Het voorkomen, schadepotentiëel en duurzaam beheer van de rijst wortelknobbelnematode Meloidogyne graminicola op laag- en hoogland rijst in Myanmar

Rice cultivation is the major source of food and cash income for many small-scale farmers in Myanmar, and the most important agricultural crop of the country. It is followed by oilseed crops and pulses ranking second and third most important, respectively. Due to the high diversity of agro-climatic conditions in Myanmar, rice is cultivated in different cropping sequences using suitable cultivation practices under different agro-ecosystems. The rice root-knot nematode Meloidogyne graminicola is an important soil-borne pathogen of rice and can cause a varying degree of yield losses under different agro-ecosystems in South and Southeast Asia. However, no detailed information is presently available on the occurrence of M. graminicola in rice-based production systems under different agro-ecosystems of Myanmar along with the damage and yield losses this nematode can cause.Therefore, in the 1st part of our study (Chapter 2), two surveys were carried out during 2009. The first survey was during the dry summer season (mid-January to mid-May) in 450 rice fields from ten regions representing the summer-irrigated lowland rice ecosystem in the lower Ayeyarwady River Delta area of Myanmar. The second survey was during the rainy (monsoon) season (mid-May to mid-October) in 102 rice fields from three regions representing the rainfed upland rice ecosystem in the northern hilly area of Myanmar. The two surveys revealed that M. graminicola is unquestionably a major pathogen of the summer-irrigated lowland rice ecosystem in Myanmar. Meloidogyne graminicola was found in 78% of 450 summer-irrigated lowland rice fields but only 9% of 102 rainfed upland rice fields. The practice of delayed irrigation and intermittent flooding is the most commonly used practice in the summer-irrigated lowland rice growing area while rainfed upland rice is cultivated in a 2-year rotation system in the northern hilly area. In lowland rice, M. graminicola was found in 87% of the delayed irrigated rice fields and 45% of the early irrigated rice fields. The rice root nematode Hirschmanniella oyzae was detected in only 15% of the summer-irrigated lowland rice fields.In the 2nd part of our study (Chapter 3), a study was undertaken from December 2009 until December 2010 in the Ayeyarwady River Delta area, 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 were obtained from two rice varieties, Yatanartoe and Taungpyang, that are commonly cultivated in double rice cropping sequences in Myanmar and that represent a summer-irrigated and a rainfed lowland rice variety, respectively. The results of this study illustrated the remarkable influence of the long rice growing season on the occurrence of these two important rice nematodes. Meloidogyne graminicola could build up high population densities and induce root galling only during the summer-irrigated rice growing season while H. oryzae could build up high population densities only during the monsoon rice growing season. 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 (10,056 J2/g roots) in January and at the heading stage of the rice plants (13,923 J2/g roots) in March 2010. During the rainfed monsoon rice growing season, the root population density of H. oryzae juveniles and adults showed also two distinct peaks: at the maximum tillering stage of the rice plants (176/g roots) in August and at the heading stage of the rice plants (280 H. oryzae/g roots) in October 2010. In the 3rd part of our study (Chapter 4), the host response to M. graminicola infection of 15 lowland rice varieties and nine upland rice varieties, which are commonly being grown in the summer-irrigated lowland and rainfed upland rice ecosystems in Myanmar, were 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). Based on the multiplication factors (Mf –eggs) at 8 weeks after inoculation (WAI), none of the 15 lowland and nine upland rice varieties were found to be 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 to M. graminicola infection, five (or 33.3%) as moderately susceptible while four (or 26.7%) as highly susceptible. One (or 11.1%) out of the nine upland varieties examined was classified as less susceptible to M. graminicola infection, three (or 33.3%) as moderately susceptible while five (or 55.6%) as highly susceptible. 