EVALUATION OF APOMICTIC REPRODUCTION IN A SET OF 39 CHROMOSOME MAIZE-TRIPSACUM BACKCROSS HYBRIDS

An apomictic form of hybrid maize (Zea mays L.) would provide an immor talized line which would be stabilized against genetic change. The dev elopment of agronomically superior, apomictic maize hybrids could prov ide a superior level of food security in developing nations as well as altering commercial and public maize breeding programs systems in dev eloped nations. Backcross selections obtained from an apomictic, 38-ch romosome (20 maize + 18 Tripsacum L.) maize-Tripsacum hybrid have resu lted in the development of apomictic, 39-chromosome individuals with 3 0 maize + nine Tripsacum chromesomes. The Identification of these mate rials advances two major objectives: (i) the elimination of nine Trips acum chromosomes which do not possess the gene(s) controlling apomicti c reproduction; and (ii) the continued refinement of an apomictic maiz e line. This study was conducted to determine whether the 39 chromosom e materials reproduce by apomixis. Evaluations were performed by means of cytological, isozyme, and molecular DNA methods to assay the cytol ogical and genetic uniformity within and between the families. The lac k of variation within families and among their offspring indicates tha t both families reproduce by apomixis. In addition, the successful tra nsfer of apomictic genes from Tripsacum, into a maize-Tripsacum backcr oss hybrid with 2n = 3x = 30 maize and 1n = 1x = 9 Tripsacum chromosom es, is demonstrated. The generation of these materials indicates that continued breeding and selection within such materials could result in the eventual development of a hybrid maize with an apomictic reproduc tive system.