| Grant number: | 92/03792-7 |
| Support type: | Research Projects - Thematic Grants |
| Duration: | May 01, 1993 - June 30, 1997 |
| Field of knowledge: | Biological Sciences - Genetics - Quantitative Genetics |
| Principal researcher: | Tsai Siu Mui |
| Grantee: | Tsai Siu Mui |
| Home Institution: | Centro de Energia Nuclear na Agricultura (CENA). Universidade de São Paulo (USP). Piracicaba , SP, Brazil |
Abstract
The study of the genetic control of the Biological Fixation of N2 (FBN) by the plant has advanced greatly in recent years through experimentation with mainly cellular techniques, couple with molecular techniques in Rhizobium. The FBN process already has some practical results to show, and others almost there. For example, through molecular techniques, a higher production in alfalfa was obtained with the insertion of the nifA gene; the use of mutants (sensitive to succinate) of Rhizobium and Bradvrhizobium induced a greater competitive capacity with the bacteria introduced, with the formation of a larger number of nodules, and, consequently, increase in production. In other promising results this time related to the plant, are included those recently found by molecular geneticists, which proved to be the transcription of the genes of Rhizobium responsible for controlled nodulation by specific flavonoids, produced by the host plant (Long, 1989). The idea that FBN by legumes could be improved through genetic crossing is of recent date and emerged after the results in some forage legumes - alfalfa and clover, associated with the production of biomass (Barnes et al 1984; Mytton 1984). Studies with peas and soya and more recently bean plants revealed a high variability of symbiosis (measured by several parameters), with great potential for transfer of this characteristic in hosts with superior agronomic characteristics (McFerson et al. 1982; Graham and Temple 1984; Bliss 1985). With the development of a linkage map of the common bean genome in the laboratories of Dr. Paul Gepts (Univ. of California - Davis, EUA), in which we participated (Nodari et al. 1992b), it was possible to locate four putative loci for the quantitative characteristic (QTL- Quantitative Trait Loci) of the number of nodules formed by Rhizobium. The number of nodules formed by Rhizobium was demonstrated. Also demonstrated was the correlation between nodulation and the susceptibility to Xanthomonas campestris pv. phaseoli, an idea which had been previously held from the similarity between the susceptibility of the plant to infection by Rhizobium and to bacterial pathogens. Four regions were identified where the QTLs acted in relation to susceptibility to bacteriosis, one of which mapped in the same region of the chromosome for number of nodules, which in turn should act in the expression of phaseoline and another QTL - size of seed. For these results, there would still be the need to determine the correlation between low nodulation and resistance to bacteriosis provoked by X. campestris pv. phaseoli using other populations with similar histories of genetic selection. A complementary genetic analysis of the pleiotropic effects or simply of linkage would be important to guide the method to be adopted in future programs of improvement. Genetically altered material such as a non nodulant mutant (nod) would be used in specific crossings for this study. The effect of the greater stress factor on the nodulation, N-mineral, will be studied using a deleterious subdose for the process in the F3 progenies of the BAT-93 x JaIo EEP558 crossing, for construction of a new map. In a similar way to the development of QTLs for Rhizobium (nodulation), we intend to determine the occurrence of mycorhizal infection in parentals used in the crossings between different bean strains (Andean, meso-American and wild), and if variation is observed, also map this characteristics on the already existing linkage map of Jalo EEP558 and BAT-93. (AU)