A common way to maintain fruit quality during storage and transport is by cooling of the fresh produce, to halt metabolism and prevent over-ripening. However, low temperature storage can also lead to chilling injury, an effect that is often worse than the beneficial effects of cooling. Chilling injury leads to uneven or arrested ripening, loss of flavour and change in texture. During transport, fresh products are often stored at suboptimal temperatures, leading to problems such as mentioned above.
Recently a cold-induced MYB transcription factor was identified in pepper fruit (Ge et al, 2023). Transient down-regulation and overexpression of this gene in injected pepper fruits led to increased and decreased postharvest cold-tolerance symptoms, respectively. This study provided some interesting leads for the underlying mechanisms, but this is far from complete and mainly based on in vitro experiments.
Using allele mining of a sequenced tomato collection we identified a heirloom/vintage tomato accession with a beneficial allele of the tomato ortholog of this MYB gene. Visual inspection of fruits in pilot cold storage experiments (1 month storage at 4 degrees, followed by two weeks storage at 20 degrees) clearly showed an improved cold tolerance of this accession compared to all control accessions tested. The lack of any visual chilling injury symptoms in this accession suggests that this MYB allele prevents or delays the development of at least some, if not all, aspects of chilling injury.
We aim to further proof and unravel the role of this MYB transcription factor allele in the response to postharvest refrigeration of tomato fruit. We aim to further elucidate the genetics underlying postharvest cold tolerance, to unravel the regulatory gene networks controlled by this MYB transcription factor gene using stable gene-edited MYB KO and promoter mutant lines and to perform a detailed study of its effect on various chilling injury parameters (colour, texture, visual symptoms, membrane damage, off-flavours) and basic fruit quality characteristics (sugars, acids, aroma). Possible effects of this gene on cold-tolerance during cultivation will be studied in this project as well. Last but not least, we will translate the knowledge generated in tomato to other horticultural crops. We expect that the generated knowledge (in the form of QTLs, genes and alleles) and the developed plant materials will significantly increase the flexibility in the postharvest chain and improve the quality of stored fruits, thereby reducing food waste.

The main objective of this project is:
• To study the genetic, molecular and physiological basis underlying (postharvest) cold tolerance in tomato
o Unravel the genetics of postharvest cold tolerance (WP1)
 Confirm the causal role of the cold-tolerance related MYB gene in postharvest cold tolerance
 Is the MYB gene the major gene for postharvest cold-tolerance or does it have a polygenic nature with additional QTL’s?
 Detailed phenotypic evaluation of chilling injury symptoms and general fruit quality
o Study the effect of the postharvest cold-tolerance related MYB gene on pre-harvest cold tolerance (WP2)
 Cultivation in regions with cold periods during cultivation
o Unravel the postharvest cold tolerance gene network (WP3)
 What are downstream target genes of the MYB transcription factor and what’s their gene function?
 Which genes or epigenetic marks regulate the MYB?
o Develop (Pre)-Breeding materials with enhanced postharvest cold tolerance (WP 4)
 Introgress the MYB allele from the heirloom variety in modern tomato backgrounds to facilitate breeding
 Identify and introgress beneficial alleles of downstream MYB target genes in modern tomato backgrounds
o Apply the generated knowledge to other cold-sensitive crops (WP5)
 Allele mining of MYB orthologs in other crops, such as pepper, eggplant, cucumber and melon and the effect on postharvest chilling injury

The exponential growth of the world population and the reduction of available land for agriculture, due to political choices and climate change, poses one of the largest challenges for the near future: how can we provide sufficient food to feed the growing world population. Of all the fresh produce, up to 40% is discarded at any point in the chain from farm to fork. Therefore, reducing food loss/waste in the postharvest chain is a very effective strategy to increase the availability of food, even without an increased production.
At ambient temperature, the shelf life of horticultural products is generally short and refrigeration is one of the most effective strategies to prolong the shelf life of fresh produce by slowing down metabolic processes leading to deterioration. However, refrigeration leads to postharvest chilling injury in several major crops, such as tomato, pepper, potato and banana. Although difficult to quantify, there is a general consensus that postharvest chilling injury is a major contributor to food loss. The development of crop varieties with improved resilience to postharvest refrigeration could have a major impact on the flexibility in the postharvest chain and the reduction of food waste.

Expected results:
• Development of (pre-)breeding materials with enhanced (pre- and) postharvest cold tolerance. Such tomatoes would strongly increase the flexibility in the postharvest chain and avoid postharvest losses due to chilling injury;
• Detailed insight in the genetic, molecular and physiological basis of (pre- and) postharvest cold tolerance in tomato fruit
• Identification of the key genes and alleles involved in (pre- and) postharvest cold tolerance, which can be used as molecular markers to efficiently select and breed for (pre- and) postharvest cold tolerant tomato varieties or can be used as potential targets for reverse genetics approaches, such as TILLING and gene editing
• Insight in the applicability of the generated knowledge in other crops, e.g. by the discovery of novel alleles in postharvest cold tolerance-related genes in pepper, eggplant, cucumber and melon (allele mining, TILLING)