Source: Newsquest, 10 February 2004 via BioScience News

Aphid-resistant varieties of lettuce now provide a viable alternative for growers hit by the devastating aphid over the past few years.

Auckland-based Terranova Seeds seed manager John Phillips said resistance had been bred into most commercial varieties by Dutch company Rijk Zwaan, using conventional rather than genetic engineering breeding techniques.

The company is supplying commercial and home garden seedling growers throughout the country.

Mr Phillips said work on developing the resistant strain had been going on for the past 20 years but it was only recently that the form had been refined to be commercially viable, particularly for the New Zealand market.

He said the resistant characteristic was first identified in a wild lettuce strain, and had been bred into established varieties which in the initial stages were too small to be economic.

The breeding breakthrough was established when the gene conferring aphid resistance was isolated from gene regulating plant size, produce an acceptable-sized resistant lettuce.

"The first varieties released overseas weren't as large as the New Zealand market prefers, with the big size and lots of outer leaves."

But subsequent breeding had established bigger lettuces that appealed to the New Zealand market.

Mr Phillips said the resistance was very strong and stable. Two lettuces growing side by side, one resistant and the other not, would produce totally different results, with the susceptible variety being infested with aphids but the resistant variety unaffected.

While he said the price difference of the resistant strains was "reasonably significant", the benefit of using them meant reduced use of sprays.

"Yes, there is a tradeoff but it also offers peace of mind."

He said the lettuce aphid tended to be temperature-specific. Infestation peaked over summer and autumn, which made use of the resistant varieties particularly worthwhile during those times.