The objective of this study was to determine whether leaf color change in rice plants predicts ammonia (NH3) volatilization during the late grain-filling period. In a pot study of indica and indica–japonica hybrid cultivars, the leaf color-changing rate was highly significantly positively correlated with NH3 volatilization during the grain-filling stage. Cultivars with fast leaf color-changing had higher NH3 volatilization loss due to their higher apoplastic NH4+ concentration and NH3 compensation point, along with lower glutamine synthetase (GS) activity. N application, although it delayed leaf color change, led to increased NH3 volatilization. Selecting cultivars with slow leaf color-changing characteristics and managing fertilization to delay the leaf color change process could reduce N gas loss and increase N use efficiency.
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To study the relationship between rice leaf color change and grain filling, two indica-japonica hybrids with distinct leaf colors were grown under three N fertilizer dosages (LN, 0 kg ha−1; MN, 150 kg ha−1; HN, 300 kg ha−1). The leaf color change features of flag leaf, 2nd leaf and 3rd leaf, as well as grain filling traits of superior and inferior grains were compared. Compared to cultivar CY167 (normal green leaves) under the same N level, cultivar CY927 (dark green leaves) exhibited delayed leaf color change onset time (T0) by 0–3.6 d, reduced mean leaf color change rate (Rm) by 1.98%–9.45%, and increased leaf color index at maturity (CIf) by 3.77%–53.48%. Additionally, CY927 prolonged the grain filling period (D) of inferior grains by 0.6–2.0 d, resulting in a yield increase of 8.13%–25.46%. N supply significantly increased rice yield, primarily by delaying T0 and reducing Rm of flag leaf, improving initial grain filling potential (R0) and maximum grain weight (A), delaying the time to reach the maximum grain filling rate (Tmax), and prolonging the grain filling activity period (D) of inferior grains. The time interval (TL-G) between the T0 of the flag leaf and Tmax of inferior grains was negatively correlated with yield (−0.780, P < 0.01). Suggesting that rice yield can be improved by optimizing N fertilizer management to shorten the TL-G. These findings provide valuable knowledge about the relationship between leaf senescence and grain filling, and benefit the understanding of the physiological mechanisms underlying high-yield rice production.
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The change in leaf color during the later reproductive period of rice is directly related to photoassimilate accumulation and nutrient reuse, and it ultimately affects grain filling and yield. This study aimed to explore an assessment model that depicts the leaf color change process, and extract parameters that can precisely distinguish differences in leaf color changes among different treatments and varieties. A total of 31 rice varieties were selected as the field experiment materials in 2019 and 2023. The SPAD values of the flag, 2nd and 3rd leaves were measured after heading, and they were normalized to the leaf color index (CI). A functional model for the variation of leaf CI with time (t) in the late reproductive stage of rice was established based on CI=at2+bt+c, and seven color change parameters were extracted for the quantitative comparison and assessment of leaf color changes, including three time related parameters for color change (onset time, T0; midpoint time, T50; and color change duration, T100); one leaf color index (final value of CI, CIf); and three parameters related to the color change rate (the rate during T0−T50, R1; the rate during T50−T100, R2; and the mean color change rate, Rm). In 2023, Chunyou 927 (CY927) with a dark leaf color and Yongyou 1540 (YY1540) with a normal leaf color were used as materials, and three N fertilizer amounts were applied to explore the effects of N fertilizer on the leaf color change process through the established assessment system. The T0 of the flag leaf was delayed by 2.6−3.0 d compared to the 2nd and 3rd leaves. The CIf of the flag leaf was 12.12 and 21.15% higher than those of 2nd and 3rd leaves, respectively. In addition, the R1, R2 and Rm of the 3rd leaf were 10.75–19.82%, 17.99–20.09% and 18.23–11.61% higher than the flag and 2nd leaves, respectively. Rice yield was significantly positively correlated with T0, positively correlated with T50 and T100, and negatively correlated with R1, R2 and Rm. The average T0, T50, and T100 of rice varieties with yields higher than 8,000 kg ha−1 were 6.8, 22.2, and 31.8 d, respectively, with a CIf of 0.563 and an Rm of 0.015 d–1. N applications delayed T0 by 4.5–6.2 d, reduced Rm by 30.06–32.33%, and increased CIf by 35.78–39.69%. The established leaf color change model and extracted parameters quantitatively depicted the leaf color change process during the later reproductive period. They also effectively distinguished the differences in leaf color change among leaf positions, rice varieties and N treatments. This approach is valuable for selecting and cultivating high-yield and nutrient-efficient rice varieties, as well as for analyzing the underlying mechanisms.
