The need for speed – developing new methods for reducing the juvenility period in trees


Supervisors: Prof Timo HytonenMs Amanda Karlstrom, Dr Richard Harrison (NIAB EMR); Tracy Lawson (University of Essex)

This student will be registered with the University of Essex. Beginning in October 2021, the successful candidate should have (or expect to have) an Honours Degree (or equivalent) with a minimum of 2.1 in Plant Science, Biology, or other related science subjects.


The juvenility period of trees has long been a barrier to more rapid cycling of generations in breeding programmes. Juvenility is the period in which a seedling remains in an immature vegetative growth state, without the differentiation of meristems into floral tissue. For tree fruit crops this is usually 7-10 years without the use of grafting. Empirical studies have shown that there is natural variation in this trait, reducing the time taken to floral differentiation to as little as 1.5 years in apple, post-germination. Understanding and harnessing this, in combination with ‘speed breeding’ approaches using optimised growth conditions under high light and temperature, could lead to a dramatically shortened breeding cycle and enormously decrease the time to market of tree fruit selections from breeding programmes, taking a roughly 12-20 year cycle to as little as 5-7 years.

Objectives and approaches

This PhD aims to understand the genetic and environmental control of the juvenility process. The student will carry out QTL mapping to identify loci controlling juvenility. For this purpose, a cross between parents with contrasting juvenility period has been carried out and genotyped population is available. This data will be utilised to identify candidate genes for transformation into the genetically tractable Gala line of apple for functional validation.

CRISPR-Cas9 gene editing will be used for genetic transformation to knock out candidate genes, which is expected to lead to a dramatic decrease in the length of the juvenile period. Based on these studies genetic markers will be developed for the length of the juvenility period. In addition, the effect of greenhouse forcing on shortening the juvenile phase will be tested following the approaches used in the birch research programme at the University of Helsinki, where birch trees can be forced to flower in the first year by manipulating growing conditions. This PhD also offers the opportunity for a study visit to the University of Helsinki in the lab of Timo Hytönen.


The successful candidate will gain a wide range of experience in plant genetics, breeding, genomics and gene functional analysis.


Anyone interested should fill the online application form before the deadline of 8th February 2021. If need further help or clarification, please contact

Contact Prof Timo Hytonen for an informal discussion on research contents.