Lowland Rice Varieties Research Articles

Genetic diversity of Vietnamese lowland rice germplasms as revealed by SSR markers in relation to seedling vigour under submergence

ABSTRACTIn the direct-seeding rice cultivation system, seedling vigour is one of the most important traits for stable stand establishment during early seedling stages, particularly under submergence that is caused by temporal flash flood. We studied the genetic diversity in a set of 40 Vietnamese lowland rice varieties using 30 simple sequence repeat (SSR) markers covering all rice chromosomes. A total of 111 alleles were detected, with a mean of 3.7 alleles per locus. The number of polymorphic alleles detected by each SSR marker ranged from 2 to 6. The fragment size of a given SSR locus varied between 85 and 650 bp and the frequency of a major allele at each locus ranged from 32.5% to 76.9%. Polymorphism information content value varied from 0.355 to 0.774 with an average of 0.594. The genetic similarity calculated between pairs of rice varieties ranged from 0.03 to 0.97 with an average of 0.27. According to a constructed dendrogram of unweighted pair group method with arithmetic mean based on the SSR marker analysis, the tested rice varieties were clustered into two major groups consisting of five subgroups. Significant correlations existed between the mean genetic similarity and the mean seedling vigour estimated by shoot length under submergence among the tested varieties. Our results suggested usefulness of the SSR marker system to assess genetic diversity in Vietnamese rice germplasms in relation to their seedling vigour under submergence.

EFFECTS OF FERROUS TOXICITY ON SEEDLING TRAITS AND ION DISTRIBUTION PATTERN IN UPLAND AND LOW LAND RICE UNDER HYDROPONIC CONDITIONS

Environmentally, nutritional disorders are the major constraints due to the change in soil pH for rice crop cultivated under different irrigation system. Iron toxicity is one of the famous nutritional disorders caused by the excessive uptake of ferrous ion in low pH under aerobic conditions. This research study was focused to measure the effect of different levels of ferrous stress on seedling traits, distribution of ferrous, potassium ions in two upland rice and three lowland rice varieties. The mean comparison of growth parameters were formulated using least significant differences, as well as the experimental treatments were compared by analysis of variance. Varieties showed significant differences for growth parameters; however, lowland rice varieties like Pokkali and Firat exhibited the minimum deterioration in growth parameters. The root length was significantly reduced under ferrous stress in all varieties. Ferrous accumulation was high in roots compared to aerial plant parts and flag leaves exhibited the minimum accumulations. Reduction of potassium reflected in all plant parts when an increased in stress was imposed. Upland rice varieties were found sensitive compared to lowland rice varieties. It is therefore; concluded that the growth parameters would be a reflecting index for ferrous toxicity in rice. Furthermore, the availability and uptake of potassium is improved, it may minimize the effects of ferrous toxicity.

Linkage Mapping of Quantitative Trait Loci for Traits Promoting Aerobic Adaptation on Chromosome 8 in Indica Rice (<i>Oryza sativa</i> L.)

Identification of major effect QTLs for traits promoting aerobic adaptation using molecular markers can greatly enhance the efficacy of breeding programs to develop high yielding, direct seeded, water efficient rice varieties. The Filial (F 2 ) population derived from HKR47 high-yielding low-land indica rice variety, and MAS26, aerobic adapted rice variety, was developed and analyzed for the identification of larger and consistent effect QTLs for yield, yield attributing and root traits under aerobic cultivation conditions. The population displayed large variation for all the physio-morphological traits including grain yield per plant and root traits. Phenotypic correlation analysis revealed that grain yield per plant showed positive correlation with root length (r 2 =0.279), fresh root weight (r 2 =0.232) and dry root weight (r=0.269). A total of 803 SSR markers, distributed on 12 rice chromosomes, were analyzed for parental polymorphism survey; of these 125 (about 16%) displayed polymorphism. NTSYS-pc UPGMA tree cluster analysis and two-dimensional PCA scaling showed scattering of the F 2 population between the two distinct parental genotypes; the population was inclined towards MAS26. Composite interval mapping (CIM) analysis revealed a total of six QTLs (qTN 8.1 , qTN 8.2 , qTN 8.3 , qTGW 8.1 , qYPP 8.1 and qRL 8.1 ) on chromosome 8 (within a region of 24.9 cM) which individually explained 13.7%~27.3% of the phenotypic variation. Chromosome 8 also possesses QTL for aroma and kernel elongation demonstrating that it might be difficult to introgress these QTL promoting aerobic adaptation in Basmati rice.

