Evaluating the imapact of different tropospheric ozone conditions and ambient temperature on yield of HD 2967 wheat (triticum aestivum) cultiva

Abstract

In this study I investigated the determinants of the yield parameters of HD2967 cultivars of triticum aestivum using data obtained during wheat growing season from November 2017 to April 2018 and November 2018 to April 2019. Seeds of the cultivar HD2967 were acquired from breeders. To study our objective, wheat was grown in two plots sown one day apart (15 th November and 16 th November) in 2017-18 and three different plots sown on November 1 st for plot 1, November 15 th for plot 2 and December 1 st for plot 3 in 2018-19 growing season. Different parameters such as grain yield per plant, 1000 grain weight, number of effective tillers, head length, number of shrivelled grains, temperature and ozone experienced by the plant during different growth stages and the time period taken for reaching specific growth stages were analysed. These analyses were performed to observe the effects temperature stress and ozone exposure on the yield of wheat cultivars. HD2967 cultivar took almost the same number of days to reach flag leaf stage during both years and on all sowing dates (84 to 87 DAS) and required a thermal sum of 1560±100ºC. It appears that the cultivar requires vernalization to enter reproductive growing. Plants sown on December 1st did not reach tillering growth stage before temperatures dropped as winter started early. Late sowing and sudden rise in temperatures after vernalization significantly reduced the thermal time to Anthesis for this cultivar by 300 ºC and 200 ºC, respectively. The thermal time after anthesis that the crop requires to reach maturity differs widely between plots and depends on the number of days of heat stress the plant experienced in the period from anthesis to maturity as well as the timing of those heat stress events. When heat stress is incorporated into the phenology treatment all plots reach harvest maturity at around 1125±25°C after Anthesis. For this cultivar, the number of active tillers seems to be primarily driven down by high ozone exposure during the period from emergence to flag leaf stage (R=-0.88) and by a shortening of the period from anthesis to maturity (R=-0.86). Surprisingly, high ozone during anthesis week appears to be impacting the tiller number favourably (R=0.85), indicating that rain and overcast sky during this crucial week can significantly reduce the yield of this cultivar Higher average temperatures during anthesis week appears to shorten the heads (R=-0.94), while flower sterility and grain abortion appeared to be driven both by a high maximum temperature during anthesis week (R=-0.74) and higher ozone in the period from anthesis to maturity(R=-0.73). The grain weight of each tiller and the grain weight per plant is most strongly reduced by high maximum temperatures during anthesis week (R=-0.94 and R=-0.83, respectively), while ozone exposure during anthesis week (R=0.6) and a high number of heat stress days during the period from anthesis and maturity (R=0.6) appear to be associated with a higher number of shrivelled grains. Surprisingly, heat stress during anthesis reduces the number of shrivelled grains (R=-0.8) likely because the reduction in the number of grains available for filling caused by heat stress during this period results in a higher probability that the remaining grains are better filled if conditions are adverse at this stage but better later on during growing season. The 1000 grain weight is anticorrelated with ozone exposure before the plant reaches the flag leaf stage (R=-0.86) and the maximum temperature during anthesis week (R=-0.71). This data seems to suggest that ozone exposure and heat stress after anthesis were not the only drivers of yield loss in wheat and that the availability of health biomass for translocation to the grain plays a role in determining the yield. Surprisingly, the 1000 grain weight just like tiller number was positively correlated with the ozone observed during anthesis week (R=0.75) indicating that sunshine during this crucial period is also important for proper initiation of the grain filling process in this cultivar. Overall, my work proposes that a consistent treatment of the temperature response of the wheat plant in crop models and in the DO3SE model appear possible and beneficial. Another important finding is, that it is not safe to ignore the plant exposure to ozone prior to the flag leaf stage while deriving exposure yield relationships.