-Interspecific hybrid between common fig (Ficus carica) and wild fig (F. erecta)-
The National Agriculture and Food Research Organization (NARO), in cooperation with the Hiroshima Prefecture, has successfully developed "Reikodai 1 go", a new cultivar for fig rootstock which is extremely resistant to Ceratocystis canker. "Reikodai 1 go" was produced through backcrossing hybridization between the wild fig (Ficus erecta) and the common fig (F. carica). "Reikodai 1 go" has grafting compatibility with "Masui Dauphine" and "Houraishi", both of which are the most popular common fig cultivars in the market. It also has excellent reproductive ability by cutting, and there are high expectations for the new rootstock cultivar to become the solution for the fig producers against the soil infectious disease.
Ceratocystis canker is a serious disease affecting fig cultures in Japan. Figs infected with the disease die after leaves wilt and fall. The disease is primarily caused by the soil-borne fungus, Ceratocystis ficicola. Once Ceratocystis canker becomes established within an orchard, the resilient chlamydospores produced by the fungus remain in the soil, thus allowing the disease to reoccur in 2~3 years even after replacing the infected trees with the new ones. Recommended countermeasures are top dressing or fungicide application by soil injection, but both methods are labor-consuming and expensive. Therefore, there has been a strong demand in the market for a new rootstock cultivar that is resistant to Ceratocystis canker. A current choice of rootstock by producers is a few cultivars of common fig (Ficus carica) that has a relative field resistance to the disease, but the risk of infection cannot be denied. On the other hand, the native wild fig, F. erecta, is known for the true resistance to the disease, but the grafting incompatibility with figs makes it impossible to use them as the rootstock.
This led NARO, together with the Hiroshima Prefecture, to develop a new rootstock cultivar through interspecific hybridization between common fig (Ficus carica) and wild fig (F. erecta). The newly developed rootstock cultivar "Reikodai 1 go" has the same level of resistance to Ceratocystis canker as F. erecta and excellent grafting compatibility with "Masui Dauphine" and "Houraishi".
Yakushiji H., Morita T., Jikumaru S. (2019). Ceratocystis canker resistance in BC1 populations of interspecific hybridization of fig (Ficus carica) and F. erecta, Scientia Horticulturae, vol. 252, 71-76. https://doi.org/10.1016/j.scienta.2019.03.039
Photo 5 One month after the wound inoculation experiment
"Reikodai 1 go" (left), and "Masui Dauphine" (right)
Table 1 Transition of the cumulative mortality rate after wound inoculation experiment
Table 2 Transition of the cumulative mortality rate after infection to the fungus via soil
Table 3 The excellent rooting rate of the "Reikodai 1 go" cuttings