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 (Aac1Rif). Leaves of 18-day-old melon plants grown in greenhouse and field were sprayed with mutant suspensions at concentrations of 3.4 x 10², 3.4 x 10³ and 3.4 x 10(4) cfu.ml-1. To determine survival on roots and rhizosphere, seeds of Yellow melon were sown in soil infested with suspensions of Aac1Rif at 3.4 x 10(5), 3.4 x 10(6) and 3.4 x 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 log10 for regression analysis. On melon leaves, in greenhouse and field Aac1Rif 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 10³ 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 10² to 10³ cfu.g-1 of roots and 10¹ cfu.g-1 of soil. Aac1Rif was not detected as an endophyte in leaves or roots of melon plants.
Cucumis melo; Fruit blotch; ecology of bacterial plant pathogens; plant pathogenic bacteria
