【Objective】The study investigated the impact of salicylic acid (SA) priming on the germination vigor and physiological response of rice seeds under low temperatures. It aimed to reveal the expression patterns of genes related to abscisic acid (ABA) and gibberellin (GA) metabolic pathways as well as cell wall relaxation genes by SA priming. This research provided a theoretical basis for the study of rice seed germination at low temperatures.【Method】Using indica three-line hybrid rice Taifengyou 208 seeds as materials, the effects of SA on seed germination vigor and physiology responses under low temperature were analyzed through seed priming treatment, and the expression patterns of genes related to ABA, GA and expansin in response to SA were analyzed by qRT-PCR.【Result】Low temperature (15 ℃) significantly delayed the germination process of rice seeds. In seeds germinated at low temperatures for one day, the endogenous SA concentration was 1.7 times higher than that at normal temperatures (28 ℃). However, for five-day-old seedlings, the SA concentration under low temperature was only 0.6% of that at normal temperatures. SA could effectively enhanced germination vigor of seeds at low temperature, with the most significant effects observed at 2 000 μmol·L-1 SA. This concentration significantly increased the germination index, vigor index, shoot length, root length, fresh weight, and dry weight of seeds under low temperature conditions. Notably, the vigor index was three times that of non-primed seeds (CK1) and two times that of water-primed seeds (CK2). In terms of physiological indexes, SA priming increased the contents of soluble sugar, proline and active oxygen, enhanced the activities of total amylase, β-amylase, superoxide dismutase (SOD) and catalase (CAT), and decreased the content of malondialdehyde (MDA). Compared with CK1, 2 000 μmol·L-1 SA decreased the ABA content by 79%, and increased the IAA and GA1 contents by 32.2% and 2.66 times, respectively. In terms of gene expression, the expression levels of ABA synthesizing genes OsNCED2 and OsNCED3 were decreased by 94.26% and 90.24% compared with CK1 in seeds primed by 2 000 μmol·L-1 SA, respectively, whereas the expression levels of ABA decomposing genes OsABA8’ox2 and OsABA8’ox3 were 5.9 and 3.9 times higher than that of CK1, respectively. Compared with CK1, SA priming significantly upregulated the expression of GA synthesizing genes OsCPS1, OsKAO and OsGA20ox1, while it significantly downregulated the expression of GA decomposing genes OsGA2ox2 and OsGA2ox6. In several candidate genes encoding cell wall relaxation protein, e.t. expansin, all but OsEXPB11 were significantly upregulated to some extent by priming. Compared with CK1, 2 000 μmol·L-1 SA increased the expression levels of OsEXPA2, OsEXPB4 and OsEXPB6 to 12.2, 5.9 and 6.1 times, respectively.【Conclusion】SA priming can significantly alleviate the impact of low temperatures on rice seed germination and seedling growth, which is likely due to SA enhancing the activity of antioxidant enzymes such as SOD and CAT, reducing the production of MDA, and increasing the content of soluble sugars and proline, thereby strengthening the tolerance of seeds and seedlings to low temperatures. On the other hand, SA priming decreases endogenous ABA content, increases GA1 content, enhances the activities of total amylase and β-amylase, and promotes the expression of genes related to cell wall relaxation, thus facilitating seed germination and seedling growth at low temperature.
Pre-harvest sprouting (PHS) refers to the germination of cereal crops on the spike in high humidity conditions before grain harvest. Wheat PHS is a significant problem that affects both the yield and quality of wheat. Seed dormancy level is a major factor influencing the resistance of wheat PHS, and domesticated crops often exhibit reduced seed dormancy levels, making cultivated wheat more prone to PHS compared to its wild ancestors. Wheat PHS is mainly regulated by external environmental factors such as temperature and humidity, as well as internal plant hormones (GAs, ABA, IAA, MeJA, ET, BR). Researchers have identified a range of materials resistant to PHS, cloned key genes regulating PHS resistance, such as PM19, MFT, MKK3, Myb10-3D, Vp1. New wheat materials resistant to PHS have been successfully developed through molecular marker-assisted selection, artificial synthesis of wheat, and CRISPR/Cas9 gene editing technology. This article reviews the genetic mechanism of PHS resistance in wheat and the latest progress in PHS resistance breeding research. In the future, it is necessary to continue exploring key genes related to PHS resistance, and employ biotechnological breeding methods to cultivate new PHS-resistant wheat varieties.
