Fertilizer Deep Placement Significantly Affected Yield, Rice Quality, 2-AP Biosynthesis and Physiological Characteristics of the Fragrant Rice Cultivars

The management of fertilizers in a context of climate change and the preservation of the environment is strongly related to the regulation and accumulation of 2-acetyl-1-pyrroline (2AP) in fragrant rice. However, the feasibility of such management strategies in terms of enhancing the accumulation of 2AP has not yet been explored in aromatic cultivars. Here, we investigated the impact of the application of two fertilizers at three depth (surface, 5 cm and 10 cm) levels of placements to improve the aromatic rice quality, including such aspects as the 2AP content-, protein-, amylose- and yield-related traits. For this purpose, two known rice cultivars, Basmati 385 (B-385) and Yunjingyou (YJY), were grown in pots during 2019 and 2020 under fluctuating climates. The deep application of fertilizer at 10 cm significantly affected the 2AP content with such values as 127.53 μg kg−1 and 111.91 μg kg−1 obtained for Fragrant Fertilizer (FF) and Urea in B-385 cultivar, and 126.5 μg kg−1 and 114.24 μg kg−1 being observed for FF and Urea in YJY, respectively, during 2019. In addition, values of 108.41 μg kg−1 and 117.35 μg kg−1 were recorded for FF and Urea in B-385, while 125.91-μg kg−1 and 90.71-μg kg−1 were measured for FF and Urea in YJY, respectively, during 2020. Similarly, B-385 had better 2AP content and yield-related traits, as well as amylose content and cooked rice elongation, as compared to the YJY rice cultivar. The 2AP accumulation and its related biochemical parameters, and their relationships in different plant tissues at different growth stages under FF and Urea treatments, were also improved. Further, the 2AP content and the P5C activity demonstrated strong correlations during the grain filling periods in both fragrant rice cultivars. In conclusion, our findings have the potential to provide useful information to farmers and agriculture extension workers in terms of the saving of fertilizers and the improvement of rice grain quality under fluctuating climate conditions.

The Regulatory Mechanism of 2-Acetyl-1-Pyrroline Biosynthesis in Fragrant Rice (Oryza sativa L.) Under Different Soil Moisture Contents

2-acetyl-1-pyrroline (2-AP) is the key compound of rice aroma. However, the responses of 2-AP biosynthesis in fragrant rice under different soil moisture and the corresponding mechanism are little known. The present study evaluated the effects of different soil moisture on 2-AP biosynthesis through a pot experiment. Four soil moisture contents, that is, 50% (SM50), 40% (SM40), 30% (SM30), and 20% (SM20), were adopted, and SM50 treatment was taken as control. The pots were weighed and watered to maintain the corresponding soil moisture content. The results showed no significant difference in growth parameters (plant height, stem diameter, and plant dry weight) among all treatments. Compared with SM50, SM40, SM30, and SM20 treatments significantly (p<0.05) increased 2-AP content by 32.81, 23.18, and 53.12%, respectively. Between 20 to 90% higher proline content was observed in SM40, SM30, and SM20 treatments than in SM50. Enzymes including proline dehydrogenase, ornithine transaminase, and 1-pyrroline-5-carboxylate synthetase exhibited lower activities with soil moisture declined. Higher diamine oxidase activity was observed in SM40, SM30, and SM20 treatments compared with SM50, and real-time PCR analyses showed that transcript level of DAO1 was greatly increased under low soil moisture treatments, especially in SM20 treatment. Transcript levels of PRODH, DAO2, DAO4, DAO5, OAT, P5CS1, and P5CS2 decreased or maintained in SM40, SM30, and SM20 treatments compared with SM50. We deduced that low soil moisture content enhanced 2-AP biosynthesis mainly by upregulating the expression of DAO1 to promote the conversion from putrescine to 2-AP.

A New Organic-Inorganic Compound Fertilizer for Improving Growth, Yield, and 2-Acetyl-1-Pyrroline Biosynthesis of Fragrant Rice

