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Fukai S.,University of Queensland | Ouk M.,Cambodia Agricultural Research and Development Institute
Crop and Pasture Science | Year: 2012

Rice in Thailand, Laos and Cambodia (the Mekong region) is grown mostly as a mono crop once a year in the wet season in the rainfed lowlands. Some lowland areas have access to irrigation water, and rice double cropping is practised while non-rice crops are grown in a limited area in the dry season after harvesting wet season rice. In all cases wet season rice is grown mostly for subsistence under rainfed with low input, and combined with low soil fertility and frequent occurrence of drought, the yield is generally low with a mean of 2.5t/ha and the yield increase was slow in recent years. More recently demand for labour in the regional centres has caused labour shortages in the rural area and rice crops may not be managed in the traditional manner such as the practice of manually transplanting of rice seedlings. For the last two decades research efforts have been made to minimise the adverse effect of abiotic factors and to meet the changing nature of the socioeconomic environment, resulting in increased understanding of factors determining productivity of rainfed lowland rice and the cropping systems based on it. This review describes such achievements in five sections - water environment characterisation to quantify drought problems, soil environment and fertiliser management, direct seeding to develop technology to cope with the labour shortage, variety improvement for rainfed lowland rice in drought-prone environment, and crop intensification and diversification that shift practices from traditional subsistence agriculture to more market-oriented agriculture. Each section is concluded with issues for future research need. The last section of the paper describes future research challenges for the rainfed rice-based lowland cropping systems in the Mekong region and possible implication on rainfed lowland rice system on other regions. © CSIRO 2012. Source


Ntui V.O.,Chiba University | Ntui V.O.,University of Calabar | Ntui V.O.,King Abdullah University of Science and Technology | Kong K.,Chiba University | And 8 more authors.
PLoS ONE | Year: 2015

Cassava ranks fifth among the starch producing crops of the world, its annual bioethanol yield is higher than for any other crop. Cassava cultivar KU50, the most widely grown cultivar for non-food purposes is susceptible to Sri Lankan cassava mosaic virus (SLCMV). The objective of this work was to engineer resistance to SLCMV by RNA interference (RNAi) in order to increase biomass yield, an important aspect for bioethanol production. Here, we produced transgenic KU50 lines expressing dsRNA homologous to the region between the AV2 and AV1 of DNA A of SLCMV. High level expression of dsRNA of SLCMV did not induce any growth abnormality in the transgenic plants. Transgenic lines displayed high levels of resistance to SLCMV compared to the wild-type plants and no virus load could be detected in uninoculated new leaves of the infected resistant lines after PCR amplification and RT-PCR analysis. The agronomic performance of the transgenic lines was unimpaired after inoculation with the virus as the plants presented similar growth when compared to the mock inoculated control plants and revealed no apparent reduction in the amount and weight of tubers produced. We show that the resistance is correlated with post-transcriptional gene silencing because of the production of transgene specific siRNA. The results demonstrate that transgenic lines exhibited high levels of resistance to SLCMV. This resistance coupled with the desirable yield components in the transgenic lines makes them better candidates for exploitation in the production of biomass as well as bioethanol. © 2015 Ntui et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Source


Bunna S.,Cambodia Agricultural Research and Development Institute | Sinath P.,Cambodia Agricultural Research and Development Institute | Makara O.,Cambodia Agricultural Research and Development Institute | Mitchell J.,University of Queensland | Fukai S.,University of Queensland
Field Crops Research | Year: 2011

In rice-based lowland areas in the Mekong region, the lack of full irrigation water availability for post-rice legume crops and the poor soil physical and chemical conditions are major constraints for development of sound rice/legume double cropping system. In order to improve legume productivity, use of rice straw mulch and various crop establishment methods were examined in two series of mungbean experiments in Cambodia where soils were coarse and strongly compacted. In one set of experiments conducted at four locations in the first year the effect of straw mulch, planting method (manual vs seed drill) and tillage method (conventional vs no-till) was examined. Another set of experiments were conducted in the second year at three locations with four levels of mulch under two planting densities. On average in year 1, mulching of rice straw at 1.5. t/ha increased mungbean crop establishment from 72 to 83%, reduced weed biomass from 164 to 123. kg/ha and increased yield from 228 to 332. kg/ha. Mulch was effective in conserving soil moisture, and even at maturity the mulched area had on average 1% higher soil moisture content. The amount of mulch between 1 and 2. t/ha did not show consistent effects in year 2, partly because some mulch treatments resulted in excessive soil moisture content and were not effective. Rice straw mulch had a significant effect on mungbean yield in 6 out of the 7 experiments conducted in two years, and mean yield increase was 35%. This yield advantage was attributed to better crop establishment, improved growth and reduced weed pressure, but in some cases only one or two of these factors were effective. On the other hand, planting method, tillage method and planting density had only small effects on mungbean yield in most experiments. Only in one location out of four tested, the no-till treatment produced significantly higher yield than the conventional method. Seed drill produced similar mungbean establishment and grain yield to the manual planting suggesting that the planter can be used to save the labour cost which is increasing rapidly in the Mekong region. Maximum root depth varied little with mulch or planting density, and was shallow (<20. cm) in all three locations where this character was determined. It is concluded that while rice straw mulch increased yield of mungbean following rice, the inability of mungbean roots to penetrate the hard pan is a major constraint for development of a sound rice/mungbean cropping system in the lowlands with compacted soils. © 2011 Elsevier B.V. Source


Mitchell J.,University of Queensland | Cheth K.,University of Queensland | Cheth K.,Cambodia Agricultural Research and Development Institute | Seng V.,Cambodia Agricultural Research and Development Institute | And 3 more authors.
Field Crops Research | Year: 2013

Crop diversification is advocated for improvement of income of lowland rice farmers in the Mekong region, including Laos, Cambodia and Thailand. One common problem of adding non-rice crops after wetland rice is excess water caused by reduced drainage associated with the hard pan that is commonly created to store water in the paddy for the rice crop. This paper firstly describes the water balance in the lowland fields particularly on how deep percolation is decreased by the hard pan, and the effect of wet cultivation on soil compaction and water availability in the subsequent crops such as mungbean. Experimental work in Cambodia shows how non-rice crops such as mungbean and peanut often fail completely or partially due to excess water. The common experience is complete failure of the early wet season non-rice crop when rain started earlier and the lowland paddy is saturated with water, but also non-rice crops often do not grow well due to shallow root systems confined to the top soil above the hard pan. Destructing the hard pan may help non-rice crops, but the process is expensive and may have an adverse effect on subsequent rice crops. Experimental work has also demonstrated that where irrigation water is available, irrigation is often not effective as it causes soil saturation in the top soil. Ways to minimize the excess water problem are discussed. © 2012 Elsevier B.V. Source

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