b"time to not only natural pressures like pests, disease and tem-perature changes, but also human needs.As we want new things out of our crops, such as tomatoes, that diversity provides the portfolio of options where you can find something that's redder, bigger or tastier. It allows not only adaptation, but also resilience. If there's some sort of shock, like a big weather event, some of that diversityparticularly diversity among individuals or among varietieswill probably be wiped out, but other ones will make it. In total, there's a resilience across the group, explains Colin Khoury, senior director of science and conservation at the San Diego Botanic Garden.One major disaster that shocked the U.S. system, specifically for corn, was the southern corn leaf blight epidemic a little over 50 years ago in 1970. An estimated 15% of corn was lost, with close to $1 billion in losses for the U.S. due to a pest that discovered how to capitalize on the massive uniformity within the corn crop, accord-ing to the USDAs Agricultural Research Service (ARS).That was a big realization for scientists that there needed to be more attention to maintaining diversity within and among crop varieties, adds Khoury. If you get too uniform, then your resilience and ability to deal with these challenges of pests and diseases gets pretty tenuous. Since then, there has been more focus on trying to keep that diversity, but there's always this ten-sion both on the supply and the demand sides of food systemsEars of teosinte (smallest upper left side), maize (largest ear, lower that lead towards uniformity. But the science tells us that weright side) and two hybrids with their seeds.PHOTO: MARYLIN WARBURTONneed to push back against that by continuing to generate and cultivate diversity.Thats where wild relatives come in. When left to their ownWild Relatives Allow Diverse Sets of Cropsdevices, plants in the wild evolve and create new alleles, increas- When a breeder needs to create resistance in a crop, they typi-ing the amount of diversity. While not all of the traits from wildcally begin by looking at what is already domesticated, mixing relatives are desirable, some can be very valuable, primarilyand matching while trying to breed something with resistance. If in terms of resistance to pests and diseases, as well as abioticthat is not successful, the breeder will go to old, cultivated varie-stresses. In some instances, those wild relatives are so imperativetiesthe landraces or farmers varieties. If the breeder is still that the crops would no longer be able to survive without theunable to find what they need, they will take a look at the wild disease resistance traits found in their wild relatives. relatives.Access to these traits in wild relatives are vital for newer varie- We know that there's more genetic diversity in the wild rela-ties, as newer varieties have already gone through two bottlenecks:tives compared to the land races. Looking beyond disease, what first from domestication, and then from modern crop breeding.happens if I want to modify the type of proteins that are found This greatly limits their diversity, particularly for corn plants.in my corn seeds? Corn doesnt have a lot of protein. What if I Corn has always been a major crop in the U.S. In 1969, thewanted to make it healthier? What if I wanted to increase levels U.S. was exporting around $690 million worth of corn, while inof vitamin A, zinc or some of the other micronutrients that corn 2021, corn exports hit a record high at $18.7 billion, shared thedoes not have a lot of? Some of the diversity that I need is in the USDAs Foreign Agricultural Service (FAS). To reach this increas- genes of older varieties, or in wild relatives, because we haven't ing demand for corn globally, experts have selected strongly tobottlenecked those out yet, explains Warburton.output extremely high yields under specific conditions, resultingThe diversity found within many of the modern crop plants in a loss of diversity.are composed of the best genetic forms for the traits that are The Midwestern Corn Belt is a prime example. The corndeemed important as of now, but that does not necessarily grown in the Corn Belt has very particular traits and has lost ainclude what traits will be needed in the future.majority of the diversity found in the older landracesor farm- There are other traits that we know we will need. For exam-ers varietiesthat werent bred by scientists but were culti- ple, we need to adapt plants to require less nitrogen fertilizer. vated by farmers for generations. We need to adapt plants to use less water, as droughts are more In the case of corn, if you have a new disease, chances arecommon. At the same time, we need to adapt crop plants to you're not going to have resistance to it because you didn't saveother weather extremes that are happening by climate change, a lot of that genetic diversity during domestication and modernshe continues.crop breeding, says Warburton. That doesnt even cover the traits that are not yet foreseen. As To regain that allelic diversity, breeders must call upon wilddiseases move to new regions and evolve to be able to attack new relatives. crop species, or an insect appears in a climate that it would usually 100/ SEEDWORLD.COMDECEMBER 2022"