Comparison of Hardening/De-Hardening Conditions in Lolium perenne and Festulolium

De-hardening resistance and re-hardening capacity plays a significant role in determining plant hardiness during late winter and early spring when plants are particularly vulnerable to cold-injury. Understanding the mechanisms of de-hardening/re-hardening is important for cultivar development of perennial ryegrass and Festuloliumwhich lacks adequate winter survival.

In this research our aim was to study the relationship between global transcriptome changes and frost tolerance as affected by vernalization and cold acclimation in Lolium perenne and Festulolium genotypes with different vernalization requirements. Clones of two genotypes (201, 204) from the Norwegian L. perenne cv Fagerlin and two genotypes (266, 329) from the Festulolium candivar FuRs9806 (F. pratensis x L. perenne) which differed in vernalization requirement under natural field conditions, i.e. genotype 201 and 266 which flowered without vernalization and genotype 204 and 329 which needed vernalization to flower, were given two pretreatments: 1) Vernalization for 10 weeks at +6 ºC and 2) No vernalization, i.e. grown at +15 ºC. Following this the plants undergone hardening for 4 weeks at +2 ºC, then de-hardening for 8 days at +9 ºC followed by re-hardening for 2 weeks at +2 ºC. Freezing tests were conducted after every treatment with test temperatures ranging from -4 ºC to -20 ºC. Crown samples (3 biological replicates) were collected at each time point and used for RNA extraction.

LT₅₀ results showed that vernalization (pre-hardening) at +6 ºC led to higher frost tolerance than pre-hardening at +15 ºC. Lolium perenne hardened more, i.e. displayed lower LT₅₀ values, than Festulolium irrespective of pre-hardening treatments. Genotypes with vernalization requirements pre-hardened at +6 ºC showed the largest capacity to re-harden which resulted in differences in LT₅₀ values of 3-6 ºC. The transcriptome of the crown tissues sampled during the hardening/de-hardening/re-hardening cycles (108 samples) is being analyzed by pair-end sequencing of cDNA libraries using Illumina Hiseq 2000.