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Raw data: Spikelet stop determines the maximum yield potential stage in barley

Citation

Thirulogachandar, Venkatasubbbu; Schnurbusch, Thorsten (2022), Raw data: Spikelet stop determines the maximum yield potential stage in barley, Dryad, Dataset, https://doi.org/10.5061/dryad.ffbg79cth

Abstract

Determining the grain yield potential contributed by grain number is a step towards advancing cereal crops' yield. To achieve this aim, it is pivotal to recognize the maximum yield potential (MYP) of the crop. In barley (Hordeum vulgare L.), the MYP is defined as the maximum spikelet primordia number of a spike. Previous barley studies often assumed the awn primordium (AP) stage as the MYP stage regardless of genotypes and growth conditions. From our spikelet-tracking experiments using the two-rowed cultivar Bowman, we found that the MYP stage can be different from the AP stage. Importantly, we find that the occurrence of inflorescence meristem (IM) deformation and its loss of activity coincided with the MYP stage, indicating the end of further spikelet initiation. Thus, we recommend validating the barley MYP stage with the IM's shape and propose this approach (named Spikelet Stop) for MYP staging. Following this approach, we compared the MYP stage and the MYP in 27 two- and six-rowed barley accessions grown in the greenhouse and field. Our results reveal that the MYP stage can be reached at various developmental stages, which majorly depend on the genotype and growth conditions. Furthermore, we found that two-rowed barleys’ MYP and the duration reaching the MYP stage may determine their yield potential. Based on our findings, we suggest key steps for the identification of the MYP in barley that can also be applied in a related crop such as wheat.

Methods

Plant materials and growth conditions

We conducted one greenhouse and one field experiment using a panel of twenty-seven barley accessions chosen from a worldwide collection (Alqudah et al., 2014). The field study was conducted at the Leibniz Institute of Plant Genetics and Crop Plant Research, Gatersleben, Germany (51° 49′ 23″ N, 11° 17′ 13″ E, altitude 112 m) from March to August 2017 and greenhouse from July to December 2017. For both the experiments, we followed similar sowing and pre-treatment protocols. Grains were sown on 96 well trays and grown under greenhouse conditions (photoperiod, 16h/8h, light/dark; temperature, 20o C/16o C, light/dark) for two weeks. Then, the grown plants were vernalized at 4o C for four weeks and then given hardening in the greenhouse for a week. Following the acclimatization, plants were directly transplanted in the silty loam soil for the field experiment; however, in the greenhouse experiment (photoperiod, 16h/8h, light/dark; temperature, 20o C/16o C, light/dark), plants were potted in a 9 cm pot (9 × 9 cm, diameter × height). For the field experiment, we followed a single plot per genotype design, in which each plot had eight rows with a 15 cm distance between the rows. The rows are 0.8 m long, wherein we sowed five plants per row. Details of the selected barley panel and their field growth conditions were given in tables S1 and S2, respectively.

The series of experiments on cultivar Bowman were performed in the greenhouse and climate chamber. The growth conditions and different pot sizes of the experiments are given in table S3. In all the greenhouse and climate chamber experiments, plants were grown in pots that contain two parts of autoclaved compost, two parts of ‘Rotes Substrat’ (Klasmann-Deilmann GmbH, Germany), and one part of sand. We followed the standard practices for irrigation, fertilization, and control of pests and diseases in these experiments.

Methods of phenotyping the traits

All traits were measured only from the main culm of a barley plant due to its higher phenotypic stability across growth conditions and its major contribution to the final grain yield (Cottrell et al., 1985; Elhani et al., 2007). In all Bowman spikelet-tracking experiments, plants were randomly selected, and spikes were dissected out almost every alternate day. In the spikelet-tracking experiments with the 27 accessions, random plants were dissected every two to three days or more, depending on their developmental rate. Dissection of spikes was performed according to the methods described in Kirby and Appleyard, 1984. Different spike developmental stages were identified by following the description provided earlier (Waddington et al., 1983; Kirby and Appleyard, 1984). For every stage of a spike, the decimal code suggested by Waddington et al., 1983 was given following the letter ‘W’ (Waddington). A decimal code was assigned to a spike when the specific stage was found in a minimum of three or a maximum of four consecutive nodes of a spike (Waddington et al., 1983; Kirby and Appleyard, 1984). These nodes are always the most developed nodes of a spike (Kirby and Appleyard, 1984) and may be found close to the spike base, two to three nodes above the spike base, or in the center of a spike.

For the potential spikelet number (PSN) of a spike, differentiated spikelets and undifferentiated spikelet ridges (usually found at the base and tip of a spike) were counted (Appleyard et al., 1982). Generally, barley forms three spikelets at every rachis node (Bonnett, 1935; Bonnett, 1966; Komatsuda et al., 2007; Koppolu et al., 2013), so the number of undifferentiated spikelet ridges were multiplied by three. The number of ridges developed on a spike was considered as spikelet ridge number (SRN), and the final spikelet number (SN) and grain number (GN) of a spike were enumerated after physiological maturity. Growing degree days (GDD) or thermal time was calculated from the average maximum and minimum air temperature of a day subtracted by the base temperature (McMaster and Wilhelm, 1997). We considered 0o C as the base temperature for barley (Gallagher et al., 1976). GDDs and PSN/SRN were taken from three plants, while SN and GN were from six plants.   

Data analysis

The data were analyzed using the Prism software, version 8.4.2 (GraphPad Software, LLC), and outliers were detected by the ‘ROUT’ method (Motulsky and Brown, 2006). Mean value comparison of different traits was made with either the multiple Student’s t-tests or paired Student’s t-test (parametric). The false discovery rate approach of the two-stage linear step-up procedure of Benjamini, Kreier, and Yekutieli (Q=5%) (Benjamini et al., 2006) was used to calculate the significance of Student’s t-tests. For traits like the Waddington scale and Growing Degree Days at MYP, a two-way ANOVA with Tukey’s multiple comparison test (alpha=5%) was used to identify the mean values' significance. For the spikelet ridge number (SRN), a one-way ANOVA with Tukey’s multiple comparison test (alpha=5%) was used to identify the mean values' significance. All the replicates of a genotype were analyzed individually and without assuming a consistent standard deviation. Linear regression was done using the appropriate dependent (Y values) and independent (X values) traits. The 95% confidence intervals were identified for every linear regression and plotted as confidence bands along with the ‘goodness of fit’ line.

Usage Notes

Please refer to the 'Readme' file/sheet for further information on the data. 

Funding

European Research Council, Award: 681686 “LUSH SPIKE,” ERC-2015-CoG