Mutation Breeding for Low Seed Content In Citrus

The citrus breeding program at the University of California, Riverside has developed and released low-seeded selections of several mandarin (C. reticulata) cultivars by gamma irradiation of budwood followed by selection of trees having fruit with few seeds in mixed plantings.  This process has been very successful in some cultivars where the number of seeds per fruit has been reduced ten-fold or more, but others are recalcitrant.  Development of the low-seeded cultivars ‘Tango’, ‘DaisySL’, ‘FairchildLS’ and ‘KinnowLS’ will be summarized and compared with results for Clementine cultivars in which low-seeded selections are much less frequent.  Recently, we have found that some low-seeded cultivars developed by this process produce a very low frequency of seedy fruits.  In some cases, several seedy fruit occur on the same branch or in a cluster.  The distribution of seedy fruit among trees within and between trial locations is variable, but is not strongly associated with location across different cultivars.  Possible causes of this problem will be discussed in relationship to possible mechanisms by which low-seeded cultivars may arise.