Genetic transformation of lowland rice variety GR11 for drought tolerance and its ratification for upland paddy cultivation

In the current investigation experiments were performed to produce high yielding transgenic rice plants, suitable for upland paddy cultivation in Gujarat. DREB 2A gene isolated from drought tolerant rice variety was placed in a binary vector driven by 35S promoter of cauliflower mosaic virus (CaMV) and a 5’non-coding region (5’-UTR) of rice alcohol dehydrogenase (ADH) gene acting as translational enhancer. Three to four weeks old proliferating calli of GR 11 variety of rice were used for transformation with Agrobacterium strains LB 4404 harbouring pRION_DREB 2A plasmid. NPT II selectable marker gene in putatively transformed plants confers resistance to kanamycin which is used for selection of positively transformed GR 11 callus. In vitro regeneration of the transformed callus produced T0 lines of rice harbouring DREB 2A cassette. The frequency of transformation was 10%. Stable integration of transgene conferring tolerance to drought in T0 rice plants were verified using PCR, Reverse transcription PCR (RT PCR), Real Time PCR (absolute and relative quantification). The transgenic copy number in T0 cisgenic lines were calculated as one to three copies of stably integrated DREB 2A gene per copy of genome of GR 11 rice variety.

Genetic transformation of lowland rice variety GR11 for drought tolerance and its ratification for upland paddy cultivation

Genetic transformation of lowland rice variety GR11 for drought tolerance and its ratification for upland paddy cultivation

Microbial Effects on Seed Germination in Malaysian rice (Oryza sativa L.)

Seed germination is the basis of plant growth as it determines the viability of rice. A laboratory experiment was conducted to observe the effect of microbial inoculation on seed germination and seedling growth of two lowland rice varieties (Mahsuri and Sri Malaysia 1) and two upland rice landraces (Panderas and SK-1). The experiment was conducted using wet filter paper in Petri dish. The design of the experiment was completely randomized (CRD) with three replicates. Three selected growth promoting microbes Nitrosomonas europaea , Rhodopseudomonas palustris and Acinetobacter sp . were used in the experiment. Seeds inoculated with those microbes and the Petri dish were kept in the dark for five days and subsequently subjected to light condition for another five days. The seed germination and other related attributes were measured. Significance and non significant differences were observed for growth parameters and germination traits, respectively. Among the microbes, Nitrosomonas europaea and its combination performed better in root length and combination of Rhodopseudomonas palustris and Acinetobacter sp . promotes the best growth of shoot. Nitrosomas europaea has shown to play a major role in the germination rate growth in all varieties. It is therefore concluded that growth promoting microbes may have positive effects on germination of rice seeds.

Leaf area development in response to meristem temperature and irrigation system in lowland rice

Growth and grain yield reductions have been widely observed when traditionally flooded rice fields were subjected to water-saving irrigation measures, where a continuous floodwater layer is avoided. These observations led to the perception of rice being a plant extremely sensitive to water stress even when grown in soils where water is sufficiently available. Since the rice plant's meristem is below the water surface during the vegetative stage in flooded fields, the difference in heat capacity between water and air will lead to changes in meristem temperature, when a ponded water layer is omitted. Therefore, the objective of this study was to investigate leaf area development in response to meristem temperature under flooded and non-flooded conditions in the field. In Ndiaye, located in the Senegal River valley, a lowland rice variety (IR64) was sown on 13 staggered dates between July 2008 and June 2010. In a flooded treatment (FL), a continuous water layer was maintained, whereas in a non-flooded treatment (NF), irrigation water was applied until soil saturation every 2 or 3 days. Temperature at the soil surface as well as leaf area and tiller number were recorded. In most cases, leaf area was reduced under non-flooded conditions. Leaf area expansion rate was correlated with meristem temperature during the night. With temperature at the soil surface being lower under non-flooded conditions, lower leaf area expansion rates under non-flooded conditions could be attributed to lower meristem temperature. The omission of a floodwater layer can expose the rice plant's meristems to larger temperature extremes and thus affect plant growth. In environments with large temperature amplitudes, this effect should be considered when water-saving measures are applied in lowland rice fields.

