Acccepted:2016.4.7
Corresponding author: Yasuhiro, Izumi ([email protected])
Evaluation of the Resistance to "Multiple Environmental Stress" of Oryza sativa, O. glaberrima
and their Interspecifi c Progenies. - Effect of Drought and Re-watering on the Growth and
Physiological Parameters of Rice Cultivars.
-Yasuhiro Izumi
1）, Yuki Okazaki
1）, Koji Yamane
2）and Morio Iijima
2）， 3）1）School of Environmental Science, The University of Shiga Prefecture
（2500 Hassaka, Hikone, Shiga 522-8533, Japan）
2）Graduate school of Agricultural Science, Kinki University
（3327-204 Nakamachi, Nara 631-8505, Japan）,
3）JST/JICA, SATREPS
Summary: We conducted fi eld experiments to select rice cultivars that are resistant to "multiple environmental
stress", i.e., drought, flood and salinity for two years. We used Oryza sativa, O. glaberrima and NERICA cultivars that showed both fl ood and salinity tolerance, and compared drought resistance and recovery among these cultivars. Drought treatment was imposed by rain shelter, and after the treatment plants were rewatered to evaluate recovery for 10 days. During drought and recovery period, shoot dry weight, photosynthesis and transpiration were measured. Further, root research and growth analysis was conducted in the fi rst and second year, respectively. Among the cultivars with drought resistance selected with relative shoot weight of drought treatment to control, O. glaberrima cultivars have a property as deep water rice, hence they may be candidate cultivars for regions prone to both drought and fl ood. In comparison of the recovery, only O. glaberrima showed negative correlation between the physiological parameters in drought period and those in recovery period. Moreover, two O. glaberrima cultivars showed greater relative growth ratio during recovery period in drought treatment than in control, suggesting that their high ability in the recovery is one of the important strategies for drought resistance.
Key words: Drought resistance, NERICA, Oryza glaberrima, Recovery, Rice
Introduction
In sub-Sahara area (SSA) demand for rice as a staple food crop is drastically increasing in parallel with the population increase, however, the yield of rice in this area is quite low, such as 2.8 t ha -1 (FAOSTAT 2015), as compared to that in Southeast
Asia (4.2 t ha -1) or South Asia (3.8 t ha -1). One of the reasons of
this low yield in SSA is that most of rice cultivation is practiced under rainfed condition (Balasubramanian et al. 2007). With neither irrigation nor drainage system, rainfed rice is prone to the water stresses such as drought and fl ood. Moreover, possibly because of the climate change, rice cultivation in recent years tends to be endangered by both drought and flood in a same region as north-central part of Namibia where the authors are conducting some research and dissemination activities on rice. Further, in such semi-arid regions salinity stress must be also considered for rice cultivation. Therefore, rice cultivars to be introduced into such regions are required to have tolerance to all the three environmental stresses.
In the previous study (Okazaki et al. 2014) we compared the tolerance to drought, fl ooding and salinity stress among dozens of rice cultivars with different genetic background, origin and ecotype, and different morphological and physiological traits, and selected some "candidate" cultivars on a basis of shoot dry weight (SDW) ratio to each stress condition. However, all the evaluation was conducted in a pot experiment where root system development is restricted. In such condition, drought treatment by limiting irrigation tends to be severer as compared to that in fi eld conditions (Kamoshita 2011), and some cultivars that show drought resistance by deep rooting cannot sufficiently demonstrate its ability.
Therefore, in this study we conducted field experiments for two years. Rice cultivars that showed relatively high fl ood and salinity tolerance in the previous study (Okazaki et al. 2014) were used. Drought stress was imposed during vegetative growth period and both morphological and physiological responses were compared among tested cultivars. Recovery from drought stress was also evaluated 10 days after re-watering. The aim of this study is to newly select "candidate" cultivars for SSA under fi eld condition, and to examine whether mechanisms to show drought
論 文
resistance are different among three genotypic groups of Oryza species.
