ALTERNATIVES TO IMPROVE HYBRIDIZATION EFFICIENCY IN Eucalyptus BREEDING PROGRAMS

Abstract

Simple and quick hybridization procedures and ways to keep pollen grains viable for long periods are sought in plant breeding programs to provide greater work flexibility.  The present study was carried out to assess the efficiency of pollinations made shortly after flower emasculation and the viability of stored pollen from Eucalyptus camaldulensis and Eucalyptus urophylla clones cultivated in Northwestern Minas Gerais State.  Controlled pollinations were carried out at zero, one, three, five and seven days after emasculation.  Hybridization efficiency was assessed by the percentage of viable fruits, number of seeds produced per fruit, percentage of viable seeds and also by cytological observation of the pollen development along the style.  Flower buds from clones of the two species were collected close to anthesis to assess the viability of pollen grain storage. Pollen was then collected and stored in a freezer (-18^oC) for 1, 2 and 3 months.  Pollen assessed was carried out by in vitro and in vivo germination tests. The efficiency of the pollinations varied with their delay and also between species.  The greatest pollination efficiency was obtained when they were carried out on the third and fifth day after emasculation, but those performed simultaneously with emasculation produced enough seeds to allow this practice in breeding programs.  The decrease in pollen viability with storage was not sufficiently significant to preclude the use of this procedure in artificial hybridization.