The use of <sup>32</sup>P Method to Evaluate the Growth of Lowland Rice Cultivated in a System of Rice Intensification (SRI)

A pot experiment has been conducted to evaluate the growth of the Dyah Suci, a lowland rice variety, in an SRI (System of Rice Intensification) planting system. The phosphorus-32 ( 32 P) isotope technique was used to evaluate the growth of plants in relation with their phosphorus uptake. The uptake was assumed to vary in the same direction as the growth of the plant. The 32 P uptake is assumed to vary in the opposite direction to the plant’s total phosphorus uptake. Here the 32 P uptake is expressed in count per minutes (cpm) which is then transformed to disintegration per minute (dpm). The results show that , in terms of promoting the plant’s uptake of phosphorus, the SRI planting system is superior to the conventional planting system, and it i s manifested in the higher dry weight of straw and grain. From this experiment it is concluded that the 32 P method can be used satisfactorily as a tool for explaining the relation between P-uptake and plant growth . Received: 04 Juny 2013; Revised: 22 August 2013; Accepted: 30 August 2013

Evaluation of the host response of lowland and upland rice varieties from Myanmar to the rice root-knot nematode Meloidogyne graminicola

The rice root-knot nematode Meloidogyne graminicola is considered one of the most potentially important nematode pathogens of rice, especially in South and Southeast Asia, in a range of rice production systems. Identification of M. graminicola-resistant or -tolerant rice varieties will enable breeding programmes to develop rice varieties which are able to limit yield losses caused by this nematode species. The host response to M. graminicola infection of 15 lowland rice varieties and 9 upland rice varieties, which are being grown in the summer-irrigated lowland and rainfed upland rice ecosystems in Myanmar, was evaluated in two experiments under screenhouse conditions. The lowland rice experiment was carried out under intermittently flooded conditions in a clay loam soil (i.e. simulating the summer-irrigated lowland rice ecosystem) and the upland rice experiment was carried out at field capacity in a sandy loam soil (i.e. simulating the monsoon rainfed upland rice ecosystem). None of the15 lowland and 9 upland rice varieties were resistant to M. graminicola infection although differences in susceptibility and sensitivity were observed. Six (or 40%) out of the 15 lowland varieties examined were classified as less susceptible (LS) to M. graminicola infection, five (or 33.3%) as moderately susceptible (MS) while four (or 26.7%) as highly susceptible (HS). One (or 11.1%) out of the nine upland varieties examined was classified as LS to M. graminicola infection, three (or 33.3%) as MS while five (or 55.6%) as HS. Five (or 33.3%) out of the 15 lowland varieties examined were classified as either less sensitive or tolerant to M. graminicola infection. One (or 11.1%) out of the nine upland varieties examined was classified as tolerant to M. graminicola infection. This study offers interesting information for the farmer regarding which rice variety should be grown in M. graminicola-infested fields under either lowland or upland conditions.

Mulching upland rice for efficient water management: A collaborative approach in Benin

Since the 2007 food crisis, the Government of Benin has created enabling conditions that urge small scale farmers to intensify rice production in inland valleys. Unsuitable irrigation infrastructures and lack of willingness to act collectively has led farmers to complain about water shortage. Adoption of mitigating technologies offered by government (extension) and scientists (e.g. Benin Agricultural Research Institute, AfricaRice) has been low due to the institutional context within which farmers are working. A socio-technical approach which combines technical and institutional dimensions was used to identify and test mulching as a potential method for improving irrigation water efficiency in growing rice in upland parts of Benin's inland valleys. Rice farmers (from three production areas), an extension agent and a researcher formed a multi-stakeholder platform and collaborated to test the application of mulch (three doses) and the use of a lowland rice variety in replacement of an upland rice variety during two growing seasons. Multiple methods derived from researchers and farmers’ perspectives were used to evaluate trial results: quantitative scientific evidence was combined with qualitative evaluation using indicators agreed upon by the collaborative group. Results show that the lowland rice variety IR-841 with 10Mgha−1 ‘rice-straw’ mulch allows farmers to better use available water in the upland areas and increase yields. Although the preference for IR-841 over the special bred upland variety Nerica-4 is risky because of its high water demand and the uncertainty in rainfall, farmers use IR-841 for profit maximisation. Beyond its technical output, the joint experimentation facilitated the interaction of knowledge, experiences and practices among the involved actors.

