Ceratocystis canker resistance in BC1 populations of interspecific hybridization of fig (Ficus carica) and F. erecta

Abstract

Ceratocystis canker is a serious disease in fig (Ficus carica L.) caused primarily by the soil borne fungus Ceratocystis ficicola. The disease mainly invades the roots and trunks of figs, eventually killing the tree. Ficus erecta and F1 (F. carica × F. erecta) were found to be extremely resistant to this fungus. F. erecta is not practical as a rootstock due to extremely low grafting compatibility with F. carica between F. carica. F1 hybrids had been found to be unusable as a rootstock because of a root disorder. Then, we performed backcross hybridizations (BC1) between four common figs (seed parent) and F1 caprifig type (pollen parent) through artificial pollination. The leaf morphology of BC1 progeny was similar to that of F. carica rather than those of F. erecta or F1. Hardwood and softwood cuttings of BC1 progeny readily rooted. BC1 populations were inoculated with C. ficicola by direct wounding of the shoot. The segregation ratios of resistance and susceptibility in BC1 populations were consistent with a 1:1 Mendelian model. In a wound inoculation experiment using cuttings from 4 BC1 individuals identified as being disease resistant, all examined lines were healthy and unwithered 100 days after inoculation. This result suggests that Ceratocystis canker resistance in F. erecta is controlled by a single dominant gene. BC1 progeny exhibited sufficient graft compatibility with fig, indicating that Ceratocystis canker-resistant BC1 would be a practical fig rootstock source.