The responses of the rice grain qualities to the climate factors during the grain filling period were studied to facilitate the variety screening and the agronomic practices optimization for japonica rice during the late rice season in southern rice region in China.
To evaluate the effects of different climate factors during the grain filling period on the qualities of late japonica rice, the field experiment was conducted in Fuyang and Wenzhou, Zhejiang province, in 2018, using three late indica rice as control varieties and 20 japonica rice (including 10 inbred japonica rice, 3 japonica hybrids and 7 indica-japonica hybrids) as evaluating varieties.
(1) Based on the results of clustering with grain qualities, the late indica rice varieties were classified as an unique category due to its highest aspect ratio (3.18) and high amylose content (19.40%). Compared with the late indica rice, the most of hybrid varieties had greater brown rice rate (4.31%−5.28%), milled rice rate (6.51%−9.33%), head rice rate (25.83%− 28.34%), gel consistency (1.81%−4.27%), alkali spreading value (11.62%−50.85%), and tasted value (2.31%−2.85%), with lower amylose content (20.98%−28.14%) and protein content (1.16%−14.85%), showing obvious improvement of rice quality. Whereas, the rice quality performance response to late season were differentiated within inbred japonica varieties, and some inbred japonica rice varieties originating from southern Jiangsu and Jiaxing (4 varieties) were similar to the those in the hybrid-japonica category, while the rest inbred japonica varieties from Jiangsu and Shanghai (6 varieties) belonged to another category due to their relatively poor rice quality performances (high chalkiness, chalky grain rate and protein content) in the late season. (2) The rice grain qualities were closely related to climate factors during grain filling period of late rice season. The stage of 10-20 days after full heading was identified as the sensitive period of climate factors on rice qualities. The brown rice rate was negatively correlated with daily solar radiation (R: -0.40−-0.19, P<0.05) and daily temperature difference (R: -0.45−-0.28, P<0.05), and positively correlated with daily minimum temperature (R: 0.24−0.53, P<0.05) and precipitation (R: 0.38−0.45, P<0.05). The chalkiness rate and chalkiness grain rate were significantly increased with the rainfall and night temperature (R: -0.37−-0.16, P<0.05; R: -0.43−-0.12, P<0.05), resulting in reducing rice appearance quality. Meanwhile, the rainfall and night temperature were negatively correlated with rice tasted value (R: -0.37−-0.16, P<0.05; R: -0.43−-0.12, P<0.05). The daily maximum temperature at grain filling stage was positively correlated with rice tasted value (R=0.37, P<0.05), while the daily minimum temperature was positively correlated with rice protein content (R=0.19, P<0.05), chalkiness (R=0.16, P<0.05), and chalkiness grain percentage (R=0.12, P<0.05).
The stage of 10-20 days after full heading was the key period for affecting rice grain quality by climate factor, and the improvement of rice qualities for late japonica varieties in southern rice region should focus on the integration of high-quality japonica genes with an indica gene of local adaptation, and the choice of hybrid rice (including indica-japonica hybrids and japonica hybrids) was more reliable and convenient than inbred japonica rice. The breeding of inbred japonica varieties should consider their ecological adaptability in combined with local climatic conditions.