Materials and methods
The experiments were conducted at the upland field of the University of Shiga Prefecture, Hikone, Japan (35°15'N, 136°13'E) in the year 2013 and 2014. Total rainfall and average daily temperature during the experiments are 479.5 mm and 21.1°C in 2013, and 646.0 mm and 25.3°C in 2014. Property of the soil in the fi eld was light clay. The pH, total N, Total C, CEC of the soil was 7.02, 1.75 g kg -1, 20.09 and 15.15 cmol kg -1, respectively
(Zegada- Lizarazu et al. 2006). For both years rotary tillage was conducted twice before cultivation. As a basal dressing, chemically synthesized fertilizer was applied with a ratio of 4: 4: 4 g m -2 for N: P
2O5: K2O, respectively before the tillage practice,
and no top dressing was done. If necessary, weeding was conducted manually as farmers conventionally do in Namibia.
In 2013, total 32 rice cultivars, which showed relatively high shoot biomass ratio under flood and salinity stress treatment (Okazaki et al. 2014) were used (Table 1). These consist of 13 cultivars of Asian rice (Oryza sativa L.), 10 cultivars of African rice (Oryza glaberrima Steud.) and 9 cultivars of their interspecific progenies, NERICA (New Rice for Africa). They
are also different in origin (African countries or India) and ecotype (lowland, upland, rainfed, deepwater).
The field (230.4 m2) was divided into 8 plots, and drought
treatment and control were set up with 4 replications. Within a plot tested cultivars were randomly arranged. On June 5 and 6, 2013, three rice seeds per planting hole were sown with 0.25 m in inter-row spacing and 0.1 m in inner-row spacing (40 hills m-2). From 21 days after sowing (DAS) thinning was started to
keep 1 plant per hill. Until 49 DAS all the plants were well irrigated. On July 25 (50 DAS) the field was covered with a plastic rain shelter to avoid rainfalls, and no irrigation was done for drought treatment during 30 days, whereas irrigation was properly conducted for control plots. On August 25 (81 DAS) plants in the drought treatment were re-watered to evaluate the recovery from drought stress.
At 63 DAS (drought period) and 84 DAS (recovery period) photosynthesis and transpiration rates of the uppermost fully expanded leaf were measured by the portable photosynthetic analyzer (LI-6400, LI-COR Biosciences) during morning hours. At 92 DAS plants were harvested. Shoots were dried in electric oven with 80°C for 72 hours, and then their dry weight were measured. Stainless tube (Liner Sampler, DIK-110B, Daiki Rika Kogyo Co., Ltd.) with 0.3 m long and 0.05 m diameter was used for soil sampling. Sampled soil blocks of 0-0.05 m (upper layer) and 0.2-0.3 m (lower layer) were carefully washed to collect rice roots. Roots were oven-dried and weighed to calculate root weight density (RWD).
In 2014, 8 rice cultivars shown in Table 1 with asterisk, i.e., three O. sativa, three O. glaberrima and two NERICAs, were selected from the result of previous year. In this year seeds were sown in plastic cell trays and then transplanted into the fi eld to reduce variation in individual plant growth. Procedures of the experiment, such as size of each plot, number of replications and method of drought treatment, etc, basically followed the experiment in 2013 except for following: On June 17, seedlings were transplanted with 0.30 m in inter-row spacing and 0.15 m in inner-row spacing (22.2 hills m-2). At around 14 days after
transplanting (DAT) thinning was done. From July 16 (35 DAT) to August 29 (79 DAT) drought treatment was conducted. After the re-watering, plants were grown for 10 days to evaluate the recovery from drought. The SDW at 79 DAT (just before the re-watering) and 89 DAT was used for the calculation of relative growth ratio (RGR).
Results
Experiment of the fi rst year (2013)Effect of drought treatment on the shoot growth of rice was shown with relative values of SDW in drought treatment to those in control (Fig. 1). All the cultivars showed relative value less Table 1. List of the tested cultivars used in the fi rst
than 1, indicating shoot growth was reduced by water deficit condition. However, among 32 cultivars the SDW ratio of two O. sativa cultivars, Chinois (2), CK 90 (5), three O. glaberrima cultivars, Dembou Bourawana Blanc (15), Guayaba (18) and Mala Noir IV (20), and two NERICA cultivars, NERICA 4 (27) and NERICA 8 (31) were relatively high. A wide range of the SDW ratio was observed regardless of the groups, i.e. 0.48-0.83 in O. sativa, 0.41-0.90 in O. glaberrima, and 0.45-0.84 in NERICAs, but among three groups the difference was not clear, although the average was slightly higher in O. glaberrima than the other groups.
