Lodging Resistance Related to Root Traits for Mechanized Wet-Seeding of Two Super Rice Cultivars

Zhang Minghua, Mo Zhaowen, Liao Juan, Pan Shenggang, Chen Xiongfei, Zheng Le, Luo Xiwen, Wang Zaiman

Research Paper

Lodging Resistance Related to Root Traits for Mechanized Wet-Seeding of Two Super Rice Cultivars

Zhang Minghua1, #, Mo Zhaowen2, #, Liao Juan1, Pan Shenggang2, Chen Xiongfei3, Zheng Le1, Luo Xiwen1, Wang Zaiman1

(Key Laboratory of Key Technology on Agricultural Machine and Equipment / College of Engineering, South China Agricultural University, Guangzhou 510642, China; College of Agriculture, South China Agricultural University, Guangzhou 510642, China; School of Engineering, Jiangxi Agricultural University, Nanchang 330045, China; These authors contributed equally to this work)

Mechanical hill wet-seeded rice machine isbeneficial for establishing and growing uniform rows of seedlings. However, there is limited knowledge regarding the effects of the establishment of furrows on growth, lodging and yield, and their relationships with root traits. In this study, field experiments were conducted during 2012 and 2013 using two super rice varieties (hybrid rice Peizataifeng and inbred rice Yuxiangyouzhan) under three furrow establishment treatments (T1, both water and seed furrows were established by the machine; T2, only seed furrows were established by the machine; and T3, neither water nor seed furrows were established by the machine). Lodging index, lodging-related traits, grain yield, above-ground dry weight and root traits were measured. The results showed that the lodging index was significantly affected by the treatments with furrows (T1 and T2). The strongest lodging resistance was detected in the mechanical hill wet-seeded rice with furrow treatment (T1) in both 2012 and 2013. Lodging resistance was strongly related to the breaking resistance. No significant difference was found in grain yield or dry weight of the mechanical hill wet-seeded rice. Therefore, the mechanical hill wet-seeded rice with furrow treatment increased rice lodging resistance, which was related to root traits.

seed furrow; grain yield; lodging resistance; root trait; mechanical wet-seeded rice

Rice is an important food crop for over half of the global population. Rice planting methods differ in their production costs, gross returns and benefit-cost ratios (He et al, 2008; Huo et al, 2012; Wang et al, 2015). Among the two principle rice planting methods, direct- seeding shows higher efficiency than transplanting (Zhang et al, 2017; Chen et al, 2020). However, the direct-seeding method is difficult to implement because it is susceptible to adverse environments. A machine for planting wet-seeded rice was developed by Luo et al (2008) and is widely used in China and many other Asian countries, including Thailand, Laos and Vietnam. This machine establishes water and seed furrows as shown in Fig. 1 and the pre-germinated rice seeds are uniformly sown in the correct positions in the seed furrows by the mechanical hill wet-seeded rice machine (Pan et al, 2017; Zhang et al, 2017). The root lodging is significantly improved using this machine comparedto manual direct-seeding methods (Zhang et al, 2017). However, whether the use of the mechanical hill wet-seeded rice machine in paddy fields affects rice plant growth requires further investigation.

Lodging can lead to a reduction in grain yield, quality and trade price of rice (Lang et al, 2012; Salassi et al, 2013). Generally, root lodging and stem lodging have been known as the two main lodging types of rice plants. Among the two lodging types, stem lodging is the main lodging type that commonly accompanies reductions in grain yield and quality (Duan et al, 2004; Zhang et al, 2014; Wang et al, 2020).Genetic characteristics, crop management practices (i.e. planting methods, plant growth regulators, irrigationand fertilization) and environmental conditions (e.g. soil temperature, CO2and O3levels and ultraviolet light) are strongly related to lodging resistance in rice (Kashiwagi et al, 2010; Na et al, 2011; Wang et al, 2011; Sinniah et al, 2012; Wu et al, 2012; Liang et al, 2013; Zhu et al, 2013; Matsushita et al, 2014; Zhang et al, 2014; He et al, 2015; Hu et al, 2015; Corbin et al, 2016a, b; Plaza-Wüthrich et al, 2016; Zhu et al, 2016). For planting methods, the direct-seeded rice method results in higher lodging than the transplanting method (Li et al, 2011; Xing et al, 2017). Additionally, the direct-seeded rice method using the machine developed by Luo et al (2008) increased the lodging resistance in rice (Shi et al, 2017). For wet-seeded rice, the water and seed furrows established by the machine might contribute to better lodging resistance of the rice. However, the mechanism behind this still remains unknown.

