Rice Cultivar IR24 Research Articles

Isolation and Selection of Growth Promoting Phyllosphere Bacteria from Leaf of Rice (Oryza sativa L.) Cultivar IR-64

Phylosphere bacteria are bacteria live on the leave surface. Phylosphere bacteria have been reported to improve thegrowth of several plants such as rice. However, in Indonesia, the study concerning phylosphere bacteria is very rare.The aims of this study were to isolate and select phylosphere bacteria which are able to stimulate the growth of ricecultivar IR-64. Phylosphere bacteria were isolated from leaves of rice cultivar lR-64 grown at Ciherang (Sindangbarang) andat Pasirkuda (Ciomas) Bogor at the age of two, four and eight weeks after planting. The media used to isolate the phylosphere bacteria was Agar Ashbey.The surface of rice seeds was sterilized and then inoculated by deeping the rice seeds into bacterial suspention with acell density of 1 x 106 cells mr'. Leave inoculation was done by deeping leaves of three weeks old rice seedling into bacterialsuspension with a cell density of 1 x 106 cells mr'.Parameters measured were plant height, upper part biomas and root biomas. Phyllosphere bacteria were identifiedbased on Bergey's Manual of Determinative Bacteriology.Nineteen isolates ofphyllosphere bacteria were isolatedfrom rice leaves, nine isolates were from Pasirkuda (Ciomas)and ten isolates were from Ciherang (Sindangbarang); eleven isolates were from rice phyllosphere and eight isolates werefrom endophyllosphere. Based on the age of the rice, two isolates were from two weeks old rice, nine isolates were from four weeks old rice and eight isolates were from eight weeks old rice.Phyllosphere bacteria significantly increased the plant height, upper parts biomass as well as root biomass. Six isolates were able to improve the growth of rice seedling IR-64 were Aureobacterium seperdae (two isolates), Arthrobacteriumglobiformis (one isolate) and Microbacterium lacticum (three isolates).

Growth Complementation of hrpXo Mutants of Xanthomonas oryzae pv. oryzae by Virulent Strains in Rice Cultivars Resistant and Susceptible to the Parental Strain

pv. oryzae (X. o. pv. oryzae) T7174 is virulent on rice cultivar IR24 and avirulent on IR-BB2. From recent reports, some virulence and avirulence factors of plant pathogenic bacteria are transferred to plant cells through the hrp-dependent type III secretion system. In this study, we investigated the involvement of hrp genes in the compatible and the incompatible interactions between rice and X. o. pv. oryzae after co-inoculation with hrpXo mutants derived from T7174 and virulent strains. Growth of the mutants, named 74ΔHrpXo and 76ΔHrpXo, was repressed in IR24 when the mutants were applied alone. However, growth of the mutants was complemented by co-inoculation with virulent strains. Growth of bioluminescent hrpXo mutant 76ΔHrpXo in IR24 and its growth in IR-BB2 after co-inoculation with T7133, which is virulent on both cultivars, was equally complemented, as detected by bioluminescence from the mutant. On the other hand, only partial complementation of growth of T7174L76, which is a bioluminescent and pathogenic derivative of T7174, by T7133 was observed in IR-BB2. Thus, growth of the hrpXo mutant of X. o. pv. oryzae was complemented by virulent strains in both susceptible and resistant rice leaves with the parental strain.

Enhanced resistance to sheath blight by constitutive expression of infection-related rice chitinase in transgenic elite indica rice cultivars

Genetic transformation has been attempted for management of rice sheath blight disease, caused by Rhizoctonia solani. We introduced a PR-3 rice chitinase gene ( RC7), isolated from R. solani-infected rice plants, into indica rice cultivars IR72, IR64, IR68899B, MH63, and Chinsurah Boro II by the biolistic and PEG-mediated transformation system. Inheritance was studied up to the T 2 generation by Southern blot analysis. Western blot analysis of transgenic plants with polyclonal antibody revealed the presence of chitinase protein with a molecular weight of 35 kDa that reacts with chitinase antibody. The transformants synthesized different levels of chitinase proteins constitutively and progeny from the plants containing the chitinase gene showed different levels of enhanced resistance when challenged with the sheath blight pathogen R. solani.

Isolation and characterization of disease resistance gene homologues from rice cultivar IR64

We initiated a search for disease resistance ( R) gene homologues in rice cultivar IR64, one of the most agronomically important rice varieties in the world, with the assumption that some of these homologues would correspond to previously identified disease resistance loci. A family of rice R gene homologues was identified using the Arabidopsis NBS–LRR disease resistance gene RPS2 as a hybridization probe. Because member genes of this rice R gene family exhibit features characteristic of the NBS–LRR class of resistance genes, the family was given the name NRH (for NBS–LRR resistance gene homologues). Three members of the NRH family, NRH1, NRH2, and NRH3, were cloned and studied in detail. In IR64, NRH1 and NRH2 appear to encode full-length polypeptides, whereas NRH3 is prematurely truncated with a stop codon generated by a frameshift. NRH1 maps on chromosome 5, and NRH2 and NRH3 are less than 48 kb apart on chromosome 11. Although NRH1, NRH2, and NRH3 map to regions of the rice genome where disease resistance loci to Xanthomonas oryzae pv. oryzae ( Xoo) have been identified, susceptible rice varieties transformed with either NRH1 or NRH2 failed to exhibit increased resistance to a set of well-characterized Xoo strains.

Behavior of Bioluminescent Transconjugants of Xanthomonas oryzae pv. oryzae in Compatible and Incompatible Rice Leaves.

