Crop Protection Screening for resistance to brown planthopper (Nilaparvata lugens) in rainfed rice in the Lao PDR K. Khamphoukeo 1, S. Litmalaysy 1 an

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1 Screening for resistance to brown planthopper (Nilaparvata lugens) in rainfed rice in the Lao PDR K. Khamphoukeo 1, S. Litmalaysy 1 and B. Douang Boupha 1 1 National Agricultural Research Centre, Vientiane, Lao PDR. khamouan@laotel.com Abstract Due to an expansion of the irrigated areas, the number of rice crops has increased to two crops per year and together with the more frequent use of new improved varieties and fertilizers the yields per area and the total production of rice in the Lao PDR have increased. However, this increase has also resulted in more frequent outbreaks of diseases and pests, such as brown planthopper (Nilaparvata lugens; BPH). As part of the effort to reduce damage caused by this pest, the National Rice Research Program has initiated an experiment for the screening of rice varieties with a natural resistance to BPH. The screening was conducted in the laboratory of the National Agricultural Research Centre (NARC), in Vientiane Municipality. In the dry season 2001, 117 varieties were screened for resistance. Seedlings were raised in boxes containing both a resistant (TDK 1) and a susceptible Variety (RD 10) as control varieties. The insects were transferred to the seedling boxes seven days after sowing. After a further seven days, the damage resulting from BPH infestation was evaluated using standards of SES (IRRI 1980). From the total of 117 varieties screened, the results indicated 38 varieties with good resistance, 73 with medium resistance and six non-resistant varieties. As this experiment was the first of its kind, the experiment will be repeated in dry season Key words: Brown plant hopper Nilaparvata lugens, resistance, Standard Evaluation System, SES, lowland rice, Lao PDR. 117

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3 rice was sown into wooden boxes (60x40x10 cm) with each box containing 41 varieties including the two control varieties. Commercially available soil mixed with NPK fertiliser was used as substrate and the water level was kept at 3 cm. Five to six days after sowing, when seedlings had three leaves, they were ready for testing. Brown plant hoppers The BPH were trapped in the field or collected at night using electric lamps, then raised in enclosures. When the BPH had produced egg masses the enclosure was removed. Twelve to fifteen days later, when seedlings were ca. seven days old, the insects were transferred to the seedling boxes with 10 BPH/ seedling. After a further seven days, evaluations were made and note taken of the damage caused by BPH. Damage was assessed using the Standard Evaluation System (SES; IRRI, 1980; Table 1). Table 1. Standard Evaluation System score (SES) used for damage assessment caused by brown planthopper (Nilaparvata lugens). score damage 1 No damage at all 2 Very little damage 3 First and second leaf of hill have some yellow parts 4 More than 50% of hill is dead 5 More than 50% of hill is dead and growth has stopped 6 Whole plant is dead Results The screening of rice varieties and promising new lines according to the IRRI SES Evaluation Systems indicated a large number of varieties with good and medium resistance to BHP (Tables 2, 3 and 4). A total of 38 varieties showed a strong resistance of score 1 (Table 2) thus scoring better than the resistant control variety TDK 1, which achieved only a medium resistance of score 2 according to SES along with another 73 varieties in that category (Table 3). Only six varieties scored higher than score 2, achieving scores between four and six (Table 4) whereas the susceptible control RD 10 was clearly the most affected variety (score 7). Discussion The screening of the 117 varieties indicated 38 varieties with good resistance, 73 with medium resistance and 6 susceptible varieties. The 38 varieties and lines all scored better than the resistant control variety TDK 1, which only achieved a score 2 or medium resistance to BPH whereas no variety screened scored lower than the susceptible control RD 10. The high number of resistant varieties found could provide a good basis for breeding new resistant varieties in future breeding programs for the irrigated environment. However, the results have to be regarded with caution as the screening for rice varieties resistant to BPH was the first of its kind in National Agricultural Research Centre and due to lack of experience with such experiments not all activities followed the schedule of the protocol. The collecting of BPH insects from the field other preparatory activities was done late. In addition, the expertise in rearing the BPH insects and the experience with the scoring by the standard evaluation system (SES) was small. Therefore the experiment should be repeated in the dry season 2002 to reconfirm this seasons results. Those varieties should be screened again and may be some varieties can be adopted by BPH. 119

