QTL analysis of morphological traits in an intergeneric BC1 progeny of Citrus and Poncirus under saline and non-saline environments

The effects of salinization with 40 mM sodium chloride on Poncirus trifolia ta (L.) Raf., Citrus grandis (L.) Osb., their F-1, and a BC(1)progeny popul ation [C. grandis (F-1)] were investigated by measuringgrowth and dry mass production of different tissues and by QTL (quantitative trait locus) mappi ng. A total of 36 traits related to growth (six traits) and tissue or whole plant dry mass production (30 traits) in salinized and non-salinized BC1 p rogeny clones were evaluated. The comparison of the three parental types to the BC1 progeny under control and saline conditions showed that the BC1 pr ogeny plants segregated transgressively for many of these traits. Mapping a nalyses of these quantitative traits resulted in a total of 70 potential qu antitative trait loci (PQTL) with LOD scores greater than or equal to 3.0 l ocated on a previously generated linkage map. Sixty-nine percent of the map ped PQTLs were for traits associated with salinity. The small progeny popul ation size used made further analyses of these PQTLs necessary. By consider ing LOD scores, map locations, and correlation analyses ofthe traits, it wa s possible to identify 16 regions of the citrus genome of interest, six of which were involved in both growth and dry mass production. Correlation ana lyses and locations of PQTLs indicated that many of these regions may conta in one or a few genuine QTLs of large effect. This is a first step in ident ifying QTLs that have a major impact on growth and dry mass production inCi trus under both optimum and stressful environments.