Exploring Key Yield Components Influencing Grain Yield in Ultrashort- and Short-Duration Rice Cultivars

Abstract

Identifying the key yield components influencing rice yield is crucial for developing high-yielding ultrashort- and short-duration cultivars, which could meet the demands of intensified cropping systems. This study used data collected over 6 years to compare grain yield and yield components between the ultrashort-duration (85–100 days) and short-duration (100–110 days) rice cultivars under mechanical transplanting conditions. Grain yield in the ultrashort-duration group ranged from 5.71 to 10.47 t ha⁻¹ (mean: 7.97 t ha⁻¹), while that in the short-duration group ranged from 6.00 to 11.84 t ha⁻¹ (mean: 7.67 t ha⁻¹), with no significant difference between the groups (p > 0.05). The ultrashort-duration group had 15.56% fewer spikelets per panicle but a 7.9% higher grain filling percentage than the short-duration group (p < 0.01). In terms of importance, grain weight was the most critical factor in the ultrashort-duration group (contributing 42.8% to yield), followed by the grain filling percentage (37.5%). Conversely, in the short-duration group, spikelets per panicle was the most important factor, contributing 43.1%, with grain weight accounting for 32.1%. In summary, the ultrashort-duration varieties should prioritize grain weight and the grain filling percentage, while the short-duration varieties should focus on spikelets per panicle and grain weight. Future research should integrate these insights into breeding programs to develop high-yielding short-duration cultivars for intensified cropping systems.

1. Introduction

Rice (Oryza sativa L.) serves as the staple food for over 65% of the population in China [1,2]. Chinese agricultural practices are characterized by the extensive use of double-cropping rice systems and multiple cropping patterns, such as the rapeseed–rice–rice triple-cropping system. These intensive cropping strategies are crucial for maximizing land use efficiency and ensuring food security, given the constraints of limited arable land [3]. However, the success of these strategies is contingent upon the availability of rice varieties with a suitably short growth duration that can fit within narrow seasonal windows. Ultrashort-duration and short-duration rice varieties are particularly important in this context, as they effectively reduce the growth period, thereby increasing the cropping index and enhancing crop yield per unit area [4,5].

Previous studies have shown that cultivars with a growth period of less than 105 days are classified as short-duration varieties [6], and those with a growth period of about 95 days are classified as ultrashort-duration varieties under direct-seeded conditions [4]. Transplanted rice generally has a growth period about 2 to 6 days longer than direct-seeded rice [7]. According to recent reports, the newly developed ultrashort-duration rice line CPPC18, used for both early and late seasons in the double-season rice direct-seeding system, had a single-season growth duration of less than 95 days and an annual growth duration of 180–183 days, and it achieved an annual yield of 14.9 t ha⁻¹ [8,9]. The grain yield of ultrashort-duration rice varied from 3.76 to 7.58 t ha⁻¹ in early seasons (with a growth duration of 96 days) and from 5.54 to 7.42 t ha⁻¹ in late seasons (with a growth duration of 87 days) [4]. Short-duration varieties also achieved considerable yields. Xu et al. [6] found that the yield range of five short-duration rice varieties reached 6.40 to 9.88 t ha⁻¹, with a total growth duration of 89 to 105 days. Chen et al. [5] reported that the short-duration rice Lingliangyou104 achieved a high yield of 7.55 t ha⁻¹, with a growth duration of 108 days.

Rice yield is determined by the integrated effects of multiple key factors, including the panicles per m², the spikelets per panicle, the grain filling percentage, and the grain weight [10,11]. Previous studies reported that the number of panicles per m² was a key factor influencing rice yields [12]. The number of panicles per m² was closely correlated with spikelets per panicle [13,14]. Other studies reported that the grain filling percentage was a key factor in increasing rice yield [15,16]. However, some reports indicated that increasing the grain weight of rice was crucial for boosting rice yield [17,18]. These differences suggest that the relative importance of yield components can be influenced by multiple factors, including variety characteristics, growth duration, seasonal environmental conditions, and cultivation practices. These observations further indicate that the key yield components of short-duration and ultrashort-duration rice varieties may differ significantly. For example, short-duration varieties can compensate for their shorter growing period by increasing the grain filling percentage and grain weight [17,19], whereas ultrashort-duration varieties can maintain yield through enhanced spikelets per panicle and grain filling percentage [4,9].

