Pollen Effects on Chilling Requirements of Almond and Almond-Peach Hybrid Seeds1

Effect of genotype on variation in chilling requirement among almond seed populations was studied. Pollen of different varieties used on the same seed tree changed embryo genotype and, subsequently, the chilling requirements of the populations of seeds produced. There was a direct correlation between time of bloom of seed and pollen parents and the length of chilling required by their offspring seeds. Chilling requirements were not significantly different in seed populations resulting from reciprocal crosses involving varieties of long and short chilling. Such seed populations had comparable genotypes but were exposed to different maternal effects. Embryo genotype was a controlling factor in determining seed chilling requirement in almond. A distinction between systems affecting inheritance of time of bloom in almond was shown in that ‘Tardy Nonpareil’, a late-blooming bud mutation of ‘Nonpareil’, transmits later bloom to its seedling offspring but did not transmit longer chilling to the seeds.