FLOWERING CHARACTERISTICS AND FERTILITY OF INTERPLOIDY PROGENY FROM NORMAL AND 2N GAMETES IN DACTYLIS-GLOMERATA L

We performed an extensive experiment to compare male fertility, flower ing period, seed set and germination rate between triploid and tetrapl oid cross-progeny of Dactylis glomerata L. originating from reciprocal diploid (2x) x tetraploid (4x) crosses. Four hundred and forty-five t riploid and tetraploid individuals, constituting the cross progeny of 2x-4x reciprocal crosses between diploids from nine distinct subspecie s, and tetraploids from five subspecies, were tested for male fertilit y and phenology under homogeneous conditions. A significant negative c orrelation was observed between the parental genetic distance and the frequency of sterile panicles (ST) in 3x progeny, suggesting that sele ction may occur against fertility in triploid progeny from interploid crosses involving closely related subspecies. Genetic distance between the parental subspecies was not significantly correlated with the fre quency of fertile panicles (FT), non-spreading panicles (NT, non-dehis cent anthers with pollen inside), and ST panicles in the 4x progeny, n or with the frequency of FT and NT panicles in the 3x progeny. Among t he 4x progeny individuals that produced panicles, more than 60 % were fully fertile, but 24 % possessed only sterile panicles. In the triplo ids, 63 % of the reproductive plants were male-sterile, but 31 % had v ariable proportions of fertile panicles and 6 % possessed only fertile panicles. Male fertility in the progeny was significantly affected by individual ploidy level, parental diploid subspecies identity, and by the interaction between these 2 factors in the case of the fertile pr ogeny plants. The frequency of vegetative plants was higher in 4x prog eny than in 3x progeny, more particularly when the seed parent was tet raploid. However, when the seed parent was diploid, the frequencies of vegetative plants were similar in 3x and 4x progeny. Pollen viability was significantly higher in anthers from fertile panicles than in ant hers from non-spreading panicles; viability of pollen from non-spreadi ng panicles was, in turn, significantly higher than in sterile panicle s. Also, seed set was higher in panicles with fertile anthers than in the two other types. However, seeds from plants with fertile, non-spre ading and sterile anthers showed no differences in germination rate. T herefore, in Dactylis glomerata, tetraploid cross progeny arising from 2n gametes possess higher fertility, on average, than triploid cross progeny involving normal gametes. In addition to lower male fertility (non-spreading or atrophied anthers), the triploids also showed signif icantly lower pollen fertility in anthers and lower seed set in open p ollinating conditions, probably because disturbance in meiosis, due to odd chromosome associations, also occurs in eggs. Moreover, triploids were observed to reproduce preferentially with individuals possessing the same ploidy levels as their seed parent. These results suggest th at the production of 4x individuals, derived from 2n gametes in interp loid crosses, is likely to be the main effective means of direct gene transfer in contact areas of populations or subspecies possessing dist inct ploidy levels.