Therefore, based on these reports, it was hypothesized that short- and ultrashort-duration rice varieties have distinct key yield components. This study aimed to investigate these differences and their underlying mechanisms through comparative analysis. The objectives were to (1) compare grain yield and yield components between the two types, (2) analyze the relative importance of yield components in different growth duration rice cultivars, and (3) provide recommendations for the cultivation of short- and ultrashort-duration rice. These findings will provide a scientific basis for optimizing and breeding short- and ultrashort-duration rice varieties to meet modern agricultural needs.

2. Materials and Methods

2.1. Data Collection

The data used in this study were primarily collected from late-season rice paddy field experiments conducted in Yongan, Hunan Province, China (28°09′ N, 113°37′ E, 43 m a.s.l.), using machine-transplanted methods between 2015 and 2022. The experimental information is summarized in Table 1. The dataset was filtered to include yield, panicles per m², spikelets per panicle, grain filling percentage, and grain weight for rice cultivars with a total growth duration of less than 110 days. The data were categorized into two groups based on the total growth duration of the cultivars: the ultrashort-duration group (85–100 days) and the short-duration group (100–110 days). Each individual plot was defined as a replicate, and these replicates were subsequently analyzed as independent samples. Data from all seasons were combined to facilitate comparative analysis between the two groups.

2.2. Measurement Method

At maturity, rice grains were harvested from a 5 m² area in each plot and sun-dried for three to five days. A subsample of 50 g of sun-dried grains was oven-dried at 70 °C until a constant weight was achieved to determine the grain moisture content. The grain yield was then calculated by adjusting the grain moisture content to 14%. Additionally, ten hills of rice plants were sampled from each plot. The roots were removed, and the number of effective panicles was recorded. The grains were manually threshed and placed in mesh bags to be sun-dried for approximately 1 day. Subsequently, the grains were separated into filled and empty grains using a water selection method. Three samples of 30 g of filled grains were weighed and counted, while all empty grains were counted. The filled and empty grains were then dried at 70 °C in an oven until a constant weight was achieved and then weighed again. Finally, panicles per m², spikelets per panicle, grain filling percentage, and grain weight were calculated. In this study, grain weight refers to the dry weight.

2.3. Data Analysis

t-tests were used to compare the two groups using SPSS software (Version 26.0, IBM, Armonk, NY, USA). Box-and-whisker plots were created with GraphPad Prism software (Version 8.0.2, San Diego, CA, USA). The importance of yield components influencing yield was assessed using decision tree regression analysis conducted with SPSSPRO, an online data analysis platform (https://www.spsspro.com [accessed on 15 February 2025]). Decision tree regression operates by recursively partitioning the data into subsets based on the values of input features, aiming to minimize the variance within each subset. This process results in a tree-like model, where each internal node represents a decision rule and each leaf node represents a predicted value. The importance of each feature is assessed by measuring the reduction in variance achieved by the splits on that feature across the tree. A feature with a larger total reduction in variance is considered more important in predicting the target variable.

3. Results

3.1. Grain Yield in Ultrashort- and Short-Duration Rice

The grain yield in the ultrashort-duration rice group ranged from 5.71 t ha⁻¹ to 10.47 t ha⁻¹, with a mean of 7.97 t ha⁻¹ (Figure 1). In the short-duration rice group, the grain yield ranged from 6.00 t ha⁻¹ to 11.84 t ha⁻¹, with a mean of 7.67 t ha⁻¹. No significant difference was observed in yield between the ultrashort- and short-duration rice groups (p > 0.05).

