Quanto ao espectro de virulência, todos os 46 isolados analisados foram virulentos sobre a cultivar de tomate 'Kada'. A maioria foi virulenta em plantas de tomate com os genes Ph1 (91%) ou Ph2 (95 %). Todos os isolados foram virulentos em batata 'Bintje'. Houve pequena variação do espectro de virulência sobre clones de batata, quando esses foram inoculados com isolados coletados em diferentes anos. Há evidências que a população de P. infestans da Zona da Mata, MG é constituída de isolados da linhagem clonal US-1, de várias raças e baixa sensibilidade ao fungicida metalaxyl.

Mating type, mefenoxam sensitivity, and pathotype diversity in Phytophthora infestans isolates from tomato in Brazil

“…Due to the host specificity of clonal lineages of P. infestans in Brazil, only isolates of the mating type A1 have been found associated with tomato plants. Isolates of the mating type A2 (BR-1 clonal lineage), and only sporadically A1, are associated with potato plants (Reis et al, 2002(Reis et al, , 2003. As only isolates of the mating type A1 remain associated with tomato plants, there is no risk at all or low risk of sexual reproduction of P. infestans on this host.…”

“…Its isolates have the A1 mating type, and the restriction pattern of mitochondrial DNA (mtDNA) is of the Ib type. The new lineage, BR-1, is associated with potato crops, and its isolates have the A2 mating type, and mtDNA IIa (Reis et al, 2002(Reis et al, , 2003. The host specificity of clonal lineages is, at least in part, due to quantitave differences in aggressiveness components (Suassuna et al, 2004).…”

“…Besides mutation, migration and recombination are often mentioned as the main evolutionary mechanisms that shape genetic variability in P. infestans populations (Fry, 2008). As the population of P. infestans from tomatoes in Brazil remains very uniform (Reis et al, 2002), migration and recombination are not acting on pathogen population, and mutation is the main source of variation. Despite the apparent genetic uniformity of the Brazilian population of P. infestans, it is expected that factors affecting disease management, such as fungicide insensitivity and virulence, must be variable, due to mutation.…”

Metalaxyl resistance in Phytophthora infestans: An overview

“…The isolates of this lineage have the A1 mating type with Ib type restriction pattern of mitochondrial DNA (mtDNA). The other lineage, having A2 mating type with mtDNA IIa BR-1, was found to be linked with potato crops (Reis et al, 2002(Reis et al, , 2003) [74,75] . The presence of quantitative differences in the components of aggresivity in the clonal lineages contributed to the specificity of host (Suassuna et al, 2004) [89] .…”

“…However from the subsequent analysis of oospore progeny, it was observed that metalaxyl resistance and fitness were not linked (Gisi and Cohen, 1996). In Brazil, the P. infestans population from tomatoes showed uniformity (Reis et al, 2002) [75] , as recombination and migration does not occur within pathogenic population, the prime reason of variability may be mutation. Though, P. infestans population in Brazil has apparent genetic uniformity, mutation is the expected factor which can affect the management of disease, like insensitivity to fungicides and variability in virulence.…”