Fig. 1. Mechanical hill wet-seeded rice machine and a schematic of seed and water furrows in paddy field.

Previous studies have assessed the methods of evaluating crop plant lodging, with many aspects of the plant reported to be highly related to plant lodging (Torro et al, 2011; Shah et al, 2017). For example, Hu et al (2015) reported that lodging is related to the plant morphology indices (e.g., plant height and leaf morphology). Additionally, studies have indicated that lodging is strongly associated with stem morphological characteristics (i.e. matter accumulation and internode length) (Kashiwagi et al, 2006; Ishimaru et al, 2008; Liang et al, 2013; Jiang Y H et al, 2014; Zhu et al, 2016; Weng et al, 2017; Wu et al, 2017; Huang et al, 2018). Moreover, lodging is significantly affected by the cellulose, hemicellulose and lignin contents as well as the physiological attributes related to cellulose, hemicellulose and lignin synthesis (Jiang M J et al, 2014). Hormones, such as GA3, are strongly related to the rice plant lodging (Sinniah et al, 2012; Plaza- Wüthrich et al, 2016). However, Wang et al (2010) indicated that lodging resistance may be affected by water and seed furrows that are established by the hill direct-seeded machine but no data supports this. Therefore, the relationship between lodging and root traits of the mechanical hill wet-seeded rice is still unknown.

In this study, two field experiments were conducted using two super rice cultivars to investigate the lodging resistance and root growth of the mechanical hill wet-seeded rice under different furrow establishment treatments and to estimate the relationship between lodging resistance and root traits of the mechanical hill wet-seeded rice.

RESULTS

Lodging index and lodging resistant traits of rice

Both water and seed furrow (T1) treatment had the lowest lodging index in both 2012 and 2013. Only seed furrow (T2) and neither water nor seed furrow (T3) treatments significantly increased the lodging indexes as compared to T1 in 2012. T2 had the highest lodging index in 2013 (Table 1).The height of the gravitational center and breaking resistance were in a trend of T1 > T2 > T3 in Peizataifeng in 2013. T3 showed the highest height of gravitational center in Yuxiangyouzhan in 2013. The average lodging index of Peizataifeng was higher than that of Yuxiangyouzhan, and the lodging indexes for both Peizataifeng and Yuxiangyouzhan in 2012 were higher than those in 2013. The analysis of variance on the height of gravitational center and lodging index between years was significant. The rice cultivar significantly affected the breaking resistance and lodging index. The furrowing and ridging treatment obviously affected the lodging index. Year × variety and year × treatment significantly affected the height of the gravitational center and lodging index, respectively. Variety × treatmentsignificantly affected the height of the gravitational center breaking resistance and lodging index (Table 1).

Table 1. Lodging index and lodging resistance traits of rice.

T1, Both water and seed furrows were established by the machine; T2, Only seed furrow was established by the machine; T3, Neither water nor seed furrow was established by the machine.

Means in the same column followed by different lowercase letters for the same cultivar indicate significant differences at the 5% level by the LSD test. * and ** indicate significant differences at 5% and 1%, respectively; ns, nonsignificant.

Grain yield and above-ground dry weight of rice

Grain yield and above-ground dry weight differed significantly between variety and years (Table 2). T1 had significantly higher dry weight than T2 and T3 for Yuxiangyouzhan in 2012. T2 showed a significantly higher dry weight for Yuxiangyouzhan in 2013. T1 had no obvious effects on grain yield and above- ground dry weight in both 2012 and 2013. Year × variety and year × variety × treatment significantly affected the grain yield and above-ground dry weight, respectively (Table 2).

Root traits

Root dry weights at the tillering and booting stages were significantly different between years (Table 3). T1 significantly increased root dry weights in Peizataifeng and Yuxiangyouzhan at the booting stage and in Yuxiangyouzhan at maturity as compared to T2 and T3 in 2012. T1 significantly decreased root dry weight in Peizataifeng at the booting stage in 2013 as compared with T3. T1 significantly improved the root dry weight in Yuxiangyouzhan at the tillering stage in 2013 as compared to T2. The root dry weight of rice differed significantly between varieties. T1 had no obvious effects on the root dry weight. Year × varietysignificantly affected the root dry weight at the tillering and booting stages. Year × treatment significantly affected the root dry weight at the booting stage (Table 3).

