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BackgroundSelenium (Se) is a beneficial element for higher plants and essential for mammals. To study the effect of the foliar application of sodium selenate on fragrant rice performance, a pot experiment was conducted in Guangdong, China. At the initial heading stage, one-time foliar application of sodium selenate with concentrations of 0, 10, 20, 30, 40 and 50 μmol·L− 1 (named CK, Se1, Se2, Se3, Se4 and Se5, respectively) were foliar applied on two fragrant rice varieties, ‘Meixiangzhan-2’ and ‘Xiangyaxiangzhan’.ResultsSelenate application at the initial heading stage not only improved the grain yield of fragrant rice by increasing the seed-setting rate and grain weight, but also promoted the grain quality by increasing crude protein contents and lowering the chalky rice rate. Furthermore, Se applications enhanced the biosynthesis of 2-acetyl-1- pyrroline (2-AP), the main aromatic compound, by increasing the contents of precursors (△1- pyrroline, proline and pyrroline-5-carboxylic acid (P5C)) and the activities of enzymes (proline dehydrogenase (PRODH), △1-pyrroline-5-carboxylic acid synthetase (P5CS), and ornithine aminotransferase (OAT)) in fragrant rice. The results also showed that foliar application of sodium selenate enhanced the antioxidant system of both varieties by promoting the activities of peroxidase (POD), superoxide dismutase (SOD), catalase (CAT) and reducing the contents of malondialdehyde (MDA). Furthermore, the real-time PCR analyses depicted that foliar application of selenate up-regulated the GPX1, GPX4 and CATC transcripts. The higher antioxidative enzymatic activities might strength the stress resistant to ensure the stability of yield in fragrant rice form abiotic stress.ConclusionsFoliar applications of sodium selenate at the initial heading stage increased the grain 2-AP content by enhancing the biosynthesis-related enzymes and precursors. The grain yield and quality of fragrant rice also increased due to selenate application. Furthermore, foliar application of selenate promoted the activities of enzymes such as POD, SOD and CAT and up-regulated the expression of gene GPX4, GPX1 and CATC.

In order to study the effect of foliar application of sodium selenate on fragrant rice performance at the heading stage, the present study was conducted with two fragrant rice cultivars, 'Meixiangzhan-2' and 'Xiangyaxiangzhan'. At the heading stage, six concentrations of sodium selenate solution (0, 10, 20, 30, 40, and 50 μmol L-1) were sprinkled to plants. Our results showed that foliar application of sodium selenate increased chlorophyll contents in rice leaves and upregulated net photosynthetic rate at the grain-filling stage. The enhancement was observed in grain yield, seed-setting rate, and in 1,000-grain mass. The highest yield and net photosynthetic rate were both recorded at 40 μmol L-1 treatment for both cultivars. Furthermore, foliar application of sodium selenate also improved some grain quality attributes, such as head rice rate and crude protein content. The Se concentration in fragrant rice grain also increased due to sodium selenate application. In conclusion, sodium selenate has potential to be the exogenous plant growth regulator in fragrant rice production to increase yield and quality.

Effects of deep fertilizer placement on rice growth and yield were investigated with two rice cultivars Meixiangzhan2 and Xiangyaxiangzhan. Four treatments of pre-transplant tillage + fertilizer application were set: (CK) twice puddling with rotary cultivator + manual surface broadcast; (CD) twice puddling through rotary cultivator + 10-cm deep mechanized placement; (ZB) no pudding + manual surface broadcast; (ZD) no pudding + 10-cm deep mechanized placement. Treatments CD and ZD both significantly improved the grain yield and panicle number unit area compared with treatments CK and ZB. Dry accumulation, chlorophyll contents and net photosynthetic rate at both the heading stage and maturity stage were enhanced by the deep fertilizer placement. Thus, we think the benefits of mechanical deep fertilizer placement have potential to break the production limitation and popularization in conservation tillage.

