Screening rice (Oryza sativa L.) genotypes for resistance against drought

Drought is regarded as one of the limiting factors in rice production nationally and globally. The present study was conducted to study morpho-physiological and biochemical responses of rice genotypes to drought stress, to identify potential traits for use as a selection criterion in breeding drought-tolerant rice at seedling stage and finally to identify rice genotype resistant to drought stress for use as parents in future breeding. The experimental design used was a split-plot design with three replications, with drought stress as the main plot and rice genotypes as the sub-plot. The main plots consisted of control (normal irrigation) and drought stress. The sub-plots consisted of twelve rice genotypes namely Apami (V1), Boewani (V2), Basmati 370 (V3), Cica-4 (V4), Dular (V5), Jarom mas (V6), Kalarata (V7), Biris (V8), Haiboq (V9), Moroberekan (V10), MR 297 (V11) and Aerob 1 (V12). Results showed that drought stress led to a decrease in plant height, leaves size, root length, total dry weight, and number of leaves but an increment in proline content. The genotype Apami and Kalarata were found to accumulate higher proline content indicating potential resistant ability towards drought stress. Dular and Aerob1, along with tolerant control genotype, Moroberekan, on the other hand, recorded a lower SES score. Leave size, root length, and plant height could also be used as a selection criterion in breeding drought-tolerant rice due to high values of broad-sense heritability and genetic advance by percentage of mean (GAM). Nevertheless, further study on the genetics and physiological basis of tolerant ability at reproductive growth stages are necessary in order to assess grain yield potential of the potentially tolerant genotype reported in this study

Susceptibility of Malaysian Rice (Oryza sativa L.) Cultivar to Saline Water Submergence Based on the Morphological Traits

Saline water submergence is a newly emerge abiotic stress jeopardizing rice production especially for the rice fields located nearby or alongside coastal areas. The stress was caused by the intrusion of sea water into those rice fields causing flash flood mainly during monsoon season. The present study was conducted to evaluate susceptibility level of selected Malaysian rice cultivars to saline water submergence at seedling stage based on the morphological traits and survival rate. There were six genotypes involved in the study mainly IR64-Sub1 as submergence tolerant control, Pokkali as salinity tolerant control, IR64 as susceptible control and MR297, MR284 and MR253 as local rice cultivars, respectively. The experiment was conducted using split plot design with three replications. On the day 14 after germination, all rice seedlings were totally submerged of about one-meter depth in a polyethylene tank containing saline water at 0, 4, 8 and 12 dS/m for 14 days while the non-submerged plant was control of the experiment. Seedling growth attributes and survival rate were recorded before, right after de-submerged and 14 days after de-submerged. All genotypes however were susceptible to saline water submergence at 4, 8 and 12 dS/m. In contrast, under 0 dS/m, IR64-Sub1 recorded significantly higher survival rate at 83% as compared to MR284 (17%), MR297 (17%), Pokkali (8%), MR253 (0%) and IR64 (0%).  All genotypes were not survived under saline submergence. Therefore, further phenotypic screening of rice genetic resources originated from or nearby coastal areas could be suggested in order to increase chance of identifying potentially tolerant genotype to saline water submergence

Morphological, Biochemical and Genetic Variation of Rice (Oryza sativa L.) Genotypes to Vegetative Stage Salinity Stress

Salinity is one of the most serious issues in rice cultivation and production. Salt stress significantly reduced seedling growth performance of rice. This research was conducted to study the effects of vegetative stage salinity stress on morphological, biochemical, molecular and genetic variation of 12 rice genotypes as well as 2 check varieties, MR297 (susceptible) and Pokkali (tolerant). The experiment was arranged in a split-plot design with 3 replications. Normal freshwater at 0 dS m-1 (L1), saline water at 6 dS m-1 (L2) and saline water at 12 dS m-1 (L3) were the main plot and rice genotypes were the sub-plot. In general, morphological and biochemical traits of all genotypes showed an overall reduction of about 47.41% in L3 as compared to L1 except for the tolerant check, Pokkali. The genetics and correlation analysis indicated that plant height, leaf size and standard evaluation system (SES) score might be used as a selection criterion in developing salt tolerant rice. The multivariate analysis revealed that a Malaysian landraces, Jarom Mas was clustered together with Pokkali as tolerant genotype. Screening using tightly linked Simple Sequence Repeat (SSR) markers (RM1287, RM10748, RM493) of salinity tolerant QTL, Saltol indicated that this QTL was absence in Jarom Mas. This finding might indicate the presence of other QTL associated with salinity tolerance in Jarom Mas. Further study on identifying the speculated QTL may be conducted to confirm this postulation

Effects of pre-anthesis drought stress on yield components and seed quality of rice (Oryza sativa L.)

