Interspecific hybridization in Phalaris: Hybrids between Phalaris tuberosa and the hexaploid race of Phalaris arundinacea

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Abstract
Interspecific hybrids from the cross Phalaris tuberosa (2n = 28) x Phalaris arundinacea (2n = 42) are described. The close relationship between P. tuberosa and the hexaploid race of P. arundinacea is indicated by the ease of hybridization. The F1 hybrid is functionally male-sterile, but sets occasional seed when backcrossed to P. tuberosa. Meiosis in the 35-chromosome F1 hybrids was irregular. Pairing at diakinesis averaged 11.3 bivalents, with a range of 7–14. Univalents were present in all hybrids, averaging 10.3 per cell, and were observed as laggards at anaphase I and II. Sterility appears to be largely chromosomal, associated with numerical and structural differences between partially homologous genomes. The cytological behaviour of the 70-chromosome allopolyploids, produced by doubling the F1 hybrids, was fairly regular. The predominant diakinesis association was in the form of bivalents, with a mean value of 32.1. Univalents and quadivalents were present, but at a low frequency. There was a continued expression of allosyndetic pairing as indicated by the formation of bridges and fragments at anaphase. The average fertility of allopolyploids, despite irregularities at meiosis, was high, and only 30% below the P. tuberosa controls. The growth of the F1 hybrids was superigr to that of the parents, both in the seedling stage and in swards. This superiority was most pronounced in the autumn and summer. In this respect the hybrid combines the seasonal growth characteristics of both parents. The unusual vigour, long growing season, and adaptability of the hybrid justify efforts to develop it as a commercial variety. Three possible plant-breeding approaches to achieve this objective are presented.

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