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CARDI Books
Title:
Effects of straw mulch on mungbean yield in rice fields with strongly compacted soils, by Som Bunna, Pao Sinath, Ouk Makara, Jaquie Mitchell, Shu Fukai. Field Crops Research 124 (2011) 295–301
Description:

Abstract
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.

Full article
 

keyword:
Lowland rice field Mungbean Straw mulch Crop establishment Weed biomass

Abstract
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.

Full article
 

Title:
Ecophysiological study on weed seed banksand weeds in Cambodian paddy fields with contrasting water availability, by AKIHIKO KAMOSHITA, HIROYUKI IKEDA, JUNKO YAMAGISHI, MAKARA OUK, Weed Biology and Management 10, 261–272 (2010)
Description:

Abstract
Weed infestations are a major cause of yield reduction in rice (Oryza sativa) cultivation, particu-larly with direct-seeding methods, but the relationship between weed dynamics and wateravailability in Cambodian paddy fields has not been documented previously.We surveyed theweed abundance and weed seed banks in the soil of paddy fields with inferred differences intheir water regime in 22 farm fields in three provinces of Cambodia in the 2005 and 2006 rainy seasons.We studied rainfed lowland fields in upslope and downslope topographic positions andfields at different distances from the irrigation water source inside an irrigation rehabilitation area.The weed seed banks were estimated by seedling emergence in small containers and weedabundance and vigor were estimated by a simple scoring system.The estimated weed seed bankin the top 5 cm of soil ranged from 52.1 to 167 * 103 seeds m-2 (overall mean of 8.5 * 103 seeds m-2) and contained a high proportion (86%) of sedge species, such as Fimbristylis miliacea L. and Cyperus difformis. Several fields had particularly large seed banks, including one near the reservoir. No clear difference was found in the weed seed banks between the irrigated fields thatwere located close to (upstream) and distant from (downstream) the water source or betweenthe irrigated and rain-fed lowland fields, but the weed scores were larger in the rain-fed fieldsand the downstream fields within the irrigated area. A water shortage during the late growingseason in 2005 led to a proliferation of weeds in some fields and an associated increase in weedseedbank size in 2006. However, the weed scores in 2006 were more strongly associated with that year’s water conditions than with the weed seedbank size.

Full article
 
keyword:
Cambodia, direct seeding, irrigation rehabilitation, rain-fed lowland rice.

Abstract
Weed infestations are a major cause of yield reduction in rice (Oryza sativa) cultivation, particu-larly with direct-seeding methods, but the relationship between weed dynamics and wateravailability in Cambodian paddy fields has not been documented previously.We surveyed theweed abundance and weed seed banks in the soil of paddy fields with inferred differences intheir water regime in 22 farm fields in three provinces of Cambodia in the 2005 and 2006 rainy seasons.We studied rainfed lowland fields in upslope and downslope topographic positions andfields at different distances from the irrigation water source inside an irrigation rehabilitation area.The weed seed banks were estimated by seedling emergence in small containers and weedabundance and vigor were estimated by a simple scoring system.The estimated weed seed bankin the top 5 cm of soil ranged from 52.1 to 167 * 103 seeds m-2 (overall mean of 8.5 * 103 seeds m-2) and contained a high proportion (86%) of sedge species, such as Fimbristylis miliacea L. and Cyperus difformis. Several fields had particularly large seed banks, including one near the reservoir. No clear difference was found in the weed seed banks between the irrigated fields thatwere located close to (upstream) and distant from (downstream) the water source or betweenthe irrigated and rain-fed lowland fields, but the weed scores were larger in the rain-fed fieldsand the downstream fields within the irrigated area. A water shortage during the late growingseason in 2005 led to a proliferation of weeds in some fields and an associated increase in weedseedbank size in 2006. However, the weed scores in 2006 were more strongly associated with that year’s water conditions than with the weed seedbank size.

