The use of field and artificial freezing studies to assess frost tolerance in natural populations of<i> Pinus oocarpa</i>

Abstract

The susceptibility of Pinus oocarpa to freezing temperatures limits the commercial deployment of the highly productive Pinus patula × P. oocarpa hybrid in South Africa. Identifying P. oocarpa germplasm with increased frost tolerance is important. Twenty-three P. oocarpa provenances, originating from Mexico, Honduras, Guatemala and Nicaragua, were therefore assessed for their tolerance to freezing conditions by analysing field survival after frost events, subjecting needles to freezing temperatures and assessing damage using the electrolyte leakage test, and exposing young plants to freezing temperatures in a semi-controlled environment and scoring tissue damage based on a visual assessment. The performance of many of the provenances represented in the field and artificial freezing studies were similar and there was a strong correlation between provenance ranking in the whole plant freezing and electrolyte leakage test. We therefore support the use of these techniques as a means to assess cold tolerance in P. oocarpa at the provenance level. Provenances from north-western Mexico demonstrated more frost tolerance than those from southern Mexico. Provenances representing Honduras and Guatemala appear to be highly susceptible to frost.

Keywords: artificial freezing, field assessment, frost tolerance, Pinus oocarpa, provenances