Aside from new varieties that have lower water requirements, pest- and disease-resistant gene-spliced crop varieties also make water use more efficient indirectly.
For example, widespread failure in our handful of remaining major crops and animal breeds due to disease or pest outbreaks is a very real possibility: given that pest and pathogens are constantly evolving, a diverse gene pool is essential if we are to develop insect- and disease-resistant strains in the future.