Flowering characteristics and fertility of interploidy progeny from normal and 2n gametes in Dactylis glomerata L.
Authors: SATO T. , MACEIRA N. , LUMARET R. , JACQUARD P. 
Published: April 2006

We performed an extensive experiment to compare male fertility, flowering period, seed set and germination rate between triploid and tetraploid cross‐progeny of Dactylis glomerata L. originating from reciprocal diploid (2x) × tetraploid (4x) crosses. Four hundred and forty‐five triploid and tetraploid individuals, constituting the cross progeny of 2x‐4x reciprocal crosses between diploids from nine distinct subspecies, and tetraploids from five subspecies, were tested for male fertility and phenology under homogeneous conditions. A significant negative correlation was observed between the parental genetic distance and the frequency of sterile panicles (ST) in 3x progeny, suggesting that selection 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 frequency of fertile panicles (FT), non‐spreading panicles (NT, non‐dehiscent anthers with pollen inside), and ST panicles in the 4x progeny, nor with the frequency of FT and NT panicles in the 3x progeny. Among the 4x progeny individuals that produced panicles, more than 60% were fully fertile, but 24% possessed only sterile panicles. In the triploids, 63% of the reproductive plants were male‐sterile, but 31% had variable 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 progeny plants. The frequency of vegetative plants was higher in 4x progeny than in 3x progeny, more particularly when the seed parent was tetraploid. 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 anthers from non‐spreading panicles; viability of pollen from non‐spreading panicles was, in turn, significantly higher than in sterile panicles. Also, seed set was higher in panicles with fertile anthers than in the two other types. However, seeds from plants with fertile, non‐spreading and sterile anthers showed no differences in germination rate. Therefore, 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 significantly lower pollen fertility in anthers and lower seed set in open pollinating 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 that the production of 4x individuals, derived from 2n gametes in interploid crosses, is likely to be the main effective means of direct gene transfer in contact areas of populations or subspecies possessing distinct ploidy levels.