Sufficient supply of high quality planting materials is vital for a successful rice production. Pre-anthesis drought stress significantly reduces yield components of the lowland cultivated rice hence scientific information on its effect on seed quality is still very much lacking. This study was conducted to compare the effects of pre-anthesis drought stress on yield components and seed quality of two rice genotypes, a drought tolerant Moroberekan (V1), and local drought susceptible MR297 (V2). Three durations of drought stress used in this study were well-watered condition (S1), five days stress duration (S2), and ten days stress duration (S3). Complete (100%) spikelet sterility was observed for MR297 as compared with Moroberekan (31%) under S3. The seed germination rate of Moroberekan was significantly lower (p<0.05) under S1 (48%) as compared with S2 (80%) and S3 (70%). However, embryo of the non-germinated seeds of Moroberekan were still alive based on tetrazolium test thus indicated that the seeds were still viable yet dormant. In contrast, seed germination rate of MR297 was not affected by pre-anthesis drought stress (88% for S1 compared to 93% for S2). Therefore, seeds of MR297 produced under pre-anthesis drought stressed condition could be safely distributed in rice seeds supply chain

Bacteria associated with rice panicle blight and grain discolouration in Penang

Rice panicle blight and grain discoloration condition is a newly paddy disease that firstly discovered from China in 2020 and recently discovered in Malaysia with adverse impact on our granary production. The symptoms first appeared on the glumes as light-brown spots that progressed to darker brown or black spots, dotted spots that varied in shape and size, hollow light weight panicles, or even unfilled grains. Therefore, the objective of this research was to study the bacteria associated from rice panicle blight and grain discolouration by identifying the causal pathogen based on their phenotypic and molecular characterization. Sampling was done in naturally infected granary areas and the collected panicles have been performed throughout surface sterilization for bacteria isolation until obtained single pure colony. 11 representatives of pure isolates obtained have been identified and classified through phenotypic and molecular characteristics. Based from that, 4 genera of bacteria were obtained. They were from Pseudomonas sp., Pantoea sp., Enterobacter sp. and Paenibacillus sp. Hence, to alleviate this serious disease, a precise identification of the pathogen is required in order to control the disease from spreading which results in a rice grain yield reduction

Drought-induced changes in the flowering capacity, anthesis quality and seed set in rice (Oryza sativa L.)

Drought stress significantly reduces grain yield (GY) due to poor spikelet fertility and anthesis quality. Aim of this study was to understand the changes of flowering capacity, anthesis quality traits and seed set in the re-watered drought stressed modern high yielding drought susceptible rice cultivar, IR64 at heading (DSH) and booting (DSB) stages. The wellwatered plants served as control of the experiment. Results obtained suggest that spikelet moisture content at above 80% was required to maintain optimum anthesis process in rice. Anthesis process in DSH plant was suspended when leaf relative water content (LRWC) dropped to below than 70%. Effects of drought stress on the spikelet moisture were irreversible as compared to the leaf rolling and LRWC. Hence, seed set was failed to occur at the upper rachis branches of the DSH plant. Anthesis process in the re-watered drought stress plants was resumed on the third day after re-watering with about 50% and 80% of anthers managed to dehisce in the DSH and DSB plants. Consequently, percentage of spikelet fertility and seed set in the DSH and DSB plants were increased towards the lower parts of the panicle. The GY, number of seeds, spikelet fertility, and harvest index however were significantly lower in the DSH plant (0.30 g, 13, 16.40%, and 14.81) as compared to DSB plant (1.34 g, 57, 59.14%, and 48.30), respectively. In addition, all interrelated traits involved in the flowering process of rice could be collectively termed as the anthesis quality traits due to their significant correlation with the grain yield and other yield components

Response of primed rice (Oryza sativa L.) seeds towards reproductive stage drought stress

Seed priming could be promoted as a potential alternative in alleviating drought stress challenges in rice cultivation. The present study was conducted as an attempt to verify potential performance of seed priming in improving seedling growth and harvestable grain yield of rice under reproductive stage drought stress (RS). Seed treatments involved were non-primed seeds as control (T1), hydro-primed (T2) and osmo-primed at -1.0 mPa with polyethylene glycol (PEG6000) (T3). Reproductive stage drought stress (RS) was imposed at soil water potential lower than -60 kPa. The well-watered plants served as control of the experiment. In general, seedling growth of T3 was better than T2 and T1 for all growth parameters in both planting seasons. Yield components were significantly lower in RS as compared to well-watered treatment (WW). The agronomic performance of primed seeds in T2 and T3 were not significantly different with T1 under both RS and WW for both planting seasons. As a conclusion, seed priming treatments used in this study was ineffective in improving agronomic performance of rice under RS. Therefore, other alternatives such as development of drought tolerant rice should be highly emphasized in order to minimize the impact of drought on growth and yield of rice plant

Screening for Tolerant Genotype to Saline Water Submergence in Rice (Oryza sativa L.).

