Screening of Inter-Specific Rice Progeny Lines for African Rice Gall Midge (AfRGM) Resistance

Nine hundred and seventeen inter-specific rice lines were subjected to field screening for African Rice Midge Resistance in both Rainfed and Irrigated lowland ecologies at Badeggi and Edozhigi experimental fields respectively in 2009 cropping season, to determine the levels of African Rice Gall Midge (AfRGM) resistance in Bc 3 F 3 inter-specific lines. The field was laid out in an Augmented Block Design, comprising of three blocks with 305 progenies in each block. The checks were randomized three times in each block. The result indicated that the progenies differ significantly in their resistance to AfRGM, four progenies were found to be resistance across the two locations. However, 7 out of the 146 progenies that have good phenotypic acceptability were resistant at Badeggi, while 5 out of 122 progenies with phenotypic acceptability were found resistant at Edozhigi location. Considering both resistance and phenotypic acceptability scores, only 16 progenies were selected for yield trial in both locations. Augmented Block Design (Federer, 1956). The experiment comprises of three blocks with 305 accessions in each block, local checks were randomized three times in a block after every 100 entries. One seedling was transplanted per hill with plot size of 5m long single row for each accession in the field. The fields were mechanically, ploughed, harrowed and leveled. The rice germplasm that was used in this study was lines from a single population of a cross between O. glabberrima (TOG 7442) and O sativa, FARO 52 (WITA 4). The F 1 was back crossed to WITA 4 to have BC 1 -then back crossed to WITA 4 to get BC 2 which was back crossed to WITA 4 to get BC 3 . The trial, consisting of 917 accessions and three different checks (FARO 37, FARO 52 and Tog 7442), were collected from National Cereals Research Institute rice breeding unit. The seeds were sowed on the nursery bed before they were transplanted at 21 days old with a spacing of 20 cm x 20 cm. Fertilizer application includes NPK 15:15:15 as basal application at the rate of 150 kg/ha during land preparation and urea that was applied is at the rate 50 kg /ha as top dressing first at tillering and second time at booting stage. Manual hand weeding was carried out at 21 and 42 Days after transplanting. Galls which are symptoms of insect damage or level of infestation were counted on all the twenty five plants in each row at 42 and 63 days after transplanting. The total number of tillers from each of the twenty five plants was also counted. Percentage hill and tiller infestations were computed using the following formula.


INTRODUCTION
Rice is the stable food for more than three billion people, which is over half of the world's population. It provides 27% of dietary energy and 20% of dietary protein in the developing world. Rice is cultivated in at least 114, mostly developing, countries and is the primary source of income and employment for more than 100 million households in Asia and Africa (FAO, 2004). Of the 840 million people suffering from chronic hunger, over 50% live in areas dependent on rice production (FAO, 2004). About 80% of the world's rice is produced on small farms, primarily to meet family needs, and poor rural farmers account for 80% of all rice producers (FAO, 2004). Less than 7% of the world's rice production is traded internationally (MacLean et al., 2002).
In West African sub-region, whereas the share of the traditional cereals mainly sorghum and millet consumed as food fell from 61% in early 1970 to 49% in the early 1990s and still tending down wards. The share of rice in cereals consumed as food has risen from 15% to 26% within the same period and is still increasing (Akpokdge et al., 2001). Going by the FAO (2000) projection of the West African-sub region rice consumption growth rate of 4.5% through the year 2000, the regional consumption of the staple in the first decade of the 21 st century is likely to increase by about 70%.
In Nigeria, rice as an important source of food and cash income to both the urban and rural dwellers of the population is steadily on the increase. WARDA (1996) reported that there has been a structural increase in rice consumption in the country averaging an annual growth rate of 7.7% from 2.1 million tons in 1992 to 2.8 million metric tons in 1996. There are numerous and diverse factors that limit rice production which depends on the agroecologies. Basically, they can be classified as abiotic, which include physio-climatic conditions such as drought, flood, soil fertility, nutrient deficiencies and toxicities, erosion etc; and the biotic, which include weeds, diseases, insects and various vertebrate animal pests particularly birds and rodents. In general, yield losses due to insect pests are difficult to quantify due to field and environmental factors and the role of natural enemies of insect pests. African Rice Gall Midge (AfRGM) has been reported to have caused over 80% losses on farmers' field in Abakaliki, Ebonyi state of Nigeria, (Ukwungwu et al., 1998). Yield loss assessments in field with up to 30% tiller infestation suggest that for each 1% increase in tiller infestation, a farmer can expect to lose 2-3% grain yield, (Nacro et al., 1996). Heavily infested fields may produce no grain at all (WARDA, 2000). Therefore, there is the need to diversify the genetic base of improved rice varieties, and the first step towards this is to evaluate and characterize available rice germplasm or genotypes at the morphological levels. This trial is therefore conducted in order to screen the resistance ability of the B 3 F 3 pedigree lines of the crosses made between FARO52, an improved Oryza sativa cultivar with Tog 7442 an O. glaberrima land race. The lines that are found to be resistance to pest will then be subjected to further yield trail in the subsequent year.

