Complete: Genotypic differences in susceptibility to frost damage

Outcomes / Key Message For Growers And Industry

We observed clear differences between varieties in their susceptibility to frost damage; however, there are several caveats. Firstly, this was a rust trial, and there was a positive association between the percentage of foliage affected by rust and frost damage, although it is unlikely that this was a major contributing factor to frost susceptibility. Secondly, this was one trial on one field in one season: it is well known that varieties change rankings from one location or environment to another, H:\documents\bbro\BBRO Frost damage final report 10-99 revision 16-8-12.doc 9 16/08/2012 12:47:00 particularly when ranked for traits with low heritability such as yield. It is not known how consistent are the varietal rankings for frost susceptibility. There is anecdotal evidence that the size of the canopy may afford some degree of protection from frost, and therefore the frost ‘resistant’ varieties simply may have had better canopies due to greater rust resistance. Therefore, the genetic component may be related to rust resistance, not to frost resistance per se. Nevertheless, it is unlikely that rust is the entire explanation of varietal differences in frost damage. For instance, the variety with the smallest amount of damage was not very resistant to rust, and the varieties with the most damage did not show the greatest levels of rust. A photo of the trial shows that overall, the canopy was reasonably full and healthy at the end of October (Fig. 4). Adjacent to this trial was a commercial crop of Bullfinch that received a full two-spray fungicide programme, showed little rust, but was substantially damaged by frost. It remains unclear what causes such large differences between plants within the same row of the same variety, but clues to understanding this would be extremely helpful in making genetic improvements in new varieties, or perhaps identify ways to manage late lifted crops differently. There are many hypotheses that can be posited to explain varietal differences in frost damage. It is worthwhile to explore these methodically. Better understanding of these differences could enable breeders to develop more frost resistant varieties in the future.