The effect of manganese on seed yield and the split seed disorder of sweet and bitter phenotypes of Lupinus angustifolius and L. cosentinii

Abstract

In two experiments at Lancelin, on soil highly prone to the split seed disorder of lupins, the responses of 10 Lupinus angustifolius and 21 L. cosentinii phenotypes to manganese fertilizer rates were examined.

In the absence of manganese, the concentration of the element in the seed was less than 10 ppm in all phenotypes of angustifolius, and they carried an average of 41 seeds per plant. In the sweet lupins only, the incidence of split seeds increased rapidly as the manganese concentration fell below 10 ppm. No phenotypes of cosentinii showed any split seed symptoms.

Manganese sulphate at 15 kg/ha reduced split seed from an average of 48% of the seed numbers to 6%, and increased seed numbers to an average of 55 per plant.

The difference between lupin species is probably due to differences in their ability to take up manganese and transport it from vegetative to reproductive plant parts, which in augustifolius would appear to be associated with the biochemical process of alkaloid synthesis by the iucundus gene. This aspect warrants further investigation.

In sweet angustifolius lupins there is a negative relationship between split seed and seed yield, superimposed over a manganese deficiency effect of reduced seed numbers found in both sweet and bitter phenotypes. Application of manganese increased seed yield by an average of 45% in the sweet angustfolius lines, through higher seed numbers and heavier seed weight (less split seed).

The genes for non-shattering of pods in angustifolius (tardus and lentus) and the very early-maturing genotype (Bo + xe) in L. cosentinii doubled the percentage of abnormal seeds (aborted ovules), a problem not related to manganese availability or the split seed disorder.

The non-susceptibility of cosentinii should provide a useful low alkaloid lupin for the soils prone to the split seed disorder.