Molecular breeding enables growers to get the improvements they want far more precisely, by zeroing in on the genes responsible for a given trait. If genetic engineering is a tool for “bludgeoning the genome,” as Cornell University researcher Susan McCouch puts it, what molecular breeding does instead is to “open a window” into how the genome works, enabling researchers to collaborate with it.
Sequencing the entire genome of a species is the first step, and this process, which cost millions of dollars a decade ago, is down now to the low thousands. Next, researchers sort out which genes are responsible for a given function, the bottleneck in the process so far, though McCouch says it becomes faster and cheaper with each new species that gets sequenced, because nature tends to employ the same mechanisms from one species to another. Finally, researchers map out markers – bits of genetic material that are linked to those genes, to flag whether or not the desired genes are present in a given individual.
“It’s not uncommon for a company to want to combine 10 or 20 traits in a variety,” says Harry Klee, a specialist in tomato breeding at the University of Florida in Gainesville. In the past, to get the perfect combination of traits using conventional methods, “you would have to put out millions of plants in the field.” Instead, breeders typically simplified, narrowing down their wish list to a few key traits.
With tomatoes, for instance, as many as 30 or 40 different genes influence taste – too many variables to juggle. So shelf life and appearance inevitably trumped taste. “But this is where molecular breeding really pays off,” says Klee. Breeders now use genetic markers to automatically screen one-inch-tall seedlings and immediately weed out the 99 percent they don’t want, cutting years off the breeding timetable. That makes it easier to get to desirable cross-breed quickly – and also stack up a complex array of traits in a single strain. As a result, says Klee, even mass-produced supermarket tomatoes should actually taste good five years from now.