Estimation of Stem-Solidness and Yield Components in Selected Spring Wheat Genotypes

Solid-stemmed wheat genotypes are better protected from damage caused by wheat stem sawfly (Cephus pygmaeus L.) larvae and at lower risk of lodging, as they are additionally strengthened. The aim of the study was to analyse the stem-solidness of fifty spring wheat cultivars with pith. A field experiment was conducted at the Agricultural Research Station Dłoń, Poland in the years 2012–2014. The method recommended by the International Union for the Protection of New Varieties of Plants (UPOV) and the methodology described by DePauw and Read were used to analyse the stem-solidness. The statistical analysis of the results showed that the stems of the wheat cultivars differed in their, therefore, they were divided into seven classes. There were nine Polish cultivars, two genotypes from Canada (BW 597 and AC Elsa) and one Portuguese genotype (I 836) with hollow stems. There were only nine solid-stemmed cultivars. Both methodologies were used to assess the filling of the stem in the whole plant upon analysis of its filling at the cross-section of the first internode. Both methods gave the same results. The DePauw and Read methodology showed that the internodes in the lower part of the plants were filled to the greatest extent. The same genotypes collected in the consecutive years of the study differed in the filling of their stems with pith. These differences were influenced by the environmental conditions.

Stability analysis of stem solidness, grain yield and grain protein concentration in spring wheat

The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), is a major pest of wheat (Triticum aestivum L.) in the northern Great Plains where it is a constant threat in Montana and is resurging in Alberta, Saskatchewan and North Dakota. Adoption of solid-stemmed cultivars is an important management tool for wheat growers; however, the inconsistent pith expression first noted with the release of ‘Rescue’ has been repeatedly observed in modern cultivars such as ‘Lillian’ in Canada. Given the extensive hectares planted to solid-stemmed wheat cultivars during an outbreak, identification of cultivars that display stable stem solidness, grain yield and grain protein concentration across a wide range of environments where stem sawfly infestations occur is desirable. We assessed spring wheat plant responses in eight solid-stemmed and two hollow-stemmed genotypes grown across diverse environments using multiple statistical models. Study sites included southern Alberta and Saskatchewan, Montana and North Dakota. Most models agreed that the genotypes, ‘Choteau’ ‘BW925’ and ‘Mott’ consistently displayed high and stable stem solidness concomitant with high grain yield. ‘Choteau’ and ‘BW925’ also consistently met or exceeded the desired threshold of a 3.75/5 pith rating (averaged from the lower four stem internodes) for optimum resistance whereas, ‘Mott’ developed optimal pith at a specific (early) phenological stage when resistance to WSS infestation is critical. Exploring stability of stem solidness identified ideal genotypes that would enhance germplasm development efforts, which exemplifies how this approach can facilitate the selection, production, and adoption of solid-stemmed wheat cultivars in regions prone to WSS attack.

Genetic variation of stem characters in wheat and their relation to physiological characters and yield under drought

Stem characters such as stem solidness and stem carbohydrates (water soluble carbohydrates and non-structural carbohydrates estimated as fructan) play an important role in stabilizing grain yield in stressful environments. Ten wheat genotypes were screened for carbohydrate content (Water soluble sugars and fructan) in peduncle along with other stem parameters namely, stem solidness, grain growth rate and stem osmotic potential under irrigated and drought conditions. Data was analyzed for correlation among these parameters along with biomass and yield. The results of present study indicated that stress-tolerant genotype RIL-S1-38 and WH 1235 accumulated higher fructan content in stem and contributed in grain growth rate, reduced osmotic potential and further imparted drought tolerance. Clear differences in stem solidness and fructan content exhibited lesser grain yield reduction under drought condition.

Copy number variation ofTdDofcontrols solid-stemmed architecture in wheat

Stem solidness is an important agronomic trait of durum (Triticum turgidumL. var.durum) and bread (Triticum aestivumL.) wheat that provides resistance to the wheat stem sawfly. This dominant trait is conferred by theSSt1locus on chromosome 3B. However, the molecular identity and mechanisms underpinning stem solidness have not been identified. Here, we demonstrate that copy number variation ofTdDof, a gene encoding a putative DNA binding with one finger protein, controls the stem solidness trait in wheat. Using map-based cloning, we localizedTdDofto within a physical interval of 2.1 Mb inside theSSt1locus. Molecular analysis revealed that hollow-stemmed wheat cultivars such as Kronos carry a single copy ofTdDof, whereas solid-stemmed cultivars such as CDC Fortitude carry multiple identical copies of the gene. Deletion of allTdDofcopies from CDC Fortitude resulted in the loss of stem solidness, whereas the transgenic overexpression ofTdDofrestored stem solidness in theTdDofdeletion mutantpithless1and conferred stem solidness in Kronos. In solid-stemmed cultivars, increasedTdDofexpression was correlated with the down-regulation of genes whose orthologs have been implicated in programmed cell death (PCD) in other species. Anatomical and histochemical analyses revealed that hollow-stemmed lines had stronger PCD-associated signals in the pith cells compared to solid-stemmed lines, which suggests copy number-dependent expression ofTdDofcould be directly or indirectly involved in the negative regulation of PCD. These findings provide opportunities to manipulate stem development in wheat and other monocots for agricultural or industrial purposes.