Desenvolvimento de um mapa genético de ligação de macieira saturado para a região com resistência à mancha foliar de Glomerella (Colletotrichum gloeosporioides)

Abstract

Since the 1980’s, the apple prodution in Brazil has experienced great losses due to a disease, Glomerella Leaf Spot – GLS, caused by Colletotrichum spp., not known previously. This disease has spread to all the apple orchards of southern Brazil, and has begun to spread in the USA. Due to the great economic damage caused by GLS the demand to understand the genetic mechanisms involved in the disease’s resistance is increasing, since effective chemical control measures that respect the norms of IAP are not available. In this sense, the objective of this work was the development of genetic linkage map of an apple segregating population to Glomerella Leaf Spot (Colletotrichum gloeosporioides) to contribute for the efficiency in the generation of new apple cultivars resistant to that disease. The GLS reaction in three mapping populations was analyzed (M13/91 x M-46/94, M-13/91 x ‘Gala’ and ‘Pink Lady’ x ‘Imperatriz’). Biological assays results indicated the necessity of making adjustments of methodology for GLS incubation in each case. The reaction identified in the study populations points to a recessive monogenic control agreeing, therefore, with the results found in literature. However, the obtained results also do not allow the rejection of the segregation hypothesis of 9:7. The selection of markers RAPD, SSR and AFLP was accomplished for genetic mapping of apple in two segreganting populations. For the RAPD markers the strategy of selection of markers used was BSA. Of the 195 RAPD initiators tested none presented amplification product co-segregating with the resistance gene GLS. In the case of the SSR markers the found polymorphism was abundant and among the 93 pair of primers tested, 63 were polymorphic between the parents M-13/91 and ‘Gala’. The AFLP markers presented an average of 13.1 and 10.5 polymorphic fragments among the parental of the two study populations. A genetic linkage map was made for the population M-13/91x 'Gala' covering 23 linkage groups including 1,179.7 cM with a average distance among markers of 8.8 cM. The GLS resistance gene was mapped on linkage group 15, close to SRRs NZ02b1 (2.1 cM), CH03b06 (6.8cM) and Hi03g06 (7.5 cM). The relatively low recombination frequency among them and the resistant gene to GLS assigns to SRR-NZ02b1 a useful marker for indirect selection.