Tae-Hwan Noh

Development of breeding lines with three pyramided resistance genes that confer broad-spectrum bacterial blight resistance and their molecular analysis in rice

BackgroundThe development of resistant cultivars has been the most effective and economical strategy to control bacterial leaf blight (BB) disease of rice caused by Xanthomonas oryzae pv. oryzae (Xoo). Molecular markers have made it possible to identify and pyramid valuable genes of agronomic importance in resistance rice breeding. In this study, three resistance genes (Xa4 + xa5 + Xa21) were transferred from an indica donor (IRBB57), using a marker-assisted backcrossing (MAB) breeding strategy, into a BB-susceptible elite japonica rice cultivar, Mangeumbyeo, which is high yielding with good grain quality.ResultsOur analysis led to the development of three elite advanced backcross breeding lines (ABL) with three resistance genes by foreground and phenotypic selection in a japonica genetic background without linkage drag. The background genome recovery of the ABL expressed more than 92.1% using genome-wide SSR marker analysis. The pathogenicity assays of three resistance-gene-derived ABL were conducted under glasshouse conditions with the 18 isolates of Xoo prevalent in Korea. The ABL exhibited very small lesion lengths, indicating a hypersensitive reaction to all 18 isolates of Xoo, with agronomic and grain quality traits similar to those of the recurrent parent. Pyramiding the resistance genes Xa4, xa5 and Xa21 provided a higher resistance to Xoo than the introduction of the individual resistance genes. Additionally, the combination of two dominant and one recessive BB resistance gene did not express any negative effect on agronomic traits in the ABL.ConclusionsThe strategy of simultaneous foreground and phenotypic selection to introduce multiple R genes is very useful to reduce the cost and the time required for the isolation of desirable recombinants with target resistance genes in rice. The resistance-gene-derived ABL have practical breeding value without a yield penalty by providing broad-spectrum resistance against most of the existing isolates of BB in South Korea and will have a high impact on the yield stability and sustainability of rice productivity.

Effects of Bacterial Leaf Blight Occurrence on Rice Yield and Grain Quality in Different Rice Growth Stage

We investigated the first symptom emerging date of rice bacterial leaf blight disease during four years from 2002 to 2005. The disease occurrence date was earlier 2030 days in 2005 than that of 2002. The damage in different rice growth stage by the bacterial disease on rice yield and grain quality in southern part of Korea was examined. The disease decreased rice yield following by increased infection rates. Slight loss in rice yield and brown head rice rate were observed at below 10% level of infected leaf area, while over 25% infected leaf area caused the significant decrease in rice yield and brown head rice rate. More than 50% of the infected leaf area rate caused 29% yield reduction in case of infection at panicle formation stage and 18% of brown head rice rate. Cooked rice quality was also affected in the diseased rice by damage in palatability score and viscosity.

Expression levels of three bacterial blight resistance genes against K3a race of Korea by molecular and phenotype analysis in japonica rice (O. sativa L.)

Bacterial blight, caused by Xanthomonas oryzae pv. oryzae (Xoo) is a destructive disease of rice in the major rice growing countries of Asia. In 2003, a serious bacterial blight epidemic occurred in the southwestern coastal areas in Korea, causing significant yield loss due to the emergence of a new race, K3a. IR24 near-isogenic lines containing Xa4, xa5, Xa7 and Xa21 genes conferred different degrees of resistance to the most virulent K3a isolate, HB01009 in an inoculation experiment in the greenhouse. Expression levels of the resistance genes, Xa4, xa5 and Xa21 were studied in two F2 populations derived from the crosses between elite japonica cultivars and an advanced backcross breeding line possessing Xa4, xa5 and Xa21 genes. F2 progenies segregated for K3a resistance (R) and susceptible (S) phenotypes in a ratio of 3(R):1(S) indicated that K3a resistance was controlled by a major dominant gene. Three PCR markers tightly linked to the resistance genes Xa4, xa5 and Xa21 confirmed the presence of the genes and their interaction with each gene. This study demonstrated that the Xa21 gene dominantly contributed to K3a resistance. However, the Xa4 gene also contributed to the full expression of resistance. The level of expression of strong resistance to K3a race was attributed to the presence of Xa21 and Xa4 genes irrespective of the presence of xa5 gene. Our results suggest that the R-gene combinations of Xa4+Xa21 could be a useful and effective strategy toward improving resistance to K3a race of Korean japonica cultivars.

Development of multi-resistant lines to brown planthopper, bacterial blight, and rice stripe virus using anther culture in rice.

