They say you can never be too rich or too thin. In the case of lupin seed coat, or hull, and pod wall, the latter is certainly true.

Five years of research supported by the Grains Research and Development Corporation (GRDC) and the Australian Government has focused on decreasing both.

The latest project, supervised by Jon Clements of the University of Western Australia, aims to reduce the coat proportion of seed to 15 per cent. Mostly cellulose, seed coat makes up about 24 per cent of the narrow leaf lupin seed.

Presenting at a Centre for Legumes in Mediterranean Agriculture seminar, Dr Clements explained his GRDC-supported project indicated that reductions in pod wall proportion are associated with increased yields in both narrow-leafed lupin and albus lupin.

Reducing the proportion of seed coat could increase kernel yield by six per cent - worth an extra $14/ha on the basis that kernels are worth 25 per cent more than whole grain in rations.

A thick seed coat makes de-hulling difficult and expensive and reduces the metabolisable energy levels found in the narrow leaf lupin. Reduced seed coat also increases metabolic energy, oil and protein, while a reduced pod wall could increase yield.

Seed coat percentage decreases as seed weight increases, prompting the strategy to breed for bigger seed size.

Thinner seed coat and pod wall genotypes have been identified in germplasm and mutant populations, which are now being crossed to produce improved genotypes able to be rapidly incorporated into the lupin breeding program.

Seed coat percentage, which appears not to differ, on average, between wild or domestic and hard seeded or soft seeded varieties, was low in wild plants from Turkey, Greece and Cyprus and pod wall was lower in plants from Spain, Cyprus and Greece.

The project has focussed on the identification of improved narrow leaf, yellow and albus lupin germplasm, with the researchers assessing 1425 accessions and 10 species from 28 countries.