Genetic variation refers to the differences in the sequance of DNA between individual organisms of a species. Recombination produces a new combination of allele by breaking down and recombining pieces of DNA. Mutation produces gene variants by altering gene activity or protein function. Crossing over increases genetic diversity that leads to creation of new combination of genes.
Cloning increases the chances of superior traits by copying the alleles which contain such DNA. It leads to erosion of diversity because there is no combination that is taking place since there is no fertilization along the process.
Answer - Cloning