Effects of temperature, free moisture duration and inoculum concentration on infection of sweet cherry by <i>Pseudomonas syringae</i> pv. <i>syringae</i>
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2002
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Abstract
The effects of temperature, free moisture duration and inoculum concentration on infection caused by Pseudomonas syringae pv. syringae (Pss), on sweet cherry (Prunus avium) were investigated. Epiphytic populations of Pss are an important source of inoculum for bacterial canker and it has been demonstrated that a cyclic pattern exists during the year, from undetectable during the warm and dry periods to large populations following cool and wet periods. The effects of temperature and inoculum concentration on the infection caused by Pss on immature fruits and 1-yr-old twigs were significant (P<0.001). Fruit and twig infection increased linearly in proportion to the logarithm of Pss when bacterial concentrations were higher than 10(3) cfu ml(-1) and temperatures were between 5 and 20 °C. Regardless of the inoculum concentration and the free moisture duration, fruit and twig infection was either absent or low at 5 °C but it increased linearly as temperature increased from 5 to 20 °C. Growth rate in vitro was very slow (0.03-0.04 cfu h(-1)) at 5 °C and fast (0.21-0.23 cfu h(-1)) at 20 °C. Therefore, it is possible that multiplication of the epiphytic populations may be significantly reduced in the field with air temperatures below 5 °C. A significant (P<0.001) effect of free moisture was obtained only when a low inoculum concentration (10(3) cfu ml(-1)) was used, and a significant linear response between free moisture and disease incidence was obtained only at 10degreesC. An apparent threshold population of Pss higher than 10(3) cfu ml(-1) was needed to infect immature fruits and 1-yr-old twigs of sweet cherry.
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bacterial canker, epiphytic bacteria, pear blossom blast, sour cherry, stone fruits, sweet cherry