Principles of Plant Genetics and Breeding

66 CHAPTER 4
(a)
(b)
Figure 1 (a) A highly maize-like 38-chromosome
apomictic maize–Tripsacum hybrid. This selection has no or
few tillers and exhibits a distinct maize phenotype. (b) A top
and second ear taken from one of these highly maize-like
apomictic individuals. Note the eight rows on the ear are
rarely found in other apomictic maize–Tripsacum hybrids.
Figure 2 A series of maize–Tripsacum ear types.
Left to right: dent corn, apomictic 39-chromosome
hybrid, apomictic 38-chromosome hybrid (“Yudin”),
apomictic 56-chromosome hybrid, three apomictic
46-chromosome hybids, and tetraploid Tripsacum
dactyloides.
translocation (Figure 3). RAPD (random amplified polymorphic
DNA) markers previously known to be associated
to apomixis continue to be present in this germplasm.
Cytological analysis of this particular chromosomal element
suggests the chromosome carries the nucleolus-organizing
region and the Tr16L satellite. This small isochromosome
may indeed possess the loci conferring apomixis in this
material.
Regardless of the favorable light academics and
researchers alike shed upon the prospects in this area of
study, this research endeavor continues to be difficult, timeconsuming,
and expensive. Though an apomictic maize
prototype has been developed (US patent no. 5,710,367)
gene transfer through traditional breeding approaches is
questionable. The development of apomictic maize through
its hybridization with Tripsacum offers many opportunities;
however, many years of additional research will be required
for this to be realized.
References
Borovsky, M. 1966. Apomixis in intergeneric maize–
Tripsacum hybrids. In: Meeting on problems on apomixis
in plants. Saratov State University, Saratov, Russia,
pp. 8–9.
Borovsky, M., and A.E. Kovarsky. 1967. Intergenus
maize–Tripsacum hybridizations. Izvestia Akad. Nauk
Moldovaski SSR 11:25–35.
Galinat, W.C. 1973. Intergenomic mapping of maize,
teosinte and Tripsacum. Evolution 27:644–655.
Grimanelli, D., O. Leblanc, E. Espinosa, E. Perotti, D.
Gonzalez de Leon, and Y. Savidan. 1998. Mapping
diplosporous apomixis in tetraploid Tripsacum: One gene
or several genes? Heredity 80:33–39.