Yield, tillering dynamics and harvest index of single plants of four cultivars of autumn wheat sown on three dates in Canterbury, New Zealand : A thesis submitted in partial fulfillment of the requirement for the Degree of Master of Agricultural Science at Lincoln University

Abstract

This study investigated the tillering dynamics and tillers contribution to yield across three sowing dates (27th March, 19th April and 18th May in 2023) among four wheat cultivars (‘Graham’, ‘Kerrin’, ‘Voltron’ and ‘Sorrial’) using a split-plot design with four replicates at Lincoln University, Canterbury, New Zealand. Seeds were sown at a target population of 200 plants/m2 with 15 cm row spacing. Tillering was tracked using colour-coded wire on three tagged plants per plot, and apex development was monitored using a stereomicroscope (OLYMPUS SZX16/DP71). Biological grain yield and yield components were evaluated from a 1.5 m2 quadrat harvest at physiological maturity. Marked plants (repeatedly measured) and random plants, included for comparison, were harvested individually and partitioned to determine the contribution of individual tillers to the final yield and harvest index. Grain yield exceeded 15 t/ha (15% moisture) across all sowing dates, but differed among cultivars, with ‘Kerrin’ and ‘Graham’ producing about 1 t/ha higher than ‘Sorrial’ and ‘Voltron’. Early sowing resulted in about 60 fewer heads/m2, leading to decreased grain number/m2. However, cultivars differed in their yield-building strategies, either by increasing the number of heads/m2 or grains/head. The number of grain/m2 and head/m2 are the main determinants of yield components. The number of vegetative tillers produced was highest from SD1 and for ‘Kerrin’ and ‘Graham’. The maximum number of vegetative tillers was recorded at double ridge (DR), and tiller mortality accelerated at terminal spikelet (TS). Coleoptile, first and second tiller cohorts were the main vegetative tiller contributors, while the main stem, coleoptile and first leaf cohorts were major yield builders. However, the number of fertile tillers was not different among the sowing dates and cultivars. There was a strong positive linear relationship between individual plant and grain weight, which indicated a minimum plant weight (MPW) for different sowing dates to set grain. As a consequence, there was an exponential relationship between plant weight and plant harvest index (PHI) with a plant weight of ≥26 g needed to reach the ceiling PHI of 0.55 and a range of 15-21 g to achieve 95-99% of max PHI. Overall, this study demonstrates that the survival of fertile tillers and biomass partitioning influence yield efficiency in autumn-sown wheat. Cultivar selection and sowing strategies that support early tiller establishment and achieve plant biomass (15-22 g/plant) are key to maximise harvest index and grain yield. These findings show the value of integrating physiological traits into crop management decisions to enhance productivity in high-yielding environment.