SYNAPTIC MUTANT AFFECTING ONLY MEGASPOROGENESIS IN POTATOES

A synaptic mutant was found among progeny from the cross W5295.7 (I) × W5337.3 (J), where both I and J are diploid potatoes (2n= 2x = 24) derived from crosses between group Phureja and haploid group Tuberosum. The mutant is inherited as a simple Mendelian recessive, designated sy. Meiotic abnormalities of the mutant during megasporogenesis include univalents at diakinesis; univalents, unoriented bivalents, and precocious chromatid separation at metaphase I; elongated, curved, and multiple spindles; abnormal chromosome distribution at anaphase I; restitution nucleus formation at telophase I; and abnormal cytokinesis at the tetrad stage. The expression of sy is specific to megasporogenesis, since normal synapsis occurs in microsporogenesis. It is possible that some of the abnormalities in megasporogenesis could result in first division restitution (FDR) 2n egg formation. Two mutant clones that are heterozygous for the yellow flesh gene (Yy) were crossed as females with nulliplex (yyyy) tetraploids to detect the mode of 2n egg formation by half-tetrad analysis. Initial results indicate that the clones produced 2n eggs by FDR. The sy mutant is the first report of an inherited synaptic abnormality in megasporogenesis; it is valuable as a source of both aneuploids and 2n eggs for genetic and breeding investigations. © 1979 AMRICAN GENETIC ASSOCIATION.