INTRODUCTION
Rice (Oryza sativa L., Poaceae) is an important food crop in tropical and subtropical Asia (Skorbiansky, Childs, & Hansen, 2018) and is considered as key global food security (Bandumula, 2017). Therefore, securing rice production is important to meet the demand for consumption. In Indonesia, the rice production areas distribute in a wide range of agro- ecologies including dry and wetlands cultivation systems refer to as padi gogo and padi sawah, respectively. The broad adaptability is due to the root and stem having an aerenchyma transport system to support growth in the hypoxic condition (Mulbah &
Adjetey, 2018). Predominant cultivation time in both systems is in the rainy season for nearly the whole growing period (Sridevi & Chellamuthu, 2015). Thus,
in the absence of irrigation facilities, the rice-growing period absolutely depends on the availability of rainfall.
Recently, securing food crop production including rice is a great challenge due to the escalation of the intensiy and frequency of extreme weather incidents as the impacts of global climate change (Dulbari et al., 2017; 2021; Niu, Feng, Ding,
& Li, 2016; Ray, Gerber, MacDonald, & West, 2015).
However, the effect of extreme weather on rice production that is predominantly grown in a moist field is still less studied (Dulbari et al., 2017). Many studies on the effect of extreme weather on crop production are formulated based on the scenario of hydrological scarcity models − upland crops and drought (Ewert et al., 2015; Gosling & Arnell, 2016; Watanabe & Kume, 2009). Since characteristics of the incident and impact of extreme weather could be the local case, time and ARTICLE INFO
Keywords:
Abiotic stress Climate change Extreme weather Oryza sativa Rice genotype Article History:
Received: January 21, 2020 Accepted: May 20, 2022
*) Corresponding author:
E-mail: edisang@gmail.com
ABSTRACT
To mitigate the impact of extreme weather incidents, rice cultivars Way Seputih (WS) and Way Apo Buru (WAB) were evaluated under simulation of continuous wind and rainfall treatments. The research was conducted from July to October 2017 at Leuwikopo Experimental Farm, Bogor, Indonesia. For 15 days at day time, flowering rice hills were treated with about 100 mm/h water shower (Experiment-1), and with 0, 10-15, 20-25 and 35-40 km/h wind velocity (Experiment-2). Results showed that wind and rainfall treatments reduced rice production; the effect depended on the genotypes and flowering stage. Rain treatment from panicle emergence to 50%-emerged increased the number of unfilled grains by 154.6-182.3% and 55.7-101.9% in WS and WAB cultivars, respectively. Rain treatment at 100%-emerged had no effect on WS, but it increased unfilled grain (163.5%) and decreased grain index (12.9%) in the WAB cultivar. Wind speed at 35-40 km/h promoted a high percentage of grain drop (25.7%) and unfilled grains (77.3%), and low grain index (20.8 g) in WS genotype. WAB was more tolerant of wind stress than the WS. The present experiment showed that genotype had different responses to wind and rain treatments implying different mitigation strategies should be applied through genotype selection.
ISSN: 0126-0537Accredited First Grade by Ministry of Research, Technology and Higher Education of The Republic of Indonesia, Decree No: 30/E/KPT/2018
Cite this as: Agusta, H., Santosa, E., Dulbari, Guntoro, D., and Zaman, S. (2022). Continuous heavy rainfall and wind velocity during flowering affect rice production. AGRIVITA Journal of Agricultural Science, 44(2), 290-302. http://doi.
org/10.17503/agrivita.v44i2.2539
Continuous Heavy Rainfall and Wind Velocity During Flowering Affect Rice Production
Herdhata Agusta1), Edi Santosa1*), Dulbari2), Dwi Guntoro1) and Sofyan Zaman1)
1) Department of Agronomy and Horticulture, Bogor Agricultural University (IPB University), Bogor, West Java, Indonesia
2) Department of Food Crop Production, State Polytechnic of Lampung, Bandar Lampung, Lampung, Indonesia
species-specific (Powell & Reinhard, 2016; Santosa, Dulbari, Agusta, Guntoro, & Zaman, 2016), it is less accurate to generalize scenarios that fit for all crops.
