Non-random inheritance of mitochondrial genomes in Citrus hybrids producedby protoplast fusion

Somatic hybridization offers the possibility of manipulating chloroplast an d mitochondrial genomes and evaluating their role on cultivar qualities in citrus. Numerous associations between Willow-leaf mandarin (Citrus delicios a Ten.), as embryogenic parent, and sweet orange cv. Valencia (Citrus sinen sis (L.) Osb.), as mesophyll parent, and between Willow-leaf mandarin (embr yogenic parent) and grapefruit cv. Duncan (Citrus paradisi Macf.) (mesophyl l parent) were obtained by the fusion of protoplasts induced by polyethylen e glycol. Regenerated plants were characterized by flow cytometry and nucle ar and mitochondrial DNA restriction fragment length polymorphism (RFLP). A ll plants were diploid. Diploid plants with the nuclear RFLP patterns of ma ndarin or sweet orange were identified in the progeny between these two par ents, while only grapefruit nuclear types were found in the mandarin + grap efruit progeny. The diploid plants with the nuclear profile of the mesophyl l parent originated systematically from cells formed through spontaneous as sociation of the nuclear genome of the mesophyll parent and the mitochondri al genome of the embryogenic parent. These plants are assumed to be allopla smic hybrids or cybrids. They were viable and have been propagated for fiel d testing.