Optimization of leaf properties and plant phenotype through yield‐based genetic improvement of rice over a period of seventy years in the Yangtze River Basin of China

Abstract

Knowledge of changes associated with the progression of growth‐related characteristics in rice plant is essential to make strategies for future breeding and crop management. However, thus far, little attention has been given to the identification of temporal changes of the traits concomitant with the year of release in rice genetic breeding. The objective of this study was to explore genetic gain for yield accrued in association with evolution of the growth phenotypes in a 2‐year field experiment conducted on the Yangtze River Basin of China. Fifteen rice (Oryza sativa L.) cultivars, including 5 super high‐yielding rice, bred or widely cultivated from 1936 to 2005, were grown in irrigated field conditions with appropriate doses of commercial fertilizers during the rice‐growing season from May to October in 2013 and 2014. In both years, SPAD reading was high during vegetative and early grain filling stages, but it declined sharply at maturity. In general, SPAD reading increased with the progression in year of release of the cultivars and it correlated with yield benefit accrued. Similar to SPAD, the evolutionary trend also accounted for significant increases in LAI (leaf area index) and SLW (specific leaf weight), CGR (crop growth rate), LAD (leaf area duration), S/LA (spikelets/leaf area), and NAR (net assimilation rate). All growth parameters, except NAR, correlated positively with grain yield. Conversely, K (extinction coefficient) exhibited significant decline along with year of release, meaning more erect canopies. Gain of SLW in the newer cultivars enabled better light energy interception probably with higher RUE, which associated with increased SPAD amounting to low K values. It was opined that the reduced K improved light distribution across the leaves, which contributed to a grain yield advantage through increase of sink size (S/LA) over the 70‐year period.

Nitrogen/potassium interactions increase rice yield by improving canopy performance

“…The gradient of light in the canopy can be described by the parameter K L ; a smaller K L indicates a better light distribution (Gu, Chen, et al, 2017). Our results showed that the application of N or K reduced the K L ; the reason may be that the fertilization influenced the canopy structure (such as leaf area, relative height, leaf angle, and height difference of adjacent leaves) and then improved light distribution (Song et al, 2013; Zhu et al, 2020). Similarly, it was observed that cultivars with more erect leaves in the upper canopy allowed more light to reach the lower layers, resulting in higher light use efficiency (Long et al, 2006; Zhu et al, 2020).…”

“…Our results showed that the application of N or K reduced the K L ; the reason may be that the fertilization influenced the canopy structure (such as leaf area, relative height, leaf angle, and height difference of adjacent leaves) and then improved light distribution (Song et al, 2013;Zhu et al, 2020). Similarly, it was observed that cultivars with more erect leaves in the upper canopy allowed more light to reach the lower layers, resulting in higher light use efficiency (Long et al, 2006;Zhu et al, 2020). In addition, rice with reduced chlorophyll content may improve canopy light distribution and the photosynthetic rate .…”

Improvements in Plant Morphology Facilitating Progressive Yield Increases of japonica Inbred Rice since the 1980s in East China

“…Genetic improvement is a determinant factor for increased yields across many ricegrowing countries, such as India, Japan, the Philippines, and Thailand [6][7][8][9][10]. In China, genetic progress in rice grain yield was reported in the northeast [11,12], southwest [13], south [14], and central China [15,16]. Such studies suggested that genetic progress greatly increased rice grain yield, which was associated with prolonged growth period [6,14], expanded sink size through spikelets per panicle [12,15], and increased biomass accumulation, harvest index, or both [9,10,15].…”

On productivity, resource capture, and yield stability of cover crop species mixtures

“…Canopies consisting of plants with upright leaf angles allow for penetration of radiation to the lower canopy layers, resulting in a more homogeneous light distribution over canopy layers and therefore higher canopy photosynthesis (Marchiori et al, 2010;Sarlikioti et al, 2011). This better distribution of radiation within the canopy is usually associated with low light extinction coefficient and high biomass (Zhu et al, 2020). For crucifers, the horizontal leaf orientation leads to a high capture of radiation in the top layers of the canopy, resulting in light saturation and comparatively inefficient conversion of light into assimilates.…”

“…At the same time, this also leads to more shading of the lower layers of the canopy, and a poor contribution of the lower layers to overall canopy photosynthesis. The higher light extinction coefficient and better radiation interception is thus associated with a relatively low RUE (Zhu et al, 2020).…”