Development new rice varieties in the coastlines of Mekong Delta, Vietnam

— To increase productivity and improve quality, new rice varieties need to be salinity tolerance and resistant to many kinds of insects, diseases, and high levels of nutrients, resistant to disadvantageous conditions, and promises to reduce using pesticides, chemical fertilizers. Great efforts have been focused on germplasm research to discover genes resistant to disease and insect, efficient in using salinity level with good grain quality and productivity. With the development of climate-resilient varieties, scaling up or dissemination of seeds is done by province, following the locality's is Winter-Spring (DongXuan Season) and Summer – ( Wet season ). For instance, in the case of Winter-Spring crop, the plan of Mekong delta is to expand some lines such as HATRI 190, HATRI 192, HATRI 170were developed that can yield4-5 tons ha -1 under salt stress of 10.0 to 12.0 dS m -1 , and are being out-scaled. Normally, this expansion initiative requires inclusion of key rice varieties, that is, local or extra varieties and promising varieties, all of which will be included in the plan for developing the rice sector for each province.


INTRODUCTION
Rice is a major export commodity of Vietnam and a source of livelihood of smallholder farmers, particularly in the Mekong Delta, which contributes more than fifty percent of the country's total rice production. Millions of farmers in the Delta are living below poverty level as their farming is affected by occurrences of drought, flooding, and salinity from saltwater intrusion. An estimated 1,867,910 hectares of the total rice crop area is affected by salinity ( Buu et al 2004).High Agricultural Technology Research Institute for Mekong delta(HATRI) recognizes the importance of developing modern climate-resilient rice varieties as well as associated management practices that respond to the challenges of climatic variability in such stress-prone areas. In the case of Vietnam, a rice variety that will be seedmultiplied, first needs to undergo evaluation trials at the HATRI. Moreover, an equally daunting task is bringing the new varieties to the farmers' fields where productivity is still not at optimal level due and where there are institutional constraints related to extension activities. Country protocol for varietal release and dissemination requires that provincial officers and farmers will have to be invited to assess the performance of the varieties in the field. Upon initial assessment and acceptance, farmers and local staff in the districts and provinces will evaluate the variety this time for deployment and multiplication (Lang et al 2016a). This is an ideal strategy to bring rice varieties to the local farmers. The MARD, IFAD-CURE, and other funding institutions, which share the same goal of raising productivity in the salinityprone rice areas in the Mekong Delta, supported the development, validation (Lang et al 2015), and eventual dissemination of climate-smart varieties. The key in achieving such goal involves partnerships and participatory approaches for a need-based strategy of developing varieties and eventual delivery to farmers from 2017-2018.The estimated rice production for the three rice growing seasons 2015 correlates well with data at the district level collected from the province statistics offices with development of proper technologies for Cultivating climateresilient rice varieties in the coastlines of Mekong Deltat enhancing and stabilizing farm level productivity and for improving farmers livelihoods. This is being achieved through the development of rice varieties with tolerance to prevailing abiotic stresses, adoption of proper soil, water for higher and stable productivity of these varieties .These efforts are being supported in part, by funds provided by the Program on salinity for climated change through Tay Nam Bo project.

II. MATERIAL AND METHODS
Some lines 24 lines obtained from the High Agricultural Technology Research Institute for Mekong delta, Vietnam (HATRI).

Phenotype analysis
A field experiment was transplanted to an irrigated lowland field in a randomized complete block design in three replications in the field of HATRI at BinhThuy, Can Tho. 24 lines with their parents were used to evaluate agronomic characteristics and salinity detection through sensory test and genotypic analysis using SSR markers in lab of HATRI. Data on important agronomic traits like plant height, panicle length, filled grains/panicle, unfiled grain/panicle, 1000grain weight, harvest index and yield were recorded.
Ten randomly selected plants of each genotype were used for agronomic data analysis. Data on plant height (cm), number of effective tillers/plants, panicle length (cm), number of filled grains/panicle, 1000-grain weight (g), days to maturity and grain yield/plant (g) were recorded and subjected to statistical analyses using SAS software. After harvesting, the seeds of each genotype were dehulled for evaluation of the grain quality and aroma. The grains were classified into different types based on their dimension according to Dela Cruz and Khush.1989 . Ten seeds of each cultivar removed rice hull and mashed by hand. Take rice powder of each cultivar and put on each experimental tube or petri dish. Add 5ml KOH 1.7% into each petri dish and cover. Store the samples in room temperature for 30 minutes. The samples were scored, corresponding to absence of aroma, slight aroma, moderate aroma and strong aroma, respectively.
Technology evaluation and adaptation. While varieties have already been developed that should be adapted to the local conditions, it is still necessary to evaluate their performance to meet national varietal release requirements. As these varieties perform completely differently undersality conditions than current varieties, comprehensive management practices must be developed so that farmers can fully benefit from them. This will involve (a) initiating testing programs of new varieties in various locations in all province deemed to be susceptible to salinity; (b) conducting comparisons of differing sources of salinitytolerance and combinations of sources to determine which are best suited for different salinity affected areas (different levelstress); (c) conducting of field trials (on-farm and on-station) to refine best management practices for each location; and (d) obtaining feedback results from field and agronomic experiments into varietal development and gene identification programs.

