The genetic control of highly restricted branching in narrow-leafed lupin (Lupinus angustifolius L.)

Most current cultivars of narrow-leafed lupin have an indeterminate growth habit such that vegetative growth continues while the pods are being filled , causing strong intra-plant competition for assimilates. Restricted-branch ing (RB) genotypes can reduce this tendency and raise the proportion of the plant's biomass going into grain. Studies on the inheritance of the RB tra it showed that two spontaneous mutants, P25598 and P21227, each carried a s ingle incompletely dominant allele conferring the trait, whereas two other spontaneous mutants, P24743 and P25582, and two induced mutants, P26021 and P21238, each carried a single recessive allele conferring the trait. The R B alleles present in P26021 and P21238 seem to be the same, and to be at th e same locus as (or tightly linked to) the allele controlling the RB trait in P21227. Similarly, the genes present in P21227 and the induced mutant P2 5735 appear to be the same when these lines are crossed. However, they do n ot behave the same in crosses with P26021: thus we propose that there are a t least three alleles at the same locus (or at tightly linked loci) that co nfer RB. Normal-branching plants that are heterozygous at an RB locus gener ally have fewer leaves on the uppermost branch than homozygous-normal plant s. Similarly, RB plants that are heterozygous generally have fewer branchle ss nodes on the main stem than homozygous-RB plants. The RB trait is associ ated with a small but significant reduction in the number of leaves on the main stem. However, this relationship is weak and will not prevent plant br eeders from selecting both early- and late-flowering RB genotypes.