Crossability and Characterization of Interspecific Hybrids between Sexual Pennisetum glaucum (Pearl Millet) and a New Cytotype (2n=56) of Apomictic P. squamulatum

Abstract

Summary Pennisetum squamulatum is an important species belonging to tertiary gene pool of cultivated pearl millet as potential donor of several genes. Recently a new cytotype with 2nϭ56 chromosmes has been identified. Crossability of this cytotype has been studied with diploid and induced tetraploid pearl millet. The hybrids produced with this novel cytotype were compared for their characteristics with the hybrids previously reported with widely reported 2nϭ54 P. squamulatum cytotypes. Strong incompatability barriers were observed between 2nϭ56 cytotype with diploid pearl millet, and hybrids could not be obtained even after embryo rescue. Limited crossability was obtained with tetraploid pearl millet and 2 successful hybrids were produced. Their hybridity was confirmed by morphology, flowcytometry and cytology. The hybrids were highly fertile, perennial and segregated for mode of reproduction. Segregation for other traits confirmed heterozygous nature of P. squamulatum 2nϭ56 cytotype. Cytological investigations suggested 2nϭ8x nature of this cytotype. Successful hybridization between pearl millet and this new cytotype shall be important for introgression of useful traits as well as to study inheritance of traits such as perenniality, apomixis and tolerance to stresses.

Sequential Reduction of Pennisetum squamulatum Genome Complement in P. glaucum (2n=28)*P. squamulatum (2n=56) Hybrids and their Progenies Revealed its Octoploid Status

“…Cytological studies on F 1 hybrids involving P. glaucum (4x) and P. squamulatum 2nϭ56 (8x?) supported the view on this species being octoploid based on xϭ7 (Kaushal et al 2007). Had the species been a hexaploid, the contribution of P. squamulatum in its F 1 hybrid with 4x, P. glaucum, would be a triploid gamete that will not show a near normal meiotic system with predominant bivalent associations and higher fertility, as observed by the present workers.…”

“…The present studies on crossability of P. squamulatum with P. glaucum together with earlier reports (Dujardin and Hanna 1983, Kaushal et al 2007, Marchais and Tostain 1997, it is clear that P. squamulatum hybridizes easily with P. glaucum when the chromosome number of latter is doubled (2nϭ4xϭ28). The success of the cross is an ample indication that the two species are close enough and only barriers to crossability is the difference in ploidy level between the two species, and not the basic chromosome number (accounting for Endosperm Balance Number (EBN) considerations).…”

“…Flow cytometric analysis was useful in hybrid identification where parents were polymorphic in total DNA content, such as in crosses involving P. glaucum (2x, 4x), P. squamulatum and their F 1 hybrids. Flow cytometry was performed on young and disease free leaves, chopped with fine razor blade and the isolated nuclei stained in DAPI (4Ј-6 diamidino-2 phenylindole) following Kaushal et al (2007) and observations with Partec PA1 flow cytometer.…”

“…Sporadic evidences for closeness of P. glaucum with P. squamulatum have been gathered by reports on crossability between the two species (Dujardin and Hanna 1983, Kaushal et al 2007, Marchais and Tostain 1997, DNA content trends in Pennisetum species (Martel et al 1997), isozyme studies (Kaushal et al 1997), internal transcribed spacer (ITS) sequences (Martel et al 2004), and crossability with other xϭ7 species such as P. purpureum (Hanna 1990).…”

Morphological, cytological and reproductive characterization of tri-species hybrids (GOS) between Pennisetum glaucum, P. orientale and P. squamulatum

“…Interspecific hybrids (F 1 s and advanced back-cross generations) involving pearl millet were produced with P. orientale (Patil and Singh 1964;Hanna and Dujardin 1982;Hanna 1983a, 1984a;Zadoo and Singh 1986), as well as with P. squamulatum Hanna 1983b, 1985;Kaushal et al 2007) in a view to improve genepool, study inheritance of apomixis and to determine their cytotaxonomic relationships with pearl millet. Cytogenetic studies on interspecific hybrids revealed limited affinity of chromosomes of these two species with pearl millet.…”