Wheat Genome Finally Sequenced – This is a Big Deal

November 23, 2017 – Scientists have been sequencing the genome of all kinds of animals and plants for the last two decades. But for a number of reasons wheat has presented a challenge, described by researchers as equivalent to decoding Mount Everest.

Why? Because the wheat genome dwarfs the human genome being five times bigger than ours. One of the reasons is, instead of 23 pairs of chromosomes, wheat has 7  hexaploid chromosomes which means each has six identical copies, totaling 42. When that translates to nucleobase pairs, (consisting of adenine, guanine, cytosine, and thymine) of adenine-guanine, and cytosine-thymine, the total number becomes astronomical, somewhere between 8 and 8.5 billion in total. Compare that to humans with 3.2 billion nucleotides and you can begin to see the challenge. And even more challenging is the fact that the wheat genome consists of many identical genomic sequences, described by researchers as trying to put together a jigsaw puzzle made of pieces showing a homogenous blue sky.

Since 2005 the work of sequencing wheat has been ongoing leading to this year’s announcement from John Hopkins University in Baltimore that a small team of genomics researchers had finally sequenced 15.3 billion nucleobases (7.65 billion nucleotides). That represents between 90 to 95% of the entire genome and enough for scientists to begin identifying and labeling the genes and sequences responsible for some of the biggest disease challenges this staple crop faces.

Upon learning about the successful mapping of the wheat genome, I thought it would be useful to look at the major diseases impacting wheat to determine which of these could benefit from amping up wheat’s own genetic makeup. Well it turns out there are lots of which 21 of the most common are identified below:

• Cephalosporium Stripe – a lower fungal stem disease that is best treated today by crop rotation
• Common Bunt – caused by a fungus and currently treated with fungicides
• Common Root Rot – treated by controlling grassy weeds and crop rotation
• Fusarium Head Blight – caused by a fungus and treated with foliar fungicides
• Fusarium Root, Crown and Foot Rot – caused by a fungus that is most severe in dry weather and best controlled by crop rotation or elimination of grassy weeds
• High Plains Disease – a disease caused by the ssRNA wheat mosaic virus (WMoV) which stunts infected plants
• Leaf Rust – caused by a fungus and treated with foliar fungicides
• Loose Smut – caused by a fungus and treated with fungicides
• Powdery Mildew – caused by a fungus and treated with foliar fungicides
• Septoria Tritici Blotch – caused by a fungus and  treated with foliar fungicides
• Soilborne Mosaic – a winter wheat disease caused by a virus which wanes in its impact as weather warms
• Sooty Head Mold – caused by a black mold leading to discoloration of the crop but generally not treated
• Spindle Streak Mosaic – often associated with Soilborne Mosaic with a viral origin associated with wet areas in planted fields
• Stagonospora Nodorum Blotch – caused by a fungus and treated with foliar fungicides or with fungicides applied to the seed before planting
• Stem Rust – caused by a fungus and treated with foliar fungicides
• Stripe Rust – caused by a fungus and treated with foliar fungicides
• Take-all – caused by a fungus and best controlled through crop rotation and grassy weed management
• Tan Spot – caused by a fungus that survives in wheat residue and treated by tillage or foliar fungicides
• Triticum Mosaic – a viral infection closely associated with WMoV (see High Plains Disease)
• Wheat Blast – a fungus that attacks the head of the plant and is found in tropical and semi-tropical growing areas
• Wheat Streak Mosaic – a multi viral infection spread by wheat curl mites treated by delayed planting or avoiding planting near fields with maturing corn

All of the above could find resolution through modifications to the wheat genome. That’s why mapping the genome and identifying genes, that potentially can be fortified to create biological weapons, is seen as significant. So kudos to the John Hopkins team because their success marks the beginning of a new era for the world’s second most important grain staple, giving it genetic traits to fend off the worst that nature can throw at it.