Full article
 
Title:
APPLYING SIMULATION TO IMPROVE RICE VARIETIES IN REDUCING THE ON-FARM YIELD GAP IN CAMBODIAN LOWLAND RICE ECOSYSTEMS, by P. L. POULTON, T. VESNA, N. P. DALGLIESH, V. SENG, Volume 51, Issue 2 April 2015, pp. 264-284
Description:

Abstract

Achieving export growth in rice production from variable rainfed lowland rice ecosystems is at risk if depending on conventional breeding or genetic development alone. Sustained, long-term production requires building adaption capacity of smallholder farmers to better manage the challenges of seasonal climate variability and future climate change. Better understanding of the risks and constraints that farmers face in managing their current cropping system helps develop strategies for improving rice production in Cambodia. System models are now considered valuable assessment tools for evaluating cropping systems performance worldwide but require validation at the local level. This paper presents an evaluation of the APSIM-Oryza model for 15 Cambodian rice varieties under recommended practice. Data from a field experiment in 2011, conducted in a non-limiting water and nutrient environment, are used to calibrate varietal-specific coefficients and model input parameters. An independent dataset is then used to validate the model performance for a ‘real-world’ situation using on-farm data for six rice varieties planted in 54 farmer fields on 32 farms in two villages of Southeastern Cambodia. From this analysis, the APSIM-Oryza model is shown to be an acceptable tool for exploring the mismatch between current on-farm yields and potential production through yield gap analysis and the exploration of cropping system options for smallholder farmers to increase production, adapt to seasonal climate variability and be prepared for potential climate changes.

Full article
 

keyword:
N/A

Abstract

Achieving export growth in rice production from variable rainfed lowland rice ecosystems is at risk if depending on conventional breeding or genetic development alone. Sustained, long-term production requires building adaption capacity of smallholder farmers to better manage the challenges of seasonal climate variability and future climate change. Better understanding of the risks and constraints that farmers face in managing their current cropping system helps develop strategies for improving rice production in Cambodia. System models are now considered valuable assessment tools for evaluating cropping systems performance worldwide but require validation at the local level. This paper presents an evaluation of the APSIM-Oryza model for 15 Cambodian rice varieties under recommended practice. Data from a field experiment in 2011, conducted in a non-limiting water and nutrient environment, are used to calibrate varietal-specific coefficients and model input parameters. An independent dataset is then used to validate the model performance for a ‘real-world’ situation using on-farm data for six rice varieties planted in 54 farmer fields on 32 farms in two villages of Southeastern Cambodia. From this analysis, the APSIM-Oryza model is shown to be an acceptable tool for exploring the mismatch between current on-farm yields and potential production through yield gap analysis and the exploration of cropping system options for smallholder farmers to increase production, adapt to seasonal climate variability and be prepared for potential climate changes.

Full article
 

Title:
Farmers’ Management Practices and Grain Yield of Rice in Response to Different Water Environments in Kamping Puoy Irrigation Rehabilitation Area in Northwest Cambodia, by Yen Thi Bich Nguyen, Akihiko Kamoshita, Yuji Araki & Makara Ouk, Volume 14, 2011 - Issue 4
Description:

Abstract

The farmers’ management practices and grain yield were examined in the consecutive 4 cropping seasons from wet season rice (WSR) in 2008 to dry season rice (DSR) in 2010 across upstream, midstream and downstream fields, along two secondary drainage canals (located either upstream or downstream side along the main canal) in the Kamping Puoy Irrigation Rehabilitation area (KPIR). In WSR, standing water depth was much deeper in downstream fields where medium and late maturing varieties were planted from May than in upstream fields where early and early medium maturing varieties were planted later (mostly in July and August). In DSR there was less difference in water conditions between upstream and downstream fields and variation in planting and harvesting time was small. As the area percentage of fields where DSR was introduced increased from 2008 (54%) to 2010 (100%), planting time in WSR was later (e.g., from May to July) with declining proportion of dry seeding method and mid-season tillage. Grain yield was low in DSR, particularly in 2010 (287 and 247 g m-2 in 2009 and 2010 on average, respectively), due to insufficient weed control and small amount of fertilizer, and the yield was lowest in fields which practiced DSR for the first time. Grain yield in WSR (286 and 291 g m-2 in 2008 and 2009 respectively) increased by transplanting, use of high yielding Raing Chey variety, and application of a larger amount of N chemical fertilizer. These findings indicated that the agriculture extension support to farmers, particularly in DSR, is a key important factor for rice yield improvement in KPIR.

