The withdrawal of CIPC (chlorpropham) sprout suppressant has highlighted the need for other tools to control sprouting and triggered a three-year AHDB research project*.
Glyn Harper, who leads the work which has just completed its second year, says: “Using longer dormancy varieties can reduce our reliance on sprout suppressants which is particularly important post-CIPC.”
“Unfortunately, the availability of independent data on dormancy for commonly grown varieties is both sparse and conflicting.”
The project aims to generate independent relative dormancy ranking for growers to use as extra information when choosing varieties. Ranking should also help guide storage decisions, timings for other sprout control treatments and ultimately sales, adds Dr Harper.
“Longer dormancy varieties offer the potential of higher tuber quality over long-term storage with reduced need for sprout control. This project is largely concerned with endodormancy [see panel, left],” says Dr Harper.
“Dormancy break occurs before sprout development, but there’s no simple method for determining actual dormancy break. So, for this project, visible sprouting is used as a proxy and is an important quality parameter requiring management.”
Thirty-nine varieties, skewed towards those for crisping and chipping markets, have been grown on two SPot Farms demonstration plots in North Lincolnshire and Shropshire, with nine extra varieties trialled at the latter in the second season. The plots received the same crop inputs and protection as the surrounding commercial field crops.
After hand harvesting, daughter tubers were stored at 15degC and assessed for sprouting at Sutton Bridge Crop Storage Research. Dormancy was recorded as days from estimated tuber initiation to 50% sprouting (>3mm) of the 50-tuber sample population.
Many methods have been, and are, used by different organisations and companies to provide data on varietal dormancy.
“Unfortunately, in many cases the methodology or description of dormancy rating is somewhat or entirely unclear,” says Dr Harper.
“Dormancy is generally considered to be initiated at tuber initiation [TI], but in most available reports it is measured from harvest date.”
Previous work has shown growing conditions post-TI can have an effect, he adds.
“It found unusually cold or hot weather during tuber development in the field often resulted in long or short dormancy respectively.
“We found a surprisingly big difference in some varieties’ dormancy at the two sites. It ranged from nothing in Ivory Russett to as much as 47 days in Mozart.
“The reason’s unclear as there was no apparent overall site effect, although harvests were a month apart. The seed was randomly drawn from the same stock and sites were planted within a week of each other.”
However, the two years of trials have allowed a relatively robust variety dormancy ranking list [see graph] to be drawn up, Dr Harper says.
“The third and final year of the trials should provide additional data to support the ranking. The variation in the length of dormancy of seed from a common sample of the same stock when grown at different sites was unexpected and still unexplained.”
However that did not generally affect the relative dormancy when ranked as an average duration, he adds.
“This variation will be important in establishing the confidence limits of the ranking for the entire trial.”