Mar12

IRRI Agronomy Challenge 2: Rats revisited and the plasticity (flexibility) of rice

Author // Dr. Leigh Vial Categories // Achim Dobermann's blog

12 March

Among plant number, tiller number, and panicle (head) size, rice can generate grain yield in any number of ways. With a low plant population, it can tiller a lot to produce the required number of panicles. If it fails to produce enough panicles, the panicles can be large to still get the required number of grains. The result? Ask 10 different plant physiologists or breeders how to balance these components to get best yield and you will get 11 different answers!

Human opinion aside, this flexibility offers a great way to overcome adversity. Any affliction, provided it takes a moderate toll evenly across the field and the sun shines, can be compensated for with subsequent growth and development patterns. This is why a few whorl maggots, a few snails, some wide row spacing or even some stem borers don’t necessarily affect yield, even if the crop looks ugly at the time.

The one time this process breaks down is when afflictions persist—or often combine—to stop the compensation. Major snail attacks, intense injury through a major brown planthopper outbreak, or especially rats can cause an irretrievable gap in the crop or keep a gap open. This is particularly so if the sun does not shine so brightly or the rice matures quickly. We have the same problem with ducks in southern Australia. The intensity or the sheer persistence of the ailment can overcome rice’s ability to compensate.

The crop is coming to that pleasing stage, when the panicles begin to turn downward under the weight of their grain. At last, the payback begins to appear.  The downside is that, by this stage, what we call the yield potential is set. We will get no more grains in the field with anything we do from now on ... we just need to fill them.

DSC_9388-8

Drs. Vial and Clerget look at how flexible the rice plant can be to attain its yield potential.

Last year, I noticed quite a few empty grains in the field, not filled probably because the plants lacked enough carbohydrate (fuel gleaned from the sun) to fill them. I hope we will fill more this year. In the end, a plant can fill only the grains if it dangles enough leaf area out to catch sunlight to make the fuel—no witchcraft here I am afraid! This is why many breeders love a big, wide flag leaf that keeps harvesting sunshine right up until the end, and this is why Achim was upset when he saw that many plants had not completely shaded the area around them.

Nothing left to do now, but wait until the harvest is near and pick the moment to drain the field.

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About the Author

Dr. Leigh Vial

Dr. Leigh Vial

Dr. Leigh Vial is former head of IRRI's Experiment Station. Read more.