The average rice root diameters were significantly affected in both varieties at the tillering and booting stages. The average root diameter was in trend of T1 > T2 > T3 for both varieties in 2012. T1 significantly increased the average root diameter in Yuxiangyouzhan at the heading stage in 2012 as compared to T2 and T3. T1 and T2 significantly decreased the average root diameter in Yuxiangyouzhan at the tillering stage in 2013. The average rice diameter at the tillering stage was significantly affected by year × variety. Year × treatment and variety × treatment significantly affected the average rice root diameter at the tillering and booting stages (Table 3).

The total root length per hill at the tillering, booting and maturity stages differed significantly between years (Table 4). T1 significantly increased total root length in Peizataifeng at the booting stage and in Yuxiangyouzhan at the maturity stage in 2012 as compared to T2 and T3. T2 significantly increased total root length in Peizataifeng at the tillering stage in 2013 as compared to T3. Total root length per hill differed significantly between the varieties at the tillering and heading stages. T1 and variety × treatment significantly affected the total root length per hill at the tillering stage (Table 5).

Table 2. Grain yield and above-ground dry weight of rice affected by different rice varieties and treatments in 2012 and 2013.

T1, Both water and seed furrows were established by the machine; T2, Only seed furrow was established by the machine; T3, Neither water nor seed furrow was established by the machine.

Means in the same column followed by different lowercase letters for the same variety indicate significant differences at the 5% level by the least significant difference test. * and ** indicate significant differences at 5% and 1%, respectively; ns, nonsignificant.

Table 3. Root dry weight and root diameter affected by different rice varieties and treatments at various growth stages in 2012 and 2013.

T1, Both water and seed furrows were established by the machine; T2, Only seed furrows were established by the machine; T3, Neither water nor seed furrows were established by the machine.

Means in the same column followed by different lowercase letters for the same variety indicate significant differences at the 5% level by the least significant difference test. * and ** indicate significant differences at 5% and 1%, respectively; ns, nonsignificant.

Correlation analysis

The lodging index was strongly and negatively associated with the breaking resistance (Fig. 2).

DISCUSSION

It is no doubt thatmechanical hill wet-seeded rice has better lodging resistance than manually wet-seeded rice, it may due to hill wet seeded as well as the water furrows and seed furrows that established by the mechanical hill wet-seeded rice machine (Luo et al, 2008; Zeng et al, 2012; Chen et al, 2014; Shi et al, 2017). In this study, we confirmed that the lodging index of the mechanical hill wet-seeded rice was significantly decreased under the furrow establishment treatments (T1 and T2) than the treatment without any furrows (T3) in both 2012 and 2013 (Table 1).

Plant height (Chandler, 1969), leaf morphology (Hu et al, 2015), and stem morphological characteristics (Kashiwagi et al, 2006; Jiang Y H et al, 2014) are strongly related to lodging, particularly in stem lodging. In this study, the breaking resistance was significantly affected by the variety and the furrow establishment treatments, and it was confirmed that the lodging resistance in the super rice was strongly related to the breaking resistance (Fig. 2), whereas the bending moment of the plant was not significantly closely related to the lodging (data not shown). The root-shoot communication is commonly recognized with the supplementation of adequate nutrients and the application of plant growth regulators (Osaki et al, 1997; Yang et al, 2004a; Li Y Z et al, 2019; Mo et al, 2019). In addition, management practices such as water and nutritional management are important for grain yield, plant growth and matter/element allocation (Mo et al, 2017, 2018, 2019). Nevertheless, the crop root system plays a critical role in regulating plant growth, especially the yield and quality formation (Hodge et al, 2009). The strong relationship between the root system and shoot performance has been shown by Ling et al (1989) and Zhang et al (2009). In this study, significant variety and furrow establishment treatment effects on root traits varied among stages. Peizataifeng showed unfavorable lodging resistance but better root growth attributes than Yuxiangyouzhan, indicating genotype differences (Tables 3 and 4). These results are in agreement with those of Wang et al (2010), who proposed that the improvement of lodging resistance in mechanical hill wet-seeded rice is related to rice root growth.There is a significant effect of the furrowing and ridging treatments on the average rice diameter and total root length at the tillering stage, which affected the lodging resistance and root development. However, it is not clear how the root traits affected the stem properties and reduced the lodging index under mechanical hill wet-seeding.