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 based on plant growth variables at 8 WAI. In the 4th part of our study (Chapter 5), the damage potential and yield loss of M. graminicola infection was investigated on 15 lowland rice varieties under screenhouse conditions and in a naturally-infested farmer’s field in the Ayeyarwady River Delta area and on nine upland rice varieties under screenhouse conditions. The lowland rice varieties were intermittently flooded in a clay loam soil and the upland rice varieties were maintained at field capacity in a sandy loam soil. The results of these studies confirm that M. graminicola is potentially a very important constraint for rice production in Myanmar. In the screenhouse and the field experiment it reduced the yield of 15 commonly cultivated lowland rice varieties on average with 31.1 and 16.5%, respectively. In the screenhouse experiment with nine commonly cultivated upland rice varieties it caused a 44.9% yield reduction. All rice varieties examined, except one upland variety (Khaukphephan), were highly sensitive to M. graminicola. This part of our study also confirms the results of the host response study in Chapter 4 that upland rice varieties are more susceptible and sensitive to M. graminicola compared with lowland rice varieties.In the 5th part of our study (Chapter 6), two screenhouse experiments were carried out. The first to evaluate the effects of three water regimes (permanent flooding, intermittent flooding, upland) on the damage and yield loss potential of M. graminicola on a commonly cultivated lowland (Thihtatyin) and upland (Kone Myint 2) rice variety in two soil types (clay loam and sandy loam). The second to evaluate the effects of two irrigation (early irrigation and delayed irrigation) and two planting (direct seeding and transplanting) practices on the damage and yield loss potential of M. graminicola on two commonly cultivated lowland rice varieties (Thihtatyin and Yatanartoe). In the first experiment, no significant effects were observed of any of the water regimes on the population densities of M. graminicola of both rice varieties in both soil types with exception of the higher number of J2/g roots of the variety Kone Myint 2 under upland conditions compared with permanent flooding (11,013 vs 2,336 J2/g roots) in the sandy loam soil. Based on the multiplication factors (Mf –eggs ), the effect of water regime on the population density of M. graminicola is influenced by the soil type in which the rice plants are grown but this effect can vary among rice varieties. Less root galling severity was observed under permanent flooding in both soil types (clay loam and sandy loam). Tolerance of both rice varieties was observed under permanent flooding in the clay loam soil. However, the grain yield of the variety Kone Myint 2 was reduced by M. graminicola in the sandy loam soil under all water regimes including permanent flooding (38.7%). Under intermittent flooding, grain yield reduction was 21.9% on the variety Thihtatyin and 45.2% on the variety Kone Myint 2 in the clay loam soil while grain yield reductions higher than 70% on both varieties were observed in the sandy loam soil. Under upland conditions, grain yield reduction was 24.1% for the variety Thihtatyin and 57.9% for the variety Kone Myint 2 in the clay loam soil while grain yield reductions higher than 90% were observed on both varieties in the sandy loam soil.In the second experiment, both