NATURAL AND EXPERIMENTAL HYBRIDIZATION IN POTENTILLA

Abstract

SUMMARY Three natural hybrids have been reported in Potentilla subseries Tormentillae: Potentilla Y. suberecta, P. ×mixta and P. × italica. This paper presents results of morphological and cyto‐logical studies and experimental crosses made to clarify the origins and taxonomy of the hybrids, and to investigate the possibility of introgression. All natural hybrids examined were hexaploid (2n= 42). Experimental crosses confirmed that P. × suberecta is the hybrid between P. erecta (2n= 28) and P. anglica (2n= 56), but the origin of the other hybrids is less clear. It is suggested that the names P. ×mixta and P. ×italica have been applied to different forms of a single variable taxon, and that P. × italica should be regarded as a synonym of P. ×mixta. The origin of this natural hybrid remains uncertain. It is generally considered to be P. reptans (2n= 28) ×P. anglica, but numerous attempts to hybridize these species have failed, although one unpublished, successful hybridization is cited. Experimental crosses have indicated an alternative origin for P. ×mixta, by hybridization between P. reptans and P. erecta, in which the former either contributes an unreduced gamete or occurs as an autopolyploid cytotype. Vigorous backcross progenies were raised from both P. ×suberecta and P. ×mixta and the importance of backcrossing and introgression in natural populations is discussed.

The allopolyploid origin and genomic constitution of Potentilla anglica

“…Plate I, F shows a somatic metaphase from the individual with 2n = 53. The single octoploid (2n = 56) showed no evidence of hybridity and may have resulted from accidental self-pollination or from the apomictic The individual with 2n = 43 differed from the others in morphology and fertility and resembled the natural hybrid P. x mixta (Matfield, Jones and Ellis, 1970). Its pollen grain stainability was less than 1 per cent, and no seed was set.…”

“…All three possible hybrid combinations have been reported, but it is doubtful whether the tetraploid hybrid between P. reptaris and P. erecta actually occurs in nature (Matfield, 1972). It has recently been synthesised experimentally (Schwendener, 1969;Matfield, 1972) but previous attempts to hybridise the tetraploid species failed as a result of genetic incompatibility barriers (Brukss, 1931;Matfield, Jones and Ellis, 1970). For this reason confirmation of the allopolyploid origin of P. anglica by experimental synthesis has proved difficult.…”

“…They were maintained in pots sunk into the soil. Auto-octoploid (2n = 56) strains of P. reptans and P. erecta were induced by coichicine treatment as described previously (Matfield, Jones and Ellis, 1970 Thomas (1940). Buds were fixed for at least a week in acetic-alcohol containing ferric acetate as a pre-mordant and the anthers were squashed in strong aceto-carmine solution.…”

“…Buds were fixed for at least a week in acetic-alcohol containing ferric acetate as a pre-mordant and the anthers were squashed in strong aceto-carmine solution. The techniques for somatic chromosome counts and experimental hybridisations have been described previously (Matfield, Jones and Ellis, 1970 The points on the graph show average values for each species determined from all the plants kept in cultivation. Characters were not recorded until the plants had been in the experimental garden for at least a year in order P. erecta and P. reptans are both highly fertile but self-incompatible.…”

“…contained 28 bivalents. The remainder contained one to five multivalents and cells with two, four, six and even ten Previous attempts to hybridise the tetraploid species failed because of incompatibility barriers (Matfield, Jones and Ellis, 1970). P. reptans pollen did not stimulate seed set in P. erecta, and although the reciprocal cross produced many seeds germination was very rare: a total of more than 3000 seeds yielded only one inviable seedling.…”