Percloreto de ferro como sinalizador de injúrias em tubérculos de batata e caracterização de isolados de Pectobacterium spp

Abstract

The use of iron perchlorate as a marker of injury in potato tubers may help preventloss of lots during storage and transport. The objectives of this study were to determine the concentration of iron perchlorate solution and the immersion time for the marking of pectolytic bacteria in potato tubers; the evaluation of potato batches for the presence of these bacteria; the biochemical, physiological and molecular characterization of Pectobacterium spp. isolates; and the indication of pectobacteria by iron perchlorate in inoculated and commercial batches of potato tubers. The experiments were done at the Universidade Federal de Uberlândia, from 2009 to 2011. Marking of pectolytic bacteria in potato tubers was done using iron perchlorate concentrations of 0, 8, 21 and 44%, in which a sample of 10 tubers were immersed for 10, 20 or 30 minutes, and evaluated after 10, 20 and 30 minutes at room temperature, evaluating the appearance dark spots on the tubers. The isolates were characterized culturally, biochemically and physiologically by the tests of: Gram, glucose fermentation, catalase, oxidase, growth at 37ºC, reduction of substances from sucrose, phosphatase activity, indol production and acid production from sorbitol, melibiose, citrate or lactose, hypersensibility reaction in tobacco and pathogenicity in potato baits. Molecular characterization was done using the primers: EXPCCR/EXPCCF; ECA1f/ECA2r, 1491f, L1RA/L1RG Br1f. The indication of pectobacteria by the product studied in inoculated seed potato tubers was done with the cultivars Ágata and Atlantic. The tubers were perforated, or not, with a needle and immersed in distilled water or in bacterial suspension (isolate UFU A14 of Pectobacterium spp.) for 5 minutes and incubated at different temperatures (22, 28 or 35°C) and times (0, 24, 48, 72 or 96 hours), and subsequently immersed in the de perchlorate solution for the evaluation of lesion diameter. The experimental design was randomized blocks with four repetitions, as split plots in space 5 x 4. The indication of pectobacteria by the product in commercial potato batches was done with cultivars Ágata and Asterix. The samples with six tubers were evaluated 12 and 24 hours after harvest and incubated in five temperatures (8, 18, 28, 38 or 48°C), and immersed in 8% iron perchlorate solution for 10 minutes, removed and left at room temperature for 20 minutes before evaluation with a rating scale, varying from 0 to 4. Immersion for 10 minutes in iron perchlorate at 21% and evaluation after 20 minutes at room temperature was adequate to indicate the presence of pectobacteria. The isolates could not be characterized biochemistry and molecular. The inoculation test was able to confirm the presence of pectobacteria in the tubers by perchlorate. Storage and transport of commercial potatoes should be done at lower temperatures; the cultivar Ágata was more susceptible than Asterix to the pectobacteria.