RFLP analysis of the origin of Citrus bergamia, Citrus jambhiri, and Citrus limonia

Biotechnology provides new tools that can be used to address questions about the origin and relationships among Citrus taxa. Many Citrus taxa are believed to have originated as hybrids between ancestral species. We describe the use of molecular markers to assess the parentage of several putatively hybrid taxa. Seventy-three accessions from 45 Citrus species and twelve accessions from six related genera were examined for restriction fragment length polymorphisms (RFLPs) using 25 probe/enzyme combinations. We wrote a computer program to identify pairs of accessions that could have contributed the bands found in putative hybrid accessions such as C. bergamia, C. jambhiri, and C. limonia. The potential parent/hybrid relationships were then evaluated on the basis of previously existing biochemical, isozyme, morphological, geographical and historical information. The RFLP profile of C. bergamia was fully accounted for by C. aurantium x C. limetta. The profile of C. limonia was fully accounted for by any of six mandarin species x C. aurantifolia or C. macrophylla. Five mandarins x C. medica account for all but one C. limonia band, and C. medica may have stronger geographic credibility than C. aurantifolia. This data set was not strong enough to unambiguously define the ancestors of C. jambhiri because C. limon x three different species could generate the C. jambhiri profile, and C. limon x three mandarins had one mismatch each. Molecular markers provide new evidence about the origin of taxa, but until sufficiently large data sets have been compiled, they cannot be used exclusively to prove parentage but must be balanced with existing information.