International Center for Tropical Agriculture

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   Internal report of activities New crosses of breeding lines  Introduction The main objective of the breeding program of tropical forages is to produce hybrids which outperform in yield, biotic and abiotic resistances and nutritional quality. Brachiaria species of agronomic importance are apomictic and tetraploids. The forage group at CIAT adapted a breeding methodology that exploits these characteristics plus heterosis. This methodology follows a scheme of recurrent selection based in specific combining ability, in which a population of sexual clones is selected in every cycle based on the performance of their progeny when crossed against a tester genetically complementary. Every cycle of selection consist in three years (some times more in the case of B. humidicola): 1) open pollinated cross of sexual clones; 2) Test crosses formation against the tester; and 3) Multienvironmental evaluation of hybrids performance for further selection. For each of the breeding programs, 2017 was a year to produce crosses, which is developed depending on the physiology of the plant as explained in the following sections.   Description of activity 1: Crosses in the interspecific breeding program (Urochloa ruziziensis x U. decumbens x U. brizantha) This corresponds to the oldest breeding scheme, out of the three in the tropical forages team at CIAT. Despite the long dormancy period and long time to flowering, the crop cycle can be completed in one year. The conditions required for the flowering induction are managed routinely. Therefore, open pollinated crosses and testcrosses are usually very successful. 25 sexual clones, selected from an initial 772, were recombined by open pollination (OP) in a small, isolated recombination block. Each clone was replicated (vegetatively) three times for a total of 75    individual potted plants. OP seed was harvested and will generate the 2018 version of the sexual population, SX18.  Description of activity 2: Crosses in the U. humidicola breeding program  In contrast of the interspecific breeding scheme mentioned before, the U. humidicola scheme is much younger. Although some germplasm U. humidicola accessions are well known in terms of phenology and physiology, there is a lack of information regarding the behavior of all the rest of the germplasm collection, specifically what refers to physiology of reproduction (conditions required for flowering, gametes formation and viability and seed dormancy). Those are still promising research areas for B. humidicola that would increase effectiveness of the crosses.  51 sexual clones (BhSX14 series) selected based on hybrid performance, are currently being recombined by open pollination (OP) in a small, isolated recombination block. Each clone was replicated (vegetatively) four times for a total of 204 individual plants.  Additionally, 27 putative apomictic clones, selected from an initial 1794, were established in the field at CIAT headquarters for seed increase. With the aim to confirm apomictic reproduction by progeny test.  Although climatic conditions did not allow satisfactory flowering for both experiments, the limited amount of seed obtained was harvested. Additionally, two strategies will be tested for further flowering induction: i) Extension of photoperiod, and ii) planting in a different location characterized by higher altitude and lower temperature (Tenerife).  Description of activity 3: Crosses in the M. maximus breeding program  A progeny of 274 individuals was obtained out of the cross between 90 apomictic accessions from CIAT´s germplasm bank and a sexual tetraploid identified by USDA. This progeny was genotyped with the University of Georgia marker of the “apospory-specific genomic region” (ASGR) and 156 identified sexual clones were planted in two replicates at CIAT Palmira for recombination by open pollination (OP) in a small and isolated recombination block. OP seed was collected in 5 harvests (17.05.2017; 16.06.2017;    24.07.2017; 31.08.2017; 1.09.2017). For each harvest filling percentage was measured. The seed from the first harvest was treated by scarification and used to identify the proper dormancy time by 1) creating subgroups and 2) measuring germination in each subgroup after 1, 2, 3 4, and 5 months of dormancy. High variability in terms of seed production, filling percentage, germination and dormancy were observed.  The distribution of the data for all characteristics were quantitative, therefore quantitative breeding methods will be used for further selection. This seed will generate the first sexual population that will enable the beginning of a breeding program following a scheme of recurrent selection for specific combining ability.   Conclusion and further steps Successful progress in two out of three of the breeding schemes was achieved during 2017. The interspecific Urochloa program as well as M. maximus did an important step towards a new generation of improved hybrids, which will be evaluated on the field during 2019. U. humidicola sexual clones are still on the field pursuing an open pollination round. An important lesson learned consist in the importance of investing new efforts on physiology of the reproduction for U. humidicola. This research has already started in 2018, through the management of biologic clock inducing changes in the photoperiod using artificial light. 

New crosses of breeding lines

https://cgspace.cgiar.org/bitstream/10568/102383/1/D3266_3.2.2_New_crosses_of_breeding_lines.pdf

New crosses of breeding lines

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