Extreme weather as represented by heavy rainfall and strong wind velocity have a negative impact on production of many food crop species including rice, therefore it could be classified as a kind of abiotic stress (Auffhammer, Ramanathan, & Vincent, 2012;
Calzadilla et al., 2013; Dulbari et al., 2017; Niu, Feng, Ding, & Li, 2016). In tropical countries like Indonesia, it is important to evaluate the response of rice to extreme weather incidents because the incidents are usually associated with the rice-growing season (Dulbari et al., 2017; 2021; Santosa, Dulbari, Agusta, Guntoro, & Zaman, 2016). Santosa, Dulbari, Agusta, Guntoro, & Zaman (2016) estimated that the annual economic loss of rice due to extreme weather is US$
270 million. The present experiment was conducted based on hypotheses that stages of rice growth and different genotypes might respond differently to the stress.
Heavy rainfall, strong wind, and their combination have an adverse effect on rice production, especially during the reproductive stage (Sridevi &
Chellamuthu, 2015). The incidents have detrimental effects on rice production through decreasing the availability of sunlight, extending growth duration, increasing sterile grain and reducing the effectiveness of fertilizer applications (Auffhammer, Ramanathan,
& Vincent, 2012; Sridevi & Chellamuthu, 2015).
Shock of strong wind incident causes direct crop lodging (Martinez-Vazquez, 2016); otherwise persist exposure promotes shredding leaves, shattering of grains, failure of pollination and reduce the number of panicles (Baker, Sterling, & Berry, 2014; Ishimaru, Hirabayashi, Kuwagata, Ogawa, & Kondo, 2012;
Lin-Meng, Chen-sue, Chang-Shue, Lin, & Lin, 1994;
Marchezan & da Silva Aude, 1993). Marchezan &
da Silva Aude (1993) stated that rice anthers and ovaries desiccate due to the prevalence of dry wind speed of 43-48 km/h. Although the response to wind stress depends on genotype, wind speed, growing stage, plant architecture and nutrient status (Martinez- Vazquez, 2016; Onoda & Anten, 2011; Santosa, Dulbari, Agusta, Guntoro, & Zaman, 2016; Sridevi &
Chellamuthu, 2015), the heading stage and 14-30 days after heading are the most vulnerable stages in rice to wind speed between 8-9 to 57-70 km/h (Sridevi
& Chellamuthu, 2015) and the its impact on rice varieties production is rarely studied.
The present study aimed to evaluate responses of yield component and production of two rice genotypes treated with continuous heavy rainfall and different wind speed as a simulation of extreme weather incidents. Elucidating the genotypic response under extreme stress is essential for further steps of selecting and breeding rice genotypes, and mitigation to climate change.
MATERIALS AND METHODS
Two simultaneous experiments were conducted in dry season July-October 2017 at Leuwikopo Experimental Farm (240 m above sea levels), Bogor Agricultural University, West Java, Indonesia. Seedlings of two rice cultivars, namely Way Seputih (WS) and Way Apo Buru (WAB) aged 20-days-after-sowing were planted in the pot containing 10 kg media. Pots were arranged at an equal distance of 30 × 30 cm and maintained in the open space. Each pot contained two seedlings. The description of WS and WAB genotypes is presented in Table 1.
Table 1. Characteristic of Way Seputih (WS) and Way Apo Buru (WAB) genotypes
Characteristics Genotype
WS WAB
Plant height (cm) 72.7±4.8 70.6±3.0
Average leaf length (cm) 39.3±12.1 36.7±13.6
Basal hill diameter (cm)z 16.2±1.8 13.2±1.8
Heading time (DAT) 60 60
Number productive tiller/hill 33.0±4.6 32.0±6.2
Number tiller/hill 34.7±7.1 37.7±5.4
Harvest time (DAT) 110 110
Grain drop rate* Low Low
Yield (t/ha)** 5-8 5-8
Lodging resistant* Resistant Medium
Brown leafhopper (Nilaparvata lugens) biotype 2&3*** Tolerant Tolerant Bacterial leaf blight (Xanthomonas oryzae pv. Oryzae) strain III & IV*** Tolerant Tolerant Remarks: z =Measured at 10 cm above soil level; DAT = day after transplanting; Mean±S.D.; * = adopted from http://
pangan.litbang.pertanian.go.id; ** = adopted from www.bbpadi.litbang.pertanian.go.id; *** = adopted from www.litbang.