The aim of the study was to evaluate the differences between rice yield and its components, as well as quality of double cropping early japonica rice which was selected from various accumulated temperature zones in cold region to plant in the lower reaches of the Yangtze River, so as to provide a theoretical basis to select the proper japonica varieties as the double cropping early season rice in this area.
Field experiments were carried out at Taizhou (121°13′ E, 28°78′ N) and Hangzhou (119°94′ E, 30°08′ N) of Zhejiang province in 2018, 2021 and 2022. Six (2018), thirteen (2021) and forty-one (2022) japonica varieties were selected from different accumulated temperature zones in Heilongjiang province, respectively, and the early indica rice Zhongzao 39 was picked out as a control in 2018 and 2022. The differences of productive panicle number, spikelets number per panicle, percentage of filled grain, thousand grains weight, number of spikelets unit area, yield, and harvest index were analyzed among double-cropping early japonica and indica rice; the quality indexes were compared among this two types rice too, such as head rice rate, diaphaneity, gel consistency, amylose content, chalkiness degree, and chalky grain rate.
The harvest dates of early japonica rice with beforehand sowing were about 0-15 days earlier than that of local double-season early indica rice. The total mean yield of early japonica rice was 6 637.77 kg·hm-2 in 2018; and the yield of Kongyu 131 were the highest with 7 724.70 kg·hm-2. Moreover, the field production verification in 2022 suggested that the yield of Kongyu 131 could reach 7 194.77 kg·hm-2. The averages of chalkiness degree, diaphaneity, gel consistency and amylose content in all varieties met the quality of second-class edible rice variety criterion, but the head rice rate was low. The total mean yield early japonica rice was 6 630.45 kg·hm-2 in 2022, in order as follows: Longken 257 (8 324.99 kg·hm-2), Longken 263 (8 170.94 kg·hm-2), and Liandao 1 (8 108.34 kg·hm-2). Compared with Zhongzao 39, the productive panicle number in early japonica rice were higher, however, the spikelets number per panicle, percentage of filled grain, thousand grains weight were lower than the control, which induced the yield decrease of 54.75%-93.28%. The average yield of the third accumulated zone was higher than that of other accumulated zones due to the relative superior percentage of filled grain. The correlation analysis within yield and its components of different japonica cultivars showed that, the yield had significantly positive correlation with productive panicle number (P<0.05) and number of spikelets unit area (P<0.01).
It was practicable to plant double cropping early japonica rice varieties in the Yangtze River area selected from different accumulated temperature zones in Heilongjiang province, confirmed by appropriate performances on growth duration, yield and quality. It was suggested that Kongyu 131, Longken 257, Longken 263, and Liandao 1 could be selected as double cropping early japonica rice for the next large-scale demonstration planting.
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Because of the higher nitrogen (N) recovery efficiency (NRE) of panicle-stage fertilization compared with basal and tillering fertilization, increasing the proportion of N topdressing at the booting stage (panicle-N) is recommended and commonly practiced in parts of China. To investigate the effects of increasing panicle-N on grain yield and N use efficiency (NUE) and the relationships of the increase and the rice cultivar and soil fertility status, we increased the percentage of panicle-N from 20% to 40% by correspondingly reducing the N amount applied only at the tillering stage in both high- and low-fertility blue clayey paddy fields in 2018 and 2019. Four indica cultivars with diverse panicle types were used, and their grain yield, dry matter accumulation, and NUE were compared. In high-fertility soil, increasing topdressing panicle-N from 20% to 40% reduced tillering ability and reduced the effective panicle numbers of the multi- and medium-panicle cultivars Huanghuazhan (HHZ), C Liangyouhuazhan (CHZ), and Tianyouhuazhan (THZ). These cultivars gave the greatest yield when 30% of N was supplied as panicle fertilizer, whereas the yield, NRE, N agronomic efficiency (NAE), and nitrogen physiological efficiency (NPE) of the heavy-panicle inbred cultivar Yangdao 6 (YD6) continued to increase, resulting in improved dry matter accumulation and grain filling in the late growth stage. The yield, NAE, NRE, and NPE of YD6 peaked when the panicle-N constituted 40%. While in low-fertility soil, the multipanicle cultivar HHZ showed the greatest yield when 30% of fertilizer-N was applied once at the panicle initiation (PI) stage, while the medium-panicle cultivar CHZ showed the greatest yield when the panicle-N percentage was 40%. Our results suggest that the percentage of panicle-N fertilizer should not exceed 30% for multipanicle cultivars, while can be appropriately increased to 40% for heavy-panicle indica cultivars. The effect of increasing topdressing panicle-N on the yield of medium-panicle cultivars was related to soil fertility. The optimum panicle-N percentage was 30% in the high-fertility soil and 40% in the low-fertility soil.
