Abstract
To improve rust resistance of bunching onion (Allium fistulosum L.), we applied a recurrent selection program by using six cultivars (C0): ‘Seito Ippon’, ‘Iwai 2’, ‘Choju’, ‘Senami’, ‘Fuyuogi Ippon’ and ‘Toyokawa Futo’. Each cycle of recurrent selection consisted of two steps: selfing and selection among selfed progenies in the first year, and intercrossing and maternal-line selection in the second year. A second-cycle improved population (C2), consisting of 10 maternal lines, was obtained by two cycles of recurrent selection. Furthermore, we conducted two generations of selfing and progeny selection, and obtained 13 C2S2 lines. To evaluate the effectiveness of this recurrent selection, we conducted two rounds of simultaneous inoculation tests and compared the rust resistance of all generations obtained in the selection program. Under inoculation tests in the spring and autumn, the value of the area under the disease progress curve (AUDPC), an index of disease intensity, definitely decreased with the progress of recurrent selection. Although the resistance gain from C1 to C2 was small, much progress was made in the C2S2 generation; the AUDPC in C2S2 lines was approximately 38% of that in the initial parental cultivars. Our results demonstrate that recurrent selection is effective in improving the rust resistance of bunching onion.
