The use of isozymes as an aid in distinguishing in vitro produced zygotic and nucellar genotypes in citrus sinensis and citrus limon seedlings

Abstract

Five isozyme systems, esterase (EST), glutamate oxaloacetate transamlnase (GOT), malate dehydrogenase (MDH), malic enzyme (ME) and peroxidase (PXD) were assayed using embryos, calli, roots, cotyledons and leaves of Citrus sinensis CV. "Valencia" and Citrus limon cv . "Rough Lemon" by polyacrylamide gel electrophoresis. Ls ozyrne profiles of these five enzyme systems were used to dist ingui sh nucellar from zygotic genotypes of in vitro produced seedlings. The frequency of zygotic seedlings resulting from open-pollination was found to vary between 0.0% and 6. 3%. Embryo culture significantly enhanced the recovery of zygotic seedlings in "Rough Lemon" hut not in "Valencia". All, except, one, of 86 plantlets produced via in vitro nucellar embryogenesis were found to be genetically uniform. Tissue and age specific PXD isozyme patterns were ·observed. Isolation and culture of preformed embr-yos resulted in the production of upto 13 and 9 seedlings per seed ln "Valencia and "Rough Lemon", respectively. The use of isozymes and tisspe culture as tools for the identification of nucellar and zygQtic genotypes in polyembryonic Citrus species is discussed. Isozymes can be used for the preliminary identification of potential new genotypes resulting from cross-pollination and tissue culture manipulation.