By Cecile Bester

In 2018, the national seed board of Bangladesh approved the release of the wheat cultivar “BARI GOM 33”. This cultivar offered resistance against Wheat Blast, one of the most troublesome and devastating wheat pathogens. The quick-release was remarkable, since the seed- and wind-borne pathogen was only detected in Bangladesh two years prior, in 2016. Usually, wheat breeding is a lengthy process that involves extensive crossings, selections and trials. Collectively, the process can take longer than a decade from start to finish. The almost immediate availability of a resistant cultivar helped Bangladeshi farmers keep the devastating fungus at bay and prevented vast wheat losses. This raises an important question; What allowed breeders to drastically speed up the normal breeding process?

The answer lies in the utilisation of a pre-existing 2NS-2AS translocation from the goatsgrass Aegilops ventricosa. The translocation was previously studied and used due to the rust resistance that it offered. When the realization came that it also offers effective protection against Wheat Blast, it could be rapidly employed against the new threat. With an efficient source of resistance already introduced into wheat, the chromosome segment could easily be transferred to a locally adapted wheat line. This serves as an example of the important role of wild relatives in wheat breeding.

Centuries of domestication and selection have dramatically reduced the genetic diversity found in wheat. As a result, there is a limited amount of resistance genes in present-day bread wheat. Unfortunately, the emergence and evolution of new pathogens are not limited. The sustainable production of wheat is constantly under attack. Breeders need to be on top of their game, ready to tackle any new threat that emerges. Wild relatives can provide the necessary arsenal of resistance genes required in this ongoing battle.

The origin of wheat lends it as a perfect candidate for wide crosses and interspecies hybridization. Wheat is an allohexaploid consisting of an A, B and D genome. All three genomes can be traced back to a different genome donor. About half a million years ago, Triticum urartu (AA) hybridised with Aegilops speltoides (SS) forming T. turgidum (AABB) or durum wheat. Much later, about 8000 years ago, durum wheat hybridised with Ae. tauschii (DD), forming modern-day bread wheat (AABBDD). Breeders have used the three genome donors and other close relatives as a source of genetic variation in wide crosses. By crossing wild relatives with wheat, recombination can take place and chromosome segments can be transferred. These segments can contain important genes.

Over 52 genes from 13 different genera have been introduced into wheat through wide crosses. This includes genes that offer pest- and disease resistance, as well as agronomically important traits. The micro-nutrient content of wheat can also be improved since various Aegilops species have a high zinc and iron content. Wild relatives of wheat provide endless possibilities for crop improvement. Breeders need to be proactive rather than reactive, to make use of these opportunities sooner rather than later.

In 2016, the 2NS-2AS translocation provided the necessary genetic material to breed for Wheat Blast resistance. However, if this translocation had not already been present in common wheat, the process would have been much longer. Even if we cannot predict the next big threat to wheat, we can prepare for it. As breeders, we need to prioritize the conservation, evaluation and utilisation of wild relatives in preparation for the future. By intentionally increasing the genetic base of wheat through wide crosses, we can enrich the resistance available to us. This will provide us with a larger arsenal, helping us to persist in the ongoing battle for sustainable wheat production.

Importance of wide crosses in wheat breeding