rice varieties were less susceptible in direct seeded rice that had been early irrigated. For both varieties, the highest Mf –eggs were observed in transplanted plants that had been delayedirrigated. For both varieties, the highest number of J2 and eggs per root unit and per root system, and on Mf –eggs were observed in transplanted plants compared with direct seeded plants irrespective of irrigation practice. The highest root galling index (7.4) was observed on transplanted delayed irrigated plants of the variety Thihtatyin while the lowest root galling index (1.8) was observed on direct seeded early irrigated plants of the variety Yatanartoe. Reduction in most of the plant growth and yield variables measured caused by M. graminicola was observed in transplanted plants of both rice varieties grown under delayed irrigation. Tolerance of both rice varieties was observed in direct seeded rice that had been early irrigated. The variety Yatanartoe was more tolerant than the variety Thihtatyin. For the variety Yatanartoe, grain yield loss caused by M. graminicola was observed only in transplanted rice that had been delayed irrigated (30.8%). For the variety Thihtatyin, grain yield loss was observed in both direct seeded rice and transplanted rice (40 and 37%, respectively) under delayed irrigation and in transplanted rice (41.3%) under early irrigation.In the 6th part of our study (Chapter 7), screenhouse experiments were conducted to evaluate the response to M. gramnicola infection of 27 varieties belonging to 14 crops (blackgram, cabbage, cauliflower, chickpea, cowpea, garlic, ginger, greengram, groundnut, maize, potato, sesame, soybean, sunflower) which are grown in rotation with rice in both lowland and upland rice-based ecosystems in Myanmar. Our observations indicate that all 27 varieties belonging to 14 crops examined except chickpea variety Yezin 4 were poor or non-hosts of M. graminicola.In the 7th and last part of our study (Chapter 7), a microplot experiment was carried out under natural lowland rice field conditions to evaluate the effect of different rice-based crop rotation sequences on the population densities of M. graminicola and on the yield of rice. Ten treatments of cropping sequences were grown in four successive growing seasons: continuous growing of the susceptible rice variety Thihtatyin (rice-rice-rice-rice), four treatments of 1-season crop rotation sequences (rice-rice-chickpea-rice, rice-rice-blackgram-rice, rice-rice-soybean-rice, rice-rice-cowpea-rice), five treatments of 2-season crop rotation sequences (groundnut-rice-chickpea-rice, greengram-rice-balackgram-rice, cowpea-rice-soybean-rice, sesame-rice-cowpea-rice, sunflower-rice-sesame-rice). In the 2nd season, the susceptible rice variety Thihtatyin was cultivated in all cropping sequences since rice is the only crop which can be grown under flooding during the rainy season. At the harvest of the summer-irrigated rice variety Thihtatyin in the (last) 4th season, the soil and root population densities of M. graminicola recovered from the rice plants and the nematode multiplication factors in the soil (Mf –soil) in the continuous rice cropping sequence was the highestamong the ten cropping sequences. The lowest Mf soil was observed in the 2-season crop rotation sequence sunflower-rice-sesame-rice (5.9) and the highest Mf soil was observed in the 1-season crop rotation sequence rice-rice-cowpea-rice (38.2) among the nine crop rotation sequences while Mf soil in the continuous rice cropping sequence was 61.5. The root galling indices caused by M. graminicola on the roots of rice plants in the continuous rice cropping sequence were significantly higher than those of the 2-season crop rotation sequences. However, no significant difference was observed with the 1-season crop rotation sequences. All the plant growth and yield variables except % filled grain/plant and number of filled grains/panicle of summer-irrigated