Unreduced embryo sacs escape fertilization via a ‘female-late-on-date’ strategy to produce clonal seeds in apomictic crabapples

• Embryo sac maturation time influenced formation of clonal seeds.
• 2n embryo sac escaped fertilization via to development delay.
• Artificial manipulation of FLD was useful in apomictic breeding program.

Tea crabapple (Malus hupehensis Redh. var. Pingyiensis) is a typical facultative apomictic apple rootstock. Its asexual seed formation is affected by environmental temperature; however, little is known regarding the mechanisms underlying this phenomenon. In this study, we found that unreduced embryo sacs escaped fertilization due to a developmental delay, which is referred to as the female-late-on-date (FLD) strategy. The percentage of FLD was positively correlated with the apomictic capacity and was greatly affected by the environmental temperature during blossoming and pollination. Temperature also affected the FLD and apomictic capacity by altering pistil longevity. Taken together, FLD is a crucial developmental event for apomixis in apomictic crabapples, which prevents the unreduced embryo sacs from pollination and fertilization. Artificial manipulation of FLD by shortening pistil longevity may be used to control the percentage of apomictic seeds, which is helpful not only for uniform seedling production but also for the apomictic breeding program.