Problems in the identification and utilisation of interspecific hybrids of poa in a plant breeding programme

Abstract

Twenty-four Poa ampia X P. pratensis hybrids were obtained following high temperature treatment of P. ampia prior to anthesis, and 49 hybrids following short day treatment of P. ampia; parental biotypes of both species were highly apomictic. The amphimictic species P. iberica and P. longifolia were both crossed with P. pratensis; four F1 hybrids were obtained from each series of crosses. Somatic chromosome numbers of Fl hybrids indicated that probably 60 per cent were derived from two reduced gametes, 34 per cent from one unreduced and one reduced gamete, a further six per cent could not be classified. Most F1 hybrids were fertile but 12.3 per cent were sterile or nearly so. Principal co-ordinate analysis and canonical analysis of discriminance on data from spaced plant field trials were used to confirm identification of hybrids and maternal types.Data from two spaced plant field trials with eleven hybrid progenies and six control parental biotypes were used to examine the possibility of distinguishing between predominantly apomictic and predominantly sexual families. Discrimination between different types of progeny was possible from examination of both the relative magnitude of determinants from within family dispersion matrices and the clustering of individual points on scatter diagrams from principal component, principal co-ordinate or canonical analyses. Similar techniques also enabled separation of apomictic and sexual families on seedling characters. Aberrants could be distinguished from maternal individuals using multivariate methods; precision was improved where data from vegetative clones were used. Univariate analyses were helpful in confirming results. The need for a more objective procedure is discussed. Three to six variates gave adequate discrimination, characters were chosen for high repeatability, ease of measurement and low correlations.Two trials were conducted, the first on P. ampia and P. pratensis biotypes, the second on eleven hybrid progenies to examine the influence of light regimes from just before ear emergence until anthesis on the resulting seedling progenies. Both photoperiod and total irradiance affected seedling characters and variability but the direction and magnitude of response differed between biotypes of P. pratensis and between hybrids. Results from P. ampia indicated that a higher proportion of sexual seed matured after ten hour than after twenty hour photoperiod treatments. Different pollen parents used in pair crosses between P. ampia and P. pratensis biotypes gave progenies differing in seedling characters and in homogeneity of dispersions from the same maternal parent.The need firstly for improved techniques for assessment of apomixis, and secondly for more information on the control of apomixis and the developmental physiology of reproduction in facultative apomicts is discussed, with the broad objective of increasing the scope of a breeding programme.