Morphology, Origin and Cytogenetics of a 48-Chromosome Panicum maximum

Abstract

Chromosome behavior, method of reproduction, fertility and morphological characteristics were studied in 48-chromosome plants derived from a 32-chromosome accession (PI 298996) of guineagrass (Panicum maximum Jacq.). Multivalent associations were found at diakinesis and metaphase I which resulted in 33% of the microsporocytes having one or more laggards at anaphase I. Pollen stainability in I₂KI ranged from 65% to 85%. Embryo sac analyses indicated that plants reproduced by a high level of apomixis with some sexual embryo sac development which probably accounts for the occasional off-type plants produced. The 48-chromosome plants apparently originated from the fertilization of a 32-chromosome unreduced egg from an apomictic plant by a reduced 16-chromosome male gamete. The 32- and 48-chromosome plants were morphologically simlar. A 40-chromosome plant resulting from a reduced 24-chromosome egg fertilized by a 16-chromosome male gamete was also found among the open-pollinated offspring from a 48-chromosome plant. The discovery of a 48-chromosome plant in a 32-chromosome accession and a 40-chromosome plant in a 48-chromosome offspring are other examples of the influence of apomixis in formation and maintenance of new cytoypes in nature.