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 immortalized line which would be stabilized against genetic change. The development of agronomically superior, apomictic maize hybrids could provide a superior level of food security in developing nations as well as altering commercial and public maize breeding programs-systems in developed nations. Backcross selections obtained from an apomictic, 38-chromosome (20 maize + 18 Tripsacum L.) maize- Tripsacum hybrid have resulted in the development of apomictic, 39-chromosome individuals with 30 maize + nine Tripsacum chromosomes. The identification of these materials advances two major objectives: (i) the elimination of nine Tripsacum chromosomes which do not possess the gene(s) controlling apomictic reproduction; and (ii) the continued refinement of an apomictic maize line. This study was conducted to determine whether the 39 chromosome materials reproduce by apomixis. Evaluations were performed by means of cytological, isozyme, and molecular DNA methods to assay the cytological and genetic uniformity within and between the families. The lack of variation within families and among their offspring indicates that both families reproduce by apomixis. In addition, the successful transfer of apomictic genes from Tripsacum, into a maize-Tripsacum backcross hybrid with 2n = 3x = 30 maize and In = 1x = 9 Tripsacum chromosomes, 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 reproductive system.