LEAF EMERGENCE RATE AND TEMPERATURE IN EARLY AND LATE SPRING WHEAT-VARIETIES

Spring wheat varieties, early Haruyutaka and late Selpek, were grown u nder field conditions to find the relation between leaf emergence rate and temperature. Fourteen sowings were made at two week intervals fro m March 17 (S1) to September 13 (S14). Leaf expanding degree (Haun's s cale) were measured daily, and shoot apices were checked every day to determine the date double ridge stage (DRS) appeared. Final leaf numbe rs differed by only one, although the first nine sowings ranged over f our months from March (S1) to July (S9). Late variety Selpek always ha d one more leaf than early variety Haruyutaka for S1-S9, suggesting th at the final number of leaves was closely related to the earliness of varieties. Leaf emergence rates with accumulated temperature (AT) were higher before than after DRS. and those before DRS decreased with del ay in sowing time. The leaf expanding degree at DRS did not vary great ly among sowing times, but were synchronized with phenology. We establ ished regressions before and after DRS for the relation between leaf e xpanding degree and AT. The coefficients (a) before DRS were higher th an those after DRS for both varieties. In addition, their standard dev iation was large so that inclinations of regressions before DRS differ ed with sowing time. We concluded that leaf emergence rate has a squar ed relation with mean temperature before DRS and a linear relation wit h mean temperature after DRS.