Sobrevivência de Acidovorax avenae subsp. citrulli em Meloeiro

Abstract

The ability of Acidovorax avenae subsp. citrulli to survive epiphytically and endophytically on leaves, roots and rhizosphere of melon plants was determined by using a mutant resistant to rifampicin (Aac1 Rif). Leaves of 18-day-old melon plants grown in greenhouse and field were sprayed with mutant suspensions at concentrations of 3.4 × 10 2, 3.4 × 10 3 and 3.4 × 10 4 cfu.ml -1. To determine survival on roots and rhizosphere, seeds of Yellow melon were sown in soil infested with suspensions of Aac1 Rif at 3.4 × 10 5, 3.4 × 10 6 and 3.4 × 10 7 cfu.ml -1. At 6-day intervals samples of leaves, roots and rhizosphere soil were collected and processed for isolation on NYDA medium amended with rifampicin. Bacterial populations were determined as cfu.g -1 of sample and the data were transformed to log 10 for regression analysis. On melon leaves, in greenhouse and field Aac1 Rif survived epiphytically for 54 days. These epiphytic bacterial populations increased initially and decreased after a certain period of time. Both final populations were similar under the two conditions and ranged from 10 3 to 10 4 cfu.g -1 of leaf, without correlation with the inoculum concentration used. In greenhouse, bacterial populations on the roots and rhizosphere decreased with time, and 60 days after soil infestation they ranged from 10 2 to 10 3 cfu.g -1 of roots and 10 1 cfu.g -1 of soil. Aac1 Rif was not detected as an endophyte in leaves or roots of melon plants.