Genetic Background, Inbreeding, and Genetic Uniformity in the National Citrus Breeding Program, Japan

We analyzed the pedigree records (1995-2010) of the Kuchinotsu Citrus Breeding Program (KCBP) at the National Institute of Fruit Tree Science (NIFTS) in Japan, abbreviated as NIFTS-KCBP, to reveal the genetic background and current status of inbreeding and genetic uniformity of the parental cultivars/genotypes and their F1 breeding progenies. The founding genotypes mostly used for crossing in NIFTS-KCBP were satsuma mandarin (Citrus unshiu Marcow.), sweet orange (C. sinensis [L.] Osbeck), king mandarin (C. nobilis Lour.), clementine (C. clementina hort. ex Tanaka), mediterranean mandarin (C. deliciosa Ten.), dancy tangerine (C. tangerina hort. ex Tanaka), and ponkan (C. reticulata Blanco). The intensive use of these seven genotypes and their progenies as crossed parents has led to a high degree of inbreeding in the breeding population. Moreover, these seven genotypes have dominated about 80% of the genetic composition of the breeding population. Although further studies are needed to reveal the influence of inbreeding and genetic uniformity on agronomically important traits, these data offer useful information for the selection of cross combinations and breeding strategies in the ongoing NIFTS citrus breeding program, Japan.