Genetic architecture of fruit size and shape variability in non-flat peach

Peach is an important tree fruit, widely cultivated throughout the world. Its fruit has a distinctive flavor and abundant nutrition. Some peaches are eaten fresh, whereas others are processed into a variety of products, such as juices, beverages, and jams. Peach has a high development, utilization, and market value.

At present, the major peach varieties grown worldwide can be broadly classified into flat and non-flat peaches. Pronounced variations in fruit shape have been reported across non-flat peach accessions, ranging from oblate to ovate/elongated. Fruit size is another important agronomic and pomological trait that affects both appearance and yield. These traits are the products of diverse genotypes and environmental factors. In addition to the primary impact of temperature, orchard management—including rootstock selection, fertilization, irrigation, and/or pruning—also has a significant effect on these traits.

Fruit color, shape, and size are important factors that influence customers’ purchasing decisions. Therefore, they are also the main target traits for breeders. Dr. Marco Cirilli recently published the article “Genetic and phenotypic analyses reveal major quantitative loci associated to fruit size and shape traits in a non-flat peach collection (P. persica L. Batsch)” in Horticulture Research. Dr. Cirilli is an associate professor in the department of Agricultural and Environmental Sciences at the University of Milan.

The study was performed under field conditions over two consecutive growing seasons in Imola, Italy and included 172 round and 11 flat occidental peach cultivars. Dr. Cirilli and his colleagues used objective quantitative measurements to phenotype fruit size and shape under controlled fruit load conditions. They then dissected the genetic architecture of fruit size and shape by identifying loci that showed strong trait-genotype associations.

The team collected quantitative phenotypic data using a digital caliper and image-analysis software. Compared with other methods, this image-based approach more accurately captured variability in fruit shape. GWAS was then performed to detect loci associated with fruit size and shape traits in the panel of 172 non-flat accessions using three statistical methods: MLMM, FarmCPU, and Blink. A total of 15 (2018), 13 (2019), and 10 (average) SNPs were found to be significantly associated with the fruit traits. The high LD region qSHL/Fs6.1 was associated with both fruit size and longitudinal shape by GWAS and linkage analyses, suggesting that it may have pleiotropic effects. Allelic variation at this locus was largely represented by two haplotype blocks (H1 and H2), and the H1, H1H2, and H2 genotypes were strongly associated with ovate, round, and oblate shapes.

This work is the first effort to characterize the genetic architecture of fruit shape variability in non-flat peach cultivars. As the authors state, “The identification of major loci controlling fruit shape and size, and associated markers, provides useful information for breeding and opens opportunities for more in-depth studies aimed at improving their resolution and identifying underlying variant(s).”