Poor development of transmitting tissue in tetraploid grape pistils causing inhibition of pollen tube growth

Anatomical investigations were carried out to study the cause of poor berry set in tetraploid grape cultivars, Using 6 diploid and 6 tetraploid grape cultivars, the development of the transmitting tissue (TT) and pollen tube growth in their pistils were examined. The rates of berry set and seed numb er per berry were also investigated. TT was found to be cylindrical in the style and elliptic-conical in the ovaries. In the middle part of the ovary, the TT had developed along the inner surface of each septum projecting fro m both sides of the ovary wall. In the middle style, the TT diameter of tet raploid cultivars was larger than in diploid cultivars, However, TT develop ment in the septum was markedly poorer in most of the tetraploid cultivars examined except for cv, Fujiminori where a sufficient number of seeded berr ies developed on the clusters. Most pollen tubes penetrating into the ovary tissue were inhibited to grow further in tetraploid cultivars except for c v, Fujiminori, These findings suggest that the poor set of normally seeded berries in most tetraploid grapes may be due to poor development of TT in t he septum, which severely inhibits pollen tube penetration into the micropy le.