Epsilon Open Archive

Abstract

The variation in cold hardiness in Salix in the autumn was investigated using clones of different geographic origins. In late growing season, the variation was small and inversely related to a phenotypic variation in potential growth rate. When growth had stopped in response to the reduction in daylength, however, large differences in cold hardiness developed. Northern/continental clones started cold hardening up to two months earlier and showed up to three times higher inherent rates of cold hardening than the southern/maritime ones. The two components of cold hardening, the timing of onset and the inherent rate, seemed to be separately inherited traits, as judged from analyses of the prodigy of a crossing between an early-and-rapidly hardening clone and a late-and-slowly hardening one. This suggests that cold hardiness can be improved without adversely affecting growth by selecting for a late onset of cold hardening combined with a rapid rate. Also, in the early stages, cold hardening was more sensitive to low, non-freezing temperatures in the southern/maritime clones than in the northern/continental ones. Cold hardening of stems in the autumn could be monitored from the accumulation of sugars, most predominantly sucrose, raffinose and stachyose. The accumulation of sucrose started already with the cessation of growth, whilst the accumulation of raffinose and stachyose started later and was stimulated by cool temperatures. Multivariate models using sugar data could explain 76% of the variation in cold hardiness in the early stages of hardening. Changes in levels of sugars and other compounds during cold hardening could be assessed non-intrusively from the visible and infrared reflectance spectra of stems. Multivariate models using spectral data could predict up to 96% of the variation in cold hardiness. This technique is expected to greatly facilitate breeding for improved cold hardiness by allowing rapid screening of large populations. The variation in cold hardiness in spring was also investigated. Loss of cold hardiness in spring was closely related to the bursting of buds. A relatively large genetic variation in the temperature requirement for bud burst was demonstrated indicating that this might be modified in sensitive clones to improve their cold hardiness in spring.