VARIETAL DIFFERENCE IN YIELD RESPONSE TO DELAYED SOWING DATES IN SPRING WHEAT OF HOKKAIDO

Three spring wheat varieties, old tall Haruhikari and modern semi-dwarf Haruyutaka bred in Hokkaido, and tall late Selpek bred in Germany, were sown at a 5cm equi-distant square pattern on 3 sowing dates, i.e. early (April 11), middle (April 25) and late (May 10). Varietal difference in yielding ability with delaying of sowing dates was investigated through changes in growth phases, process of spikelet initiation and crop growth rate. The first growth phase, from emergence to the double ridge, stage and the total growing period were shortened with delaying of sowing dates in all varieties. The spikelet initiation phase was also shortened resulting in a decrease of spikelet number. CGR and NAR in the late grain filling period (growth phase V) decreased with delaying of sowing dates, resulting in a decrease of final biomass. Grain yield decreased with delaying of sowing dates in all varieties, mainly due to the decrease in biomass and grain number. The extent of decrease of grain yield was smaller in Selpek than in the other two varieties; the late sowing yielded less than the early sowing by 34% in Haruhikari, 36% in Haruyutaka and 14% in Selpek, because ear and spikelet number and CGR for grain filling period did not decrease with delaying of sowing dates in Selpek. At late sowing dates, the grain yield was 418gm-2 in Haruhikari, 523gm-2 in Haruyutaka and 551gm-2 in Selpek. Ear weight type variety (e.g. Selpek) may be useful for late sowing cultivation in Hokkaido.