Full article

keyword:
Cambodia, Double cropping, Irrigation rehabilitation, Rice, Water distribution

Abstract

The farmers’ management practices and grain yield were examined in the consecutive 4 cropping seasons from wet season rice (WSR) in 2008 to dry season rice (DSR) in 2010 across upstream, midstream and downstream fields, along two secondary drainage canals (located either upstream or downstream side along the main canal) in the Kamping Puoy Irrigation Rehabilitation area (KPIR). In WSR, standing water depth was much deeper in downstream fields where medium and late maturing varieties were planted from May than in upstream fields where early and early medium maturing varieties were planted later (mostly in July and August). In DSR there was less difference in water conditions between upstream and downstream fields and variation in planting and harvesting time was small. As the area percentage of fields where DSR was introduced increased from 2008 (54%) to 2010 (100%), planting time in WSR was later (e.g., from May to July) with declining proportion of dry seeding method and mid-season tillage. Grain yield was low in DSR, particularly in 2010 (287 and 247 g m-2 in 2009 and 2010 on average, respectively), due to insufficient weed control and small amount of fertilizer, and the yield was lowest in fields which practiced DSR for the first time. Grain yield in WSR (286 and 291 g m-2 in 2008 and 2009 respectively) increased by transplanting, use of high yielding Raing Chey variety, and application of a larger amount of N chemical fertilizer. These findings indicated that the agriculture extension support to farmers, particularly in DSR, is a key important factor for rice yield improvement in KPIR.

Full article

Title:
Field level damage of deepwater rice by the 2011 Southeast Asian Flood in a flood plain of Tonle Sap Lake, Northwest Cambodia, by Akihiko Kamoshita • Makara Ouk, Paddy Water Environ (2015) 13:455–463
Description:
Abstract
The 2011 flood damaged about 11 % of planting area in Cambodia, but the damaged proportion reached 30 % in Sangke district, Battambang province, located in the flood plains of Tonle Sap Lake. The aim of this study was to characterize completely damaged deepwater rice production due to the flood along the transect from the town-side shallower fields to the lake-side deeper fields. The flooding water from Tonle Sap Lake rose with 7 cm/day in September and October in the deeper fields where floating rice was grown and 8–10 cm/day in October in the shallower fields where lowland rice was grown. The maximum water was recorded on 16 October with 3.2 and 2.0 m at the deepest and shallowest edge fields. The area was characterized as flatness with only 1.2 m elevation differences in 4.3 km distance along the transect. The flooding water took 13.7 h for approaching 100 m distance. Complete recession of flood water was end of November at the shallow edge and at late December in the deep edge in 2011. The flooding duration deeper than 50 cm was 2.5 month and nearly 3 months in the middle zone and deeper floating rice area, respectively. The complete submergence started first in some fields in the middle zone on 12 September, followed by the shallower lowland rice area, and finally in the deep floating rice area by 1 October.

Full article


keyword:
Floating rice ; Flood damage ; Flood-prone rice ; Rice ecosystem ; Tonle Sap Lake
Abstract
The 2011 flood damaged about 11 % of planting area in Cambodia, but the damaged proportion reached 30 % in Sangke district, Battambang province, located in the flood plains of Tonle Sap Lake. The aim of this study was to characterize completely damaged deepwater rice production due to the flood along the transect from the town-side shallower fields to the lake-side deeper fields. The flooding water from Tonle Sap Lake rose with 7 cm/day in September and October in the deeper fields where floating rice was grown and 8–10 cm/day in October in the shallower fields where lowland rice was grown. The maximum water was recorded on 16 October with 3.2 and 2.0 m at the deepest and shallowest edge fields. The area was characterized as flatness with only 1.2 m elevation differences in 4.3 km distance along the transect. The flooding water took 13.7 h for approaching 100 m distance. Complete recession of flood water was end of November at the shallow edge and at late December in the deep edge in 2011. The flooding duration deeper than 50 cm was 2.5 month and nearly 3 months in the middle zone and deeper floating rice area, respectively. The complete submergence started first in some fields in the middle zone on 12 September, followed by the shallower lowland rice area, and finally in the deep floating rice area by 1 October.

Full article


Title:
Description:
Abstract

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 2.5 t/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.

Full article
 
keyword:
cropping system, direct seeding, drought, rainfed lowland rice, rice breeding, soil fertility.
Abstract

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 2.5 t/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.