3.2. Yield Components in Ultrashort- and Short-Duration Rice

The panicles per m² in the ultrashort-duration rice group ranged from 241.67 to 530.91, with a mean of 390.07 (Figure 2a). In the short-duration rice group, the panicles per m² ranged from 263.8 to 511.08, with a mean of 387.44. No significant difference was observed in the panicles per m² between the two groups (p > 0.05). The spikelets per panicle in the ultrashort-duration rice group ranged from 61.66 to 130.49, with a mean of 96.12 (Figure 2b), whereas the short-duration rice group ranged from 78.25 to 142.21, with a mean of 111.08. The ultrashort-duration rice group had 15.56% fewer spikelets per panicle than the short-duration rice group (p < 0.001). The grain filling percentage in the ultrashort-duration rice group ranged from 63.56% to 91.30%, with a mean of 79.41% (Figure 2c), compared to 59.66% to 84.96% in the short-duration rice group, with a mean of 73.57%. The ultrashort-duration rice group had a 7.90% higher grain filling percentage than the short-duration rice group (p < 0.001). Furthermore, the grain weight in the ultrashort-duration rice group ranged from 22.13 mg to 27.30 mg, with a mean of 24.12 mg (Figure 2d), while that in the short-duration rice group ranged from 19.03 mg to 26.94 mg, with a mean of 23.55 mg. No significant difference was observed in the grain weight between the two groups (p > 0.05).

3.3. Proportion of Importance of Yield Components to Yield in Ultrashort- and Short-Duration Rice

Among the yield components, the grain weight exhibited the highest importance, accounting for 42.8% (Figure 3a). The grain filling percentage followed closely, contributing 37.5%. The panicles per m² accounted for 17.3%, while the spikelets per panicle had the lowest importance, at only 2.4%, in the ultrashort-duration group. In the short-duration group, the spikelets per panicle exhibited the highest importance, accounting for 43.1% (Figure 3b). The grain weight ranked second, with a proportion of 32.1%. The grain filling percentage followed, contributing 18.5%. The panicles per m² had the lowest importance proportion, at 6.3%.

4. Discussion

This study comprehensively compared the grain yield and yield component traits between ultrashort- and short-duration rice cultivars. The mean grain yield for the ultrashort-duration rice was 7.97 t ha⁻¹, while that for the short-duration rice was 7.67 t ha⁻¹. Notably, these yields were comparable to those of ultrashort-duration cultivars, such as CPPC18 and XZX6 [4,9], and short-duration cultivars, like Lingliangyou104 and JZ05 [5,6], in late seasons. Moreover, these grain yields exceeded the national average of 7.64 t ha⁻¹ for mid-season and single-cropping late rice in China in 2022, as reported by the National Bureau of Statistics [20]. Importantly, no significant difference in yield was observed between the ultrashort- and short-duration cultivars, suggesting that ultrashort-duration cultivars could achieve yield levels comparable to those of short-duration cultivars despite their shorter growth period. In China, farmers commonly believe that varieties with a longer growth period yield more than those with a shorter growth period. Therefore, they assume that short-duration rice varieties have higher yields than ultrashort-duration varieties. However, our research has shown that the yields of both types are actually comparable. This finding may serve as a basis for farmers when choosing ultrashort-duration varieties in the future.

The ultrashort-duration rice varieties exhibited 15.6% fewer spikelets per panicle, but they achieved a 7.9% higher grain filling percentage compared to the short-duration varieties. The current result corroborates those of previous studies [9]. In this study, the lower spikelets per panicle in the ultrashort-duration rice compared to the short-duration rice may stem from the greater overlap between vegetative and reproductive growth phases. This overlap may cause nutrient competition, leading to inadequate resource allocation to panicles and suboptimal panicle development, characterized by fewer grains and smaller panicle size [21,22]. Concurrently, the higher grain filling percentage in the ultrashort-duration rice compared to the short-duration rice may stem from the distribution of most grains on primary branches and fewer grains on lower secondary branches, leading to fewer weak grains and more efficient grain filling [23,24]. This suggested that ultrashort-duration varieties could maintain high yields through a compensatory mechanism that enhances the grain filling percentage despite having fewer spikelets per panicle [25,26]. Thus, this compensatory mechanism is vital for breeding high-yielding rice varieties in regions with short growing seasons.

