Molecular variability of vanilla (Vanilla planifolia) and three wild species was assessed to explore the possible sources of variation that can be used for crop improvement. A total of 154 ISSR loci were analysed by the UPGMA, assignment tests of individuals (STRUCTURE) and indices of genetic diversity. The assignment tests were done at two levels: first considering the four species and then only the accessions of V. planifolia. The molecular analysis indicated 99.3% polymorphism among all species and 70.45% within V. planifolia. The UPGMA showed the separation of these four species into three groups and grouped V. planifolia accessions into three subgroups. The more genetically differentiated accessions were of the Rayada morphotype and a wild accession was from Oaxaca, followed by a wild accession from Quintana Roo; all the commercial accessions of V. planifolia (Mansa morphotype) were grouped together. The STRUCTURE analysis differentiated between V. planifolia and the three wild species, and among the accessions of the Mansa and Rayada morphotypes and the wild accessions. The STRUCTURE analysis also indicated the presence of mixed individuals. These results are of great importance since the accessions of V. planifolia that are genetically more differentiated are the most threatened due to the scarcity of these individuals, the destruction of habitat and replacement by the commercial morphotype. These individuals should be salvaged and used to expand the genetic background of vanilla.
Currently, premature fruit fall is one of the major problems of vanilla (Vanilla planifolia Jacks.) cultivation. This phenomenon has been related to its high susceptibility to drought, a consequence of the low genetic variability of this crop. For this reason, it is of great importance to undertake genetic improvement programs in order to obtain genotypes with greater tolerance to this abiotic factor. With this aim, the present work was developed, in order to select in vitro irradiated shoots, with different doses of gamma rays (0.5 to 19 Gy), cultivated in Murashige & Skoog (MS) medium containing: 0, 10 and 15% of polyethylene glycol (PEG). The results showed a greater proliferation of irradiated shoots, with doses of 0.5 and 1 Gy (8.88 ± 3.04 and 6.43 ± 0.98). Shoots irradiated with 0.5 Gy had a faster growth (19.26 ± 6.87 mm) while those irradiated with 3 Gy showed a higher number of leaves (2.38 ± 0.71). Nodal segments of shoots irradiated with 9, 15, 17 and 19 Gy, lost their ability to multiply. Vitroplants from 13 Gy, grown in a medium containing 15 %, showed greater tolerance to water deficit. These vitroplants kept their leaves and showed significant differences in the accumulation of betaine glycine (21.46 ± 4.55 μmol betaine glycine/dry weight), in relation to the accumulation of non-irradiated vitroplants. Therefore, it is considered that the dose of 13 Gy can generate variability and improve tolerance to simulated water stress in vitro.
Las vainas de la vainilla (Vanilla planifolia Jacks. ex Andrew) son la fuente natural de vainillina e internacionalmente son consideradas un producto de alto valor comercial. Sin embargo, el cultivo de vainilla presenta varios problemas que han impulsado el desarrollo de investigaciones para su mejoramiento genético mediante diversas estrategias. Estas investigaciones han desarrollado trabajos de prospección para establecer bancos de germoplasma y evaluado la hibridación sexual intra e interespecífica. Además, han empleado herramientas biotecnológicas, particularmente las basadas en el uso de las técnicas de cultivo de tejidos vegetales, para conservar in vitro el germoplasma disponible. Asimismo, han intentado ampliar la base genética combinando la inducción de mutagénesis con técnicas de selección ante diferentes agentes de estrés, hacer hibridación somática mediante fusión de protoplastos y usar técnicas de ingeniería genética para la inserción de genes. A pesar de que el mejoramiento de vainilla se inició desde mediados del siglo pasado, solo se ha registrado una variedad de vainilla a nivel mundial. A la fecha, la biotecnología está impulsando la generación y selección de material promisorio, sin embargo, aún faltan más resultados de campo que muestren una etapa avanzada de estos trabajos de mejoramiento. En conclusión, aún quedan aspectos por retomar en el mejoramiento de este valioso cultivo.
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