pertanian.go.id
The Latosolic soil (sand:silt:clay, 13.1%:22.1%:64.8%, m/m) that had pH 5.7 and contained 0.27% total N, 38.02 ppm P, and 187.62 ppm available K was used as the planting media. In each pot, 100 g goat manure was added. The manure contained 2.21% total N, 0.09% P, and 0.32% K. To obtain final pH 5.8-6.0, 20 g lime (CaCO3) was applied.
Before planting, the media was water-saturated for 30 days and mixed once a week.
Nitrogen, phosphorus, and potassium fertilizers were applied at the level of 300 kg urea (46% N), 100 kg P2O5 and 100 kg K2O/ha, respectively. Two-third N, all P, and all K fertilizers were applied at planting time and the remaining N was applied at three weeks after planting. The water level was maintained 10 cm above the soil level. Pests and diseases were controlled using Deltamethrin and Mankozeb 2%.
Experiment 1. Heavy Rainfall Simulation
Rice hills at the different flowering stages were showered with 86-104 mm/h (average 100 mm/h) as rain simulation for 15 days from 07:00- 17:00 (10 h/day). The rain intensity on simulation is classified as heavy rain according to Mannan &
Karmakar (2008). The simulation was generated by using a mixture of fixed and rotation sprinklers to produce droplets about mist to 2.0 mm in diameter.
During the treatment, a plastic sheet was installed at two meters above the rice hills to protect from natural rainfall. Before treatment, individual tiller in a hill was tagged according to
its flowering emergence, i.e., panicle emergence (PE), 25% emerged (F1), 50% emerged (F2), and 100% emerged (F3). Flowering emergence was determined from the ratio of panicle length to its sheath. It was F1 and F2 levels when one-fourth and half of the panicle length emerged from the sheaths, respectively. Panicle with up to one spike emerged was defined as PE, and F3 for panicle with all spikelets had completely emerged. To estimate the effect of treatment on spikelet development, pollination, and grain filling, a hypothetical developmental stage were drawn (Fig. 1).
The control plot had day temperature 28-37°C and RH 45-68%, while the plot of rain treatment under plastic sheet had 23-28°C and 98-100%, respectively. In each treatment, five hills were used and 15 panicles were further evaluated in each hill.
All treatments were replicated three times. After rain treatment, the plastic sheet was removed and the plants were maintained until harvest.
Experiment 2. Strong Wind Simulation
Rice plant at the flowering level of F2 to F3 (64-67 days after transplanting) was selected and exposed to different wind speeds, i.e., control (without wind treatment), 10-15, 20-25 and 35-40 km/h. The dynamic wind flow was generated by using high-speed axial fans (diameter 90 cm), the wind velocity was measured using the anemometer.
The fan was operated horizontally against the plants from 07:00 to 17:00 for 15 days.
Remarks: PE = panicle emergence, F1 = 25% flowering, F2 = 50% flowering, F3 = 100% flowering
Fig. 1. Hypothetical composition of spikelet development, pollination and grain filling in each flowering stage
The treatment was conducted in the greenhouse (average temperature 30-35°C and RH 45-68%) using five pots per treatment and replicated three times. The water level was adjusted every morning; transpiration and evapotranspiration rates were measured using the Lysimeter method. After treatment, plants were transferred and maintained in the open field until harvest. New panicle production after treatment was excluded from the calculation.
The number of total grains per panicle, percentage of empty grains, and total weight were collected from wind and rain shower treatments.
Data were evaluated using ANOVA, and further evaluation was performed using the Fisher’s LSD test at a level of confidence of 95%.
RESULTS AND DISCUSSION Effect of Heavy Rainfall
Heavy rain treatment did not cause any detrimental effect on culm and leaf morphology of both WS and WAB cultivars, although the culm curved slightly during the treatment. After treatment, about 75% of plants showed browning spikelet and rachis like as early senescence. The cause of such browning was unknown, but it was likely as physical damage.
