The trials, conducted at Higham in Essex, featured 29 brown varieties, with nine being trialled for the first time, and seven reds, including one new variety.
"There are a lot of nice new varieties coming through," Napier told Grower. "There is a trend toward reds now. As with any crop, yield is a target, and as with courgettes, there is the aim of producing a UK crop for as much of the year as possible."
The Santero variety from New Zealand, aimed mainly at the organic market, "has come into its own, though it's not as high-yielding as some other varieties," he explained.
"On the whole though, crops have suffered. They are one-to-three weeks behind and may end up maturing early without filling out - you'll end up with onion-smelling golf balls. Our trial site has heavy soil and the ground went from sodden to baked hard, causing distorted bulbs. There will be issues."
Bulbs' storing quality will also be affected, he added. "Ordinarily, most varieties will store well in ambient conditions until March. Syngenta's Vision will take you through to May. Controlled-environment stores will almost take you through to next harvest.
"The British Onion Producers Association has a target of supplying for 46 weeks of the year. Last year, it was 50, but it was a very good year. We won't hit that this year, with the weather, quality and yield we're seeing."
The NIAB will hold an assessment of harvested varieties on 1 November.