University of Tasmania

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Physiological and genetic studies of an alternative semi-dwarfing gene Rht18 in wheat

posted on 2023-05-27, 20:33 authored by Tang, T
Conventional semi-dwarfing genes Rht-B1b and Rht-D1b have successfully improved grain yield of wheat. This study investigates the physiology and genetics of a new semi-dwarfing gene, Rht18. Isogenic lines including Tall, semi-dwarf (Rht-D1b/B1b or Rht18) and Double dwarf (Rht18+Rht-D1b/B1b) were developed. There was no difference in developmental stage between semi-dwarfs from the time of terminal spikelet to maturity. However, Rht18 slowed the growth of the spike and distal internodes to reduce plant height by 20-35% compared with Tall lines. Dry matter was relocated from the stem to the spike post-anthesis, and semi-dwarfs relocated less on a whole stem basis, but more per unit length compared with Tall. Rht18 and Rht-D1b/B1b had similar spike weight, grain number, grain size and harvest index. Rht18 maintained long coleoptile length in both bread and durum wheat. Coleoptile length was positively correlated with emergence percentage when sown deep under controlled conditions and in the field, indicating the potential for Rht18 to replace Rht-D1b in future cultivars to improve crop establishment of wheat. In terms of seedling leaf area and biomass, Rht18 has no advantage to Rht-D1b/B1b and both performed poorer than Tall. There was no evidence that Rht18 has any effect on seed dormancy. Genetic studies in durum wheat mapped Rht18 to chromosome 6AS and a co-segregating SNP marker (csRht18-SNP). The Rht18 associated allele of csRht18-SNP was absent in a wide range of international bread wheat germplasm. Allelism tests established that Rht18 is most likely allelic to Rht14, but not to Rht16. Further mapping studies of Rht14 confirmed this result, and located Rht16 on chromosome 5B. The SNP marker tightly linked to Rht18 will assist wheat breeders who aim to replace Rht-B1b and Rht-D1b with Rht18. The study also suggests that future cultivars with Rht18 are likely to have longer coleoptiles and better emergence in water-limited and high soil temperature regions.


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