The relative root weight density (RWD) of drought treatment to control is plotted against SDW for both upper (0-0.05 m) and lower (0.20-0.30 m) soil layer in Fig. 2. The RWD ratio in upper layer was below 1 in most of the cultivars, whereas that in lower layer was more than 1 in nearly half of the tested cultivars. Comparing among three groups, relative RWD averaged within a group in NERICAs (0.70) and O. glaberrima (0.69) was higher than that in O. sativa (0.53) in upper layer. On the other hand, in lower layer O. glaberrima (1.42) showed the highest ratio followed by NERICAs (1.14) and O. sativa (0.78). Namely, root growth in O. sativa was restricted by drought stress regardless of soil depth. Relative RWD of upper soil layer had a positive correlation with relative SDW (r2=0.367, P<0.01). This linear
correlation was also signifi cant in O. sativa (r2=0.382, P<0.05)
and NERICAs (r2=0.530, P<0.05) but not for O. glaberrima
(r2=0.337, P>0.05). However, such correlation was not
signifi cant for either all the cultivars or three individual groups in lower layer.
Both the relative values of photosynthesis and transpiration rates during recovery period (84 DAS) are plotted against that of photosynthesis rate during drought period (63 DAS) in Fig. 3.
Fig. 1. Eff ect of drought on the shoot growth of O. sativa (white), O. glaberrima (black) and interspecifi c (grey) cultivars in the fi rst year experiment (2013). Cultivar names are shown in Table 1. Each bar indicates relative value of drought treatment to control in shoot dry weight at 92 days after sowing. Cultivars with bold letters are mentioned in
the text. Fig. 2. Relation between relative values of drought
treatment to control in shoot dry weight and that in root weight density through upper (0-0.05 m) and lower (0.2-0.3 m) soil layer in the first year experiment (2013). ** and * indicates significant correlation at P<0.01 and P<0.05, respectively, and ns indicates not signifi cant.
Fig. 3. Relation between relative values of drought treatment to control in photosynthesis rate during drought stress (63 DAS) and that in photosynthesis (a) and transpiration rate (b) during recovering period (84 DAS) in the fi rst year experiment (2013). * and ns indicates significant correlation at P<0.05 and not signifi cant, respectively.
When all 32 cultivars are involved, no significant correlation was found in physiological parameters in drought and recovery period. Among three groups, however, only in O. glaberrima, both the relative photosynthesis rate (upper) and transpiration rate (lower) during recovery period had significant negative correlation with the relative photosynthesis rate in drought period.
Experiment of the second year (2014)
The SDW of tested 8 cultivars is summarized in Table 2. Although both the main effects of drought and cultivars were signifi cant (P<0.01) on the SDW at the end of drought treatment (79 DAT) and 10 days after the re-watering (89 DAT), no signifi cant interaction between the factors was found. Among 8 cultivars CK90 showed the lowest ratio (0.52) in the SDW of drought treatment to control whereas this ratio was relatively high in Mala Noir IV (0.80) and NERICA8 (0.82) at 79 DAT. These two cultivars also showed high ratio as 0.87 in the former
and 0.83 in the latter after 10 days of recovery followed by Soutane Blanc (0.76) and Dembou Bourawana Blanc (0.76).
The RGR during 10 days, i.e., just before and 10 days after the re-watering are illustrated in Fig. 4. A large cultivar difference was found, and CG14, NERICA4 and NERICA8 showed relatively small RGR as compared to the other cultivars. In comparison between the treatments, Chinois and CK90 showed smaller RGR whereas Mala Noir IV, Dembou Bourawana Blanc and NERICA4 showed larger RGR in the drought treatment than in the control. As in the year 2013, measurement of the physiological parameters such as photosynthesis rate and transpiration rate was attempted for several times, but no clear trend among the cultivars or groups was found (data not shown).