Table 4. Total root length per hill (1 × 103 cm) affected by different rice varieties and treatments at various growth stages in 2012 and 2013. (cm)

T1, Both water and seed furrows were established by the machine; T2, Only seed furrows were established by the machine; T3, Neither water nor seed furrows were established by the machine.

Means in the same column followed by different lowercase letters for the same variety indicate significant differences at the 5% level by the least significant difference test. * and ** indicate significant differences at 5% and 1%, respectively; ns, nonsignificant.

Fig. 2. Relationship between lodging index and breaking resistance of the two super rice varieties.

Many previous studies have reported the yield improvements of mechanical hill wet-seeded rice compared to manual wet-seeded and transplanted rice under different plant density, water management and fertilization conditions (Tang et al, 2009; Chen et al, 2014; Wang et al, 2014; Pan et al, 2017). In this study, we assessed the effect of the establishment of water and seed furrows on two super rice varieties.Generally, better root growth is attributed to better shoot growth and may result in higher matter accumulation. The root system is highly related to the stem and affects the stem matter allocation (Burylo et al, 2009, 2012). Therefore, supplementation of appropriate nutrients to the rhizosphere to build an ideal plant morphological performance is a feasible approach for avoiding crop lodging and increasing yield (Chen et al, 2011; Fallah, 2012; Li et al, 2013; Zhang et al, 2014; He et al, 2017).Zhang et al (2009) reported that the improvement in root and shoot growth contributes to higher grain yield and the grain yield is related to the enhancement of grain filling due to increased root activity. However, we observed that the root morphological traits were improved in precision mechanical hill wet-seeded rice under the establishment of the water and seed furrows treatments, but no significant difference was observed in the grain yield and dry weight (Table 2). Even with good root growth, the supply of nutrients was similar among treatments; therefore, a combination of fertilization dose and method would improve the grain yield and dry weight. No visible rice lodging was detected in either 2012 or 2013; therefore, no significant influence of the establishment of the water and seed furrow treatments on yield was investigated.

Root morphological and physiological traits are regarded as important attributes for better root and plant growth (Ramasamy et al, 1997; Samejima et al, 2004; Yang et al, 2004b). Higher root activity is necessary to yield high root and shoot biomass and to improve ion uptake (Ramasamy et al, 1997; Yang et al, 2004b). The establishment of water and seed furrows may be beneficial for crop root growth by affecting the rhizosphere soil (Sidiras et al, 2001). Additionally, thelodging index was significantly affected by the soil environmental change resulting from the establishment of the water and seed furrows. Therefore, the furrowing treatment affected the soil environment and then affected the traits measured in ways of furrows treatments-soil environment-root growth-plant growth. The difference in weather data during the rice-growing seasons between the experimental years was great and led to a significant difference in some of the experimental data. Future studies evaluating the root activity under mechanical hill wet-seeded rice are required. Moreover, it is necessary to investigate the application of appropriate water and fertilization management programs for the mechanical hill wet-seeded rice owing to the establishment of the water and seed furrows.

Table 5. Mean monthly air temperature, mean sunshine hours, precipitation and average humidity in 2012 and 2013.

The lodging index was significantly affected by the mechanical hill wet-seeded rice owing to the establishment of both water and seed furrows, with the lowest lodging index found in both 2012 and 2013. The lodging index was strongly associated with the breaking resistance. The establishment of both water and seed furrow treatment (T1) did not significantly affect the grain yield or the dry weight of the mechanical hill wet-seeded rice as there was no visible lodging detected during the study. Further studies to assess the lodging and yield performance of mechanical hill wet-seeded rice with the establishment of both water and seed furrows under various crop management and adverse environmental conditions are required.

METHODS

Experimental treatments and design

Field experiments were arranged in a split-plot design, with rice varieties as the main plot and the establishment treatments of the furrows as the subplot, and were conducted in the experimental field of South China Agricultural University in Guangzhou, China, during 2012 and 2013. This region has a sub-tropical and monsoonal climate type and the mean monthly air temperature, precipitation, mean daily radiation and average humidity during the rice-growing seasons are presented in Table 5. The experimental soil was sandy loam with medium soil fertility.

The three treatments were both water and seed furrows (T1), only seed furrow (T2), and neither water nor seed furrows (T3) (Fig. 3), which were conducted using a mechanical hill wet-seeded rice machine developed by South China Agricultural University. There were three replicates for each treatment and the plot size for each treatment was 300 m2.

