(go to KOMUGI Home) (go to WIS List) (go to NO.79 Contents)

Although the maturity time has been advanced by about one week during the past 60 years, wheat cultivars with earlier maturity are still required for the implementation of double cropping and for avoiding rain damage at ripening time. In order to achieve this objective, some difficult problems need to be solved. First, wheat cultivars in Japan, especially those cultivated in the warm regions west of the Kanto district, belong to the earliest maturing group in the world, and therefore the introduction of genes conferring earlier maturity is very difficult. Accordingly, attempts to induce new genes for earliness by mutation breeding have been made (Yamagata et al. 1989). Secondly, there is a highly negative correlation between the time to maturity and yielding ability. Recently, it has been shown at the Kyushu National Agricultural Experiment Station that yield decreases by about 3 percent a day with the advancement of the maturity date (Taya 1993). In order to develop cultivars with early maturity and high yielding ability, it will be necessary to find a strategy to overcome this negative correlation. Thirdly, in cultivars with early maturity internode elongation occurs earlier, and hence the cultivars are prone to suffer from cold or frost damage. Therefore, breeding of early maturing cultivars with photosensitivity or a slight winter habit is now being attempted. Such characters are expected to be effective in delaying the onset of internode elongation and hence avoiding cold or frost damage.


2) Breeding for resistance to leaf rust: Leaf rust disease of wheat caused by Puccinia recondita Roberge ex Desmazieres causes considerable damage especially in the cold regions of Japan, i.e., Tohoku and Hokkaido. There is no type of immunity to leaf rust among Norin varieties. Extensive efforts to breed resistant cultivars, have been made, mainly at the Tohoku National Agricultural Experiment Station, by interspecific and intergeneric crossing, and four parental lines have been developed (Table 1).

Sabikei 40, a leaf rust resistant wheat parental line, was developed at the Tohoku National Agricultural Experiment Station from a cross between a F3 line derived from {(Shimofusakomugi x RW-12) x Nanbukomugi} and a B1F3 line derived from {(Miyaginokomugi x AR-1) x Miyaginokomugi} (Mukade et al. 1986). This cross was made in 1970 with the objective of accumulating two different leaf rust resistance genes, one from RW-12, a line which has a single dominant gene derived from Triticum turgidum ssp. dicoccoides on chromosome 6B, and the other from AR-1, a line which has a single incompletely dominant gene derived from Triticum timopheevi on chromosome 1A. Sabikei 40 shows seedling resistance to the leaf rust races 6A, 37B and 21B which are predominant in the northern part of Japan and to the naturally occurring races in the field of the Tohoku National Agricultural Experiment Station. A high level of resistance has been observed in adult plants in the field where leaf rust prevails each year the variety has been tested. No selection was made from F1 to F4 bulk populations and the F5 generation was screened for leaf rust resistance. The derived lines were selected for agronomic characters in succeeding generations. One promising line was obtained and named Sabikei 40 in the F12 generation in 1982. "Sabikei" means "leaf rust resistant line". It was registered by the Ministry of Agriculture, Forestry and Fisheries (MAFF) as a wheat parental line no. 1 in 1984 (Table 1).

Sabikei 43 is also a leaf rust resistant wheat parental line developed at the Tohoku National Agricultural Experiment Station (Mukade et al. 1986). It was selected from a cross between a 8x-Triticale line derived from the cross Norin 40 x Petkus and a wheat cultivar, Hachimankomugi. This cross was made in 1976 and attempts to transfer the leaf rust resistance from rye to wheat by spontaneous intergeneric translocation were made. After selfing the F1 plants, the generation advancement from F2 to F4 bulk populations was accelerated in the greenhouse. In the F5 generation, 546 plants were tested for leaf rust resistance and 18 plants resistant to the disease were cytologically examined. Out of these 18 plants, 11 carrying the translocated chromosome(s) were selected. Selection for agronomic characters was made in subsequent generations in the field. One promising line was obtained and named Sabikei 43 in the F9 generation in 1983. Sabikei 43 was registered by the MAFF as a wheat parental line no. 2 in 1984. Sabikei 43 also shows seedling resistance to the leaf rust races 6A, 37B and 21 B, and to the naturally occurring races collected in the field of the Tohoku National Agricultural Experiment Station. High adult plant resistance has been observed in the field where leaf rust prevails each year the variety has been tested. The resistance of Sabikei 43 to the race 21 B is controlled by a single incompletely dominant gene (Table 1).

<--Back | -->Next

(go to KOMUGI Home) (go to WIS List) (go to NO.79 Contents)