Grain-bearing spikelets are attached along the inflorescence of bread wheat. But not all spikelets are equal: central spikelets produce more grains than apical and basal spikelets. Various explanations exist for the apical spikelet decay (Whingweri, 1981), but thus far it remains unknown why basal spikelets are rudimentary (of small size and producing no grain). 

The bi-directional gradient in spikelet productivity is established early in development and using novel low-input RNA-sequencing methods, previously developed in mammalian systems (Macaulay et al., 2015), we found large transcriptional differences between basal, central and apical spike sections.

We identified the MADS-box transcription factor VRT2 to be significantly upregulated in basal-sections compared to the apical-sections. Ectopic expression of VRT2 in T. polonicum (Adamski et al., 2021) caused increased rudimentary basal spikelets development in the field and glasshouse. We hypothesise that prolonged VRT2 expression delays the transition from vegetative to floral development in basal spikelets (Backhaus et al., 2022). Preliminary data from confocal microscopy suggests that this negatively affects spikelet ridge establishment.

To investigate the effect of poor basal spikelet establishment on spikelet productivity we applied photosynthesis-limiting shading conditions to four winter wheat varieties as well as VRT2 NILs in the field. Shading of ~55% (of incoming light) was applied for two weeks just before booting, leading to a significantly reduction in the number of fertile florets. Shading had a greater effect on basal than central spikelets in all genotypes. However, fructose and glucose concentrations were the same between the central and basal spikelets as well as the central and basal rachis. This suggests that there were no differences in resource availability between central and basal sections of the spikes. Furthermore, there was no interaction between the VRT2 genotype and shading treatment. We thus hypothesise that the initial delay in basal spikelet development with respect to central spikelets could lead to the greater floret abortion in basal spikelets under the same treatment.

In conclusion, we have shown that basal spikelets diverge in development early in spike development, which negatively affects the final number of grains per spikelet. Improving the establishment of basal spikelets could therefore be targeted to increase number of grains per spike, regardless of environmental conditions.

Xm-50110

Evaluation of multiple tolerance indices for polyethylene glycol-induced water stress in durum wheat (Triticum durum desf.) genotypes

Zine El Abidine Fellahi1,2, Tahar Saraoui2,3, Amar Benmahammed2,4, Abderrahmane Hannachi5, Abou-bakr Rabti6, Ali Guendouz5

1Department of Agronomy, Faculty of Natural, Life and Earth Sciences and the Universe, University of Mohamed El Bachir El Ibrahimi, Bordj Bou Arreridj 34030, Algeria

2Valorization of Natural Biological Resources Laboratory (VRBN), University of Ferhat Abbas Setif-1, Setif 19000, Algeria

3Department of Agronomy, Faculty of Natural and Life Sciences, Hamma Lakhdar Eloued University, 789 El-Oued, Algeria

4Department of Ecology and Plant Biology, Faculty of Natural and Life Sciences, University of Ferhat Abbas Setif-1, Setif 19000, Algeria

5National Agronomic Research Institute of Algeria (INRAA), Setif Research Unit, Setif 19000, Algeria

6Institute of Agriculture and Veterinary Sciences, University of Mohamed-Cherif Messaadia, Souk Ahras 41000, Algeria

Drought is the major factor limiting plant growth and productivity worldwide and affects about 50% of the total wheat cultivation area globally. In Algeria, durum wheat is the most important crop before barley (Hordeum vulgare L.) and bread wheat (Triticum aestivum L.), and occupies approximately 1.2 million hectares area. In this study, 12 wheat genotypes including landraces, breeding lines and local cultivars were evaluated at the seedling growth stage for root length, root number, coleoptile length, shoot length, root and shoot fresh weights under optimal and 20% polyethylene glycol (PEG6000)-triggered water stress. For this purpose, seven drought tolerance indices, namely the mean productivity (MP), geometric mean productivity (GMP), harmonic mean (HM), stress tolerance index (STI), yield index (YI) and yield stability index (YSI) were computed based on total fresh biomass under non-stress (Yp) and stress (Ys) conditions to be used in screening wheat genotypes. Analysis of variance showed that there were significant differences among the genotypes as well as significant influences of water stress on all the measured traits and the indices. MP, GMP, HM and STI showed strong and positive correlations with Ys and Yp depicting that they are suitable predictors for drought tolerance selection. Based on the average of the sum of ranks (ASR) and cluster analysis across all indices, two new breeding lines (G1 and G4) along with a local landrace (G10) were identified as the most tolerant genotypes. Principal component analysis explained 98.74% of the total variability amongst indices. The first PC (75.82%) was related to Ys, MP, GMP, HM, STI, YI, YSI and RSI whereas the second PC (22.93%) related to Yp. Genotypes G1, G4, G10 and G11 with a STI higher than 1 had higher performances under stress conditions than the average performances of all the cultivars under the optimal conditions. According to Fernandez’s classification, genotypes G10 and G11 belonged to group C and performed better in drought stress conditions. Tolerant genotypes can be a candidate for further multi-growth stages tests and could be recommended for wheat breeders in selection of drought tolerant varieties under rainfed conditions in arid and semi-arid regions of Algeria.