The correct conclusion from the information given is:
If a plant has white flowers, then its genotype must be pp.
This is because white flowers result from the presence of two recessive alleles (pp). The other statements do not accurately reflect the relationship between genotype and phenotype given that dominant traits can result from either homozygous dominant (PP) or heterozygous (Pp) alleles. Thus, a plant with purple flowers could have a genotype of either PP or Pp.