Exploiting the Citrus Genome Towards Understanding Genetic Traits Related to Fruit Quality and Disease Resistance

Citriculture is a very important economic agribusiness activity in Brazil. Because of this importance, we have established a Citrus breeding program focusing on two very important traits, disease resistance and fruit quality. Among the problems that affect the Brazilian citriculture, the Citrus Variegated Chlorosis (CVC) and Citrus leprosis, caused by Xylella fastidiosa and the Citrus Leprosis Virus (CiLV), respectively, are examples of important diseases. The construction of linkage maps has fundamental importance in breeding programs, allowing the association of genomic regions with characteristics of agronomic interest. In the present study we developed high density linkage maps based on DArT_seq molecular markers using 278 citrus hybrids obtained from crosses between Murcott tangor and Pera sweet orange. Fruit traits, CVC and CiLV resistance were evaluated under field conditions in an endemic region for the diseases with eight replicates in an experimental design of eight randomized blocks. The linkage analysis produced genetic maps with 1,977 and 1,493 DArT_seq markers for Murcott tangor and Pera sweet orange respectively. The markers were distributed into 9 linkage groups for each parent. A total of 6 QTLs for disease resistance and 7 QTLs for fruit traits were detected. The QTLs explained 10.8 to 39.8% of the traits variance. The genome (pseudo-chromosomes) of Citrus sinensis L. Osbeck was compared to the genetic maps and rearrangements were clearly identified. Further analysis of the regions with the highest LOD scores was carried and we verified the presence of genes that could be associated with the characteristics. The genome sequences allowed identification of genes that may respond for phenotypic traits in Citrus.

(Financial support: Fapesp and CNPq).