Contribution à l’étude du processus de la fécondation chez trois espèces de Prunus : P. persica (L.) Batsch., P. cerasifera Ehrh., P. mahaleb L. grâce à l’utilisation de couples de variétés mâle-stériles et mâle-fertiles

L’étude de couples apparentés de clones mâle-stériles et mâle-fertiles de Prunus persica, Prunus cerasifera et Prunus mahaleb a permis de confirmer, en verger, la meilleure aptitude à la fécondation des clones mâle-stériles. Cette différence de comportement semble due non pas à une plus grande longévité des stigmates ni à une vitesse de croissance plus rapide des tubes polliniques, mais seulement à une réceptivité meilleure des ovules. Le début de leur dégénérescence se manifeste clairement au microscope à fluorescence par une luminescence progressive. Dès les premiers symptômes, l’ovule n’est plus réceptif. Or, les clones mâle-stériles étudiés présentent tous, dès l’anthèse (Stade E) et par la suite, un pourcentage significativement plus élevé d’ovules réceptifs.

Since male-sterile and male-fertile varieties generally been found to have better crossing ability, flowers of related clones of male-sterile and male-fertile varieties of P. persica, P. cerasifera and P. mahaleb have been studied for the fertilization process. Stigma, Firstly it has been confirmed, for these three species, that the male-sterile clones have a natural mode of setting more fruit, with of course good pollination. As far as peaches are concerned, we have surveyed six pairs of clones in which this phenomenon has been observed and this can be considered the general behaviour of the species. Male sterility, In a two year study, longevity of stigma, rate of growth of pollen tubes and ovule receptivity have been studied using fluorescent microscopy, with predetermined series of pollinations on the same male-sterile and malefertile varieties. Longevity of stigma and rate of growth of pollen tubes showed no significant differences. In contrast, the duration of receptivity of the ovules, which is dependent on the survival of the embryo sac, is very different and is always better with the male-sterile varieties at the time of anthesis. The differences which we have observed between these varieties in orchards are thus self-explanatory. Interspecific crosses would certainly give better results with the male-sterile clones. Studies revealed that the percentage of receptive pistils decreases very quickly in a few days after anthesis, thus, under our natural conditions, only the flowers which are pollinated near anthesis time have better chances of setting fruit. The number of receptive pistils is often less than 50 per cent at the time of anthesis in the male fertile clones. This confirms that the total number of possible fruit set on a fruit tree is much less than the total number of flowers which it produces. It is probable that all the results thus obtained for three species of Prunus can hold true for all other Prunus species.