Rain treatment decreased the number of grains and filled grain, but increased the number of the sterile grain of both WS and WAB cultivars (Table 2). Regardless of the flowering levels, rain treatment reduced the number of grains per panicle by 24.6-43.2% in WS and by 14.5-25.5% in WAB relative to control. It is likely that the reduction of grains is related to the incident of grain drop. In this case, grain drop was suspected to be to browning.
In the absence of rain treatment, WS had 80.9% and WAB had 79.7% filled grain per panicle (Table 2). When the rain was applied at PE to F2, and F3 stages, the WS genotype had 34.7−39.8%
and 76.5%, and the WAB genotype had 43.5−52.5%
and 27.7% filled grain, respectively. Thus, the filled grain number was sensitive to rain at PE to the F2 stage for WS but the F3 stage for WAB.
Rain treatment affected the number of sterile grains depending on genotypes and flowering stages (Table 2). Fig. 2 shows rain treatment at PE to F2 stages increased the number of sterile grains at 65.3-88.2% on WS and 42.7-52.1% on WAB than 19.1% and 20.4% from their control, respectively.
Heavy rain applied at F3 resulted in 72.3% grain sterile in WAB, yet only 23.5% in WS that was insignificantly different to control (19.1%).
Remarks: Control = no treatment; Mean±SE
Fig. 2. Percentage of unfilled grains from rain treatment of Way Seputih (WS) and Way Apo Buru (WAB) at PE (panicle emergence), 25% flowering, 50% flowering, and 100% flowering
Table 2. Effect of rain treatment at different flowering level on average number of grain, filled and unfilled grain per panicle, total grain weight, filled grain weight per panicle, and grain index of Way Seputih (WS) and Way Apo Buru (WAB) cultivars Flowering levelWSWABWSWABWSWAB Number of grains per panicleNumber of filled grains per panicleNumber of unfilled grains per panicle Panicle emergence (PE) 91.0±15.4 b104.9±23.3 b25.8±14.1 c 50.2±28.4 b65.2±22.4 a54.7±39.5 b 25% flowering (F1) 68.5±14.9 b 99.6±18.3 b26.1±17.2 c 57.1±17.9 b60.5±16.5 a42.5±26.7 bc 50% flowering (F2) 90.1±19.9 b113.5±18.0 b31.3±17.6 c 59.7±27.5 b58.8±25.7 a53.9±28.1 b 100% flowering (F3) 85.0±19.3 b 98.8±15.9 b65.0±17.6 b 27.4±20.6 c20.0±5.6 b71.4±20.1 a Control (no treatment)120.7±19.7 a132.7±30.0 a97.7±18.8 a105.7±31.7 a23.1±9.2 b27.1±14.3 c Total grain weight per panicle (g)Filled grain weight per panicle (g)Grain index 1000 seeds (g) Panicle emergence (PE)0.993±0.32 a1.646±0.60 b0.638±0.38 a1.325±0.79 b24.5±4.1 ab25.6±3.8 b 25% flowering (F1)0.971±0.44 a1.669±0.37 b0.643±0.47 a1.454±0.47 b23.5±3.7 a25.4±1.8 b 50% flowering (F2)1.069±0.33 a1.941±0.68 b0.746±0.42 a1.592±0.78 b23.9±2.4 ab26.3±2.1 b 100% flowering (F3)1.874±0.45 b1.018±0.45 a1.737±0.44 b0.647±0.52 a26.9±1.3 c23.0±2.2 a Control (no treatment)2.657±0.53 c2.999±0.92 c2.522±0.54 c2.823±0.96 c 25.8±1.8 bc26.4±2.3 b Remarks: Mean± SD; n=15; Values in the same column followed by different letters is statistically different under Fisher’s LSD test (P ≤ 0.05)
Total grain and filled grains weight per panicle decreased under rain treatment; the effect was determined by the flowering level and genotype (Table 2). Rain treatment at PE to F2 produced the lowest grain weight per panicle on WS. On the WS, there was a tendency that reduction rate on grain weight become more markedly when rain was applied at the early flowering stage (PE) than the later stage (F3). A similar tendency was also found on WAB; nevertheless, F3 stages on WAB produced the lowest weight than other stages. It indicated that the F3 was the most sensitive stage to rain treatment in the WAB.
