The establishment of seed banks for ex situ plant germplasma conservation is widely used. However, seedborne pathogens may affect germplasma integrity when it is regenerated and/or multiplied. The objective of this experiment was to monitor the longevity (survival) and viability (maintenance of infectivity) of Xanthomonas axonopodis pv. phaseoli in a contaminated bean (Phaseolus vulgaris) seed lot (cv. Roxão), stored at -18 and 5 ºC, which are, respectively, the normal temperatures for long and average term conservation of plant germplasma. Another sample was maintained at room temperature. Longevity of the bacteria was evaluated by the percentage of infected seeds, scoring typical colonies onto semi-selective medium, and the viability was determined by the capability of the isolates to reproduce the disease. The population of X. axonopodis pv. phaseoli was evaluated in seed stored for five years, by individually isolating the bacteria from seed wash and seedlings. The results showed that the initial contamination rate of 64% dropped to 36-37% for all treatments during the first six months. Final evaluations at 30 and 60 months showed that for seed stored at -18 and 5 ºC, the contamination rate was maintained. This differed significantly from seed stored at room temperature. The best temperature for bacteria survival and maintenance was 5 °C. At this temperature, the population level was as high as 1.2 x 10(8) cfu/seed. Maintenance of infectivity after storage was also demonstrated. We concluded that the optimal conditions for seed conservation are the same as those for maintenance of X. axonopodis pv. phaseoli longevity.
bacterial blight of common bean; germplasma conservation; seed-borne bacteria
