1. Extreme temperature differentially affects growth and survival of Xylella fastidiosa strains
- Author
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Román-Écija M , Landa BB, Testi L, Navas-Cortés JA
- Abstract
The development of regionalised risk models for the establishment of Xylella fastidiosa (Xf) and its subspecies requires a better knowledge of their respond to environmental factors in particular to temperature. Furthermore, since Xf is confined within the xylem, it will be relevant to determine to which extent the xylem environment differs from external conditions. Therefore, the objectives of this study were to determine the effect of temperature in growth and survival of Xf strains and to establish the dynamics of temperature in xylem vessels in olive trees. Growth and biofilm formation of 33 Xf strains representative of five subspecies and 13 STs, a wide geographic origin and hosts plants have been determined in vitro in a temperature range from 4 to 40ºC. After 7 days, planktonic cells were inoculated into 96-well plates and incubated at 28ºC for 7 days more. On the other hand, air and xylem vessels temperature was measured at 10-min intervals during 31 months by installing thermocouples in soil, branches and trunks of four 8-yr old olive trees at a 1 and 4 cm depth. Our results indicated that overall, extreme low or high temperature differentially affected growth and survival of Xf strains. Thus, when Xf bacterial cells were incubated at 4 to 10ºC showed a slower growth rate and reduced biofilm formation compared to those incubated at 16 to 32ºC. However, cells that grew at all those temperatures were able to growth further and form biofilm when incubated at favourable temperature of 28ºC in fresh medium. In contrast, incubation temperature of 36 and 40ºC for a 7-day period resulted lethal for the bacterial cells since no further cell growth was observed after incubation at 28ºC. Regression models were developed to estimate the relationship between air and xylem or soil temperature. The slope of the fitted linear models indicated a poikilothermy where air and branch temperature progress at the same rate (slope=1), but a homeothermy in trunks and the soil-root system where air temperature increases at a lower rate (slope < 1). The buffer effect of the trunk and soil are stronger for daily maximum temperature in summer and winter seasons, while minimum daily temperature was coupled with air temperature across seasons. Our results indicate the need to take into account the differences on temperature in the xylem environment when developing regionalized risk models for Xf and highlight the importance of the differential effect of low and high temperature on Xf growth.
- Published
- 2021
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