Rain treatment also affected the grain index in both WS and WAB cultivars, depending on the flowering stage (Table 2). There was no significant effect on the grain index of both cultivars when the rain was applied at PE, F1, and F2. On WAB, rain treatment did not affect grain index, except the treatment at the F3 stage that significantly had a lower grain index than control and other flowering stages. On WS, rain treatment on different flowering stages produced an inconsistent grain index. For example, F1 produced lower but F3 produced a higher grain index than control WS. By excluding rain treatment on F3 from WS, the rain irrespective of the flowering levels had a detrimental effect on the grain index. In such a case, the rain treatment disadvantaged the index of WS at PE to F2 stages;
conversely, it was beneficial at F3 (Table 2).
Rain treatment reduced grain production per hill in both cultivars, and the reduction level depended on the flowering stage (Fig. 3). On average, a hill yielded 87.7 g and 98.9 g grains in control of WS and
WAB, respectively. The rain treatment at PE to F2 levels reduced grain production by 59.82-63.46%
and at F3 by 29.49% than control WS. On the other hand, the WAB genotype yielded 35.29-44.33%
and 66.06% lower than control under rain treatment at PE to F2 and F3 levels, respectively. In short, under continuous rain simulation, yield decreased by 29.49−63.46% in WS and 35.29−66.06% in WAB genotypes; the reduction in each genotype depend on flowering level.
Effect of Wind Treatment
Wind treatments caused temporary bending, irrespective to the studied cultivars. The bending level varied from 5−30° angle degrees opposed to the source of wind, and depended on wind speed.
Close pot arrangement in this experiment might protect the hills from further bending. Wind flow caused leaves to flutter, however, no serious damage on the leaf blade was observed. Some upper leaves including flag leaf flutter more frequently than those from the lower parts. As a result, the tip of some leaves split and dried along 2-3 cm especially at the wind speed of 35-40 km/h.
Water transpiration increased during wind treatments, depending on rice genotype (Fig. 4). WS transpired 8.9 mm/day under control, and increased by 22.5% and 34.0% under the treatments of 20-25 km/h and 35-40 km/h, respectively. The increase of increasing transpiration as the effect of wind flow has also been reported by Ishimaru, Hirabayashi, Kuwagata, Ogawa, & Kondo (2012). In the present study, however, WAB had a constant transpiration rate of 9.4-10.5 mm/day, regardless wind speed.
Fig. 3. Grain weight per hill from different flowering levels after rain treatment on Way Seputih (WS) and Way Apo Buru (WAB)
The number of filled and total grains per panicle decreased by increasing wind speed on the WS, however, the treatments had no effect on the WAB (Table 3). Control WS plant had 77.7% filled grain and with the treatment of wind speed 35-40 km/h the filled grain was 77.5% lower than that of control. It means that genotype and wind strength determined the number of filled grains.
On the other hand, the number of sterile grains increased in both WS and WAB cultivars by increasing wind speed (Table 3; Fig. 5). Wind at the level of 35-40 km/h increased sterility up to 76.7%
from 22.3% in control WS, and 53.3% from 31.1%
in control WAB. From the sterility level, WAB was more tolerant to the wind in the present simulation than the WS genotype. The sterility of both genotypes was lower than the report by Ishimaru, Hirabayashi, Kuwagata, Ogawa, & Kondo (2012) in the Koshihikari variety that ranges from 28.4 to 86.9% as wind velocity increase from 4.0 to 12.2 km/h. It is likely that genotype determines sterility in response to wind stress.
During the wind treatment, panicles smashed
other panicles in a random direction, resulting in 1-3 grains dropped from the distal part of a panicle. The rate of grain drop depended on the genotype and wind speed. The average grain drop per hill during the treatment was 19 grains under 10-15 km/h and 31-35 grains under 20-40 km/h on WS. On the WAB, the drop rate was 7-9 grains, irrespective of wind speed. It is probably that WS is sensitive to drop, although officially it is classified as drop tolerant (Table 1). It was noted that in presence of wind velocity, grain dropped was marked at heading, pollination, and grain filling stages. However, we did not classify the grain drop according to grain developmental stages.