Data Analysis
The agro-morphological data were initially analyzed through examining variance to verify genetic variation in the traits measured. The few traits with insignificant genetic variation, based on the F-test, were not considered for further analyses

Breeding for salinity tolerance in rice
The results show that some lines such as at 20 days after transplanting. At 35 days after transplanting, the highest variety was Evaluation of breeding lines from with local check varieties namely Pokkali and OXY 10 is conducted regularly in both wet season 2018.These lines are evaluated in farmers' fields as well as on station at HATRI. Different traits were assessed, including crop duration, plant height, panicle/ filling and sterility/ plants, quality traits as well as salinity tolerance. Lines that are early maturing (90-110 days) semi dwarf (90-110 cm) with medium number of panicles/hill (7-15 panicles) and high number of grains/panicle (77-199 grains) were selected for further testing in rice-rice cropping pattern when their salinity tolerance is high (survival after 20-25 day salinity at EC = 8 DS/m) and duration of about 98 d, similar to OXy 10. They were these lines will be suitable for salitniy affected( Table 1) International Journal of Environment, Agriculture and Biotechnology, 5 (4)

Use of DNA markers to accelerate progress in breeding for salt tolerance:
Identification of molecular markers associated with quantitative trait loci (QTLs) linked with useful agronomic or adaptive traits will help speed the progress in breeding once developed, because these DNA markers will become effective tools for selection. Moreover, positional cloning using DNA markers will make it possible to isolate agronomically useful genes, which can also be used in breeding across species via transgenic approaches.The study used restriction fragment length polymorphism (RFLP) and . Two QTLs with relatively large effects were identified, one on chromosome 1 (linked to marker 18EC) and the second on chromosome 8 (linked to marker 12EC). Microsatellite markers closely linked to these loci were identified such as RM223 associated with the QTL on Chromosome 8. This marker was further evaluated for its effectiveness in breeding using a set of 24 improved varieties, including tolerant (Pokkali) and sensitive (IR28) checks. These cultivars were genotyped at this marker and then phenotyped for salinity tolerance at 12 dS m -1 in culture solution (Yoshida et al., 1976) using visual SES scores. The results indicated an accuracy of more than 95% in identifying tolerant cultivars using this marker (Table 2). These results indicated the usefulness of this marker in parental surveys and in identifying tolerant lines from segregating populations; however, further tests are needed to confirm its effectiveness in different genetic backgrounds. More efforts are needed to develop closely linked markers to these two QTLs to be used for their routine introgression into popular varieties and elite breeding lines.  10andPokkali were tested in the field and seeds provided to farmers in several provinces for further testing.

Advancing rice research
Confronting the huge challenges of developing varieties in the less-favorable rice areas necessitates partnerships and strategies that capitalize on and foster synergism among related projects in Vietnam. Having strong financial support from the government and other external programs, Vietnam has been successful in scientific and development work leading to releases of a significant number of climate-resilient varieties and suitable crop management practices. The well-focused development agenda of the national government has been a driving force in raising the level of productivity in difficult rice ecosystems. Moreover, HATRI institutions has also been instrumental in catalyzing support, resources and capacities that is now creating impact on Vietnam's rice productivity at the farmers' fields, and producing surplus for local and export markets.
The project has been breeding for salinity using MAS, building up on the prior knowledge and system of rice breeding at the (HATRI) institute. In collaboration with other Vietnam institutions, andRice Climate for salinity project, HATRI has developed several climate-resilient rice varieties such as grain quality and salinity-tolerant varieties by intro gressing Saltol and quality QTLs into elite genotypes. For its expansion efforts, partners distributed seeds of salinitytolerant elite lines for field evaluation in farmers' fields. Beginning in 2017, HATRI aim (1) to breed and develop new rice varieties (2-3 varieties) suitable for export standards and adapted to the conditions in the Mekong Delta, salinitytolerant, early-maturing, high-yielding, and with good quality, as well as with resistance to major insects/pests; (2) and to build up technical procedures for cultivation of new rice varieties in salinity tolerance of the Delta.
With HATRI 's involvement in Rice Climate activities, at least fourteen (14) varieties have been supported that have now been doing releases ( Table 3)

Yield testing on rice varieties
To select the rice varieties with high yield potential, insect pest resistance for condition in Mekong delta. To find out the rice varieties with desirable traits for hybridization in rice improvement programs.
Including lines rice varieties with Pokkali, OXY 10 for checked, growing dry seasons 2017-2018. Yield testing experiments were laid out in completely randomized block designs with 3 replications in BaTri's experimental field. Statistical analysis was cited (Gomez and Gomez, 1982). Data records on agronomic characters, yield and yield components were also guided as SES (IRRI, 1996). Insect, disease screening experiments were laid out in single replication. Evaluation of insect and disease reaction at seedling stage (IRRI, 1996). Agronomic characters were presented in table 3.

