Low temperature or cold stress is one of the major abiotic stresses limiting rice (Oryza sativa L.) production and productivity in the temperate rice growing regions as well as in tropical high lands worldwide. Low temperature at the reproductive stage causes high sterility and decreases production. In this study, we assessed recombinant inbred lines (RILs) that possessed cold‐tolerance genes and/or quantitative trait loci (QTL) from the donor line IR66160‐121‐4‐4‐2 in the genetic background of a cold‐sensitive japonica cultivar, Geumobyeo. The selected 15 RILs with QTL for cold tolerance were phenotyped for three main agronomic traits—culm length (CL), days to heading (DTH), and spikelet fertility (SF)—which were most affected during cold stress. The RILs with cold‐tolerant and cold‐sensitive parents were evaluated under cold‐water (18–19°C) irrigation in the field and cold‐air temperature (17–18°C) in the temperature‐controlled greenhouse. The RILs showed significant differences in these traits compared to the cold‐sensitive parent. Traits CL and DTH exhibited positive correlation with SF in the selected breeding lines. The SF of the selected breeding lines was higher (51–81%) than that of the cold‐sensitive parent, Geumobyeo (7%). Our results confirmed that cold tolerance was associated with SF but the traits CL and DTH were differently associated with cold tolerance. The cold‐tolerant breeding lines selected in this study had at least one of the three QTL associated with cold tolerance. The breeding lines confirmed to have cold tolerance are useful to breed cold‐tolerant cultivars and increase our understanding of the mechanism of cold tolerance in rice.

Plant phenotyping is the primary task of any plant breeding program, and accurate measurement of plant traits is essential to select genotypes with better quality, high yield, and climate resilience. The majority of currently used phenotyping techniques are destructive and time-consuming. Recently, the development of various sensors and imaging platforms for rapid and efficient quantitative measurement of plant traits has become the mainstream approach in plant phenotyping studies. Here, we reviewed the trends of image-based high-throughput phenotyping methods applied to horticultural crops. High-throughput phenotyping is carried out using various types of imaging platforms developed for indoor or field conditions. We highlighted the applications of different imaging platforms in the horticulture sector with their advantages and limitations. Furthermore, the principles and applications of commonly used imaging techniques, visible light (RGB) imaging, thermal imaging, chlorophyll fluorescence, hyperspectral imaging, and tomographic imaging for high-throughput plant phenotyping, are discussed. High-throughput phenotyping has been widely used for phenotyping various horticultural traits, which can be morphological, physiological, biochemical, yield, biotic, and abiotic stress responses. Moreover, the ability of high-throughput phenotyping with the help of various optical sensors will lead to the discovery of new phenotypic traits which need to be explored in the future. We summarized the applications of image analysis for the quantitative evaluation of various traits with several examples of horticultural crops in the literature. Finally, we summarized the current trend of high-throughput phenotyping in horticultural crops and highlighted future perspectives.