The backstory to finding sodium exclusion genes in wheat

Attentive readers may remember a piece we Nibbled a couple of weeks back about salinity tolerance genes (Nax1 and Nax2) making their way from a the wild relative T. monococcum to durum wheat. I asked around and it turned out that the monococcum cross in question was originally made decades ago, so I thought there might be an interesting backstory there. Some quick research quickly led me to this: “Parental material used in crossing and in Na+ uptake and flux experiments were durum wheat (Triticum turgidum) Line 149 and cv Tamaroi, and the parents of Line 149, Triticum monococcum C68-101 and durum cv Marrocos. Seeds were provided by Dr. Ray Hare of the Tamworth Agricultural Institute, New South Wales Department of Primary Industries.” So I contacted Dr Hare, who is now retired, and he was kind enough to send me the following, and allow me to reproduce it. It illustrates not just the importance of genebanks and crop wild relatives, but also how that importance sometimes becomes apparent through luck coupled with perseverance. Interestingly, that combination can be patented. My main question to Dr Hare was where the T. monococcum accession that started it all came from.

The C68-101 Triticum monococcum accession I believe came from the University of Sydney’s collection. It is known to carry the stem rust resistance Sr21. It is the stem rust resistance gene present in the Stakman differential set, ‘Einkorn’. Dr Dante The, a post graduate student at Sydney University, had been given the task to transfer Sr21 to hexaploid wheat so that this gene could be used in breeding rust resistant breadwheat cultivars.

Originally this accession was used as a source of Sr21, transferred from the diploid through a bridging cross (interspecific) with Marrocos (stem rust susceptible durum) to the hexaploid level. The Line 149 a stable tetraploid line carrying Sr21 (i.e. C68-101/Marrocos). It has the Australian Winter Cereal Collection (AWCC) accession number AUS 17045. This line is freely available. I am sure Greg Grimes and team, at the AWCC, will provide you with seed.

Now what has all this got to do with the salinity research, you may ask. To cut a long story short, I selected this tetraploid accession because I felt that it represented a potential divergence from the normal tetraploid genetic diversity, in that I was certain that it had a considerable content of monococcum genes. I was endeavouring to assemble a relatively small collection of tetraploid accessions (subspecies) representing the broadest range of genetic diversity from the Australian Winter Cereal Collection. At this time I was keen to look at the range of phenotypic expression for a number of breeding traits in durum wheat. I was concerned that the breeding program could be running out of genetic variability.

Being the Australian National durum breeder at the this time, my varieties were being grown on soils that we knew to contain transient salinity. Durum wheat yields were relatively poor on these soils. Durum wheat was known to be sensitive to elevated sodium levels in the soil.

My long time friend, Rana Munns, is a plant physiologist and an expert in plant/salinity research. She had all the experiment techniques sorted out nicely. So we got together and started a small project to see if there was any salt tolerance in durum.

All reports in the press were not positive. But nevertheless we pushed on. Our starting point was my collection of tetraploid subspecies. To our pleasant surprise, we found a few lines that appeared to exclude sodium from the leaves. Confirmation experiments showed that we were really onto something (i.e. high potassium and low sodium in leaf tissues, the reverse of normal when grown in elevated sodium media; this was a highly significant and repeatable reversal).

As the Marrocos line was rather wild and far from an ideal cultivar type, I commenced crossing it to my durum breeding materials. The cross with my variety ‘Tamaroi’ formed the research population for inheritance studies and subsequent molecular research. All these studies are published. Search under R. A. Munns.

I have no idea where the monococcum accession came from originally. I could check out the register of the Sydney University collection when I am at the Plant Breeding Institute, soon. I am on the staff of the PBI. I can also check Dante’s thesis when next at PBI Cobbitty. Dante’s thesis may carry more details on the source of the monococcum.

A bit long winded but I think that it is a nice little story on the value of genetic resources centres. Outcomes like this clearly demonstrate the value of such centres, many times over. A colleague of mine (Richard James in Plant Industry, CSIRO, Canberra) is transferring the two sodium exclusion genes (Nax1 and Nax2) to hexaploid wheat. Who knows what other genes for important traits can be found in monococcums and other progenitors. There are so many possibilities and exciting opportunities for gene exploration without going outside the Triticeae.