Two locally popular varieties, Yuxiangyouzhan and Peizataifeng, were used. Yuxiangyouzhan is an inbred super rice variety developed by the Guangdong Academy of Agricultural Sciences with a growth period of 127 d and plant height of 105 cm. Peizataifeng is a hybrid super rice variety developed by South China Agricultural University with a growth period of 126 d and plant height of 108 cm. The pre-germinated seeds of Yuxiangyouzhan and Peizataifeng were hill-seeded using the mechanical hill wet-seeded rice machine at a density of 25 cm × 15 cm with 3–5 seeds per hill on July 29, 2012 and August 5, 2013. Field preparation and water management in both years were conducted according to Pan et al (2017). During the entire growth period, thecommercial compound fertilizer (N : P : K = 15 : 15 : 15) was manually applied at 600 and 150 kg/hm2at the three-leaf andpanicle initiation stages, respectively. The crop management practice was implemented based on local high-yielding cultivation methods. Weeds and insects were effectively controlled to avoid yield loss.

Measurements

Lodging index and lodging resistant traits

At the heading stage, 10 main culm were sampled to measure the lodging index and resistant traits according to Islam et al (2007).

Fig. 3.Water and seed furrows establishment treatments in the field.

A, Both water and seed furrows were established by the machine.

B, Only seed furrow was established by the machine.

C, Neither water furrow nor seed furrow was established by the machine.

The first (N1) and second (N2) internodes were numbered from the plant base. The culm height (length from the plant base to the panicle neck node), height of the gravitational center, length from the lower joint of N2to the top of the plant, and the fresh weight of the upper plant portion from the lower joint of N2to the top of the panicle with leaf and leaf sheath (W) were measured. Then, N1and N2were cut at their upper joints. The breaking resistance strength of the middle point of N2with the leaf sheath was measured using a three-point bend test machine (YYD-1A, Tuopu Yunnong Technology, China). The center of the internode, where the breaking resistance was measured, was aligned horizontally with the middle point between the two joints. Bending moment at N2was calculated using the following formula:

Bending moment = Length from the lower joint of N2to the top of the panicle (cm) ×(g);

Lodging index was calculated using the following formula:

Lodging index = Bending moment (g·cm) / Breaking resistance (g·cm) × 100.

Grain yield

At the maturity stage, the effective panicle number of each plot was calculated using 50 hills in each plot and the mean value was recorded as the effective panicle number of the plot. Mature rice plant samples in 1 m2were harvested to measure the total grain number, seed-setting rate and 1000-grain weight of each plot. Grain yield was harvested from 3 m2in each plot (the moisture of the grains was adjusted to approximately 140 mg/g).

Aboveground dry weight

At the maturity stage, four representative rice samples were harvested from each plot, and the roots, culm and leaves were separated. The plant samples were oven-dried at 105 ºC for 30 min and then at 80ºC to a constant weight. The dry samples were weighed to measure the above-ground dry weight (Li S Y et al, 2019).

Root morphological traits

Roots were sampled from each plot from a 30 cm × 30 cm × 30 cm (depth × width × length) of soil using a self-made iron box. The root sample was placed into a mesh bag and washed with tap water. The roots were completely cleaned and neatly placed in transparent rectangular trays. The root scanner EPSON V700 (Seiko Epson Corporation, Tokyo, Japan) and the software WinRHIZO Reg (Regent Instruments Inc., Quebec, Canada) were used to measure the root traits including total root length and average diameter. During scanning, the roots did not overlap. The cleaned roots were refrigerated to maintain freshness and the scanning process was completed within 5 d. After scanning, the dry matter test was performed.

Statistical analysis

The data were analyzed with the Statistix version 8 (Analytical Software, Florida, USA). The significant difference was identified with the least significant difference (LSD) test.

ACKNOWLEDGEMENTS

This study was funded by the Guangdong Basic and Applied Basic Research Foundation (Grant No. 2020B1515020034), the National Postdoctoral Program for Innovative Talents (Grant No. BX201700083), the Commonweal Project (Grant No. 201203059), the Key Research and Development Program of Guangdong (Grant No. 2019B020221003) and the National Key Research and Development Program of China (Grant No. 2018YFD0100800), as well as the China Agriculture Research System (Grant No. CARS-01-41).

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27 February 2020;

5 August 2020

Wang Zaiman (wangzaiman@scau.edu.cn)

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http://dx.doi.org/10.1016/j.rsci.2021.01.009

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