Interspecific hybridization of fig (Ficus carica L.) and Ficus erecta Thunb., a source of Ceratocystis canker resistance

Abstract

Ceratocystis canker, which is caused by the fungus Ceratocystis fimbriata Ellis et Halsted, is one of the most severe diseases of the common fig (Ficus carica L.). In contrast, the wild fig species F. erecta Thunb. is resistant to this fungus. We performed interspecific hybridization between the common fig (seed parent) and F. erecta (pollen parent) through artificial pollination. Even though hybrid seeds showed high germination rates, the seedling survival rates were low. All of the seedlings contained the expected simple sequence repeat (SSR) alleles from both common fig and F. erecta at each of the three loci tested, thus confirming the parentoffspring relationships of the interspecific hybrids. The leaf morphological characters of hybrid seedlings were intermediate between those of the parents. Cuttings of cultivars of common fig, F. erecta, and hybrid seedlings were inoculated with C. fimbriata by direct wounding of the shoot. All of the common fig cultivars tested withered and died within 10 weeks. Leaves and shoots of the hybrids and F. erecta were healthy 100 days after inoculation. Our results suggest that interspecific hybridization between the common fig and the wild species F. erecta is a breakthrough in the breeding of a new fig rootstock source with resistance to Ceratocystis canker.

Xylem Dysfunction in Ficus Carica Infected With Wilt Fungus Ceratocystis Ficicola and the Role of the Vector Beetle Euwallacea Interjectus

“…This pathogen is primarily recognized as a soil-borne plant disease because fig trees planted in soil polluted with the pathogen C. ficicola are easily infected (Kato et al 1982). Therefore, application of fungicide to polluted soil and the breeding of resistant rootstocks have been tried during this decade (Hirota et al 1984;Shimizu et al 1999;Togawa et al 1999;Yakushiji et al 2012), but are not always effective to reduce the damage. Kajitani (1996) found that an ambrosia beetle, Euwallacea interjectus (Blandford), contributed as a vector of this pathogen because it carries C. ficicola on its elytron (Kajitani 1999).…”

The Ficus erecta genome to identify the Ceratocystis canker resistance gene for breeding programs in common fig (F. carica)

“…To estimate the size of the F. erecta genome, a kmer-distribution analysis was performed with short-read sequence data obtained from an F. erecta tree (Yakushiji et al, 2019; Yakushiji et al, 2012). The resultant distribution pattern indicated two peaks, representing homozygous (left peak) and heterozygous (right peak) genomes, respectively (Figure S1).…”

“…A male F. erecta tree was used for genome sequencing analysis. This tree had been used for an interspecific hybridization with F. carica ‘Boldido Negra’ to generate an interspecific F1 hybrid, i.e., FEBN-7 (Yakushiji et al, 2019; Yakushiji et al, 2012). The backcrossed lines (BC1F1, n = 121), derived from crosses between FEBN-7 and F. carica ‘Masui Dauphine’, ‘Negro Largo’, ‘Boldido Negra’, or ‘Ischia Black’ (Yakushiji et al, 2019), were used for linkage analysis (Supplementary Table S2).…”

“…A fig collection (n = 122) used in our previous study (Mori et al, 2017) was used to validate the resistance locus. The resistance levels of the accessions were evaluated as described previously (Yakushiji et al, 2019; Yakushiji et al, 2012).…”

“…Many attempts have been made to overcome these incompatibilities and generate interspecific hybrids between common fig and F. erecta . Yakushiji et al (2012) succeeded in obtaining F1 hybrids that exhibited similarly high resistance to Ceratocystis canker as F. erecta ; however, the plants had poor morphological phenotypes (Yakushiji et al, 2012). Recent research shows that Ceratocystis canker resistance in F. erecta is controlled by a single dominant gene (Yakushiji et al, 2019).…”