Extra sinks are of no value without an increased source

Dr. Graham Scoles

In the words of Jonathan Swift “whosoever could make two ears of corn or two blades of grass to grow upon a spot of ground where only one grew before, would deserve better of mankind, and do more essential service to his country, than the whole race of politicians put together.”

As genomics work continues, we are “discovering” genes that control flower and seed number and size.  There was a recent announcement in Crop Biotech Update that scientists had discovered how to triple the number of seeds in sorghum plant. Even more recently, a headline announced the “discovery of a gene controlling shape and size of wheat spikelets that could shape future crops.” These articles are often accompanied by speculation on how the discovery/understanding of such genes might increase crop yields and production, and thus support the words of Jonathan Swift.

Ever since scientists began to transfer genes into other species many of these types of discoveries have been made. I remember arriving at the University of Manitoba as a new graduate student and being impressed by the incredibly large heads of triticale that were on display. Those large triticale heads indicated the production potential. However, there is a catch: the ability of the plant to fill that potential is always limited by photosynthetic capacity.

Crop physiologists use the terms “source” (for photosynthetic capacity) and “sink” (for the structures to be filled by that photosynthate) and have shown that sink number and size are always complementary, given a limited source (termed “compensation”). Manipulation of sink capacity through increasing seed numbers or size has been – and will continue to be – futile, until we are able to improve the photosynthetic process.

We wouldn’t invite more guests to dinner (sinks) without increasing the amount of food (source) and we shouldn’t expect higher yields, by whatever means, without increased photosynthetic levels.

Photo: depositphotos.com (1913318)