Effect of genotype and environment on proportion of seed hull and pod wall in lupin

Abstract

Environmental and genetic effects on hull and pod wall proportions in lupin were examined by analysing data from 125 advanced genotypes at 17 year × site combinations in Western Australia. In Lupinus angustifolius the effect of genotype dominated the variance for seed hull and pod wall percentage and weight per seed, indicating strong heritability for these traits. Smaller but significant effects of site, and year × site and year × site × genotype interaction, were present for hull percentage, and year × site and year × site × genotype interaction effects were present for pod wall percentage. Hull percentage was found to be stable across branch orders within the plant canopy, but pod wall percentage increased and weight per seed decreased from main stem to higher branch orders. The average value of hull percentage was 24.0 in L. angustifolius with a range from 21.8 to 26.2%. L. albus (cv. Kiev Mutant) had a lower value than L. angustifolius at 18.1% and L. luteus cv. Wodjil gave a value of 24.5%. Hull percentage was found to decrease by approximately 0.5% for each 10 mg increase in seed weight. Hull thickness was found to correlate with site seasonal rainfall (r = 0.45*). The correlation between genotype means for hull percentage and pod wall percentage was not significant for this set of breeding lines and cultivars, indicating that selection for one will have little effect on the other. A low but significant correlation was identified between hull percentage and protein percentage (r = –0.38**) and protein + oil percentage (r = –0.46**), showing that selection for lower hull proportion could lead to higher protein and oil concentration in seed.

Pod wall percentage averaged 32.0% among L. angustifolius genotypes and was 28.1% in L. albus. At 41.7%, L. luteus had a very large proportion of dry matter in pod walls. Pod wall percentage was weakly negatively correlated with yield among 122 L. angustifolius genotypes (r = –0.19*). Pod wall percentage tended to increase with longer growing seasons. The results demonstrate the relatively narrow range in hull and pod wall percentage available in breeding lines and cultivars representing the current genetic base of Western Australian material but that the traits are highly heritable and selection is likely to be relatively easy. New sources with lower seed hull and pod wall proportions should be sought from wild and semi-domesticated germplasm or through mutagenesis to broaden the genetic base for these traits. The relationships between these traits and resistance to insects and disease are yet to be determined.