Yield Performance of Hybrid Mixtures for a Theoretical Mixed Refuge Application in Canola (Brassica napus L.) in Western Canada.

Cultivar mixtures are increasingly being used in integrated refuge for plant defensive resistance traits.  To support this refuge application in Canola (B. napus) yield trials were conducted in western Canada.  Hybrid mixtures may improve yield and genotypic stability across environments.  Use of alternate hybrids in refuge would reduce the need to create susceptible isoline versions of hybrids.  Many defensive traits in the allotetrapliod B. napus are native traits and may involve multiple genes dispersed throughout the genome.  Creating isoline versions of these resistant hybrids would involve multiple genetic regions and considerable resources.  Thus superior susceptible hybrids may be readily available and provide an efficient way to produce refuge for maintaining effectiveness of resistance.  Dupont Pioneer canola hybrids 45H29, 45H25 and 45H21 were used in testing at 8 locations in 2010 and 7 locations in 2011.  Two parent hybrid mixtures were produced at rates of 100% (one hybrid), 75%, 50%, 25%, 0% (another hybrid).  The hybrid mixtures were then grown at low (75 plants/m2) and high (150 plants/m2) density in a randomized complete block design with 3 replicates.  High density plantings yielded higher than the corresponding low density treatments.  Hybrid mixtures showed a linear relationship linking the high and low yielding hybrids.  This relationship showed a proportional contribution to yield of each hybrid in the mixture and did not demonstrate any synergy between hybrids.  Overall genotypic stability was not improved by different levels of mixed hybrids compared with pure stands.  The hybrid 45H29 in pure stand (100%) at the high density (150 plants/m2) produced the highest yield.  This research would favor the use of a different hybrid for refuge where susceptible high yielding hybrids are available.  If the resistant hybrid is top yielding and the trait simply inherited a susceptible isoline version would be superior for a theoretical refuge.