RELATIONSHIPS BETWEEN PLANTING DATE, WINTER SURVIVAL AND STRESS TOLERANCES OF SOFT WHITE WINTER-WHEAT IN EASTERN ONTARIO

Reduction of populations of fall planted crops in the course of winter can result in substantial losses in economic yield. Variations in pla nting date of soft white winter wheat (Triticum aestivum L.) in easter n Ontario are known to influence both survival and grain yield. This s tudy was conducted to determine relationships between fall-accumulated growing degree days (GDD), cold hardiness, ice tolerance and a number of plant characteristics with survival recorded the next spring. Loca tions were at Ottawa (45 degrees 23'N) and Douglas (45 degrees 33'N) w ith four planting dates, 27 August, 10 September, 24 September and 8 O ctober in 4 yr, 1983-1986. Delayed planting was associated with reduce d survival at Ottawa in 1987 and in all years at Douglas. Consequently , survival at Ottawa showed little association with cold hardiness and ice tolerance, but there were significant correlations at Douglas. Me asurements in 3 yr showed that late planted wheats were single tillere d, up to 10 times lower fresh weight than the 3-5 tillered August-plan ted wheat, and their cold hardiness and ice tolerance were decreased. Moisture content of the crown tissue (CrW) increased with delayed plan ting despite the growth of the plants in acclimating conditions. Highe st CrW developed in late-planted wheat at Douglas and showed a high ne gative correlation with survival. Cold hardiness and ice tolerance cor related with survival at Douglas and there were significant relationsh ips between the stress tolerances. However, no consistent associations across location-years could be defined to explain winter survival in terms of fall-measured stress tolerances and plant parameters.