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Agronomic assessment of the wheat semi-dwarfing gene Rht8 in contrasting nitrogen treatments and water regimes.

ABSTRACT: Reduced height 8 (Rht8) is the main alternative to the GA-insensitive Rht alleles in hot and dry environments where it reduces plant height without yield penalty. The potential of Rht8 in northern-European wheat breeding remains unclear, since the close linkage with the photoperiod-insensitive allele Ppd-D1a is unfavourable in the relatively cool summers. In the present study, two near-isogenic lines (NILs) contrasting for the Rht8/tall allele from Mara in a UK-adapted and photoperiod-sensitive wheat variety were evaluated in trials with varying nitrogen fertiliser (N) treatments and water regimes across sites in the UK and Spain. The Rht8 introgression was associated with a robust height reduction of 11% regardless of N treatment and water regime and the Rht8 NIL was more resistant to root-lodging at agronomically-relevant N levels than the tall NIL. In the UK with reduced solar radiation over the growing season than the site in Spain, the Rht8 NIL showed a 10% yield penalty at standard agronomic N levels due to concomitant reduction in grain number and spike number whereas grain weight and harvest index were not significantly different to the tall NIL. The yield penalty associated with the Rht8 introgression was overcome at low N and in irrigated conditions in the UK, and in the high-temperature site in Spain. Decreased spike length and constant spikelet number in the Rht8 NIL resulted in spike compaction of 15%, independent of N and water regime. The genetic interval of Rht8 overlaps with the compactum gene on 2DS, raising the possibility of the same causative gene. Further genetic dissection of these loci is required.

SUBMITTER: Kowalski AM

PROVIDER: S-EPMC4862442 | biostudies-literature | 2016 May

REPOSITORIES: biostudies-literature

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Agronomic assessment of the wheat semi-dwarfing gene Rht8 in contrasting nitrogen treatments and water regimes.

Kowalski Ania M AM Gooding Mike M Ferrante Ariel A Slafer Gustavo A GA Orford Simon S Gasperini Debora D Griffiths Simon S

Field Crops Research. 20160501

Reduced height 8 (Rht8) is the main alternative to the GA-insensitive Rht alleles in hot and dry environments where it reduces plant height without yield penalty. The potential of Rht8 in northern-European wheat breeding remains unclear, since the close linkage with the photoperiod-insensitive allele Ppd-D1a is unfavourable in the relatively cool summers. In the present study, two near-isogenic lines (NILs) contrasting for the Rht8/tall allele from Mara ...[more]

PMID: 27212788

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Project description:Optimizing wheat height to maximize yield has been an important aspect which is evident from a successful example of green revolution. Dwarfing genes (Rht) are known for yield gains due to lodging resistance and partitioning of assimilates into ear. The available and commercially exploited sources of dwarfism in Indian spring wheat are Rht1 and Rht2 genes inspite of availability of over 20 dwarfing genes. Rht8 a Gibberellic acid sensitive dwarfing gene is another reduced height gene commercially exploited in some Mediterranean countries. Two F2 populations segregating for Rht1 and Rht8 genes with each comprising 398 and 379 plants were developed by crossing European winter wheat cultivars Beauchamp and Capitole with Indian spring wheat cultivar PBW 621. Different genotypic combinations for Rht1 and Rht8 genes were selected from these populations through linked molecular markers and selected F3:4 lines were evaluated for various agronomic traits in a replicated trial. Reduction in plant height with Rht8 and Rht1 averaged 2.86% and 13.3% respectively as compared to the group of lines lacking dwarfing gene. Reduction was spread along all the internodes of wheat culm and reduction was lower as progress towards the lower internode. Grain number per spike and highest yield was observed in lines carrying only Rht1 gene. Reduction in plant biomass was observed with either of the dwarfing gene. Longest coleoptile length and seedling shoot length averaged 4.4 ± 0.09 cm and 19.5 ± 0.48, respectively was observed in lines lacking any of the dwarfing gene. Negligible reduction of 6.75% and 2.84% in coleoptile length and seedling shoot length, respectively was observed in lines carrying only Rht8 gene whereas F3:4 lines with Rht1 gene showed 21.64% and 23.35% reduction in coleoptile length and seedling shoot length, respectively. Additive effect of genes was observed as double dwarfs showed 43.31% and 43.34% reduction in coleoptile length and seedling shoot length.

