The relevance of bacterial halo blight of coffee caused by Pseudomonas syringae pv. garcae, has increased recently in the coffee crop in Brazil. Other bacterioses also affect the coffee leaves and mixed infections of P. syringae pv. garcae and Pseudomonas syringae pv. tabaci have been found in 2017 in the state of Paraná. The techniques routinely used to diagnose these bacteria may spend resources and time. In the present study, the sequences of the genes dsbA, gyrB, rpoD, recA, rpoB, rpsLG and fusA. Only from the sequence of the rpoD gene allowed the development of two primers Psg3F for the detection of P. syringae pv. garcae, with 275 bp and a sensitivity of 0.001 ng, and Pst3F for the detection of P. syringae pv. tabaci, with 585 bp, and a sensitivity of 0.01 ng. These primes can be used simultaneously in a Multiplex PCR reaction to simultaneously to detect both pathogens, from extracted DNA and from boiled bacterial suspensions. This technique allows greater precision and reduction in the time used for diagnosis. The severity of the bacterial halo blight has been related to variations in the nitrogen nutrition of the coffee crop in field and nursery conditions. Aiming to estimate this influence, two experiments were carried out in hydroponic conditions with coffee seedlings of susceptible (Bourbon and Catuaí Vermelho IAC 144) and resistant (IPR 102) cultivars. The seedlings were grown in nutrient solutions containing 0, 5, 10 e 15 mmol L-1 of nitrogen (N) and were inoculated were with P. syringae pv. garcae. The seedlings presented a higher level of N and high growth of the aerial part, and dry mass of the aerial part, as well as a higher number of leaves, in response to the N supply. The seedlings of the susceptible cultivars presented more severity of bacterial halo blight in the solution without N, reduction in the severity in the solutions 5 and 10 mnol of N.L-1 and increase in the severity in the solution containing 15 mnol of N.L-1. The seedlings of the cultivar IPR 102 maintained resistance to bacterial halo blight in all treatments.
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