Evaluation of the Relative Weed Competitiveness of Some Lowland Rice Varieties in Sierra Leone

Evaluation of the Relative Weed Competitiveness of Some Lowland Rice Varieties in Sierra Leone

Impact of Rice Nursery Nutrient Management, Seeding Density and Seedling Age on Yield and Yield Attributes

To help farmers in the mid hills of Nepal improve their crop management and rice yields, we conducted a study testing different nursery management options and their effect on grain yield and yield components under rainfed conditions. The experiment was conducted in a farmer’s field during the cropping season 2009 and 2010 at Sundarbazar, Lamjung, Nepal, using a 3-factor factorial RCB design with 3 replications. The three management factors tested were 1) fertilizer management in the nursery, 2) seeding density, and 3) seedling age at transplanting, using the rainfed lowland rice variety Radha-4. There were eight treatment combinations, consisting of two levels of fertilization (0 and 20:20:0:13 kg NPKS ha-1 at 15 DAS), two levels of seeding density (607 and 303 g·m-2) and two seedling ages (20 and 40 days old). Two years’ results showed that top-dressed fertilizer in the nursery had no consistent effect on grain yield. However, lower seeding density (303 g·m-2) resulted in taller plants, more productive tillers m-2, less sterility and higher grain yield. In addition, older seedlings (40 days) produced taller plants, more productive tillers, more filled grains, and a higher grain and straw yield. The interaction analysis between both factors indicated that 40 days old seedling with a low seeding density produced the highest grain yield, both in the drought season 2009 and the high-yielding season 2010. The economic analysis confirmed that the treatment with low seeding density and 40 days old seedlings produced by far the highest net returns and B:C ratio in both seasons, independent of the fertilizer treatment. The combination of these two management components is therefore economically viable and profitable, and can be recommended to farmers. However, the results need to be confirmed for other varieties used by farmers in the region.

Population dynamics of Meloidogyne graminicola and Hirschmanniella oryzae in a double rice-cropping sequence in the lowlands of Myanmar

The rice root-knot nematode, Meloidogyne graminicola, and the rice root nematode, Hirschmanniella oryzae, are considered potentially important nematode pathogens in lowland rice. A study was undertaken from December 2009 until December 2010 in the Ayeyarwady River Delta, the major lowland rice-producing area of Myanmar, to monitor the population dynamics of M. graminicola and H. oryzae in a naturally infested field. Root samples of the two rice varieties Yatanartoe and Taungpyan that are commonly cultivated in double rice-cropping sequences in Myanmar and represent irrigated and rainfed lowland rice varieties, respectively, were obtained for nematode analysis. During the summer-irrigated rice-growing season the root population density of second-stage juveniles (J2) of M. graminicola showed two distinct peaks – at the maximum tillering stage of the rice plants in January and at the heading stage of the rice plants in March 2010. With the onset of the monsoon rains, the J2 population densities in the roots of ratoon rice plants gradually decreased in May. During the rainfed monsoon rice-growing season, very low population densities of M. graminicola J2 were detected in the roots of rice plants, while the root population density of H. oryzae juveniles and adults showed two distinct peaks – at the maximum tillering stage of the rice plants in August and at the heading stage of the rice plants in October 2010. With the onset of the dry season, population density of H. oryzae in the roots reached the lowest density at harvest in November. Root galling caused by M. graminicola followed the same trend as the J2 population densities throughout the irrigated season. No root galls were observed during the monsoon season. Our results can be used for practical purposes aimed at a better management of both M. graminicola and H. oryzae.