Depending on genotype, grain weight per panicle decreased by increasing wind speed (Table 3). Grain weight had a negative correlation with wind strength in WS. In WAB, however, grain weight was unaffected by wind strength; grain index was similar across different wind speeds, i.e., 24.1-25.5 g. On the other side, the grain index of the WS genotype was consistently 19.4% lower under windy air than that of control.
Remarks: Mean ± SE; kmph = km/h
Fig. 4. Average daily transpiration of Way Seputih (WS) and Way Apo Buru (WAB) cultivars exposed to different wind speed treatments
Table 3. Effect of wind speed treatments during flowering stage on average total grain number, filled and unfilled grain per panicle, total grain weight, filled grain weight per panicle, and grain index of Way Seputih (WS) and Way Apo Buru (WAB) cultivars Wind level (km/h)WSWABWSWABWSWAB Number of grains per panicleNumber of filled grain per panicleNumber of unfilled grain per panicle Control 134.5±31.0 a105.7±22.2 a104.5±32.9 a72.8±15.8 a30.0±13.3 c32.9±16.8 b 10-15 (Low)131.9±29.3 ab109.8±20.3 a 68.3±17.1 ab82.3±20.7 a63.7±22.9 b27.5±11.0 b 20-25 (Medium)109.1±17.0 ab116.1±18.2 a 62.7±26.8 bc72.6±25.0 a46.3±21.0 b43.5±14.3 ab 35-40 (High)100.7±15.6 b111.3±14.9 a 23.5±19.1 c52.0±24.0 a77.3±16.0 a59.3±22.1 a Total grain weight per panicle (g)Filled grain weight per panicle (g)Grain index 1000 seeds (g) Control 2.91±0.87 c2.09±0.44 a2.72±0.91 c1.86±0.44 a25.9±1.3 b25.5 ± 1.8 a 10-15 (Low)2.00±0.44 bc2.12±0.42 a1.74±0.46 bc1.97±0.46 a25.7±3.5 b24.1 ± 2.2 a 20-25 (Medium)1.87±0.61 b2.01±0.65 a1.64±0.69 b1.81±0.67 a25.8±1.5 b24.8 ± 1.3 a 35-40 (High)0.88±0.44 a1.62±0.58 a0.53±0.45 a1.33±0.64 a20.8±6.0 a25.4 ± 1.4 a Remarks: Mean± SD; n=15; km/h-kilometer per hour; Values in the same column followed by different letters is statistically different under Fisher’s LSD test (P ≤ 0.05)
Wind treatments reduced production per hill linearly in both genotypes, but yield reduction was more marked in the WS (Fig. 6). Control WS produced 96.12 g per hill. While at wind velocity of 10-15 km/h, 20-25 km/h and 35-40 km/h, the cultivar produced 66.04 g, 61.58 g, and 29.11 g per hill, respectively.
Production decreased 23.32-28.50% in WS at 10- 25 km/h, and 66.20% at 35-40 km/h treatment than control. In WAB genotype, control plants produced
66.73 g per hill, while plants treated with 10-15 km/h, 20-25 km/h and 35-40 km/h produced 67.82 g, 64.26 g, and 51.37 g per hill, respectively. In WAB, the production decreased 29.89-33.57% and 46.89% under 10-25 and 35-40 km/h treatments than the control, respectively. In short, continuous wind velocity decreased yield by 23.32−66.20% in WS and 29.89−46.89% in WAB, depending on the speed.
Remarks: Mean±SE; kmph = km/h
Fig. 5. Percentage of unfilled grain among wind speed treatments of Way Seputih (WS) and Way Apo Buru (WAB)
Remarks: kmph = km/h
Fig. 6. Grain weight per hill from different wind speed treatments of Way Seputih (WS) and Way Apo Buru (WAB)
Sensitivity of Yield Components
Wind and heavy rainfall stresses stimulated grain drop, sterility and decreased grain index.
The wind directly promoted grain drop in the WS, resulting in the low number of grains per panicle in strong wind. Here, WS is prone to grain drop although it is classified as drop tolerant variety (Table 1). Sensitivity to grain drop is likely related to panicle length and existing grain weight. WS had a panicle 3-4 cm longer and grain weight 39.7% higher than the WAB (Table 2). It seems that the heavier and longer panicles are more sensitive to wind stress. During the treatment, longer and heavier panicles moved more forcefully by increasing wind speed resulted in distal grains being prone to drop.