MATERIALS AND METHODS
The experiment was established in 2009 cropping season in two locations, namely National Cereals Research Institute experimental field at Badeggi and Edozhigi in Guinea Savannah agro-ecological zone, (Latitude 9°45'N Longitude 6°07'E and altitude 70.5 meters above sea level (msl) for Badeggi location and Latitude 9°45'N and Longitude 6°17'E altitude 50.57 meters above sea level (msl) for Edozhigi location respectively. The field was laid out using Augmented Block Design (Federer, 1956). The experiment comprises of three blocks with 305 accessions in each block, local checks were randomized three times in a block after every 100 entries. One seedling was transplanted per hill with plot size of 5m long single row for each accession in the field. The fields were mechanically, ploughed, harrowed and leveled. The rice germplasm that was used in this study was lines from a single population of a cross between O. glabberrima (TOG 7442) and O sativa, FARO 52 (WITA 4). The F 1 was back crossed to WITA 4 to have BC 1 -then back crossed to WITA 4 to get BC 2 which was back crossed to WITA 4 to get BC 3 . The trial, consisting of 917 accessions and three different checks (FARO 37, FARO 52 and Tog 7442), were collected from National Cereals Research Institute rice breeding unit. The seeds were sowed on the nursery bed before they were transplanted at 21 days old with a spacing of 20 cm x 20 cm. Fertilizer application includes NPK 15:15:15 as basal application at the rate of 150 kg/ha during land preparation and urea that was applied is at the rate 50 kg /ha as top dressing first at tillering and second time at booting stage. Manual hand weeding was carried out at 21 and 42 Days after transplanting. Galls which are symptoms of insect damage or level of infestation were counted on all the twenty five plants in each row at 42 and 63 days after transplanting. The total number of tillers from each of the twenty five plants was also counted. Percentage hill and tiller infestations were computed using the following formula.
Infested hill percentage I X 100 Tiller damage levels were expressed as scores between the values of 0 and 9, according to standard evaluation system for rice (IRRI, 1986) as shown below.

Ranking of Rice Progenies to Different Gall Midge Reaction at 42 and 63 DAT
The result in the Table 2 shows that at 42 DAT in Badeggi, 103 progenies were found to be resistant with scores of less than 1%, 579 progenies were moderately resistant with scores of less than 3% and the remaining progenies were susceptible. In Edozhigi, 740 progenies were found to be susceptible with scores greater than 5%. It was observed that tiller % at 63 DAT across the two locations showed high susceptibility of 776 and 548 progenies in Badeggi and Edozhigi, respectively and only 15 and 21 progenies are found to be moderately resistant at Badeggi and Edozhigi.

Classification of Rice Progenies to Different Gall Midge damage sores at 42 and 63 DAT
Varietal resistance is a key component of integrated pest management (Singh et al., 1998), screening for host-plant resistance is ongoing in fields at hot-spot locations in Nigeria. Considerable diversity was observed in the reactions of 917 rice progenies to AfRGM at Badeggi and Edozhigi. The result revealed that at Badeggi, 103 progenies were identified to be resistant at 42 DAT with tiller damage scores less than1% and 579 were moderately resistant with scores less than 3%.This might be attributed to low gall midge infestation at the beginning of the season. Furthermore, at 63 DAT only15 progenies were found to be moderately resistant; this might be due high gall midge infestation at the peak of the season. This result is in line with the findings of Ukwungwu et al. (1992) who observed that, out of the lines screen under artificial infestation, only two lines, Agani and NAHTA 8 were moderately resistant.
At Edozhigi it was also revealed that, at 42 DAT, 4 progenies were found to be resistant with tiller damage scores less than 1% and 20 were moderately resistant at less than 3% tiller damage level. Also 21 progenies were found to be moderately resistant at 63 DAT. This agrees with the findings of Ukwungwu et al. (1991). Out of the lines he evaluated at Edozhigi only 32 lines had less than 5% tiller infestation.

CONCLUSION
Field screening at Badeggi and Edozhigi were conducted to identify African Rice Gall Midge resistant cultivars with good agronomic characteristics. The study discovered that out of the 917 progenies tested only 16 progenies were promising to be resistant to African rice gall midge. These lines should be evaluated further to identify materials for further genetic improvement work and release to the rice farmers in the region facing African rice Gall Midge challenges.

RECOMMENDATION
It is recommended that the rice lines from this study be evaluated in different environment in order test there genotype by environment interaction and identify their stability and response to African Rice Gall Midge.