Saline water submergence is a newly emerge abiotic stress jeopardizing rice production especially for the rice fields located nearby or alongside coastal areas. The stress was caused by the intrusion of sea water into those rice fields causing flash flood mainly during monsoon season. The present study was conducted as an attempt to screen for tolerant genotype against saline water submergence at seedling stage. There were six genotypes involved in the study mainly IR64-Sub1 as submergence tolerant control, Pokkali as salinity tolerant control, IR64 and MR297 as susceptible control, MR284 and MR253, a local rice cultivar respectively. The rice seedlings were submerged in saline water at 0, 4, 8 and 12 dS/m for 14 days while the non-submerged plant was control of the experiment. Seedling growth attributes, survival rate and recovery rate were recorded before and after de-submerged for three consecutive weeks. The highest survival rate at 83% was recorded in IR64-Sub1 under 0 dS/m, followed by MR284 (17%), MR297 (17%) and Pokkali (8%). All genotypes however were susceptible to saline water submergence at 4, 8 and 12 dS/m. Hence, potential genetic resource of rice originated from coastal area in the future screening is crucial to increase the possibility of identifying tolerance genotype to saline water submergence stress which later will be used as a donor parent in the breeding program

Morpho-Physiological Response of Rice (Oryza Sativa L.) Genotypes to Salinity Stress at Seedling Stage

Salinity stress would significantly reduce seedling growth performance of rice. In addition, salinity also affects physiological and metabolic process mainly the osmotic and ionic balance of the cells. Hence, the present study was conducted to evaluate morpho-physiological and biochemical response of selected rice genotypes to salinity stress at seedling stage. Twelve rice genotypes were used in the pot-trial experiment including two checks namely Pokkali (tolerant) and MR297 (susceptible). The experiment was conducted in a split plot design with three replications. Three salinity levels involved were L1 (normal fresh water), L2 (saline water at 12 dSm-1), and L3 (saline water at 24 dSm-1) as the main plot while rice genotypes as the sub-plot. Salinity stress was imposed for 14 days starting from 21 days after sowing. In overall, L3 salinity stress significantly reduced 47.41% of all seedling growth attributes for all genotypes except for Pokkali (V11) as compared to control condition. Meanwhile, Haiboq (V9) and Basmati 370 (V3) recorded significantly similar response as the MR297 (V10). The trend of chlorophyll content reduction could be seen in all genotypes under L2 and L3 salinity stress with average 77.72% reduced over control condition. In contrast, proline content was increased over 7 folds in all genotypes as level of salinity increases except for V11. Proline may function as a signal metabolites thus higher proline content indicates that the plant is under stress. In conclusion, chlorophyll and proline content may be used as indicators of sensitivity to salinity stress in rice cultivars along with the morphological growth responses

Genome-scale compositional comparisons towards drought tolerant genes in rice, date palm, maize and thale cress

Extreme and unpredictable weather has gradually posed a threat to the global production of the world’s staple food crops such as rice, wheat, and maize. For instance, drought had caused significant losses which makes drought-tolerant planting materials increasingly important not only for food security but also for the sustainability of agricultural activities. This could be done by first exploring the genetic materials that are responsible for survival in hot and dry conditions other than solely relying on conventional methods. The availability of various comparative genomics tools has allowed the identification of several potential drought-tolerant genes in plants such as wheat, tomato, maize and others. In this study, potential drought-tolerant genes in rice are predicted by identifying orthologous proteins between four species; Oryza sativa (rice), Arabidopsis thaliana (thale cress), Zea mays (maize) and Pheonix dactylifera (date palm) using InParanoid, SonicParanoid and Mauve software tool. From the 9,952 orthologous proteins found among the four species, 8,573 sequences were annotated and assigned to 5,729 GO terms; classified into the biological process category (54%, 2777 sequences), molecular function category (65%, 3223 sequences) and cellular component category (58%, 2539 sequences). Sixty five genes were found to be represented under four drought tolerance GO terms; regulation of response to water deprivation (GO:2000070; 1 gene, 1.54% ); response to water deprivation (GO:0009414, 47 genes, 72.31%); behavioural response to water deprivation (GO:0042630, 11 genes, 16.92%) and; cellular response to water deprivation (GO:0042631, 6 genes, 9.23%). Narrowing down potential drought-stress response genes through this study could contribute to a better understanding and knowledge on the biological and functional analysis of drought-tolerant genes in rice