Genetic factors driving variation of stomatal density in apple

Severe drought and extreme temperatures are two main impacts of climate change, resulting in increased abiotic stress response from plants and an increased demand for fresh water. Breeding for functional traits such as stomatal density can enhance the climate resilience of plants. As stomata control plant-water relations, their function makes them promising targets for improving crop performance in response to climatic stresses. We assessed the variation in stomatal density in a genetically diverse collection of 269 apple (Malus × domestica Borkh.) accessions located in Waedenswil, Switzerland, across the years 2019, 2020, and 2021. Results showed that stomatal density resembled a normal distribution across the population with a median of 361, 340 and 339 mm-2 for 2019, 2020, and 2021, respectively. Although no significant variation was observed between the three years, stomatal density was significantly different among the diverse accessions, from a minimum of 181 mm-2 to a maximum of 531 mm-2. Stomatal density was negatively correlated with intrinsic water-use efficiency (rs = -0.51, p<0.001), as determined by leaf gas-exchange. We identified single nucleotide polymorphisms (SNPs) associated with stomatal density on chromosomes 2, 9, and 10 through genome-wide association studies. Specifically, on chromosome 9, a key genetic regulator of stomatal development was identified in the haploblock including the most significant SNP. This haploblock is composed of six biallelic SNPs within 102.3 kbp. Within this haploblock, specific allelic combinations varied in stomatal density by nearly 100 mm-2. Furthermore, two additional candidate genes were identified close to the haploblocks including SNPs associated with stomatal density on chromosome 10. The physical distances to these genes were greater: approximately 530 and 1,810 kbp away from the associated SNPs. Our study identified the genomic regions driving the variation of stomatal density in apple, providing the foundation for targeted breeding of stomatal traits to enhance resilience to climate change.

Francesca Zuffa won the ISHS Young Minds Award for the best poster presentation at the XVI EUCARPIA Symposium on Fruit Breeding and Genetics in Germany in September 20233.

Francesca Zuffa, Molecular Plant Breeding group, ETH Zurich, Universitaetstrasse 2, 8092 Zurich, Switzerland, e-mail: francesca.zuffa@usys.ethz.ch

The article is available in Chronica Horticulturae