In this study, grain weight was the most critical factor in the ultrashort-duration group, contributing 42.8% to yield, followed by the grain filling percentage (37.5%). Conversely, in the short-duration group, spikelets per panicle was the most important factor, contributing 43.1%, with grain weight accounting for 32.1%. These results further confirmed that the grain weight [17,18], the spikelets per panicle [13,14,27], and the grain filling percentage [15,16,19] were critical determinants of rice yield. Rice grain weight and grain filling percentage are influenced by grain position [28], the grain filling rate and duration [29], and photosynthetic product allocation efficiency [30,31]. Grain filling derives from the carbohydrates stored in the stem and sheath before heading and the photosynthetic products from leaves after heading. During the grain filling period, non-structural carbohydrates in the stem and sheath are mobilized and transported to the grains, directly affecting the filling rate [32]. Moderate water stress can promote non-structural carbohydrate translocation and accelerate filling [33,34]. Varieties with strong leaf photosynthetic function and high chlorophyll content during grain filling have higher filling rates, photosynthetic product synthesis, and allocation efficiency [35,36]. High root vigor delays leaf senescence, prolongs the filling duration, and increases dry matter accumulation, enhancing seed setting and grain weight [37]. Increasing the length of the internode below the panicle improves panicle photosynthesis, light exposure, and material translocation, boosting the grain filling percentage [30]. Thus, to improve the yields of ultrashort- and short-duration rice, it is essential to prioritize enhancing the translocation of non-structural carbohydrates in stems and sheaths, increasing photosynthetic capacity, and maintaining root vigor in production. The high-yield cultivation of short and ultra-short-growing-period rice should focus on breeding or selecting varieties with high photosynthetic efficiency and efficient transport of non-structural carbohydrates in stems and sheaths. Additionally, attention should be paid to water and fertilizer management to sustain root vitality. In the current study, physiological data for short- and ultrashort-duration rice, such as leaf chlorophyll content, photosynthetic rate, non-structural carbohydrates in stems and sheaths, and root vigor, were not collected. Therefore, future experiments should incorporate these measurements to address this limitation and provide a more comprehensive understanding.

In this study, spikelets per panicle was the most important factor in the short-duration group. The number of spikelets per panicle is determined by the balance between spikelet initiation and degeneration. The panicle differentiation period is a pivotal phase in determining the spikelets per panicle [38]. Within this period, the nutritional status and water supply play a very vital role. Both the excessive and premature application of nitrogen fertilizer are detrimental to the increase in the number of spikelets per panicle in rice [39,40]. Water stress may increase spikelet degeneration and pollen sterility, negatively affecting the spikelets per panicle and grain filling percentage during the panicle differentiation stage [41]. In contrast, mild alternate irrigation with dry and wet conditions during this critical period has been found to promote spikelet differentiation and reduce spikelet degeneration, thereby facilitating the development of large panicles in rice [42]. However, rice varieties with large panicles are more prone to lodging due to their elevated center of gravity [43]. Therefore, in the cultivation of short-duration rice varieties, special emphasis should be placed on water and fertilizer management during the panicle differentiation stage. Moreover, enhancing lodging resistance should be prioritized in short-season rice production.

It should be noted that, unfortunately, physiological data for certain years were not collected. The inclusion of these data would provide a more in-depth interpretation of the existing results. In addition, mining genes or proteins that affect grain filling or spikelet number through modern biotechnology, such as the correlation between Os01g0140100 and spikelet number [10], will help broaden the applicability of the findings of this study.

5. Conclusions

Overall, this study demonstrates that ultrashort-duration rice cultivars can achieve comparable yield levels to short-duration rice cultivars by maintaining a higher grain filling percentage, despite having fewer spikelets per panicle. This highlights the potential of ultrashort-duration rice cultivars for high-yield production in regions with limited growing seasons. This study underscores the differential importance of yield components in both groups and emphasizes the need for tailored breeding strategies. In summary, ultrashort varieties should prioritize grain weight and the grain filling percentage, while short varieties should focus on spikelets per panicle and grain weight.

