Organogenesis in the apical meristem of Hevea sp.

Abstract

The polyploids of rubber tree (Hevea sp.) keep the same degree of resistance to leaf diseases of the diploid original clone, with an expected substancial increase in productivity, unlike the clones obtained through crosses whose increase in productivity is generally associated to a decrease in resistance it is therefore worthwhile to make an effort towards a better understanding of the apical meristem of Hevea as a support to the establishment of polyploidization methods with less erratic results. Under this prospect, the following characteristics determined up to the present state of a current research are considered pertinent: a. absence of a quiescent centre ("méristème d'attente"), probably as a result of the flat shape of the promeristem throughout the different developmental stages of the shoot apex; b. uniformity of size of the promeristem in resting and active apices, with approximately 10.000 cells in plants 1 m to 1.50 m high; c appearance of axillary bud primordial with a plastochronic distance of four to six leaf primordia; d. absence of mitotic periodicity, with a mitotic index (between) 4 to 5% during a 24 hours cycle; e. most active organogenesis up to the beginning of the rapid shoot alongation.