4 The screening of the varieties should be conducted in dry season because the seedling infestation with BPH is higher under warm temperature conditions. In the rainy season, the BPH is usually not problem due to rain and low temperature. If possible, the BPH should be raised in special rearing cages to ensure sufficient numbers of insects for the experiment. Table 2. Varieties and promising new lines resistant (SES score 1) to brown planthopper in a laboratory screening experiment conducted at the National Agricultural Research in the Lao PDR. code Name of varieties code Name of varieties code Name of varieties 107 IR TDK IR71817-B-B-1-TDK SK IR TDK IR TDK MAKING (LAO) 114 IR TDK IR B-1-TDK SPT IR TDK IR SRN-1-UBN-1-TDK NC TDK21-B B 170 IR68091-B B-TDK TDK2 134 TDK21-B B 182 IR R TDK21-B B 183 IR70824-TDK IR TDK21-B B 193 TDK IR IR CPA-1-2-TDK PNG1 252 DOGNUANH 141 IR CPA-1-2-TDK IR L IR B-TDK IR IR IR TDK VARIETY 255 IR8 153 IR B-TDK DOVIEN Table 3. Varieties susceptible (score 4 to 6) to brown planthopper in a laboratory screening experiment conducted at the National Agricultural Research in the Lao PDR. code name of variety score code name of variety score 133 TDK21B B IR71805-B-15-BTDK TDK20-B IR70827-TDK IR71805-B-13-B IR70827-TDK Outlook BPH is the main pest in the dry season lowland rice ecosystem. The screening of varieties resistant to BPH is an important experiment because new varieties should be tested before they are introduced to farmers. This experiment needs help and assistance from IRRI. 120

5 Table 4. Varieties with medium resistance (SES score 2) to brown planthopper in a laboratory screening experiment conducted at the National Agricultural Research in the Lao PDR. code Name of varieties code Name of varieties code Name of varieties 101 IR TDK IR B-TDK IR SRN-3UN-1-TDK IR TDK TDK21-B7-9-1-B 166 IR SRN-1UBN-TDK IR TDK TDK21-B8-1-1-B 167 IR69507-USRN-TDK IR TDK TDK21-B B 168 IR TDK IR TDK TDK B 172 TDK20-B B 106 IR TDK TDK21-B B 173 TDK20-B B 108 IR TDK TDK B 174 TDK20-B B 109 IR TDK TDK21-B B 175 TDK20-B B 110 IR TDK TDK21B B 176 TDK20-B B 111 IR TDK IR CPA-1-1-1TDK TDK20-B B 112 IR TDK IR CPA TDK IR70824-TDK IR TDK IR CPA TDK IR70827-TDK IR TDK IR B-TDK IR70827-TDK IR TDK IR B-TDK INTOK 118 IR DK IR B-TDK MOUANNGA 119 IR TDK IR B-TDK CSBRC1 121 IR TDK IR17805-B-6-TDK IR IR TDK IR B-TDK NSG TDK21-B B 159 IR71049-B-4-B-TDK IR TDK21-B B 161 IR B-16-TDK TSN1 121 IR TDK IR B-1-TDK CR TDK21--B B 169 IR TDK IR IR B-TDK TDK20-B B 247 HOMPHOUPHAN 148 IR B-TDK IR70824-TDK IR IR B-TDK IR70827-TDK Acknowledgements This report on the comparison study on resistant varieties from BPH on the lowland rice Lao PDR 2001 was conducted by the Plant Protection Unit and Integrated Pest Management Network of the National Rice research Program utilizing the ideas and efforts of many researchers and related people. On behalf of the head of the Plant Protection Unit, I would like to especially acknowledge: Mr. Somsanong Litmalaysy and Mr. Bounneung Douang Boupha from the National Agricultural Research Centre who summarized the data and prepared the report in Lao language and also assisted in field work and data collection. In addition, we would like to thank Philip Gibson and Dr. Renate Braun who conducted our technical writing course and corrected our English and our analyses. This study was supported with funding from the by SDC (Swiss Agency for Development and Cooperation) with logistical support from the Lao-IRRI Project. 121