Genetic analysis of reproductive, vegetative and fruit quality traits to improve Citrus varieties

To extend the harvesting period of high quality seedless fruits in citrus variety breeding programs, 20 traits related to vegetative growth (2), sexual reproduction (5), and fruit quality (13) were genetically studied in a segregating population of hybrids derived from a reciprocal cross between two commercial varieties, Fortune (a Citrus clementina hybrid) and Chandler (a Citrus grandis hybrid) that largely differ in fruit size, taste, color, and harvesting date. Juice and fruit colors and tritable acidity showed a highly significant cytoplasm x harvest interaction where Fortune cytoplasm was associated with higher means of those parameters for the first and second harvests only. Type of cytoplasm was also associated with fruit seeds content and heterostyly of flowers. Very few hybrids (11.3 %) were self-compatible, and less than one fourth of the progeny showed parthenocarpic ability. Two Quantitative Trait Loci (QTLs) governing flower heterostyly and self-compatibility were found linked in group 3 of C. clementina where segregation distortion had been previously reported. Only two major QTLs were consistently detected for fruit quality traits, one in the C. clementina map contributing up to 21.3 % to rind thickness and another in the C. grandis map contributing up to 59.7 % to tritable acidity at the optimal maturing harvest. Unexpectedly, soluble-solids content and seed number of the fruit were positively and consistently correlated in the progeny what could be explained by linkage of some QTLs involved. Present information on the positions of 68 QTLs detected will be useful to search for candidate genes at the peak regions.