In this Pioneer Interview excerpt, David Mackill, who departed the International Rice Research Institute (IRRI; http://irri.org) as a principal scientist in the Plant Breeding, Genetics, and Biotechnology Division in February 2011, discusses combining stress tolerances through rice breeding. He was the program leader for rainfed rice production at IRRI and led the development of more than 20 rice cultivars adapted to the challenging growing conditions in southern Asia. He also oversaw the IRRI project Stress-Tolerant Rice for Poor Farmers in Asia and Sub-Saharan Africa or STRASA - http://www.icrisat.org - for which he helped secure a grant worth US$19.9 million from the Bill & Melinda Gates Foundation. Over the last 28 years, Dr. Mackill held critical positions for rice genetics and breeding, including 10 years as a U.S. Department of Agriculture research geneticist stationed at the University of California, Davis. In the last 17 years, Dr. Mackill and colleagues identified and transferred a gene conferring submergence tolerance into new high-yielding rice varieties. Monsoonal rains plague southern Asia with flooding that destroys crops. These new rice strains are being adopted on a large scale and will translate into millions of tons of new rice for developing countries. He is now the strategic rice expert within the research and development arm of Mars Incorporated. Interview excerpt on combining stress tolerances: "One of the things to consider when developing a stress-tolerant variety is that, in the environment that you are targeting, the stress isn't uniform; it is not going to be in every field or in every village. So generally, when you have a new variety, that variety will be multiplied and distributed over a particular area. Ideally, you would like to have a variety that would grow well under different conditions in that area because the farmers' crops may have stress or may not have stress. So, that variety should have good agronomic characteristics; it should have high yield, it should have good quality, and in addition, it should fit into the cropping pattern. Once you have those conditions met, then you have the potential for a successful variety. We would like to incorporate stress tolerances so that, even in more unfavorable areas within a particular region, farmers can still grow the variety and get a reasonable yield. In some areas, you may have submergence, in some areas you may have risk of water stress [drought], and in some areas you may have both occurring at different times of the season or over different seasons. So, we think it's going to be useful to combine tolerances to these stresses [into varieties that are] appropriate for different locations. There are a few examples where we have been able to combine, to some extent, different stress tolerances. One of the early varieties we developed with submergence tolerance was released in the Philippines as PSBRc 68. It also has some degree of drought tolerance. Then we've developed more like prototypes of varieties or breeding lines that combine drought tolerance with submergence tolerance and also salt tolerance. Generally, it is relatively easy to combine submergence tolerance with these other stress tolerances because it is a single-gene trait. There's also some speculation that the SUB1 gene itself may have a beneficial effect on drought tolerance. So, it's certainly possible to combine these stress tolerances and that's really one of the focuses we have now. We don't only want to combine different stress tolerances but to combine these tolerances with other important traits such as disease resistance. We haven't found anything like the SUB1 gene with in the same level of tolerance in other stresses, but we found genes that have that have moderate drought tolerance and by combining several of them we can create a pretty good degree of stress tolerance in a variety. So, one of the efforts now is to introduce these kinds of genes for drought tolerance. Instead of introducing only one SUB1 gene, a variety will have two or three drought tolerance genes as well."