Associação genômica para resistência da soja a Meloidogyne javanica e Macrophomina phaseolina

• Autor(a) principal: Vinholes, Patrícia da Silva
• Data de Publicação: 2014
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1246
• topic: Soja - Melhoramento genético; Soja - Cultivo; Soja - Doenças e pragas; Soybean - Genetic improvement; Soybeans - Crops; Soybean - Diseases and pests; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOTECNIA

Soybean [Glycine max (L.) Merrill] is one of the main agricultural products in Brazil. In the 1990 s it was the main agricultural export product, with increasing areas every year, since then. Soybean was usually cultivated in southern, southeastern and most recently in the Midwest of Brazil. Currently it has grown beyond Cerrado, expanding into new areas such as Maranhão, Bahia, Tocantins, Piauí and Pará States. Because of soybean importance, large amount of resources were made available for research, aiming the development of more adapted and productive cultivars. Diseases in soybean due to weather may be responsible for severe damage and productivity losses. Among these, soil diseases are extremely important because of its difficulty to control. A very effective strategy to reduce yield loss in these cases is the use of resistant cultivars. The nematode Meloidogyne javanica is widely spread in Brazil and it is responsible for significant losses in this crop. Another important pathogen in Brazil, because of it is growing occurrence, is Macrophomina phaseolina. Studies for the identification of new sources of resistance and molecular markers associated with traits of interest have been used by scientists in order to develop resistant cultivars. To study the association of genotype with the desired phenotype, segregating populations have been developed. Another important approach is the study of genetic resistance in unstructured populations, recommended for identification of new sources of resistance. Marker x gene/QTLs associations are stronger in these populations, due to the small size of the linkage disequilibrium blocks. Thus, the objective of this study was to identify molecular markers associated with resistance to Meloidogyne javanica and Macrophomina phaseolina in soybean, in order to establish a SAM routine for the crop genetic improvement. For the Meloidogyne javanica study, it was used two populations approaches based on: (1) linkage groups, in which a population from a bi-parental cross was created, and (2) an unstructured population, constituted by commercially important past and current soybean cultivars. Families F2:3, obtained from crosses between MG/BR46 Conquista (resistant) x CD204 (susceptible) and 124 soybean cultivars representing the Brazilian germplasm were phenotypically evaluated for resistance to nematode galls. For each family or cultivar, plants were transplanted in individual tubes and after 10 days of sowing, each plant was inoculated with eggs of nematodes. Thirty days after inoculation, the galls in the roots were analyzed. Score ranging from 1-5 was used, where 1 = 10% of root system with small galls, 2 = 10-25% of root system with small galls, 3 = 26-50% of root system galled, 4 = 51 -90% of root system with large galls and 5 = 91-100% of root system with large galls and root rot. For the analysis of Macrophomina phaseolina, 169 soybean varieties were distributed into two plots, with four replicates per cultivar, in Citrus Research Center-Agricultural Experiment Station (CRCAES) at the University of California, Riverside, USA. This area has a history of Macrophomina infestation. Symptoms of mortality were evaluated for 12 weeks after the first symptoms of infection. Genotypic data from structured population (F2:3) were used for Meloidogyne javanica mapping with microsatellite markers. The genotype data from the unstructured population (cultivars) were obtained from Illumina platform iScan. Each sample was genotyped with 6,000 SNPs. After F2 population analysis, it was observed that resistance to Meloidogyne javanica in the cultivar MG/BR46 is controlled by two genes combining effects. The markers Satt114, Satt335 and Satt374, located linkage group F have been identified as associated with resistance to root-knot nematode Meloidogyne javanica. For the unstructured population, 12 SNPs markers associated with root-knot nematode resistance located on chromosome 13, same linkage group F of soybean were found. For Macrophomina resistance, 12 SNPs markers associated with the studied trait were identified, eight of those being located on chromosome 19 (linkage group L), indicating that this region is a strong candidate for the presence of genes/QTL resistant to Macrophomina phaseolina. Markers identified may be directly applied in soybean breeding programs, with the establishment of Molecular Marker Assisted Selection for resistance to nematode galls and charcoal.