Characterizing reduced height wheat mutants for traits affecting abiotic stress and photosynthesis during seedling growth

Abstract

Most high-yielding, semidwarf wheat (Triticum aestivum L.) grown around the world contains either Rht1 or Rht2 genes. The success of these high-yielding cultivars is greatest in the most productive farming environments but provide marginal benefits in less favorable growing conditions such as shallow soils and low-precipitation dryland farming. Further, growing evidence suggests semidwarf genes not only affect early seedling growth but limit grain yield, especially under abiotic stress conditions. There are 23 other reduced-height mutants reported in wheat, most of which have not been functionally characterized. We evaluated these mutants along with their parents for several traits affecting seedling emergence, early seedling growth, and photosynthetic efficiency. Two-to seven-fold differences in coleoptile length, first leaf length, root length, and root angle were observed among the genotypes. Most of the mutations had a positive effect on root length, while the root angle narrowed. Coleoptile and first leaf lengths were strongly correlated with emergence. A specialized deep planting experiment identified Rht5, Rht6, Rht8, and Rht13 with significantly improved seedling emergence compared to the parent. Among the mutants, Rht4, Rht19, and Rht12 ranked highest for photosynthetic traits while Rht9, Rht16, and Rht15 performed best for early seedling growth parameters. Considering all traits collectively, Rht15 showed the most promise for utilization in marginal environments followed by Rht19 and Rht16. These wheat mutants may be useful for deciphering the underlying molecular mechanisms of understudied traits and breeding programs in arid and semiarid regions where deep planting is practiced. | INTRODUCTIONThe incorporation of height reducing genes in both rice (Oryza sativa L.) and wheat semidwarf high-yielding cultivars were instrumental to the "Green Revolution." These high-yielding, semidwarf wheat cultivars are resistant to lodging and have a high grain yield (due to increased productive tillers and biomass) in response to nitrogen fertilizer and water applications.Together, improved genetics and agronomic management greatly increased grain yields during the 1960s, enabling autonomous wheat production in several developing countries including those in Latin America and Asia (Casebow et al., 2016;Gale & Youssefian, 1985). High-yielding, semidwarf cultivars contain the mutant form of reduced-height (Rht) gene Rht1/Rht2 (Rht-B1b/Rht-D1b), incorporated from the Japanese dwarf wheat "Norin10." These genes were cloned and mapped to homoeologous group 4 (4BS/4DS) chromosomes and encodes a DELLA domain protein negatively regulating the gibberellin-based growth response in plants (Borojevic & Borojevic, 2005;Peng et al., 1999). Since their introduction into wheat, these genes have been extensively utilized in wheat breeding Amita Mohan and Nathan P. Grant equally contributed to this study.

Yield-Related QTL Clusters and the Potential Candidate Genes in Two Wheat DH Populations

“…Plant height also heavily affects the grain yield. About 25 height reducing genes ( Rht1 - Rht25 ) have been identified in wheat; and Rht1 , Rht2 , Rht8 , and Rht12 have been used in wheat breeding even though most of them need further studies for their benefits on agronomic traits [ 40 ]. Rht_NM9 and Rht7 are on 2AS [ 41 , 42 ]; Rht4 , Rht8 , and Rht5 on 2BL, 2DS, and 3BS, respectively [ 43 ]; and Rht1 ( Rht-B1b ) on 4BS [ 44 , 45 ].…”

“…Rht22 and Rht13 were on 7AS and 7BS, respectively [ 43 , 54 ]. The locations of Rht6 , Rht15 , Rht19 , and Rht20 have not been identified [ 40 ].…”

High-Resolution Detection of Quantitative Trait Loci for Seven Important Yield Components in Wheat (Triticum aestivum L.) using a High-Density SALF-Seq Genetic Map

“…In the present study, six and four QTLs for PH and SL were identi ed, respectively. Among them, QPh.cib-2D and QSl.cib-2D were co-located in the same interval on chromosome arm 2DS, which was overlapped with the dwar ng gene Rht8 [24,39]. QPh.cib-4A and QPh.cib-5A were located near to two loci for PH reported by Luján Basile et al [40].…”

“…Additionally, two QTLs for GNS and four QTLs for SNS were identi ed in the present study. Of them, QGns.cib-2D were co-located with QPh.cib-2D and QSl.cib-2D on chromosome 2D and overlapped with the dwar ng gene Rht8 [24,39]. QGns.cib-6A was co-loctaed with QTgw.cib-6A.2 and near to two QTLs for TGW QTKW.caas-6AL and QTKW-6A.1 [31,32].…”

“…Over the past decades, numerous QTLs associated with yield or yield components have been identi ed on all wheat chromosomes [3,4,11,[17][18][19][20][21][22][23]. For example, Rht8 located on chromosome 2DS was closely linked with marker xfdc53 and reduced plant height by 10% [24]; Rht25 on wheat chromosome arm 6AS showed pleiotropic effects on coleoptile length, heading date, SL, SNS and grain weight [25]. Two major QTLs for grain size and weight were detected on chromosome 4B, which together explained 46.3% of the phenotypic variance [26,27].…”