Métodos de isolamento de inflorescências para melhorar a eficiência das autofecundações em Eucalyptus spp.

Abstract

Some Eucalyptus breeding programs have recently been trying to self-fertilize pre-selected parents to, at least in part, eliminate the genetic load, fix favorable alleles, and thus, develop semi-inbred lines aiming at highly productive hybrids. However, self-fertilizations have shown a low success rate, mainly due to contamination with foreign pollen. The objective of this work was to evaluate combinations of branch isolation methods to minimize contamination by external pollen in the production of self-fertilized Eucalyptus progenies. For this, seven different treatments were tested, varying the self-pollination methods and the material for isolating the branches (type and thickness of the tissue). The treatments were applied to six E. grandis and E. urophylla mother trees using three replicates (different branches from the same plant) and 100 pollinated buds in each replicate. The mother trees chosen were in the ideal stage of blooming for pollination. Most were already known for presenting tolerance to the generation of progenies by self-fertilization, having undergone previous analyzes based on verification by genotyping with microsatellites. The fruits were harvested and processed, and the seeds of each replicate were sown in 11 pots. Three of the seven treatments for genotyping were selected due to the high cost of self-fertilization verification by microsatellite genotyping. The following parameters were evaluated for each treatment and replicate: (1) number of viable buds 30 days after pollination; (2) number of fruits harvested 180 days after pollination; (3) number of pots with germinated seedlings 30 days after sowing; and (4) number and proportion of seedlings proven to be derived from self-fertilization via microsatellite genotyping. There were no significant differences in the number of viable buds, harvested fruits, and germinated pots between treatments. However, E. urophylla trees showed a higher success rate when compared to E. grandis. Based on genotyping, the success in self-fertilization was only significantly affected by the species and was more favorable in E. urophylla. There was also no significant difference regarding the treatments and classes of mother trees for self-fertilization. Although unexpected, this result represents a significant advance for the company’s semi-inbred line generation program. As no significant difference was detected between treatments, it is possible to implement the treatment with higher operational ease. Therefore, self-fertilization can be carried out in the company following the method that consists of simple cleaning and branch protection before budding, eliminating the need to store pollen, and perform controlled pollination, which highly facilitates the process.