Transposon Tn4431 was used to introduce a luciferase (lux) operon into Xanthomonas oryzae pv. oryzae (X. o. pv. oryzae) T7174. Two transconjugants which were highly bioluminescent and indistinguishable in pathogenicity with the parental strain were selected. The transconjugants produced more bioluminescence in the logarithmic phase in liquid cultures. Bioluminescence was also detected from rice leaves infected with the transconjugants. In the compatible rice cultivar IR24 bacteria multiplied and moved prior to the expression of disease symptoms. In contrast, in the incompatible rice cultivar IR-BB2, which has resistance genes Xa1 and Xa2, bioluminescence was restricted near the inoculation sites, but light produced by the transconjugants was detected even 3 weeks after inoculation, suggesting that bacteria could multiply, although restrictedly, and remain viable. No bacterium was reisolated from the leaf sections beyond the light-producing regions. The detection of bioluminescence makes it possible to examine the actual location or infection process of X. o. pv. oryzae continuously without destroying the infected leaves.

Brown planthopper, Nilaparvata lugens, resistance in rice cultivar IR64: mechanism and role in successful N. lugens management in Central Luzon, Philippines

AbstractWe investigated the mechanism of brown planthopper, Nilaparvata lugens (Stål), resistance in the popular rice cultivar IR64, and the current level of resistance of IR64 to N. lugens in a large rice growing area with low brown planthopper populations (Central Luzon, Philippines). In greenhouse experiments with N. lugens populations collected from Central Luzon, IR64 showed slight to moderate levels of antibiosis, antixenosis, and tolerance relative to the cultivars IR22 and Azucena, which contain no major genes for N. lugens resistance. IR64 was also more resistant than IR26 in most experiments, despite the fact that both varieties have the same major gene for N. lugens resistance, Bph1. This confirms that IR64 contains one or more additional, apparently minor, genes for brown planthopper resistance. Our findings also demonstrate that, in an area with low insecticide use, it is not necessary to have high levels of N. lugens resistance, even in a rice cultivar grown by the majority of farmers, to maintain low and stable N. lugens populations.

Response to selection for high and low partial resistance to leaf blast in F2 populations of three rice crosses

Divergent selection for higher and lower partial resistance to leaf blast was applied in F2 populations of crosses between the rice cultivars IR36, IR64 and CO39 after exposure to a virulent isolate. IR36 and IR64 are partially resistant while CO39 is highly susceptible. As selection criteria the number of sporulating lesions in leaves of the main culm or the lesion density in the topmost leaf relative to other F2 plants with the same stage of development were used. A highly significant and meaningful response to selection was obtained in most cases, but the heritability was low. Realized heritabilities varied from 0.14 to 0.25 depending on the cross and were similar for both selection criteria. Selection for improved partial resistance to leaf blast is possible as early as the F2. The efficiency of selection is probably much higher if replicated tests could be made, and better results are therefore expected if selection among F3 lines is carried out. The results indicated that the relatively low infection efficiency in IR36 and IR64 is oligo- or polygenically controlled.

Plant Regeneration through Direct Culture of Isolated Pollen Grains in Rice.

Immature pollen grains of an Indica type rice cultivar IR24 were isolated and cultured to regenerate green plants without preculture of anthers. Either low-temperature pretreatment of panicles at 10'C in the dark or exposure to sugar starvation in the beginning of culture were necessary for induction of cell division of the grains. Low-temperature pretreatment was more effective treatuent than exposure to sugar starvation. It was found that there was a complementary relationship between the effects of low-temperature pretreatuent and of exposure to sugar starvation the pollen grains required shorter period of exposure to sugar starvation to start cell division as low-temperature pretreatnent was prolonged. The optimal condition for induction of cell division of the pollen grains was 21 days of the pretreatuent with I day of sugar starvation or 28 days of the pretreatment without sugar starvation. Though 2, 4-D was not necessary for induction of cell division, the development of the derived colonies followed by shoot regeneration was observed only in the presence of 2, 4-D. Reduced nitrogen source in the induction medium also affected the frequency of both colony formation and plant regeneration. The medjum containing 20mM KN03 and 5mM glutamine as nitrogen sources gave the highest frequency of colony formation at 0.20/0 and its frequency reached 2.0 times higher than the control R2 medium containing 40mM KN03 and 2.5mM (NH4)2S04. On the other hand, the calli which were formed in the medium containing 20mM KN03 and 5mM alanine had the highest regenerating ability. In addition, the calli which were formed in the medium containing 20mM KN03 and 5mM alanine showed marked higher frequency of green plant regeneration than ones in any other media tested, when 21 days of low-temperature pretreatment without exposure to sugar starvation was applied as induction condition.

Analysis of the Interaction BetweenXanthomonas oryzaepv.oryzaeand the Rice Cultivars IR24 and IRBB21

Xanthomonas oryzae pv. oryzae causes bacterial blight of rice, and interactions between this pathogen and its host occur in a gene-for-gene manner. In contrast to other resistance genes, the dominant locus Xa21 confers resistance to all Indian and Philippine races of X. o. oryzae that have been examined. In this study, multiplication of X. o. oryzae and subsequent disease development were comparable in cultivar IRBB21 possessing Xa-21 and in the susceptible rice cultivar IR24 when plants were inoculated prior to 21 days postemergence. Resistance conveyed by Xa-21 was evident in 21-day-old plants, and the level of resistance increased with plant maturity [...]