Full article
 
Title:
Farmers’ perceptions on cassava cultivation in Cambodia, by U. Sopheap, A. Patanothaiand T.M. Aye, KHON KAEN AGR. J. 39 : 279-294 (2011).
Description:
Abstract
Cassava is one of the most important upland crops of Cambodia. While improved technologies are needed for sustainable production of the crop, their adoption depends on how farmers view cassava against other crops. The objective of this study was to assess the perception of Cambodian farmers on growing cassava, relative to other upland crops. The study was conducted in Kampong Cham province in Northeast Cambodia which has the largest cassava production area in the country. Secondary data on production and price of cassava and other crops were collected, and 45 households in four cassava production zones were interviewed to obtain information on farmer's perceptions on cassava and other crops. The results showed that production of cassava and other upland crops in Cambodia has increased substantially during recent years, reflecting increased market demand and improved prices. Farmers in the study area in Kampong Cham province regard rice and cassava as their priority crops, and have a greater preference for growing them than other crops, including maize, soybean, mungbean, peanut, sesame and rubber. Rice, however, is grown mainly for domestic consumption, while cassava is grown as a source of cash income. The marketing aspects of the crop, i.e., good price and easy to sell, were the most important considerations for farmers' strong preference for cassava relative to other upland crops. With the current trend of favorable marketing conditions, cassava production in Cambodia is anticipated to expand further, while farmers are also likely to adopt improved technologies that will sustain or improve their cassava yields, even if involving extra input costs. These findings can potentially be used as a basis for the further development and extension of technologies for sustainable production of cassava in Cambodia.

Full article


keyword:
Cassava production, upland crops, farmers’ preference, farmers’ attitude, technology adoption.
Abstract
Cassava is one of the most important upland crops of Cambodia. While improved technologies are needed for sustainable production of the crop, their adoption depends on how farmers view cassava against other crops. The objective of this study was to assess the perception of Cambodian farmers on growing cassava, relative to other upland crops. The study was conducted in Kampong Cham province in Northeast Cambodia which has the largest cassava production area in the country. Secondary data on production and price of cassava and other crops were collected, and 45 households in four cassava production zones were interviewed to obtain information on farmer's perceptions on cassava and other crops. The results showed that production of cassava and other upland crops in Cambodia has increased substantially during recent years, reflecting increased market demand and improved prices. Farmers in the study area in Kampong Cham province regard rice and cassava as their priority crops, and have a greater preference for growing them than other crops, including maize, soybean, mungbean, peanut, sesame and rubber. Rice, however, is grown mainly for domestic consumption, while cassava is grown as a source of cash income. The marketing aspects of the crop, i.e., good price and easy to sell, were the most important considerations for farmers' strong preference for cassava relative to other upland crops. With the current trend of favorable marketing conditions, cassava production in Cambodia is anticipated to expand further, while farmers are also likely to adopt improved technologies that will sustain or improve their cassava yields, even if involving extra input costs. These findings can potentially be used as a basis for the further development and extension of technologies for sustainable production of cassava in Cambodia.

Full article


Title:
Unveiling constraints to cassava production in Cambodia: An analysis from farmers’ yield variations, by U. Sopheap; A. Patanothai; T.M. Aye, Article 2, Volume 6, Issue 4, Autumn 2012, Page 409-428
Description:
Abstract
Cassava (Manihot esculenta Crantz) is currently the most important upland crop of Cambodia, but information on yield variations and causal factors which is important for efficiently targeting efforts to increase production is still lacking. The objectives of this study were to determine the yield variations and causal factors for cassava production in Kampong Cham province in Cambodia. Forty five households in four production zones were selected for the study. A farm survey employing semi-structured interviews, combined with field visits, were used for the collection of information on farmers' practices in cassava cultivation, while crop cutting was done to provide estimates of cassava yields. The data were analyzed for yield variations, yield gaps and causal factors. The results showed large variations in yield among farmers' fields, ranging from 12.7 to 37.2 t ha -1. The fields were divided into five yield categories, with the mean yields of the lower four categories ranging from 76.0 to 34.2% of the maximum yields, with corresponding yield gaps ranging from 8.9 to 24.4 t ha -1. The main yield constraints identified were soil nutrient deficits, short crop duration and weed competition. The highest yielding fields had no production constraints, but the number and/or the level of constraints increased in fields with lower crop yields. However, for different fields with similar yield levels, the main production constraints sometimes differed. The results clearly indicated that there are opportunities for yield improvement and narrowing of yield gaps through the adoption of field specific improved technologies and management practices.