Evaluation of Sowing Methods of Upland and Ratooned Rice Planted in-between Lowland Rice-Fluted Pumpkin Sequence in Derived Savannah

The technical possibility of triple cropping in inland valleys is not in doubt but economic and agronomic performance of ratooned and upland rice (Oryza sativa L.) fitted in-between lowland rice and dry season cropping need to be ascertained. A field experiment was conducted at the Federal University of Agriculture, Abeokuta, Nigeria in 2007/2008 and 2008/2009 cropping season to compare the performance of sowing methods. Dry dibble broadcast, pre-germinated broadcast, dry dibble, transplanted and pre-germinated broadcast methods of early maturing New Rice for Africa 1 (NERICA 1) upland rice were compared with ratooned crop of New Rice for Africa Lowland rice (NERICA-L) genotypes (NERICA-L 20, NERICA-L 26, NERICA-L 44, NERICA-L 41 and OFADA) in the niche between lowland rice and dry season cropping. The first crop was planted in May while the second and third were in September and December. The experiment was laid out in Randomized Complete Block Design (RCBD) with three replicates. The mean plant height, grains panicle-1, panicles m-2, 1000-grain weight and grain yield of lowland rice varieties were 126.5 cm, 220, 173, 29.3 g, and 7.75 t ha-1, respectively. The ratooned lowland rice flowered earlier (28-37 days) than the upland rice sowing methods (66-77 days). Ratooned crops of NERICA-L 20, NERICA-L 26 and NERICA-L 44 had highest number of panicles m-2 and grain yield while pre-germinated dibble upland rice and ratooned crop of OFADA had the least panicles m-2 and grain yield, respectively. Transplanted upland rice and pre-germinated broadcast methods had better grain yield than any of the sowing methods of upland rice. The fresh leaf weight of fluted pumpkin (Telfairia occidentalis Hook F.) ranged between 14.59 and 19.77 t ha-1. Ratooned crops had better agronomic and economic performance than the upland rice. Hence the productivity of triple cropping in the inland valley could be efficiently utilized by adopting ratooning lowland rice.

RATOONED LOWLAND NERICA RICE VARIETIES AS AN OPTION FOR TRIPLE CROPPING IN INLAND VALLEYS OF DERIVED SAVANNAH IN NIGERIA

SUMMARYAlthough triple cropping in inland valleys of Nigeria is technically feasible, the third crop between the main crop and dry season non-rice crop has been considered not to be economically viable because of poor crop establishment due to soil inundation. The identification of an appropriate technology with low input, such as ratooning, would allow this niche to be utilized. Field experiments were conducted at the University of Agriculture, Abeokuta, Nigeria in 2007–2008 and 2008–2009 cropping seasons to evaluate the performance of the main and ratooned crops of lowland NERICA (New Rice for Africa) rice (Oryza sativa L.) varieties in a lowland rice–ratooned rice–fluted pumpkin (Telfairia occidentalis Hook F.) sequence. The experiment was laid out in a randomized complete block design with three replicates. The lowland rice varieties used were NERICA-L 19, NERICA-L 20, NERICA-L 22, NERICA-L 24, OFADA, NERICA-L 26, NERICA-L 41, NERICA-L 42, NERICA-L 44 and NERICA-L 47. The grain yield of the main rice crop ranged from 5.0 to 7.3 t ha−1 in 2007–2008 cropping season and from 4.1 to 9.1 t ha−1 in 2008–2009. The ratooned rice had a grain yield of 1.0–4.7 t ha−1 in 2007–2008 and 1.2–3.4 t ha−1 in 2008–2009. The total grain yield obtained in 2007–2008 from the main and ratooned rice crops in seven months was 6.7–11.6 t ha−1, while in 2008–2009 it was 5.3–2.6 t ha−1. The fresh leaf yield of fluted pumpkin ranged from 14.6 to 16.9 t ha−1 in 2007–2008 and from 18.3 to 19.8 t ha−1 in 2008–2009, similar to previously reported rainy season unfertilized yields. Thus, a ratooned rice crop appears to be a feasible technology capable of boosting rice production and consequently increasing the overall productivity of the inland valley in a rice–rice–vegetable cropping sequence.

