• DMH-1 (Dhara Mustard Hybrid-1), the only hybrid released by the Indian Council for Agricultural Research (ICAR) after extensive field trials. That employed a different technique, called cytoplasmic male sterility (CMS). It’s effective but large-scale seed production isn’t possible in this system. It has problems with stability and cannot be used in many mustard lines. If we need hybrid seeds of high purity and improved production, we need a robust pollination control mechanism.
• A flower has male and female parts. [Mustard self pollinates] and so to make hybrids using different parental lines you need to first make the male plant sterile and in the other parent, you need to put something to restore it, so that the farmer gets fully-fertile seeds. The other aspect is how good the parental lines are. [The controversy over GM mustard] is that we are confusing the two.
• With the barnase-barstar system (BB system) we can keep on making newer hybrids for traits such as disease resistance and productivity, but the system is basic. Without a good system you can’t have a good hybrid seed production. We started with the observation that combining Indian and East European hybrids are more productive.

What is the difference between a CMS system and a bar-barnase-barstar system?

• CMS system is a mutation that occurs naturally in plants or can be induced. It is in the mitochondria (the part of the cell that provides energy) and changes in it can induce sterility. During reproduction the plant needs more energy and the mitochondria (in CMS mutants) tends to fail, during that critical period, in the male part.
• However for a viable seed generation system this should only work for male sterility, and not affect other parts of the plant. Such mutants are very rare but typically they tend to have side-effects.
• CMS systems have been worked upon in cotton, chickpea and rice but have had mixed results. 
• China has wonderfully exploited the CMS system for rice but that rice could never grow properly in India. I spent many years (as a scientist at The Energy Resources Institute) trying to improve CMS systems and DMH-1 was a result of that.
• Sometimes it wasn’t possible to restore the plant’s fecundity; sometimes it would make plants more susceptible to fungus. Finding a perfect CMS is a back breaking job and isn’t like going to a shop and buying it off.
• So we thought why not try a barnase-barstar (BB) system. Here genes from soil bacterium (or ‘trans genes’ that don’t naturally occur in a species) are used to induce sterility, and later restore it.
• DMH-11 has the same male parent as DMH-1 (an East-European line called EH2). Only the female parent is different. DMH-11 uses transgenic technology, DMH-1 uses CMS, and for DMH-11 we used Varuna as the female. The fundamental insight is that you will get heterosis (or high-yielding hybrids) only if you cross an East European line with an Indian pure (cultivar) line. Indian-Indian crossings won’t have that effect irrespective of what technology you use.