Читать книгу Principles of Plant Genetics and Breeding - George Acquaah - Страница 297

This pathway has been described only once and has been little examined or discussed in the literature. Consequently, some detail regarding the results in this research will be presented. In 1958, Dr. M. Borovsky, Institute of Agriculture, Kishinev, Moldova, performed a series of hybridizations between a diploid popcorn line identified as Risovaia 645 and a sexual diploid (2n = 2x = 36) T. dactyloides clone with the first maize‐Tripsacum hybrids being generated in 1960 (Borovsky 1966; Borovsky and Kovarsky 1967). The F₁ hybrids generated from the experiments possessed 28 chromosomes (10Mz + 18Tr). The F₁ plants were completely male sterile and were highly seed sterile. Backcrossing with diploid maize identified that some of the F₁ hybrids were approximately 1–1.5% seed fertile and resulted in the production of progeny possessing 28 chromosomes (10Mz + 18Tr) and 38 chromosomes (20Mz + 18Tr). When the F₁ was backcrossed to the Tripsacum parent, the fertile F₁'s generated progeny with 28 chromosomes (10Mz + 18Tr) and 46 chromosomes (10Mz − 18Tr + 18Tr). The complete set of backcrosses with maize and Tripsacum resulted in a ratio of approximately 10 (28‐chromosome plants) to one (38‐ or 46‐chromosome plant). Phenotypic observations suggested that the 28‐chromosome progeny were not different from their 28‐chromosome parent while the 38‐ and 46‐chromosome progeny were clearly different. In addition, some seed generated by the 28‐chromosome F₁'s were polyembryonic. Additional evaluations on the 28‐chromosome F₁ and its 28‐chromosome progeny suggested that these F₁ plants and their progeny were apomictic. This early, non‐replicated experiment is to date the only report where a 28‐chromosome F₁ hybrid was maintained by apomixis. Polyembryony was noted, and a diploid sexual Tripsacum was used to generate the interspecific hybrid.