Thus, panicle length and panicle weight should be considered as important traits in wind tolerant variety development. On the other hand, grain drop in rain simulation was likely indirect. Rain droplets obviously gave an additional load to panicle. It led panicle to bend more markedly and cause some rachis to break in WS. Furthermore, some tinted spot was also found around the breaking point, which presumably promoted grain drop. It is probably that excess humidity for 15 days of treatment promoted panicle or rachis senesced earlier. The low grain drop in the WAB seemed to be connected with a short-sized panicle. However, it needs further study to verify the precise factors causing grain drop after the rain treatment.
Sterility was noticeable under the simulation of both heavy rain and wind treatments. To some extends, the sterility was more marked in rice plants under wind than those under rain simulation, thus, the sterility mechanism might different in both stresses. Continuous rain at the early panicle growing stage increased sterility more markedly in WS; conversely, at the later growth stage, it caused high sterility in the WAB. For example, sterile grain increased 274.9-361.8% in WS and 109.7-155.6%
in WAB after rain treatment at PE to F2 stages from control; while 23.1% in WS and 254.3% at the F3 stage. Furthermore, the sterility in WS increased by increasing wind speed. It increased 110.5% under 10-15 km/h and 233.6% under 35-40 km/h relative to control. In WAB, sterility started to increase under 20-25 km/h, and at wind speed of 35-40 km/h the sterility increased by 73.0% relative to control.
It is concluded that the WS is more sensitive to wind. High sterility in WS is presumably related to marked transpiration rate under windy conditions
(Fig. 4), leading to water stress; this is supported by a study by Onoda & Anten (2011). Other studies show pollination failure and damage of reproductive organs under wind stress (Baker, Sterling, & Berry, 2014; Ishimaru, Hirabayashi, Kuwagata, Ogawa,
& Kondo, 2012; Marchezan & da Silva Aude, 1993; Sridevi & Chellamuthu, 2015), however, these variables were not evaluated in the present experiment.
Grain index was varied among the studied rice genotypes (Table 2 and Table 3). Wind at speed of 35-40 km/h promoted low grain index in WS (Table 3); indicated a disturbance on grain filling mechanism. This fact might be related to rachis and panicle health as the main transporter of assimilates to grains. Some rachises and panicles fractured under 35-40 km/h which might block assimilation;
however, the healthiness of panicles and rachis was not further evaluated. Damage leaves that marked under strong wind might reduce source capacity. In addition, plants under wind treatment might require extra energy to compensate for the increase in transpiration and to maintain sturdiness, leading to lower partition to grains. According to Wada et al. (2014), wind at 25 km/h during grain-filling followed by hot air (34°C) and dry condition (>2.5 kPa vapor deficit) increase the incidence of ring- shaped endosperm chalkiness. On the other side, disturbance on grain filling under rain especially in the F3 stage of WAB presumably due to decreasing source capacity because panicle damage was less severe in the rain than in the wind treatments.
Water shower seemed to modify micro-climate around the rice hills, e.g., the sunshine intensity was approximately 4-5% lower during the treatment than control, the air had 98-100% relative humidity, and temperature decreased by 3-10°C lower than the ambient. These changing micro-climate conditions might affect photosynthetic and respiration rates in the rice. However, the photosynthetic rate was not measured in the present study.
Genotype Sensitivity to Heavy Rain and Strong WindBy using a simple model to evaluate rice production under heavy rainfall stress as shown in Fig. 1, WS and WAB had different sensitivity on each developmental stage. Heavy rain during predominant spikelet development (PE), and pollination (F1, F2) and grain filling stage (F3) caused high sterility in WAB. The rain treatment stimulated a very high grain sterility level when
applied at PE to F2, but no effect at F3 in the WS.
Less grain weight per panicle were observed on both genotypes under heavy rainfall. The treatment during F3 stage, decreased average grain weight per panicle by 29.47% in WS but 66.06% in WAB. In this model, morphological characters and physiological processes are speculated to contribute to the sensitivity of the yield component.
