WINTER-WHEAT MAINSTEM LEAF APPEARANCE AND TILLER FORMATION VS MOISTURE TREATMENT

Mainstem leaf (MSL) appearance and percent tiller formation (%TF) have been used to evaluate wheat (Triticum aestivum L.) development. The assumption is that MSL appearance is a linear relationship to accumulated heat or growing degree days (GDD) and is unaffected by other environmental factors. Young wheat plants were subjected to high (HM) and low (LM) moisture levels to study their effect on leaf appearance, %TF, and the timing of tiller appearance. Four winter wheat cultivars were raised in a growth chamber with a 12-h photophase at 25 and 15-degrees-C during dark. Leaf psychrometer thermocouple readings (at the end of the study) showed significant leaf water potential differences between LM (-0.61 MPa) and HM (-0.29 MPa) treatments. The final MSL stage of the LM plants (5.5) was lower than the HM plants (6.2). Moisture treatment also reduced %TF of the coleoptile tiller, 0% LM and 36% HM. Moisture treatment did not affect %TF of the first, second, or third tillers. Even though the number of GDD required for tiller appearance was increased under LM; moisture treatment did not influence the MSL stage at which each tiller appeared. The significant effect of moisture treatment on MSL appearance demonstrates that this measurement more accurately reflects the overall growth environment of the plants until the time observations are made, rather than measuring just the preemergent seedbed environment as has been previously suggested.