Evaluation of Apomictic Reproduction in a Set of 39 Chromosome Maize‐Tripsacum Backcross Hybrids

Abstract

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 1n = 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.

Meiotic study of Zea mays ssp. mays (2n = 40) x Tripsacum dactyloides (2 n = 72) hybrid and its progeny

“…However, reduction of Tripsacum chromosome complement was observed in 65% of maize/Tripsacum F1 progeny plants. A previous report (Kindiger et al 1996b) also showed partial loss of Tripsacum chromosomes in backcrosses of an apomictic maize/Tripsacum F1 hybrid (2n = 56).…”

“…Different authors have investigated the possibility to introgress some characteristics from Tripsacum to maize, for example, disease tolerance (Bergquist, 1981), constitutive aerenchyma (Ray et al 1999), and gametophytic apomixis (Leblanc et al 1995b;Kindiger et al 1996b;Lukina and Chistyakova, 1999).…”

Co‐segregation of AFLP and RAPD markers to apospory in Guineagrass (Panicum maximum Jacq.)

“…Diplosporous form of apomixis have been identified in some species of Poa (Huff, 1992) and Tripsacum dactyloides (Dewald and Kindiger, 1998). Although there have been several attempts to transfer the apomixis from various wild relatives to the major crops (Kindiger et al ., 1996a; Morgan et al ., 1998), no apomictic commercial cultivars have been released to date.…”

Breeding Perennial Grain Crops

“…All 20-chromosome backcross plants derived to date have been annual and non-apomictic. Kindiger et al (1996) derived an annual, 39-chromosome line that carried 9 Tripsacum chromosomes and displayed an intermediate level of apomixis.…”

“…The difficulties encountered in introgressing apomixis from Tripsacum into maize (Kindiger et al, 1996) should temper hopes for a rapid synthesis of perenniality with high grain yield. Whatever the initial population, and even with marker-assisted selection, the process of recovering perennial, winterhardy segregants with maize-like ears, and then breeding for yield and other agronomic traits will be long and arduous.…”