Fragrant rice (Oryza sativa L.) is a high-valued rice type and possesses a unique aroma with 2-acetyl-1-pyrroline (2-AP) as the critical component. However, the cultivation measures in fragrant rice production are far from perfect. In this study, a new organic-inorganic compound fertilizer was made with organic matter, urea, superphosphate, potassium chloride, zinc sulfate, and lanthanum chloride. A four-year field experiment was conducted to investigate its effects on fragrant rice growth, yield formation, and 2-acetyl-1-pyrroline biosynthesis. Three treatments, i.e., (CK) no fertilizer was applied, (IF) the urea, superphosphate, and potassium chloride were applied at 234 kg ha−1, 450 kg ha−1 and 108 kg ha−1, and (OICF) this new fertilizer composed of 10% organic matter, 26% urea, 50% superphosphate, 12% potassium chloride, 1.9% zinc sulfate, and 0.1% lanthanum chloride, was applied at 900 kg ha−1, were adopted in the present study. Across four experimental years, the results showed that the grain yield in OICF treatment ranged between 5.86–8.29 t ha−1, and was significantly (p < 0.05) higher than that in IF treatment and CK. The improvement in grain yield due to OICF treatment was explained by increased effective panicle number per m2 and seed-setting rate. The highest or equally highest chlorophyll content and the net photosynthetic rate at 20, 40, 60, and 80 days after transplanting were recorded in OICF treatment among three treatments. OICF treatment also increased the aboveground biomass of fragrant rice compared with IF treatment and CK. Moreover, compared with CK and IF treatment, OICF treatment significantly (p < 0.05) increased grain 2-AP content by 30–38% and 10–21%, respectively. The contents of 2-AP related precursors, including proline and 1-pyrroline, also increased due to OICF treatment. This study provided a new organic-inorganic compound fertilizer and suggested that it could be used to achieve the goals of high yield and high grain 2-AP content in fragrant rice production.

Effectiveness of atmospheric cold plasma technology on physicochemical and functional characteristics of ST25 fragrant rice (Oryza sativa L.) flour

Vietnam is one of the leading rice export countries in the world. ST25 fragrant rice (Oryza sativa L.) won the top prize for best rice in the world in 2019 and the second at World's Best Rice Contest 2020. Plasma has been considered as an innovative food processing technology. The aim of this study demonstrated the impact of time (4, 6, 8, 10, 12 min), power (160, 180, 200, 220, 240 W) and oxygen flow rate (0.2, 0.4, 0.6, 0.8, 1.0 ml/min) to the physicochemical and functional qualities of ST25 fragrant rice flour. Results showed that under plasma treatment time at 10 minutes, power 200 W, oxygen flow rate 0.8 ml/min, the amylose content (16.67±0.01 %), pasting temperature (83.21±0.02 oC), water absorption index (14.54±0.00 gm/gm sample), water solubility index (10.31±0.02 gm/100 gm sample), swelling power (14.96±0.00 gm/gm sample) were recorded. Under plasma treatment, surface of the ST25 fragrant rice flour became more hydrophilic to absorb more water resulting to shorter cooking time. Plasma treatment provides environmentally friendly processing of rice grain to limit pesticide abuse towards ecological farming.

Preliminary Application of Vermicompost in Rice Production: Effects of Nursery Raising with Vermicompost on Fragrant Rice Performances

Vermicompost is an excellent organic fertilizer, but the application of vermicompost in fragrant rice production has not yet been reported. Seedling nursery is an important component of rice production. The present study firstly applied vermicompost in fragrant rice production through nursery raising. The seedlings of three fragrant rice cultivars were raised in matrix with different rations of vermicompost (the treatment without vermicompost was taken as the control), and the growth parameters and physiological characters of seedlings were investigated. The results showed that, compared with the control, the application of vermicompost significantly (p < 0.05) increased the plant height, stem diameter, fresh weight, and dry weight of fragrant rice seedlings by 11.22–24.73%, 38.34–65.87%, 16.74–30.46%, and 16.61–35.16%, respectively. Nursery raising with vermicompost significantly (p < 0.05) enhanced the net photosynthetic rate by 5.99–12.93%, relative to the control. Higher contents of chlorophyll a, chlorophyll b, carotenoids, and total chlorophyll were recorded in vermicompost treatments than in the control. Compared with the control, vermicompost treatments also increased root length, surface area, mean diameter, root volume, root tip number, and root activity of fragrant rice seedlings by 12.42–27.82%, 15.04–38.65%, 12.64–23.12%, 42.41–63.58%, 18.62–24.95%, and 12.01–26.29%, respectively. Moreover, nursery raising with vermicompost enhanced the activities of antioxidant enzymes including superoxide, peroxidase, and catalase by 7.97–24.21%, 17.11–44.99%, and 7.37–15.95%, respectively, relative to the control. Moreover, 7.92–29.40% lower malondialdehyde contents were recorded in vermicompost treatments compared with the control. Therefore, nursery raising with vermicompost could be a good agronomy practice in machine-transplanted fragrant rice.