New York Times: As the world`s population expands and global warming alters weather patterns, water shortages are expected to hold back efforts to grow more food. People drink only a quart or two of water every day, but the food they eat in a typical day, including plants and meat, requires 2,000 to 3,000 quarts to produce. For companies that manage to get ‘more crop per drop,’ the payoff could be huge, and scientists at many of the biggest agricultural companies are busy tweaking plant genes in …