Field Screening of Rice Germplasm (Oryza sativa L. ssp. japonica) Based on Days to Flowering for Drought Escape

Abstract

Terminal drought stress is one of the restrictive factors in rice production and is expected to upsurge under the current situation of climate change. The study evaluated the performance of 2030 rice genotypes under continuous drought stress conditions based on days to flowering (DF). The genotypes under augmented randomized complete block design were sown in May/June of 2017 and 2018 in the field with movable rainout that resulted in huge genetic diversity among the accessions. Descriptive statistics confirmed clear variation among accessions on growth duration, plant height to leaf, plant height to panicle, and germination percentage. Correlation, chemometric, and agglomerative hierarchical cluster analyses were performed that categorized the germplasm into 10 groups. Genotypes in clusters VIII and IX (drought-resistant) revealed better agronomic performance in terms of reduced days to flowering, but conversely taller plant height and higher maturity (%) under severe stress. Genotypes in clusters IV, V, and X were discovered to be drought-susceptible. The screened genotypes like Longjing 12, Longdun 102, Yanjing 22, Liaojing 27, Xiaohongbandao, Songjing 17, and Zaoshuqingsen can be utilized in rice breeding improvement programs for drought tolerance in terms of severe continuous drought, as well as terminal drought stress.

Keywords: cluster; plant height; rainout shelter; rice genotype; terminal drought stress; trait.

Figure 1

Meteorological and soil conditions at Shangzhuang Agricultural Research Station, Beijing, China from May to October for two consecutive trials in 2017 and 2018: (a) air minimum (Tmin) and maximum temperatures (Tmax; °C) at 2 m height from ground level together with soil temperatures (°C) at 10 cm, 15 cm, 30 cm, 50 cm, and 100 cm depths; (b) volumetric soil moisture content (%) at soil depths of 10 cm, 15 cm, 30 cm, 50 cm, and 100 cm accompanied by maximum and minimum relative humidity (%) of 2 m height from the ground. RHmax = maximum relative humidity, RHmin = minimum relative humidity. ^† While reading the y-axis of Figure 1b, the moisture content for RH is simply moisture content, whereas, for that of various soil depths, it is volumetric soil moisture content.

Figure 2

Frequency distribution of seven quantitatively measured and six visually scored traits: (a) days to flowering for 2017 and 2018; (b) growth duration (days); (c) plant height to leaf (cm); (d) plant height to panicle (cm); (e) tillers∙plant⁻¹ (g); (f) dead tillers∙plant⁻¹ (g); (g) drought tolerance degree; (h) germination (%); (i) growth vigor; (j) leaf anti-dead level; (k) leaf rolling; (l) culm thickness; (m) growth stage.

Figure 3

Relationship among days to flowering (DF), growth duration (GD; days), plant height to leaf (PHL; cm), plant height to panicle (PHP; cm), tillers∙plant⁻¹ (TP⁻¹), Dead tillers∙plant⁻¹ (DTP⁻¹), drought tolerance degree (DTD), and germination percentage (GP) under continuous drought stress. * p < 0.05, ** p < 0.01, *** p < 0.001.

Figure 4

The optimal number of clusters for agglomerative hierarchical cluster (AHC) analysis.

Figure 5

Electrical conductivity (EC) of soil at Shangzhuang Agricultural Research Station, Beijing, China from May to October for two consecutive trials in 2017 and 2018. Soil EC was recorded at 10 cm, 15 cm, 30 cm, 50 cm, and 100 cm.

Figure 6

Geographic origin of accessions tested. Ivory Coast and Brazil were skipped due to thempossessing three genotypes in total.