Predicting the cold hardiness of willow stems using visible and near-infrared spectra and sugar concentrations

Abstract

Closely related, fast-growing clones of willows from northern/continental and southern/maritime origins were assessed for their levels of cold hardiness. Assessments were made during active growth and, subsequently, during cold hardening at mean temperatures of 3C (the COLD regime) and 8C (the MILD regime). The onset of hardening was triggered simultaneously in all clones by administering a drastic day length reduction on the first day. The northern/continental clones showed consistently higher rates of hardening than the southern/maritime ones. This was particularly true under the COLD regime, suggesting that their hardening was less sensitive to low temperatures. The stems' visible and near-infrared absorption spectra, and concentrations of ten major soluble sugars, were also determined. Multivariate analysis revealed that spectral data could predict up to 96% of the variation in cold hardiness, when the analysis was restricted to the MILD regime and the data corrected for irrelevant systematic information. Possible direct links between spectral changes and chemical changes are discussed. Multivariate analysis also revealed that sugar concentrations could be used to predict up to 73% of the variation in cold hardiness. Different sugars displayed different patterns of variation during hardening. Concentrations of mannose and myo-inositol both decreased, whereas concentrations of galactose, sucrose, maltose, raffinose and stachyose all increased, but at different times. Dry matter increased markedly during hardening, so expressing the concentrations of sugars relative to dry matter does not provide an accurate measure of the amounts present.

Screening for efficient cold hardening in a breeding population of Salix using near infrared reflectance spectroscopy

“…1). In a previous study, however, we were able to predict as much as 96% of the variation in cold hardiness by analysing intact tissues [14]. It, therefore, seems that intact tissues provide better estimates than homogenised and dried ones, despite the fact that the former are optically more heterogeneous.…”

“…This linkage between growth and hardening cycles imposes restrictions on the extent to which either of these factors can be improved in isolation [19,22]. However, we have previously presented evidence that cold hardiness is also affected by differences in the inherent rate of cold hardening [13,14]. Some northern and continental ecotypes have the ability to undergo cold hardening up to three times as quickly as typical southern and maritime clones.…”

“…This is because genotypes that begin to harden late in the autumn will experience lower hardening temperatures than those starting early. Hardening is a temperature dependent process, with a temperature optimum at around 10°C at the start, but at lower temperatures during later stages [14]. A few studies using other woody plants suggest that there is variation in the inherent rate [1,7], but none of them have been carried out under controlled conditions.…”

“…Recently, promising results have been obtained using reflectance spectroscopy in the visible and near infrared ranges. Most of the genetic and phenotypic variation shown by conifer seedlings [23], and Salix [14] could be evaluated using this technique. Its value is that it detects the chemical changes associated with cold hardening, for instance in pigmentation and water and sugar content [14].…”

“…Most of the genetic and phenotypic variation shown by conifer seedlings [23], and Salix [14] could be evaluated using this technique. Its value is that it detects the chemical changes associated with cold hardening, for instance in pigmentation and water and sugar content [14]. Similarly, this technique is useful for the analysis of wood properties [2], characteristics that also have a strong chemical basis.…”