Beyond zygotic and nucellar origins: improving the polyembryony model in citrus

Embryos one, two, and three can give rise to plants identical, similar, and different from the mother plant. The size of the embryo does not guarantee its genetic identity. The model of polyembryony in citrus establishes that the larger embryo is identical to the mother plant, and the smaller one is zygotic. This work aimed to determine the percentage of polyembryony, the number of embryos, and the genetic similarity index (GSI) of three embryos (one, two, and three) compared to the mother plant in seeds of Mandarin amblycarpa, to provide a broader view of polyembryony. This is the first study to determine the genetic identity of embryos based on size using microsatellites and categorize them into three groups: identical to, similar to, and different from the mother plant. Open-pollinated fruits were harvested in two cycles (2020 and 2021). The percentage of polyembryony was determined, and the number of embryos per seed was counted. By comparing banding patterns produced by SSR microsatellites, the GSI was calculated. Nei distances were calculated and analyzed by UPGMA (unweighted pair group method with arithmetic mean). Since the variation occurred at different loci, Nei's genetic distances allowed embryos with the same GSI to be regrouped in different dendrogram branches. As plants identical to, similar to, and different from the mother plant were found in embryos one, two, and three, it is evident that embryo size does not determine the genetic identity of the plant; therefore, it is necessary to modify the current model of polyembryony. Additionally, we propose using the term different from the mother' instead of 'sexual origin', as the resulting plant might derive from a mutation.