Author Contributions

Conceptualization, M.H.; investigation, C.Z., F.C. and J.C.; writing—original draft, C.Z.; supervision, W.W., H.Z. and M.H.; funding acquisition, M.H. and J.C. All authors have read and agreed to the published version of the manuscript.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Conflicts of Interest

The authors declare no conflicts of interest.

Footnotes

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Figures and Table

Figure 1 Grain yield in ultrashort- and short-duration rice. The box-and-whisker plot shows the minimum (horizontal line at the end of the lower whisker), mean (horizontal line within the box), and maximum (horizontal line at the end of the upper whisker) values of the data (n = 48 and 51 in ultrashort and short-duration rice, respectively).

Figure 2 (a) Panicles per m², (b) spikelets per panicle, (c) grain filling percentage, and (d) grain weight in ultrashort- and short-duration rice. The box-and-whisker plot shows the minimum (horizontal line at the end of the lower whisker), mean (horizontal line within the box), and maximum (horizontal line at the end of the upper whisker) values of the data (n = 48 and 51 in ultrashort- and short-duration rice, respectively).

Figure 3 Proportions of the importance of yield components to yield in ultrashort- (a) and short-duration (b) rice.

Table 1

Tested rice cultivars and experimental information.

Year	Cultivar	Soil Prosperity	Fertilizer Application	Planting Density	SeasonalAverage Temperature	SeasonalDaily Solar Radiation	Reference
2015	Luliangyou 211Luliangyou 996Lingliangyou 211Lingliangyou 268Liangyou 6Xiangzaoxian 32Xiangzaoxian 42Zhongjiazao 17Zhongzao 39Zhuliangyou 819	Organic matter: 28.9 g kg−1, Total N: 2.9 g kg−1, Available P: 24.9 mg kg−1, Available K: 159 mg kg−1, Soil pH: 5.95	N: 165 kg ha−1, P2O5: 100 kg ha−1, K2O: 200 kg ha−1	25 cm × 11 cm	Max: 29.7 °C, Min: 22.3 °C	15.9 MJ m−2 d−1	[17]
2016	Lingliangyou 268Zhongjiazao 17Zhongzao 39Zhuliangyou 819				Max: 30.5 °C, Min: 22.6 °C	16.4 MJ m−2 d−1
2017	Lingliangyou 104Xiangzaoxian 42Zhongjiazao 17	Organic matter: 34.3 g kg−1, Available N: 164.0 mg kg−1, Available P: 20.1 mg kg−1, Available K: 113 mg kg−1, Soil pH: 6.12	N: 150 kg ha−1, P2O5: 75 kg ha−1, K2O: 150 kg ha−1	25 cm × 11 cm	Max: 31.3 °C, Min: 23.8 °C	14.0 MJ m−2 d−1	/
2018	Zhuliangyou 819Zhongjiazao 17Lingliangyou 104				Max: 31.8 °C, Min: 22.8 °C	16.7 MJ m−2 d−1
2021	Jiyou 421Liangyou 287Liangyou 42Lingliangyou 268Lingliangyou 674Lingliangyou 942Tanliangyou 83Zhongjiazao 17Zhongzao 39Zhuliangyou 4024Zhuliangyou 819	Organic matter: 22.8 g kg−1, Total N: 1.16 g kg−1, Available P: 23.2 mg kg−1, Available K: 80 mg kg−1, Soil pH: 5.88	N: 150 kg ha−1, P2O5: 75 kg ha−1, K2O: 150 kg ha−1	25 cm × 12cm	Max: 32.7 °C, Min: 24.5 °C	17.0 MJ m−2 d−1	/
2022	Zhongjiazao 17Zhuliangyou 819	Organic matter: 39.8 g kg−1, Total N: 1.14 g kg−1, Available P: 21.3 mg kg−1, Available K: 110 mg kg−1, Soil pH: 5.80	N: 150 kg ha−1, P2O5: 75 kg ha−1, K2O: 150 kg ha−1	25 cm × 12cm	Max: 33.6 °C, Min: 23.6 °C	17.3 MJ m−2 d−1	/

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