White lupin (Lupinus albus L.) plants develop cluster roots and have strong resistance to phosphorus starvation. Although many expressed sequences have been identified to explain the mechanisms used by white lupin to acquire phosphorus, the lack of a stable transformation technique has made it challenging to evaluate the functions of these expressed sequences. Virus-induced gene silencing (VIGS) is an attractive method for assaying gene function in species that are difficult to stably transform. Here, we show that the Peanut stunt virus (PSV) vector effectively induces silencing of endogenous genes in white lupin. It is unknown whether PSV is useful for VIGS; therefore, we first inoculated Nicotiana benthamiana plants with PSV harbouring fragments of the N. benthamiana phytoene desaturase gene (NbPDS). Two out of four distinct sequence fragments of NbPDS induced photo-bleaching in N. benthamiana, indicating that PSV can be used to knockdown endogenous gene sequences in a sequence-dependent manner. White lupin plants inoculated with PSV harbouring fragments of the L. albus PDS gene (LaPDS) developed photo-bleaching that was associated with a significant reduction in LaPDS mRNA accumulation. PSV spread systemically in leaves, roots, and cluster roots, and small interfering RNA of LaPDS was detected in these organs. This is the first study to demonstrate the use of VIGS by PSV, suggesting that this vector can be applied to supress endogenous gene expression in shoots and roots of white lupin and to clarify the mechanisms of phosphorus starvation resistance.