Combination of traits for multiple stresses.
One of the difficulties in rice areas severely affected by variability in climatic conditions is the occurrence of multiple stresses over a cropping season. To address this concern and with the advances in molecular biology particularly using MAS, the breeding program of HATRI used pyramiding technique to combine genes responsible for tolerance to a combination of stresses. For instance, in 2017, in developing high-yielding rice varieties tolerant to salinity and quality total of ten (10) single and multiple crosses were done for combining sality and quality rice into the high-yielding genetic background. Genetic diversity is emphasized as a success factor in breeding, as well as in understanding the relationship between genotype and phenotype. Strategic development of the varieties focus on the following: (a) adaptation to effects of sality, both at the seedling stage and flowering stage, (b) improved yield to exceed 5-6 tons/ha, and (c) providing the basis of genetic diversity.
Emphasis on grain quality. Grain quality is considered an important trait contributing to farmers' preference or selection of a variety. This is also taken into consideration in breeding works to know which traits are most popular among traders. For instance, to develop long and medium grain rice cultivars, 20 crosses were made in 2017. The F2, BC1, BC2, BC3 seeds were planted at HATRI in the wet season and dry season. Samples of seed from each harvested plant were sent to the Riceland quality lab for grain quality evaluation at HATRI and selected crosses were evaluated using MAS for amylose content, aroma and blast resistance. The best yielding lines selected from these experiments were advanced to the HATRI. Twenty advanced long grain lines were also tested in the 6 provinces for trials, indicating that long grain rice cultivars could be ready for release in the near future.

Evaluation of salinity stress varieties in farmers' fields
Performance stability is one of the most important properties of a genotype to be released as a variety to ensure wide adoption. To ensure this, we tested 12 indica rice verities at 7 different locations during the wet season 2018 and dry seasons of 2018-2019, using a randomized block design with three replications in each case. Duration, grain yield (t ha -1 were presented in Table 4, 5. The experiment was conducted in 7 provinces, Can tho (checked),TraVinh, Ca Mau, SocTrang,Long An, Ben Tre and Bac

Potential application site
For the salinity-tolerant varieties, scaling up can be done by region, where the stresses have been determined and estimated. In different provinces, based on results of multi-location trials, the following are the potential expansion areas for dissemination and farmers' use of the now popular varieties (Table 7).

IV. DISCUSSION
Salt-affected soils of the Mekong delta are highly degraded, with a complex of abiotic stresses including salinity, acid sulfate, toxic levels of aluminum and iron and deficiency in some nutrients such as P and K. To enhance and sustain productivity of these soils, we adopt an integrated approach involving the development of adapted high yielding and salt tolerant varieties developed via novel breeding methods, proper management of resources and introduction of effective cropping patterns that cam meet farmers' needs and market demands( CGIAR .2016).
In different provinces, based on results of multi-location trials, the following are the potential expansion areas for dissemination and farmers' use of the now popular varieties ( Table 7).The strong advocates of technology are still the leaders of the locality, who are normally the president of the commune and director of province of the agriculture agency.Farmers observe the trials or their neighbors' field and exchange of information among themselves. If the local community does not accept or refuses to accept the technology or rice variety, the varieties cannot be applied and disseminated.While it depends on the province, the farmers typically make the decision to adopt or refuse to

V. CONCLUSIONS AND FUTURE PROSPECTS
Development of salt tolerance varieties is generally considered the most effective entry point for improving productivity of salt affected soils, and it is also the cheapest option for farmers. Through the use of innovative breeding strategies involving conventional and modern tools, together with effective phenotyping techniques, good progress was made in developing salt tolerant varieties with broad adaptation to the conditions of the Mekong Delta. Some varieties such as HATRI 190, HATRI 170, HATRI 192were developed that can yield4-5 tons ha -1 under 8.0 to 10.0 dS m -1 ,and are being out-scaled. The success of new varieties is assured through eventual testing and selection in target sites in partnership with farmers and under their own management to guarantee relevance and adoption. This is achieved through combined use of salt tolerant genotypes, coupled with proper nursery management and seedling handling that ensures maximum survival of transplanted seedlings. .
Future efforts should focus on further collection and evaluation of local germplasm to identify landraces with greater tolerance of salt stress, as sources of new genes or alleles for breeding. Additional breeding efforts such as mutation breeding and identification of soma clonal variants should continue to develop better pre-breeding material. To benefit from the new and exciting developments in the field of genomics, additional resources and efforts should be directed towards identification of QTLs and genes underlying tolerance to the multiple stresses experienced in these problem soils of Mekong Delta, for their subsequent integration into modern varieties and elite breeding lines through marker aided breeding. Special efforts should also be placed on training of young scientists to prepare a new generation that can effectively tackle these problems in a team approach.
In the future, stronger linkages and exchange of knowledge through project networks and meetings will also give considerable impacts on capacity strengthening, as well as meeting with scientists, extension workers, civil society organizations in affected areas to plan on the distribution of seed and other adaptation activities to assure farmer acceptance of seed, and determine the quantity of seed required for distribution. Consultation and meetings with people from different sectors involved in the project will also address the development of seed multiplication plan for different varieties needed for different areas identifying the most likely partners to participate in the finalization of seed development and distribution; and identifying training needs of these in terms of technology adaptation, evaluation, and dissemination.