Discussion
In this study we evaluated the drought resistance of three different rice species in terms of shoot biomass production before heading stage were evaluated. As Pantuwan et al. (2004) pointed out, selection for drought resistance of rice cultivars with different photosensitivity should be conducted during vegetative growth period. Moreover, we consider that the biomass production before heading will be a good indicator for survival against severe environmental stresses, even though this study was conducted in Japan where climate and soil condition may be quite different from those in Africa. Although no signifi cant cultivars x treatment interaction was found (Table 2) indicating no cultivar with greater drought resistance than the other cultivars, two O. glaberrima cultivars as Dembou Bourawana Blanc and Mala Noir IV, and NERICA 8 showed relatively high biomass production under drought condition in two successive years (Fig. 1 and Table 2).
It was reported that O. glaberrima cultivars were resistant against both biotic and abiotic stress including drought (Furuya et al. 1994, Jones et al. 1997, Maji et al. 2010). However, in our fi eld experiments O. glaberrima cultivars did not show greater drought resistance than O. sativa and NERICAs. This is probably because many of the O. glaberrima cultivars used in this study had the characteristic of deepwater rice (Okazaki et al. 2014). Nevertheless, it is notable that some of deepwater cultivars showed comparable drought resistance as did the upland cultivars in vegetative growth stage. Deepwater rice that is usually directly seeded is known to have drought resistance in seedling establishment and early development (IRRI 1982). In this study three deepwater cultivars, i.e., Dembou Bourawana Blanc , Mala Noir IV and Guayaba showed this property during vegetative growth stage. Therefore, these deepwater rice with drought resistance may be adaptable in semi-arid regions where risk of flooding also exists, especially small seasonal wetland Fig. 4. Relative growth rate (RGR) of 8 rice cultivars
between 79 DAT (just before re-watering) and 89 DAT (10 days after re-watering) in the second year experiment (2014). The RGR was calculated with the shoot dry weight of 12 plants in each cultivar and treatment.
Control Drought
Table 2. Eff ect of drought and rewatering to shoot dry weight (g plant-1) of 8 rice cultivars (2014).
whose water level largely fluctuates during short period (Mizuochi et al. 2014).
Among three O. glaberrima cultivars, Guayaba showed both fl ood and salinity tolerance in the previous study (Okazaki et al. 2014) and also showed drought resistance all of which were results from pot experiments. Therefore this might be a "candidate" as a resistant cultivar against multiple environmental stresses. However, in the fi rst year experiment we failed to get enough seeds probably because of the difference in day length. This is why we did not use this cultivar in the second year experiment but did CG14 as a standard variety instead. Further, our co-workers in Namibia never acquired any successful result in field trials using this cultivar so far partly because of its difficulty in cultivation (unpublished data). Hence we had to exclude this cultivar from the selection. On the other hand, Mala Noir IV, which is also African deepwater rice and showed high salinity tolerance in the previous study (Okazaki et al. 2014), performed well in shoot growth under dry fi eld condition for two years. Because of its short growth duration, i.e., nearly 85 days from transplanting to harvesting in Namibia (personal communication), this seems to be one of the hopeful cultivars to introduce into regions with short rainy season.
Root system development is known to be an important property for drought resistance (Russell 1977). Therefore, we conducted root research in 2013 and found that the root growth in upper soil layer was suppressed by drought in most of the cultivars, whereas it was promoted in lower soil layer in nearly half of the tested cultivars (Fig. 2). Nevertheless, no signifi cant correlation was found between relative SDW and deep rooting ability that reportedly relates to drought avoidance (Uga et al. 2013). The reason is not clear, but we assume that RWD used in this study with its ease in measurement might not be suitable to evaluate drought resistance because it does not reflect the development of lateral roots that occupy a major part of length and surface area of a root system and contribute to water absorption (Yamauchi et al. 1987). Hence amount and distribution of roots concerning deep rooting ability should be estimated by root length density.