rice in the continuous rice cropping sequence were the lowest among the ten cropping sequences. The highest summer-rice yield (> 5 t/ha) was obtained in the 2-season crop rotation sequences greengram-rice-blackgram-rice, sesame-rice-cowpea-rice and sunflower-rice-sesame-rice, which were about 2 times higher compared with the 1-season crop rotation sequences rice-rice-blackgram-rice and rice-rice-chickpea-rice (2.7 and 2.6 t/ha, respectively), and about 3 times higher compared with the continuous rice cropping sequence (1.7 t/ha).ACKNOWLEDGEMENTS i TABLE OF CONTENTS iii LIST OF TABLES vi LIST OF FIGURES ix SUMMARY xii SAMENVATTING xviii LIST OF ABBREVIATIONS xxiv CHAPTER 1: INTRODUCTION 1 1.1 Objective of the study and outline of the thesis 1 1.2 Rice (Oryza sativa L.) 6 1.3 Rice-based cropping sequences in Myanmar 17 1.4 Rotation crops cultivated in lowland rice ecosystem 19 1.5 Contraints of rice productions 20 1.6 Plant parasitic nematodes associated with rice 20 1.7 The rice root-knot nematode, Meloidogyne graminicola Golden and Birchfield, 1965 21 1.8 Meloidogyne graminicola in Myanmar rice production 26 CHAPTER 2: EFFECT OF AGRO-ECOSYSTEM ON THE OCCURRENCE OF THE RICE ROOT-KNOT NEMATODE MELOIDOGYNE GRAMINICOLA ON RICE IN MYANMAR 27 2.1 Introduction 27 2.2 Materials and methods 29 2.3 Results 32 2.4 Discussion 38 CHAPTER 3: POPULATION DYNAMICS OF MELOIDOGYNE GRAMINICOLA AND HIRSCHMANNIELLA ORYZAE IN A DOUBLE RICE CROPPING SEQUENCE IN THE LOWLANDS OF MYANMAR 43 3.1 Introduction 43 3.2 Materials and methods 45 3.3 Results 47 3.4 Discussion 55 CHAPTER 4: EVALUATION OF THE HOST RESPONSE OF LOWLAND AND UPLAND RICE VARIETIES FROM MYANMAR TO THE RICE ROOT-KNOT NEMATODE MELOIDOGYNE GRAMINICOLA 63 4.1 Introduction 63 4.2 Materials and methods 66 4.3 Results 71 HOST RESPONSE TO MELOIDOGYNE GRAMINICOLA INFECTION OF THE LOWLAND RICE VARIETIES 71 HOST RESPONSE TO MELOIDOGYNE GRAMINICOLA INFECTION OF THE UPLAND RICE VARIETIES 78 4.4 Discussion 84 CHAPTER 5: DAMAGE POTENTIAL AND YIELD LOSS OF THE RICE ROOT-KNOT NEMATODE MELOIDOGYNE GRAMINICOLA ON LOWLAND AND UPLAND RICE VARIETIES FROM MYANMAR 92 5.1 Introduction 92 5.2 Materials and methods 94 5.3 Results 101 SCREENHOUSE EXPERIMENT WITH LOWLAND RICE VARIETIES 101 FIELD EXPERIMENT WITH LOWLAND RICE VARIETIES 106 SCREENHOUSE EXPERIMENT WITH UPLAND RICE VARIETIES 110 5.4 Discussion 115 CHAPTER 6: DAMAGE ASSESSMENT AND YIELD LOSS OF RICE VARIETIES TO THE RICE ROOT-KNOT NEMATODE MELOIDOGYNE GRAMINICOLA UNDER DIFFERENT WATER REGIMES, SOIL TYPES, PLANTING AND IRRIGATION PRACTICES 123 6.1 Introduction 123 EFFECT OF THREE WATER REGIMES AND TWO SOIL TYPES ON THE INFECTION OF MELOIDOGYNE GRAMINICOLA ON THE LOWLAND RICE VARIETY THIHTATYIN AND THE UPLAND RICE VARIETY KONE MYINT 2 126 6.2 Materials and Methods 126 6.3 Results 130 EFFECT OF TWO IRRIGATION PRACTICES AND TWO PLANTING PRACTICES OF MELOIDOGYNE GRAMINICOLA ON THE LOWLAND RICE VARIETIES THIHTATYIN AND YATANARTOE 141 6.4 Materials and Methods 141 6.5 Results 144 6.6 Discussion 155 EFFECT OF THREE WATER REGIMES AND TWO SOIL TYPES ON THE INFECTION OF MELOIDOGYNE GRAMINICOLA ON THE LOWLAND RICE VARIETY THIHTATYIN AND THE UPLAND RICE VARIETY KONE MYINT 2 155 EFFECT OF TWO IRRIGATION PRACTICES AND TWO PLANTING PRACTICES OF MELOIDOGYNE GRAMINICOLA ON THE LOWLAND RICE VARIETIES THIHTATYIN AND YATANARTOE 162 CHAPTER 7: HOST PLANT RANGE CHARACTERISATION AND EFFECT OF CROP ROTATION ON RICE ROOT-KNOT NEMATODE MELOIDOGYNE GRAMINICOLA INFECTION OF RICE 170 7.1 Introduction 170 HOST RANGE CHARACTERIZATION OF MELOIDOGYNE GRAMINICOLA 173 7.2 Materials and methods 173 7.3 Results 177 EFFECT OF CROP ROTATION ON THE MANAGEMENT OF MELOIDOGYNE GRAMINICOLA AND YIELD OF SUMMER-IRRIGATED LOWLAND RICE IN MYANMAR UNDER MICROPLOT CONDITIONS 184 7.4 Materials and methods 184 7.5 Results 192 7.6 Discussion 201 CHAPTER 8: CONCLUSIONS AND PERSPECTIVES 214 REFERENCES 223 ANNEX 1: LIST OF PUBLICATIONS 241nrpages: 241status: publishe