This study was conducted to develop multi-resistant lines to brown planthopper, bacterial blight, and rice stripe virus using anther culture in rice. A total of 213 double haploid lines were developed the cross between HR26234-12-1-1 conferring resistant to bacterial blight and rice stripe virus and SR30071-3-7-23-6-2-1-1 conferring resistant to brown planthopper, bacterial bight, and rice stripe virus. Using DNA molecular marker, HR26234 and SR30071 were confirmed to have Xa3+xa5+Stvb-i and Bph18+Xa4+Stvb-i, respectively. All double haploid lines carried Stvb-i, and Bph18+Xa3, Bph18+Xa4, Bph18+Xa3+xa5, Bph18+Xa4+xa5, bph18+Xa3, bph18+Xa4, bph18+Xa3+xa5, and bph18+Xa4+xa5 combinations were identified. Segregation distortions such as no combinations carrying Bph18(or bph18)+xa5+Stvb-i and fewer lines carrying Bph18 than bph18 were occurred in DH population. Brown planthopper resistant lines carrying Bph18 showed longer culm length than susceptible lines. Selected Bph18+Xa4+xa5+Stvb-i combination lines with short culm conferred resistant to brown planthopper, bacterial blight, and rice stripe virus, while showed deleterious effects such as spikelet sterility, lower yield, and vulnerable to lodging than standard and comparative varieties. Using anther culture, we rapidly developed multi-resistant lines to brown planthopper, bacterial blight, and rice stripe virus. However, distorted segregation in DH population and linkage drag with Bph18 were obstacles to develop practical multi-resistant cultivars.

Analysis of Damages and Rice Consumption by Golden Apple Snails (Pomacea canaliculata: Ampullariidae) at Growth Stages of Rice

The golden apple snail was introduced to the Korea from Japan as a potential food for people in 1983. It is one of the pests of direct-seeded rice in korea. This study was conducted to investigate rice(Oriza sativa) consumption and the extent of damage by the golden apple snail(Pomacea canaliculata) in direct-sown paddy fields. Food consumption of the golden apple snail was highest at 30℃. When the emergence of the 1st, 3rd, and 5th leave of rice supplied food, the consumption of young(shell height 15mm) and adult golden apple snail(over shell height 30mm) at 30℃ were 19.0/79.8, 11.0/54.5, 5.5/18.5, and 0.0/2.0 individuals, respectively. Young rice seedings(before 5th leaves of rice) are very susceptible to golden apple snail damage because the young, tender leaves and stems favor the snails feeding habits. The field experiment with four treatments (0, 2, 5 and 10 individuals respectively per 10 m 2 ) was carried out. The most serious yield loss was 16% from the plot with 10 adults released at emergency stage of rice.

Effect of Cropping System on Disease Incidence by Soil-borne Bymovirus in Barley and on Density of the Vector, Polymyxa graminis

In this study, changes in virus disease occurrence and yield were monitored in conventional cropping system(rice-barley) and soybean-barley double cropping system in virus-prone area for 5 years. Also, changes in the density of Polymyxa graminis, a fungal vector, was investigated. In assay tests, mixed infection of Barley yellow mosaic virus (BaYMV) and Barley mild mosaic virus (BaMMV) was observed. Disease severity was in the range of 7~9 in conventional cropping system. In continuous cropping of soybean-barley and 3-yearfallow land, disease severity also was around 7. However, disease severity was reduced to medium level (5) when barley cultivation was paused for one or two years in soybean-barley cropping. When barley cultivation was paused for a year, the density of P. graminis, a fungal vector for BaYMV and BaMMV, reduced in barley root and soil. Similarly, barley growth was also enhanced by adopting fallow seasons. Compared with the fifth year of conventional cropping, the number of tillers per was increased by 158 when barley cultivation was paused for an year in soybean-barley cropping. When soybean and barley were cultivated continuously or complete fallow period was extended to three years, plant height and the number of tillers of barley were decreased. Yield components of barley in soybean-barley cropping were superior to those in rice-barley cropping. Compared with the fifth year of conventional cropping and soybean-barley cropping, culm length of barley was 1.3~2.3 cm higher and the number of tillers per was 36~90 higher when barley cultivation was paused for one or two years. However, those in continuous cropping of soybean-barley and 3-year-fallow land were lower compared with conventional cropping. Similarly, yield was increased when barley cultivation was paused for one or two years in the third, forth, and fifth years when compared with conventional cropping.

Direct PCR Detection of the Causal Agents, Soybean Bacterial Pustule, Xanthomonas axonopodis pv. glycines in Soybean Seeds

Direct Polymerase Chain Reaction (PCR) method that combines biological and enzymatic amplification of PCR targets was developed for the detection of Xanthomonas axonopodis pv. glycines on soybeen seeds without DNA isolation. Primers Xag F1 and Xag R1 were designed to specifically amplify a 401 bp fragment of the glycinecin A gene of X axonopodis pv. glycines. Xag F1 and Xag R1 were used to carry out the PCR analysis with genomic DNA from 45 different bacterial strains including phylogenetically related bacteria with X axonopodis pv. glycines, and other bacterial strains of different genus and species. The PCR assay using this set of primers were able to detect X axonopodis pv. glycines with DNA concentration as low as 200 fg and cfu/ml. The Xag was detected from the seed samples incubated for 2 hrs with shaking and the intensity of the band was increase with the incubation time of seeds. The Direct PCR assay method without DNA isolation makes detection of X. axonopodis pv. glycines on soybean seeds easier and more sensitive than other conventional methods. The developed seed assay using direct PCR method will be useful for the specific detection of X. axonopodis pv. glycines in soybean seed samples.