Recovery from drought stress should be a crucial property for rainfed rice cultivars due to the high possibility of drought occurrence by the erratic rainfall. In comparison of the recovery in terms of physiological parameters in 2013 and RGR in 2014 just before and 10 days after re-watering, substantial differences among the cultivars and groups were observed. Namely, O. glaberrima cultivars that were restricted photosynthesis by drought treatment tended to show higher relative photosynthesis and transpiration rate after re-watering (Fig. 3). The reason was not clear and we did not monitor the growth during dry period, nevertheless, some O. glaberrima cultivars that endured drought seemed to own high ability in the recovery, and this may be
reflected in the greater RGR after re-watering in drought treatment than control in two O. glaberrima cultivars, Dembou Bourawana Blanc and Mala Noir IV (Fig. 4). We previously reported that O. glaberrima showed more xylem sap exudation during recovery period than O. sativa and NERICAs in the pot experiment (Okazaki et al. 2014). Better recovery from drought in O. glaberrima was also reported by Audebert (2006). We certified this ability by using physiological parameters and biomass production in the fi eld, and elucidated that the recovery is one of the important strategies for drought resistance in O. glaberrima.
In summary, we attempted to select suitable rice cultivars for semi-arid regions that are resistant to drought stress as well as flood and salinity stress. Because areas prone to suffer both drought and flood will increase due to climate change, the cultivars selected by this study may contribute to rice cultivation in SSA. Furthermore, results of this study, especially responses of physiological traits and biomass production during recovery from drought stress will be useful as basic information on the drought resistance of different rice cultivars and genotypic groups.
Acknowledgements
We are grateful to three technicians of the experimental fi eld of USP, i.e., Mr. T. Shibahara, H. Inoue and H. Kadono for their fi eld preparation and management. We also thank the students of the crop science laboratory, Mr. R. Ueda, Miss A. Nakata, Miss K. Okada and Miss N. Seki for their cooperation in research.
References
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複合ストレスに対するアジアイネ，アフリカイネおよび種間交雑系統の抵抗
性評価：乾燥ストレスおよび再灌水がイネの生育と生理形質に及ぼす影響
泉 泰弘
1）・岡崎勇樹
1）・山根浩二
2）・飯嶋盛雄
2,3） 1） 滋賀県立大学環境科学部（〒 522-8533 滋賀県彦根市八坂町 2500） 2） 近畿大学農学部（〒 631-8505 奈良県奈良市中町 3327-204） 3）JST/JICA, SATREPS 要旨：著者らは，既報において干ばつ，洪水および塩分という 3 種の環境ストレスに抵抗性を有するイネ品種の選抜をポット試 験で実施した．本報告では，深根形質等に与える制限を排除するため圃場条件下での干ばつ抵抗性を評価した．栄養成長期の乾 燥処理と再潅水がアジアイネ，アフリカイネおよびネリカ品種の生育や生理形質に及ぼす影響について 2 ヶ年にわたり調査した． 乾燥処理は降雨遮断によって行い，終了後に再潅水し，10 日間の回復期間を設けた．乾燥処理後と回復期間中に光合成・蒸散速 度，地上部乾物重などを測定し，さらに 2013 年は根の調査，2014 年は成長解析を行った．乾燥による地上部乾物重の減少程度 を判断材料として選抜した品種群の中に深水特性を有するアフリカイネ品種が存在した．すなわち，これらの品種は，干ばつと 洪水という両極端の水環境が起こりうる地域での有望品種の可能性がある．再潅水後の回復について比較したところ，アフリカ イネのみが相対光合成速度や相対蒸散速度において乾燥処理期間と回復期間との間に有意な負の相関を示し，さらにアフリカイ ネ 2 品種のみ回復期間の RGR が対照区を上回っていた．これらの品種は干ばつへの抵抗戦略として高い回復能力を有すること を示唆した． キーワード：アフリカイネ，イネ，回復干ばつ抵抗性，ネリカ 作物研究 61 号（2016） 連絡責任者：泉泰弘（[email protected]） among diverse rainfed lowland rice (Oryza sativa L.) genotypes screened at the vegetative stage in dry season and its association with grain yield obtained under drought conditions in wet season. Field Crops Res. 89: 281-297. Russell, R. S. (1977) Plant Root Systems: Their Function andInteraction with the Soil. McGraw-Hill Book Co.: London. Uga, Y., Sugimoto, K., Ogawa, S., Rane, J., Ishitani, M., Hara,
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