Abstract
Some Swedish spring wheat varieties have recently been shown to carry a rare wildtype (wt) allele of the gene NAM-B1, known to affect leaf senescence and nutrient retranslocation to the grain. The wt allele is believed to increase grain protein concentration and has attracted interest from breeders since it could contribute to higher grain quality and more nitrogen-efficient varieties. This study investigated whether Swedish varieties with the wt allele differ from varieties with one of the more common, non-functional alleles in order to examine the effect of the gene in a wide genetic background, and possibly explain why the allele has been retained in Swedish varieties. Forty varieties of spring wheat differing in NAM-B1 allele type were cultivated under controlled conditions. Senescence was monitored and grains were harvested and analyzed for mineral nutrient concentration. Varieties with the wt allele reached anthesis earlier and completed senescence faster than varieties with the non-functional allele. The wt varieties also had more ears, lighter grains and higher yields of P and K. Contrary to previous information on effects of the wt allele, our wt varieties did not have increased grain N concentration or grain N yield. In addition, temporal studies showed that straw length has decreased but grain N yield has remained unaffected over a century of Swedish spring wheat breeding. The faster development of wt varieties supports the hypothesis of NAM-B1 being preserved in Fennoscandia, with its short growing season, because of accelerated development conferred by the NAM-B1 wt allele. Although the possible effects of other gene actions were impossible to distinguish, the genetic resource of Fennoscandian spring wheats with the wt NAM-B1 allele is interesting to investigate further for breeding purposes.
Highlights
Knowledge on the efficiency of agricultural crops in using N and other nutrients can help reduce e.g., nitrogen (N) fertilization and increase the value of the crops produced
The wildtype allele of NAM-B1 originating in emmer wheat codes for a NAC-domain protein, a group of proteins known to be transcription factors involved in plant development processes
Forty of the varieties were hexaploid spring wheat (Triticum aestivum L. ssp aestivum) and one was tetraploid emmer wheat (T. turgidum L. ssp. dicoccoides), which was included for comparison
Summary
Knowledge on the efficiency of agricultural crops in using N and other nutrients can help reduce e.g., nitrogen (N) fertilization and increase the value of the crops produced. The genotypic traits affecting N uptake, N conversion to harvested product, and N retranslocation into plant parts that survive until the growing season (e.g., grain) all influence N use efficiency [2]. Effective translocation of nitrogen to the grain during grain filling has been identified as a candidate trait for improving N use efficiency in bread wheat (Triticum aestivum L. ssp aestivum) [3,4]. One gene possibly involved in nutrient translocation, and thereby nitrogen use efficiency, in wheat is NAM-B1 (Gpc-B1). The locus on chromosome 6B was originally identified in tetraploid wild emmer wheat The wildtype (wt) allele of NAM-B1 originating in emmer wheat codes for a NAC-domain protein, a group of proteins known to be transcription factors involved in plant development processes. One has a +1 bp insertion likely causing a frame shift and a loss of the NAC-domain, the other one probably has a large deletion [14,15]
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