Project description:Improving nitrogen use efficiency (NUE) represents one of the main goals to reduce N input in maximizing crop yield for sustainable agriculture. A NUE key strategy is the exploitation of genetic variation in available germplasm together with the understanding of molecular mechanisms governing this complex trait. Thus, NUE, its components, nitrogen uptake efficiency (NUpE) and nitrogen utilization efficiency (NUtE), and NUE-related traits heritability were evaluated in ancient (Cappelli, Capeiti, Russello, and Mazzancoio) and modern (Messapia, Tiziana, Svevo, and Normanno) wheat genotypes for tackling nitrogen (N) and/or water limitation in both growth chamber and field experiments. Our results exhibited a reduction of NUE, NUpE, and NUtE under water and combined (nitrogen + water) stress in all the genotypes, as expected. The contribution of genetic variability on phenotypic variation was significant for NUtE, harvest index, post-anthesis nitrogen uptake (PANU), and biomass production traits. Moreover, the stress tolerance indexes, calculated and bi-plotted for N and water stresses, exhibited two distinct clusters for many traits as then confirmed by principal component analysis. Although modern varieties showed higher crop yield and NUE under conventional N and water regimes, ancient varieties exhibited best performances to cope with both stresses, mainly under water limitation. Finally, the usage index, which takes into account total biomass increase, underlined that old genotypes were less affected by both stresses during crop cycle. In particular, these genotypes showed the best performances for NUE and its components under both stresses at stem elongation and milk ripening as shown also by PANU. In addition, at these stages, nitrate and ammonium transporter gene expressions in the root were performed, showing the highest activity in ancient varieties. In conclusion, the identification of NUE traits during a specific crop cycle stage, under both N and water limitation, will help in the breeding of more resilient varieties in Mediterranean sustainable agriculture by reducing N supply.

Project description:Background and aimsThe gibberellin-insensitive Rht-B1b and Rht-D1b dwarfing genes are known to reduce the size of cells in culms, leaves and coleoptiles of wheat. Resulting leaf area development of gibberellin-insensitive wheats is poor compared to standard height (Rht-B1a and Rht-D1a) genotypes. Alternative dwarfing genes to Rht-B1b and Rht-D1b are available that reduce plant height, such as the gibberellin-responsive Rht8 gene. This study aims to investigate if Rht8 has a similar dwarfing effect on the size of leaf cells to reduce leaf area.MethodsThe effect of Rht8 on cell size and leaf area was assessed in four types of epidermal cells (interstomatal, long, sister and bulliform) measured on leaf 2 of standard height (rht8) and semi-dwarf (Rht8) doubled-haploid lines (DHLs). The DHLs were derived from a cross between very vigorous, standard height (rht8) ('Vigour18') and less vigorous, semi-dwarf (Rht8) ('Chuan-Mai 18') parents.Key resultsLarge differences were observed in seedling vigour between the parents, where 'Vigour18' had a much greater plant leaf area than 'Chuan-Mai 18'. Accordingly, 'Vigour18' had on average longer, wider and more epidermal cells and cell files than 'Chuan-Mai 18'. Although there was correspondingly large genotypic variation among DHLs for these traits, the contrast between semi-dwarf Rht8 and tall rht8 DHLs revealed no difference in the size of leaf 2 or average cell characteristics. Hence, these traits were independent of plant height and therefore Rht8 in the DHLs. Correlations for leaf and average cell size across DHLs revealed a strong and positive relationship between leaf width and cell files, while the relationships between leaf and cell width, and leaf and cell length were not statistically different. The relative contribution of the four cell types (long, sister, interstomatal and bulliform) to leaf size in the parents, comparative controls and DHLs is discussed.ConclusionsDespite a large range in early vigour among the DHLs, none of the DHLs attained the leaf area or epidermal cell size and numbers of the vigorous rht8 parent. Nonetheless, the potential exists to increase the early vigour of semi-dwarf wheats by using GA-sensitive dwarfing genes such as Rht8.

Dataset Information

Agronomic assessment of the wheat semi-dwarfing gene Rht8 in contrasting nitrogen treatments and water regimes.

Publications

Agronomic assessment of the wheat semi-dwarfing gene <i>Rht8</i> in contrasting nitrogen treatments and water regimes.

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