26 May 1995

Encouraging alkaloids?

GLYCOALKALOIDS, first identified as the potentially toxic result of tuber greening, could be positively encouraged during seed production in a bid for healthier seed.

"We have found that seed with high glycoalkaloid levels, induced by artificial lighting, are less susceptible to a range of diseases and even mouse damage," says Glynn Percival of SAC Auchincruive. "And daughter tubers dont inherit the high levels, so we could use this for biological control."

So far, fusarium levels on seed have been cut by 50%, Rhizocto-nia solani by 30-50% and skin spot to some extent. But the results are from one year only, in laboratory conditions, he stresses.

His work also shows that lighting affects red- and white-skinned tubers differently. Mercury lamps keep glycoalkaloid levels low in white-skinned varieties but send levels 20 times higher in red-skinned types. With fluorescent lighting the effect is reversed. Sodium lighting produces high levels in all types.

That could have an implication for the display of potatoes in supermarkets, where the aim is to keep glycoalkaloids low. Red- skinned varieties would be best displayed under fluorescent lights, while white skins should go under mercury lamps. That could be particularly useful for varieties close to the recommended limit for glycoalkaloids in tubers of 20mg/100g fresh weight. Marks and Spencer has shown particular interest in the work. If greening is to be used to boost the biological control of diseases in seed, chitting stores could also take account of lighting source, he says.

Reflecting on the role of lighting in glycoalkaloid production – Glyn Percival of SAC Auchrincruive. Red and white tubers react differently.