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New indica and japonica hybrid rice cultivars, such as the Yongyou series, provide farmers with very high yield potential. However, information on their canopy light capture and solar radiation use efficiency in the late season is limited. Field experiments were performed to compare the radiation-use parameters of four rice types: indica rice (IR), inbred japonica rice (IJR), hybrid japonica rice (HJR), and hybrid indica/japonica rice (HIJR), from 2016 to 2018 during the late season in Hangzhou, China. The grain yield, aboveground biomass, intercepted solar radiation (SI), and radiation-use efficiency (RUE) of the HIJR were on average respectively 13.4%–53.4%, 14.3%–30.6%, 7.6%–21.4%, and 8.2%–14.9% higher than those of the HJR, IJR, and IR. The leaf area index (LAI) of the HIJR was 18.2%–57.0% greater than that of the IJR and HJR at four growth stages, resulting in respectively 17.8%–38.5% and 10.7%–42.8% greater canopy light interception rates (LIR) and amount of intercepted solar radiation during the vegetative stage. The prolonged grain-filling stage also led to respectively 33.9%–52.6% and 30.5%–51.4% increases in amounts of incident and intercepted radiation for the HIJR relative to the IR during grain filling. These results indicate that the SI superiority of the HIJR was caused by canopy closure as rapid as that of the IR during the vegetative stage (greater LAI and canopy LIR during the growing season) and a grain-filling stage as long as that of the HJR. For grain-filling stage, differences in leaf Pn between HIJR, IR, and IJR were not significant, suggesting that the greater RUE of the HIJR (12.7%–52.8% higher) than that of the other rice types resulted from improved canopy architecture after flowering (FL). Principal components analysis (PCA) revealed that the superiority of the HIJR in terms of solar radiation use resulted from the greater canopy light capture capability of IR and the prolonged growth period (especially during grain filling) of japonica rice in the late growing season.
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Compared to drought-susceptible rice cultivars (DSRs), drought-resistance rice cultivars (DRRs) could drastically reduce the amount of irrigation water input and simultaneously result in higher grain yield under water-saving irrigation conditions. However, the mechanisms underlying these properties are unclear. We investigated how improved agronomic traits contribute to higher yield and higher water use efficiency (WUE) in DRRs than in DSRs under alternate wetting and drying (AWD). Two DRRs and two DSRs were field-grown in 2015 and 2016 using two different irrigation regimes: continuous flooding (CF) and AWD. Under CF, no statistical differences in grain yield and WUE were observed between DRRs and DSRs. Irrigation water under the AWD regime was 275–349 mm, an amount 49.8%–56.2% of that (552–620 mm) applied under the CF regime. Compared to CF, AWD significantly decreased grain yield in both DRRs and DSRs, with a more significant reduction in DSRs, and WUE was increased in DRRs, but not in DSRs, by 9.9%–23.0% under AWD. Under AWD, DRRs showed a 20.2%–26.2% increase in grain yield and an 18.6%–24.5% increase in WUE compared to DSRs. Compared to DSRs, DRRs showed less redundant vegetative growth, greater sink capacity, higher grain filling efficiency, larger root biomass, and deeper root distribution under AWD. We conclude that these improved agronomic traits exert positive influences on WUE in DRRs under AWD.
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