The Influence of Climate, Phenology and Biomass Accumulation on the Grain Yield of Brassica napus.

Matching crop development to environment is critical to maximise biomass and its conversion into grain.  In the high rainfall cropping environment of southern Australia, the introduction of late maturing canola (Brassica napus) cultivars has produced grain yields up to 8t/ha in research experiments. However the relative importance of individual phases within the growing season for increasing grain yield is not well understood.  A study was conducted at Hamilton, Victoria, Australia (annual average rainfall 690 mm) to quantify the influence of different phase durations on grain yield. The study was an analysis of seven field experiments over five years (2010 to 2014) with 60 canola cultivars with differing phase durations and management providing data from more than 600 crop treatments.  Seasons varied with the range in annual rainfall of 476 to 981 mm.  Total biomass accumulation was strongly related to yield (R²=0.87), in particularly accumulation within the bud to harvest (R²= 0.50) and flower to harvest (R²=0.45) phases.  Both the thermal duration (^od) and growth rate (kg/ha/day) of the flower to harvest phase contributed to more grain.  Flower to harvest duration ranged between 53 to 102 days or 790-1220 (^od) and was influenced by the amount of rainfall within the period (R²= 0.47).  The wide range in duration between cultivars for a similar amount of rainfall (about 200 (^od) for 160 mm rainfall) demonstrates that genetic variation for this trait exists which may be exploited in breeding programs.  In one quarter of cases, structural (non-grain) biomass produced between the flower and harvest period was negative indicating a high reliance on translocated biomass from the pre-flowering period via stems and/or roots to form grain.