BREEDING OF ALL-MALE CULTIVAR 'YUJIRO' IN HOKKAIDO, COOL AND SNOW COVER REGION IN JAPAN

A breeding program was carried out to obtain all-male hybrids adapted to the cool and snow cover Hokkaido region of Japan in the 1980's and 1990’s. In 1982, seeds collected from a male plant 'UC873-3' introduced from California University gave 38 plants, out of which nine were super male (M/M). They were crossed with 12 female plants selected in Hokkaido and 84 all-male hybrids were obtained from 1985 to 1989. In the first yield evaluation trial of these experimental hybrids, carried out from 1990 to 1994 at Hokkai Can Research Field on a clayey soil with drainage problem, some of them gave higher yield and earlier harvest than references, 'MW500W' and 'Hokkai 100'. The best all-male hybrid 'F84 x SM19' yielded 4.65 t/ha of marketable spears, 1.4 times more than 'Hokkai 100'. Besides a higher Growth Index (plant length x stalk number x stalk width) and a better tip shape, 'F84 x SM19' produced more medium size spears and emerged 2-3 days earlier than 'Hokkai 100'. In the subsequent comparative trial carried out from 1997 to 2001. 'F84 x SM19' showed same productivity as cultivars 'Gijnlim' and 'Carlim'. Following results obtained, 'F84 x SM19' was recorded as a commercial cultivar for green and named 'Yujiro' in 2002. Yield evaluation of 'Yujiro' on the well-drained volcanic ash field at Biei Agricultural Research Center, central region in Hokkaido, 'Yujiro' yielded less than recent all-male European hybrids.