Resumo

LOZOYA-SALDANA, Héctor; RIVERA-HINOJOSA, Rodolfo  e  COLINAS-LEON, María Teresa. Phenols, peroxidase and phenylalanine ammonia-lyase: their relationship to the genetic resistance against late blight (Phytophthora infestans Mont. De Bary) in potato (Solanum tuberosum L.) clones. Agrociencia [online]. 2007, vol.41, n.4, pp.479-489. ISSN 2521-9766.

Horizontal resistance to diseases in plants involves activation of several defense genes. In order to prove this type of mechanism, a quantification was made of enzymatic activities related to diverse levels of genetic resistance in potato genotypes (Solanum tuberosum L.) against late blight (Phytophthora infestans Mont. De Bary), exposed to natural infection in the Toluca Valley, with and without protection with fungicides. There was a differential response in enzymatic presence and activity among genotypes as a function of their genetic resistance and of the presence or absence of fungicides. In the Alpha cultivar, susceptible, without fungicides, there was significant positive correlation between the infection level and the activity of the phenylalanine ammonia-lyase (PAL), as well as of phenols-peroxidase (FEN-POX; r=0.9 in both cases), whereas with chemical protection, the phenols were positively correlated with both enzymes. In the resistant clones there was direct positive correlation between the percentage of infection and the presence of phenols, with and without fungicides, but the expected inverse relationship was not observed (the higher the amount of phenols, the lower the infection). Also, in the resistant genotypes (cv. Zafiro and the clones), without fungicides, there was significant positive correlation among infection/POX, FEN/POX and POX/PAL. Furthermore, with fungicides, the clones showed significant positive correlation among all of the variables and their combinations (r>0.73; Infection, FEN, POX, PAL). It is concluded that the genetic resistance was not the result of isolated reactions against the pathogen, but rather of the combination of the factors studied, suggesting the polygenic trait or horizontal resistance.

Palavras-chave : FEN; potato; PAL; POX; genetic resistance.

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