Sexual and Nucellar Embryony in F1 Hybrids and Advanced Crosses of Citrus with Poncirus1

Abstract

Fourteen hybrid citrus progenies having polyembryonic Poncirus as a parent or grandparent were classified for their type of embryony, by seed dissection. Seedling populations from some of the hybrids were also studied. The ratio of polyembryonic (P) to monoembryonic (M) individuals was nearly 1:1 among 52 F 1 hybrids from P Citrus × P Poncirus. The ratio was about 1 P to 6 M among 121 F 1 's from 5 crosses of M Citrus with P Poncirus. Among 15 individuals from a backcross of Citrus × (Citrus × Poncirus) which was M × P, only 2 were clearly P. From backcrosses of M × M(?) parents, 28 individuals were M, 3 were probably M, and only 1 (a possible outcross?) was P. Results from the P × P and P × M crosses are in contrast to those from similar types of crosses within Citrus, where much higher proportions of P hybrids have usually been found. Results from the M × M(?) crosses probably support the concept that crosses between monoembryonic strictly sexual taxa produce only monoembryonic sexual progeny. A genetic basis for the inheritance patterns is discussed.