10 May 2001
Breeder queries hybrid rape figures

By Andrew Swallow

RECOMMENDED List scores for yield and other characteristics of hybrid oilseed rape have been questioned by breeder Nickerson.

Planting hybrid varieties along-side conventional oilseed rape up to harvest year 2000 gave the hybrids an unfair advantage, maintains senior oilseeds breeder Jo Bowman.

Even at the same crop height, the hybrids have a competitive advantage because they out-compete a conventional neighbour, he says.

But in a field situation where all plants are of the same variety, that competitive effect is not an issue.

As a result, Recommended Lists overstate the yield advantage of hybrid varieties over conventionals, he says.

Sowing conventional and hybrid variety trials in separate blocks for harvest 2000 eliminated that anomaly, but biased results will remain in the system until the 2004 list as oilseed Recommended Lists are compiled using four year average data, he warns.

It takes a while for these figures to come through, says Dr Bowman.

Similarly, statistical techniques comparing two or three years data for a new variety with four years figures for a control variety such as Apex can distort scores.

Shannon, for example, Nickersons newly recommended variety for central, south-east and south-west regions, has a stem stiffness rating of seven.

Yet Apex, which for the past two years has had stem stiffness scores below Shannons, still holds a rating of eight. Both should be eights. It is a statistical fix and makes no logical sense.

Sowing hybrid varieties at 70 seeds/m2 and conventional varieties at 120/m2 has introduced another bias. Hybrid and conventional variety lodging scores are no longer comparable, says Dr Bowman.

The one thing directly related to plant density is lodging the result is the hybrids stand in the RL trials and the conventional varieties go flat.

Sown at the breeders recommended seed rates, conventional varieties would stand too, he says. The message is that there is an advantage in the trials system for hybrids.

Tall varieties grown next to short ones in trials also have a competitive advantage not seen in crop situations, continues Dr Bowman.

Only since 1999 have National List year two and later variety trials been height grouped.

That could explain why Apexs apparent yield shortfall in trials was not seen in the field.

The highest yielding varieties on the list tend to be tall. Yet farmers prefer Apex, which has almost no yield at all according to the list. They have found the trials out.

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