Growth and Iron Uptake of Lowland and Aerobic Rice Genotypes under Flooded and Aerobic Cultivation

With increasing water shortages in China, rice (Oryza sativa L.) cultivation is gradually shifting away from continuously flooded conditions to partly or even completely aerobic conditions. The effects of this shift on the growth and iron (Fe) nutrition of different aerobic and lowland rice genotypes are poorly understood. A field experiment was conducted to determine the effects of cultivation system (aerobic vs. flooded), genotype (five aerobic rice varieties and one lowland rice variety), and Fe fertilization [no Fe and 30 kg ha−1 ferrous sulfate (FeSO4·7H2O] on rice grain yield and Fe nutrition. Plants were sampled at tillering and physiological maturity. In both aerobic and flooded plots, Fe application significantly increased shoot dry weight, shoot Fe concentration, and shoot Fe content at tillering but not physiological maturity. At physiological maturity, grain yield and Fe and grain harvest indices were significantly lower in aerobic than in flooded plots. Shoot dry weight and shoot Fe content differed among genotypes at tillering and at physiological maturity. The grain harvest index of aerobic rice genotype 89B-271-17(hun) was significantly greater than that of the other five genotypes when no Fe was applied. Because soil Fe fertilization did not improve the Fe nutrition of rice in aerobic plots, the results indicate that the shift from flooded to aerobic cultivation will increase Fe deficiency in rice and will increase the problem of Fe deficiency in humans who depend on rice for nutrition.

Effects of rhizobia and plant growth promoting bacteria inoculation on germination and seedling vigor of lowland rice

Plant growth promoting rhizobacteria (PGPR) stimulate plant growth by producing phytohormone which enhances the growth and physiological activities of the host plant. Recently, legume bacteria (Rhizobium spp.) have been considered as a PGPR for legume as well as non-legumes and have the potential for growth stimulation. A laboratory experiment was conducted to observe the effect of PGPR and Rhizobial inoculation on seed germination, seedling emergence, growth and development of lowland rice variety MR219. The experiment was conducted under laboratory condition using filter paper in Petri dish. The design of the experiment was completely randomized (CRD) with six replicates. The PGPR strains UPMB10 ( Bacillus sphaericus ), Rhizobium strains SB16, UPMR1006 and UPMR1102 were used in the experiment. Seeds inoculated with those PGPR and Rhizobium strains and the Petri dish were kept in an incubator at 30 ± 2°C for 120 h. The seeds germination and other related attributes were measured. The results suggested that inoculation significantly increased the seedling emergence, seedling vigor, root growth namely root length, root surface area and volume. Among the strains, UPMB10 performed better in seedling growth and strain UPMR1006 produced profuse hair in the radical. The results concluded that PGPR and Rhizobia strain can promote seed emergence and seedling attributes which benefits the early seedling establishment and consequently the crop growth and development. Key words : Rhizobium , PGPR, seedling vigor, germination, rice.

Aerobic rice genotypes displayed greater adaptation to water-limited cultivation and tolerance to polyethyleneglycol-6000 induced stress

Water scarcity and drought have seriously threatened traditional rice cultivation practices in several parts of the world including India. In the present investigation, experiments were conducted to see if the water-efficient aerobic rice genotypes developed at UAS, Bangalore (MAS25, MAS26 and MAS109) and IRRI, Philippines (MASARB25 and MASARB868), are endowed with drought tolerance or not. A set of these aerobic and five lowland high-yielding (HKR47 and PAU201, Taraori Basmati, Pusa1121 and Pusa1460) indica rice genotypes were evaluated for: (i) yield and yield components under submerged and aerobic conditions in field, (ii) root morphology and biomass under aerobic conditions in pots in the nethouse, (iii) PEG-6000 (0, -1, -2 and -3bar) induced drought stress at vegetative stage using a hydroponic culture system and (iv) polymorphism for three SSR markers associated with drought resistance traits. Under submerged conditions, the yield of aerobic rice genotypes declined by 13.4-20.1 % whereas under aerobic conditions the yield of lowland indica/Basmati rice varieties declined by 23-27 %. Under water-limited conditions in pots, aerobic rice genotypes had 54-73.8 % greater root length and 18-60 % higher fresh root biomass compared to lowland indica rice varieties. Notably, root length of MASARB25 was 35 % shorter than MAS25 whereas fresh and dry root biomass of MASARB25 was 10 % and 64 % greater than MAS25. The lowland indica were more sensitive to PEG-stress with a score of 5.9-7.6 for Basmati and 6.1-6.7 for non-aromatic indica rice varieties, than the aerobic rice genotypes (score 2.7-3.3). A set of three microsatellite DNA markers (RM212, RM302 and RM3825) located on chromosome 1 which has been shown to be associated with drought resistance was investigated in the present study. Two of these markers (RM212 and RM302) amplified a specific allele in all the aerobic rice genotypes which were absent in lowland indica rice genotypes.