An Easy Seedling Method to Screen Resistance of Powdery Mildew of Barley and Wheat

This study was conducted to develop a easy seedling method to test large amounts of barley and wheat cultivars for resistance of powdery mildew. In addition, we also examined the resistance of genetic resources that have been used in barley and wheat breeding programs in Korea. This seedling test used paper bag with seeds can be completed within three weeks. to-day seedlings were available to inoculation and 8 days was needed for result reading. This method can test at least 180 collections at one time. we can identify the two resistant types by leave symptoms showed non infection and necrotic spots. Among the 79 Korean barley cultivars, only two cultivar, `Sangrokbori` and `Dajinbori` were resistant and `Jejubori` showed moderate resistant. There was no resistant in hulless barley and wheat cultivars. It was same results in comparison of earlier resistant reports in field test. We confirm that this method could using in test of powdery mildew resistance in barley and wheat. Among the 1,401 genetic resources using in Korean breeding program, malting barley has more resistant collections comparing to 796 hulled and hulless barley and 273 wheat germplasms.

Development of japonica Rice Lines with Four Bacterial Blight Resistance Genes using Phenotypic and Marker-assisted Selection

Four bacterial blight resistance genes, Xa1+Xa3+xa5+Xa21, pyramid elite japonica rice lines were developed for enhancing the resistance of rice against Xanthomonas oryzae pv. oryzae in Korea. Seven doubled haploid (RDL1-7) and ten F6 lines (RPL1-10) having Xa1+Xa3+xa5+Xa21 which were derived from the cross between Ilmi, high grain quality japonica rice cultivar carrying Xa1, and Iksan575, elite line carrying Xa3+xa5+Xa21, were developed using marker-assisted selection for resistance genes and phenotypic selection for bacterial blight resistance and agronomic traits. Among resistance genes combinations in F2 population, four resistance genes combination, Xa1+Xa3+xa5+Xa21, showed the highest resistance and conferred the enhanced resistance than three genes combination, Xa3+xa5+Xa21. Four genes pyramid lines (RDL and RPL) showed broad-spectrum resistant against 16 Korean bacterial blight isolates and the yield and quality of the lines did not alter by the inoculation of K3a, the most virulent race in Korea. In addition, these lines had excellent plant type and exhibited more enhanced yield than previously developed resistant cultivars. Four bacterial blight resistance genes combination, Xa1+Xa3+xa5+Xa21, was efficient and promising combination and developed lines with four genes could be useful materials and will be applied to the breeding programs for enhancing the resistance of japonica rice against bacterial blight.

Effects of Rice Straw Amendment and Nitrogen Fertilization on Rice Growth and Soil Properties in Reclaimed Tidal Paddy Field

Farmers with forage barley (Hordeum vulgare L.)-rice (Oryza sativa L.) cropping system at reclaimed tidal lands burn crop residues to facilitate seedbed preparation or remove them for feed stock. This study was conducted to investigate the effect of rice straw amendment and N fertilization on soil properties and N uptake of rice under forage barely?rice cropping system at reclaimed tidal paddy field. Rice straw was applied at the rates of 0, 2.5 and 5.0 ton ha -1 and N was fertilized at 0, 100, 200 and 400 kg ha -1 . Although there was no significant difference in the growth and yield of rice, fresh and dry weight of forage barely increased with increasing the amount of rice straw. The amount of N uptake of rice at harvesting stage was 65.8-69.2 kg ha -1 by the amount of rice straw amendment, but there were no significant differences among rice straw amendment levels. After harvesting the rice, the soil salinity decreased with rice straw amendment compared to the control. After forage barely and rice cultivation, soil organic matter contents increased to 2.6-2.8 g kg -1 and 3.2-3.5 g kg -1 , respectively. The amount of N uptake of rice at harvesting stage increased up to 82 kg ha -1 in 400 kg ha -1 N applied plots which were 37.8 kg ha -1 higher than the control. Nitrogen fertilization decreased N recovery efficiency. The highest yield of rice was observed at 244 kg ha -1 N fertilization level, but the optimum N level was estimated at 168 kg ha -1 in order to keep the protein content of rice under 6.5%. Further researches on N uptake and application of organic matter according to soil salinity will be necessary to increase N use efficiency at reclaimed tidal paddy field.