Full Article


keyword:
Keywords: Yield gap; Yield limiting factors; Cassava cultivation; Production constraints; crop management
Abstract
Cassava (Manihot esculenta Crantz) is currently the most important upland crop of Cambodia, but information on yield variations and causal factors which is important for efficiently targeting efforts to increase production is still lacking. The objectives of this study were to determine the yield variations and causal factors for cassava production in Kampong Cham province in Cambodia. Forty five households in four production zones were selected for the study. A farm survey employing semi-structured interviews, combined with field visits, were used for the collection of information on farmers' practices in cassava cultivation, while crop cutting was done to provide estimates of cassava yields. The data were analyzed for yield variations, yield gaps and causal factors. The results showed large variations in yield among farmers' fields, ranging from 12.7 to 37.2 t ha -1. The fields were divided into five yield categories, with the mean yields of the lower four categories ranging from 76.0 to 34.2% of the maximum yields, with corresponding yield gaps ranging from 8.9 to 24.4 t ha -1. The main yield constraints identified were soil nutrient deficits, short crop duration and weed competition. The highest yielding fields had no production constraints, but the number and/or the level of constraints increased in fields with lower crop yields. However, for different fields with similar yield levels, the main production constraints sometimes differed. The results clearly indicated that there are opportunities for yield improvement and narrowing of yield gaps through the adoption of field specific improved technologies and management practices.

Full Article


Title:
Pathogenicity of Rice Blast (Pyricularia oryzae Cavara) Isolates from Cambodia, by Yoshimichi FUKUTA, Ikumi KOGA, Tochi UNG, Khay SATHYA, Akiko KAWASAKI-TANAKA, Yohei KOIDE, Nobuya KOBAYASHI, Mitsuhiro OBARA, Hun YADANA, Nagao HAYASHI,
Description:
Abstract
The evaluation of a total of 122 blast (Pyricularia oryzae Cavara) isolates collected from the Tonle Sap and Mekong river regions of Cambodia revealed wide variation. Using a new designation system, the blast isolates were categorized into 92 races based on the reaction patterns of rice (Oryza sativa L.) differential varieties (DVs) harboring 23 resistance genes and of 1 susceptible cultivar, Lijiangxintuanheigu (LTH). Cluster analysis was used to classify the blast isolates into 3 groups — I, IIa, and IIb — using data from these reaction patterns of the DVs and LTH. We used the classifications established under the new designation system, alongside cluster analysis and the geographical distribution of blast isolates, to investigate the diversity and differentiation of blast races in the Tonle Sap and Mekong river regions. The distributions of the blast races differed between the 2 regions, although blast isolates of group IIa were distributed commonly in both regions and groups I and IIb occurred at higher frequencies in the Tonle Sap region rather than the Mekong region. The blast isolates in groups I and IIb were also less diverse than those in group IIa. Accordingly, Group II blast isolates overall were distributed in both regions with high diversity, but some modified blast isolates were additionally distributed in the Tonle Sap region. We also investigated the pathogenicities of blast isolates from wild rice (Oryza rufipogon Griff) weeds neighboring the cultivated rice, and discuss the relationship between these isolates and those from cultivated rice.

Full Article
keyword:
cluster analysis, differential variety, diversity, pathotype, resistance gene
Abstract
The evaluation of a total of 122 blast (Pyricularia oryzae Cavara) isolates collected from the Tonle Sap and Mekong river regions of Cambodia revealed wide variation. Using a new designation system, the blast isolates were categorized into 92 races based on the reaction patterns of rice (Oryza sativa L.) differential varieties (DVs) harboring 23 resistance genes and of 1 susceptible cultivar, Lijiangxintuanheigu (LTH). Cluster analysis was used to classify the blast isolates into 3 groups — I, IIa, and IIb — using data from these reaction patterns of the DVs and LTH. We used the classifications established under the new designation system, alongside cluster analysis and the geographical distribution of blast isolates, to investigate the diversity and differentiation of blast races in the Tonle Sap and Mekong river regions. The distributions of the blast races differed between the 2 regions, although blast isolates of group IIa were distributed commonly in both regions and groups I and IIb occurred at higher frequencies in the Tonle Sap region rather than the Mekong region. The blast isolates in groups I and IIb were also less diverse than those in group IIa. Accordingly, Group II blast isolates overall were distributed in both regions with high diversity, but some modified blast isolates were additionally distributed in the Tonle Sap region. We also investigated the pathogenicities of blast isolates from wild rice (Oryza rufipogon Griff) weeds neighboring the cultivated rice, and discuss the relationship between these isolates and those from cultivated rice.

Full Article


Title:
Description:

keyword:
N/A

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