Growth and Yield Performance of Selected Lowland Rice Varieties under Alternate Wet and Dry Water Management

Severe water shortage in many parts of the world has caused enormous yield losses in rice. To continue feeding the increasing number of people who are dependent on rice as staple food, there is a need to address the problem on water shortage. One possible solution may be the application of alternate wet and dry (AWD) water management in rice production. This experiment was conducted to evaluate the growth and yield performance, as well as the profitability of selected lowland rice varieties under AWD water management. An experimental area of 450m2 with Umingan clay loam soil was laid out in randomized complete block design (RCBD) with three replications. Each replication was subdivided into six treatment plots with an area of 20m2 (5m x 4m) each. The treatments were: T1 – Masipag 45 (M45), T2 – Matatag 6 (M6), T3 – Masipag 129-2 (M129-2), T4 – Pinili-1, T5 -SL-8H and T6 – PSBRc-18 (check variety). Results showed that number of days from planting to heading and maturity, fresh straw yield (t ha-1), number of productive tillers per hill, number of filled grains per panicle and grain yield (t ha-1) differed significantly among treatments (p<0.05). Pinili-1 headed and matured the earliest and produced the highest fresh straw yield (t ha-1). However, M-129-2 and Matatag 6 had the highest number of productive tillers per hill, number of filled grains per panicle and total grain yield (t ha-1) which surpassed that of PSBRc18 (check variety). Masipag129-2 and Matatag 6 also gave the highest net profit of Php 23,805.00 per hectare.

A QTL for rice grain yield in aerobic environments with large effects in three genetic backgrounds

A large-effect QTL associated with grain yield in aerobic environments was identified in three genetic backgrounds, Apo/(2)*Swarna, Apo/(2)*IR72, and Vandana/(2)*IR72, using bulk-segregant analysis (BSA). Apo and Vandana are drought-tolerant aerobic-adapted varieties, while Swarna and IR72 are important lowland rice varieties grown on millions of hectares in Asia but perform poorly in aerobic conditions. Two closely linked rice microsatellite (RM) markers, RM510 and RM19367, located on chromosome 6, were found to be associated with yield under aerobic soil conditions in all three backgrounds. The QTL linked to this marker, qDTY6.1 (DTY, grain yield under drought), was mapped to a 2.2cM region between RM19367 and RM3805 at a peak LOD score of 32 in the Apo/(2)*Swarna population. The effect of qDTY6.1 was tested in a total of 20 hydrological environments over a period of five seasons and in five populations in the three genetic backgrounds. In the Apo/(2)*Swarna population, qDTY6.1 had a large effect on grain yield under favorable aerobic (R (2)≤66%) and irrigated lowland (R (2)<39%) conditions but not under drought stress; Apo contributed the favorable allele in all the conditions where an effect was observed. In the Apo/IR72 cross, Apo contributed the favorable allele in almost all the aerobic environments in RIL and BC(1)-derived populations. In the Vandana/IR72 RIL and BC(1)-derived populations, qDTY6.1 had a strong effect on yield in aerobic drought stress, aerobic non-stress, and irrigated lowland conditions; the Vandana allele was favorable in aerobic environments and the IR72 allele was favorable in irrigated lowland environments. We conclude that qDTY6.1 is a large-effect QTL for rice grain yield under aerobic environments and could potentially be used in molecular breeding of rice for aerobic environments.