The different sensitivity of both genotypes to rain treatments might associate with their ancestor. WS derived from crossing Cisadane 4/IR36 that suitable for high altitude up to 500 m for the rainy season, while WAB was derived from IR18349/IR19661//
IR19661///IR64////IR64 for dry and rainy seasons (www.litbang.pertanian.go.id).
Yield components exhibited different sensitivity to wind speed in both genotypes. WS had critical wind speed for sterility at 10-15 km/h, 20-25 km/h for grain weight per panicle, and 35-40 km/h for the number of grain per panicle and grain index. This is in line with finding of Viswambaran, Rajaram, Alexander, Chinnamma, & Nair (1989) wind velocity at a speed of 14.4 km/h inhibits rice fertilization. Matsui et al. (2021) stated that low wind speed reduces grain sterility due to increased pollination and cooling. WAB had critical speed on grain sterility, i.e., 35-40 km/h, and wind levels had no effect on other components. The mechanism of wind stress on yield reduction seemed to involve morphological and physiological characters because each plant’s parts and growing stage may have specific contributions. According to Matsui, Kobayasi, Yoshimoto, Hasegawa, & Tian (2020), strong wind causes the ideal position of the panicle for pollination to decrease. Previously, Win et al.
(2020a; 2020b) noted that pollination success in rice decreased by increasing panicle inclination.
Longer leaf in WS genotype might facilitate faster water loss; it presumably that shorter leaf will have a better adaptation to wind speed as in WAB. Onoda & Anten (2011) noted the involvement of signal sensing and transduction, plant size and architecture in responses to wind stress. WAB genotype likely got benefit from wind 10-15 km/h as indicated by lower sterility than control. It needs further study on how wind velocity favors WAB growth.
Implication on Mitigation Strategy
In natural conditions, continuous strong wind and heavy rainfall for 15 days as in the present study might be a rare case. Nevertheless, the
findings are important for production mitigation through breeding and farmer approaches. For breeding strategy, the different sensitivity on yield and yield components of WS and WAB cultivars in these simulations implies that genetic traits should be considered to anticipate the worse scenario of extreme weather in the future. The mitigation should also consider complex aspects of farmer preference to genotype, field landscapes, local technologies, and farmers’ willingness in response to the extreme incident. Ordinary farmers in Indonesia prefer to adopt rice genotype that easily-threshed manually during post-harvest handling; although such rice genotype is a disadvantage under strong wind as in the present study.
At the field level, farmers have already applied the traditional planting calendar and established wind-break trees as important components of climate change mitigation (Santosa, Dulbari, Agusta, Guntoro, & Zaman, 2016). Although planting trees such as turi (Sesbania grandiflora) along the gully of the rice field as windbreaker is common in West Nusa Tenggara Island (Santosa, Dulbari, Agusta, Guntoro, & Zaman, 2016), however, excessive tree density might shade the rice. Shading is known to have a detrimental effect on rice production (Chen, Li, Zeng, Deng, & Ren, 2019). Managing crop cultivation to avoid flowering coincides with heavy rain and strong wind incidents could be the best fit as an adaptation strategy, as this strategy has worked in other crops (Powell & Reinhard, 2016).
Therefore, it is important to integrate both genetic engineering and environmental approaches in the field in order to develop sustainable adaptation to extreme weather in rice production.
CONCLUSION
Continuous strong wind and heavy rain caused a detrimental effect on rice yield and its yield components. Way Seputih exhibited more sensitivity than Way Apo Buru to wind and rain stress as indicated by high grain drop, high sterility and low grains index. Wind speed at 35-40 km/h had a marked increase in the percentage of unfilled grains by 52.3-75.4%. It is suggested that for evaluation and breeding programs, panicle strength and its size, grains weight per panicle, and leaf size are important characters to study the effect of wind and rain impacts on rice. In a practical farmer field, selecting proper rice genotypes is advised to adapt to extreme weather incidents.
ACKNOWLEDGEMENT
Thanks to Ministry of Research Technology and Higher Education, the Republic of Indonesia for financial support under the scheme Competitive Research Grant (HIKOM) for FY 2016-2018.
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