【Objective】Pre-harvest sprouting (PHS) is a serious limiting factor for wheat (Triticum aestivum L.) grain yield and end-use quality. Synthetic hexaploid wheats (SHW) and wheat landraces (WL) are important germplasm resources for improving PHS resistance in wheat. The objective of this study is to utilize PHS-resistant loci from SHW and WL for breeding PHS-resistant elite materials, which will provide a theoretical basis for improving PHS resistance of wheat cultivars.【Method】In this study, SYN792 (a synthetic hexaploid wheat from CIMMYT) and Fulingxuxumai (a Chinese wheat landrace) were used as female parents to cross and backcross with Chuanmai 45 (a sensitive variety to PHS), respectively. Two BC1F7 populations including 1 796 lines were established. Seed germination index (GI) and seed germination rate of each spike (SGR) in different environments were used to evaluate PHS resistance. Two germination temperature of 25 ℃ (18GI) and 32 ℃ (19GI) were set to examine seed germinability in 2018 and 2019. 1 796 BC1F7 lines were evaluated preliminarily by SGR phenotype and molecular markers detection in 2017, and the introgression lines with PHS-3D and PHS-A1 resistant loci and SGR less than 35% were screened. Introgression lines with PHS-3D and PHS-A1 resistant loci were used to analyze utilization efficiency of SHW and WL in PHS-resistance breeding by identifying PHS-resistance and yield related traits in 2018 and 2019.【Result】PHS resistance of 1 796 lines was evaluated preliminarily, and 537 lines with SGR value less than 35% were screened for further molecular marker detection. A total of 332 lines with PHS-3D and PHS-A1 were selected by SSR marker, and the frequency of WL introgression lines was significantly higher than that of SHW introgression lines. 332 introgression lines were used to analyze PHS-resistance and yield related traits in 2018 and 2019. There was a significant positive correlation between different PHS indexes in different years, but there was no significant difference in the values of 18GI, 18SGR and 19SGR between SHW and WL introgression lines. The average values of 18SGR, 19SGR and 18GI in SHW and WL introgression lines were lower than 23%. As far as GI value was concerned, there was obvious difference between different germination temperatures. At the germination temperature of 32 ℃, the mean 19GI value of SHW PHS-3D introgression lines was significantly lower than that of WL PHS-A1 introgression lines. Grain color was associated with PHS resistance in SHW introgression lines, and the red-grained SHW introgression lines had lower the mean GI and SGR values than the white-grained lines. Among 73 SHW introgression lines, 11 white-grained lines showed medium or higher resistance to PHS，and the GI values of 14 red-grained lines at different germination temperatures were lower than 35%. According to the data of agronomic traits in 2018 and 2019, thousand grain weight of SHW introgression lines was significantly higher than that of WL introgression lines, but the number of grains per spike was significantly lower than that of WL introgression lines. 23 elite introgression lines including seven SHW introgression lines and 16 WL introgression lines were selected. Two SHW white-grained introgression lines had better resistance to PHS, and the GI values of two red-grained introgression lines at different germination temperatures were lower than 25%.【Conclusion】It is feasible to transfer PHS-3D and PHS-A1 resistance loci to PHS from SHW and WL for improving PHS-resistance of modern wheat cultivars. In this study, the breeding efficiency of WL for PHS-resistance was better than that of SHW. However, the stability of PHS-resistance of SHW introgression lines was better than that of WL introgression lines. 23 SHW and WL elite introgression lines could be used as parents to improve the PHS-resistance and yield traits in wheat. In particular, the white-grained SHW introgression line No.5201 and the red-grained SHW introgression lines No.5497 and No.5505 were very valuable parents for wheat breeding of PHS resistance.
【Objective】Continuous rainy weather during the wheat harvest season can cause wheat pre-harvest sprouting (PHS) and even germination, thus impacting wheat yield and quality. Evaluating the effect of flour made by blending different proportions of sprouted wheat with regular wheat on the baking/steaming quality of flour processing products can explore the possibility of using a slight degree of sprouted wheat to examine the possibility of reducing food waste. 【Method】In this study, blends of Zhengmai 583 (Zheng 583) and Kechengmai 6 (Ke 6) wheat with 30%, 50%, and 100% sprouted wheat were prepared, respectively. The degradation of wheat flour from blended wheat was evaluated by the falling number, sedimentation value, wet/dry gluten content, dough development time, and dough stability time. The baking/steaming characteristics of bread, dumpling wrapper, Chinese steamed bread (CSB), sponge cake, noodle, and cookie made from blended wheat were evaluated by sensory scores and quality parameters. 【Result】As the proportion of sprouted wheat increased (30%, 50%, and 100%), the dough development time of Zheng 583 flour first increased and then decreased, while the dough stability time gradually reduced. However, the changes in the two parameters of Ke 6 both showed a trend of first decreasing, then increasing, and finally decreasing. The falling number, sedimentation value, wet/dry gluten content, and farinogram parameters of mixed wheat decreased in both cultivars. The specific volume of Zheng 583 CSB increased and then decreased, while the particular volume of Ke 6 CSB gradually reduced. The exact volume of the Zheng 583 sponge cake gradually increased, while the specific volume of the Ke 6 sponge cake remained unchanged. The particular volume of the bread, area of the cookies, cooking loss of the noodles, and turbidity index (A*) of the dumpling soup changed the same trend in both cultivars. Compared to the control (without sprouted wheat), the specific volume of bread decreased by 11.33% and 17.44%, the cookies area increased by 24.10% and 7.49%, the noodles cooking loss increased by 22.99% and 9.69%, and the A* value of the dumpling soup increased by 8.93% and 13.32% in Z583 and Ke 6 of 100% SW, respectively. The bread, Chinese steamed bread, the dumpling wrapper of two cultivars, and the noodles of Zheng 583 showed significant deterioration in the 30% SW gradient. The sponge cake and cookie of the two cultivars showed significant deterioration in the 50% SW gradient. The noodles of Ke 6 showed significant deterioration in the 100% SW gradient. 【Conclusion】The baking/steaming quality of bread, dumpling wrappers, Chinese steamed bread, sponge cake, noodle, and the cookie was seriously affected by PHS. The influence of PHS is different in various wheat cultivars but has the same trend. When the degree of PHS is slight, it has little effect on the baking quality of cookies and sponge cakes.
