Multiplication of Xanthomonas campestris pvs secalis and translucens in host and non‐host plants (rye and barley) and development of water soaking1

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Abstract
Multiplication of the rye‐specific and barley‐specific pathovars secalis and translucens, respectively, of Xanthomonas campestris (earlier named Xanthomonas translucens f. sp. cerealis) was determined in two rye and two barley cultivars. Fresh bacterial cultures were suspended in boiled tap water, adjusted to about 3 × 107 cfu ml−1 and infiltrated into the mesophyll of young leaves. In the compatible combinations, a generation time of 1.7–2.1 h was determined. Significantly higher multiplication rates than in incompatible combinations were not observed before 3 or 4 days after inoculation. At this time, the first small water‐soaked areas appeared. Bacteria multiplied up to the seventh day after inoculation, reaching a maximum of at least 109 cells per cm2, the same time at which the water‐soaked areas had reached their maximum size. Thus, the rate of bacterial multiplication paralleled with the development of the water‐soaked areas. In the incompatible combinations, nearly the same generation times were detected during the exponential growth phase. However, water‐soaked areas did not appear, and the final bacterial concentration ranged from 1:1000 to 1:100 of that determined in compatible combinations. A distinct early lag phase, characterized by a decrease of the bacterial population down to 1:100 of the starting concentration, was detected in all cases.