JOHANNESBURG, May 22 (AFP) - South Africa will have to import about 1.5 million tonnes of maize -- the staple diet of millions of people here -- after a heat wave damaged this year's crop, officials said Saturday. The coming harvest could be as low as six million tonnes, said the Department of Agriculture's crop estimates committee head Kobus Smit, while local consumption is about 7.5 million tonnes. Smit said the estimate is one million tonnes lower than last year's harvest, the SAPA news agency reported. Smit said farmers had planted less maize this year because of drought conditions and a heat wave in the major maize production area shrivelled many plants. Maize is South Africa's most important crop. The country produced a record 13.2 million tonnes of maize in 1993/1994 and usually exports most of the surplus.  