Miniature Centric Fragment Chromosomes in Mutagen‐treated Pearl Millet, Pennisetum typhoides 1

A miniature centric‐fragment chromosome was observed in pearl millet, Pennisetum typhoides (Burm.) Stapf and C. E. Hubb., subjected to thermal neutron and ethyl methane sulfonate treatments. The very small chromatic particles oriented themselves at the metaphase I plate, and divided and moved to the poles at anaphase I, but were irregular in their behavior at anaphase II. Most plants with these centric‐fragment chromosomes were found in the thermal neutron treatments, with some in the ethyl methane sulfonate treatments, but none in the controls. One miniature centric‐fragment chomosome was the most common number present in microsporocytes of single plants, with the exception of one plant which contained two fragment chromosomes per cell. Size variation in the particles was noted in one plant. These miniature centric‐fragment chromosomes, discovered in mutagen‐treated pearl millet, may have an origin similar to the small ring chromosomes described in maize.