Proline is one of the precursors of the biosynthesis of 2-acetyl-1-pyrroline (2-AP) which is the key and characteristic volatile component of fragrant rice aroma. In order to study the effects of exogenous proline on 2-AP biosynthesis and other grain quality attributes in fragrant rice, two indica fragrant rice cultivars, "Meixiangzhan-2" and "Xiangyaxiangzhan", and one japonica fragrant rice, "Yunjingyou", were used in present study. At initial heading stage, proline solutions at 0 (CK), 0.10 (Pro1), 0.20 (Pro2) and 0.50 (Pro3) g L-1 were applied as foliar spray solution to fragrant rice plants. Compared with CK, Pro1, Pro2 and Pro3 treatments significantly increased the grain 2-AP content. The significant up-regulation effects due to proline treatments were observed in the contents of proline, △1-pyrrolidine-5-carboxylic acid (P5C) and △1-pyrroline which involved in 2-AP formation. Exogenous proline application also significantly decreased the grain γ-aminobutyric acid (GABA) content. Furthermore, proline treatments enhanced the activity of proline dehydrogenase (ProDH) as well as transcript level of gene PRODH. On the other hand, the transcript level of gene BADH2 and activity of betaine aldehyde dehydrogenase (BADH) decreased under proline treatments. Proline treatments (Pro2 and Pro3) also increased the grain protein content by 3.57-6.51%. Moreover, 32.03-34.25% lower chalky rice rate and 30.80-48.88% lower chalkiness were recorded in proline treatments (Pro2 and Pro3) for both Meixiangzhan and Xiangyaxiangzhan whilst for Yunjingyou, foliar application of proline had no significant effect on chalky rice rate and chalkiness. There was no remarkable difference observed in grain milled quality (brown rice rate, milled rice rate and head rice rate) and amylose content between CK and proline treatments. In conclusion, exogenous proline enhanced the 2-AP biosynthesis and promoted some grain quality characters of fragrant rice. Fragrant rice is famous for possessing a characteristic aroma and also fetches a high price in the international market because of the good grain quality 1,2. In the past two decades, many studies have conducted to investigate the compound of the aroma of fragrant rice. For example, the study of Widaja et al. 3 showed that the number of volatile compounds detected in the aroma exceeds 300 in both fragrant and non-fragrant rice varieties. Hashemi et al. 4 demonstrated there were more than 100 volatile compounds have been detected in the aroma of fragrant rice varieties. In recent years, with the development of many researches, it is established that 2-acetyl-1-pyrroline (2-AP) is the key compound in fragrant rice aroma 1,5,6. The process of 2-AP biosynthesis in fragrant rice is very complicated which involved many biochemical reactions while numerous studies have been conducted to understand the mechanism of 2-AP biosynthesis. An early study has evidenced that the expression of gene BADH2 which related to the betaine aldehyde dehydrogenase

Selenium (Se) is an essential element to humans, animals and plants, but little is known about roles of Se in yield and antioxidant enzyme activities of rice. In this study, sodium selenate with 10 (T1), 30 (T2) and 50 (T3) μmol L -1 concentrations and distilled water (CK) were sprayed onto rice cultivars, or more precisely Meixiangzhan-2 at rupturing stage during the experiments in South China, 2017. Treatments were arranged in a split-plot design with three replications. The result showed that spraying 10, 30 and 50 μmol L -1 sodium selenate at rupturing stage could improve the activities of oxidant enzymes such as peroxidase (POD), superoxide (SOD) and catalase (CAT) and lower the malonaldehyde (MDA) concentrations at filling stage. Furthermore, Se applications could enhance the chlorophyll content at middle and late phase of filling stage and grain yield at maturity. Therefore, Se applications could alleviate the detrimental effects of rice leaf senescence by regulating the activity of enzymatic antioxidants and also increasing chlorophyll content at the filling stage which will be helpful to sustain growth and yield formation in rice production.

Volunteer rice is a global problem in rice production, especially conservation tillage. Here volunteer rice from four rice cultivars viz. Xiangyaxiangzhan, Meixiangzhan, Changnongjing 1 and Yliangyou1173 was treated with different flooding treatments. Two weeks of water flooding were applied at four depths: 2.0-2.5 cm (F1), 3.0-3.5 cm (F2), 4.5-5 cm (F3) and 6.0-6.5 cm (F4). A control was set by maintaining the soil wet as normal farmer practice of this region. It was found volunteer rice germination was more reduced with increased submergence levels, while treatments F3 and F4 both decreased the germination index and germination energy greatly for all rice varieties. Flooding treatments also reduced the seedling rate and inhibited the growth of volunteer seedling. Treatments F3 and F4 decreased seedling rates of Changnongjing 1 and F2 generation of Yliangyou1173 to zero, while the flooding treatment induced the malonaldehyde accumulation and altered the activities of peroxidase, superoxide and catalase in seedlings for all rice varieties. Hence, we suggest 2 -week flooding at soil depth 6 cm after the harvest of early-season rice in South China in order to prevent the harvest loss in late-season rice caused by volunteer rice.

Effects of sodium selenite treatments on rice were investigated using two known cultivars Xiangyaxiangzhan and Meixiangzhan2 cultivated at two sites of Guangdong Province, China. Sodium selenite solutions at 10 (Se1), 30 (Se2) and 50 (Se3) μmol•L -1 were sprinkled to the rupturing-stage rice separately, with a control set with double distilled water instead. For Xiangyaxiangzhan, comparing with control, 6.91, 24.81 and 25.00% higher SOD, POD and CAT activity were recorded in Se1. For Meixiangzhan2, 2.10, 9.44 and 10.00% higher SOD, POD and CAT activity were recorded in Se1. Moreover, high-concentration sodium selenite (Se3) depressed the antioxidant enzyme activities and caused MDA over-production in Xiangyaxiangzhan. In conclusion, sodium selenite low-concentration applications could be an exogenous regulator to improve rice oxidation resistance in rice production.