Development of cleaved amplified polymorphic sequence (CAPS) markers linked to a green rice leafhopper resistance gene, Grh3(t)

The chromosomal location of the resistance gene for green rice leafhopper (GRLH), an injurious insect for rice, has been determined and RFLP markers closely linked to this gene have been identified. The susceptible japonica rice variety ‘Nipponbare’ was crossed with a resistant japonica rice line ‘Aichi42’, in which green rice leaf hopper resistance had been introduced from an indica variety ‘Rantaj‐emas2’, and the 100 F₂ plants obtained were used for linkage analysis. The green rice leafhopper resistance gene, Grh3(t), was mapped between RFLP markers C288B and C133A on chromosome 6 and co‐segregated with C81. Of the RFLP markers tightly linked to Grh3(t), C81 was converted to a SCAR marker and C133A to a cleaved amplified polymorphic sequence marker that could distinguish the heterozygous genotype to establish an effective marker‐aided selection system for the GRLH resistance gene.     

Genetic Analysis of Resistance to Green Leafhopper in Rice

The inheritance of resistance to green leafhopper, Nephotettix impicticeps Ichi, was studied in 11 cultivars of rice, Oryza saliva L. These resistant cultivars were crossed with the susceptible cultivar ‘TN1’. The materials consisted of F₁, F₂ and F₃ populations including parents which were assessed by the bulk screening test. It was found that resistance in the cultivars TR36′, UPR254-35-3′-2′, ‘Jhingasail’, ‘Govind’, ‘RP825-45-1-3’, ‘MRC603-303’, ‘RD4’, and ‘Irat104 ’ was conditioned by a single dominant gene, whereas resistance in ‘Ptb8’ IR9805-97-1′, and ‘BG367-7’ was controlled by one recessive gene. The test on the allelic relationships of the resistance genes in the test cultivars with the known genes Glb1 and Glb2 revealed that the single dominant gene that conveyed the resistance in ‘UPR254-35-3-2’ and ‘Jhingasail’ was allelic to Glh1 and segregated independently of Glh2. The resistance in ‘Govind’ and ‘RP82S-45-1-3’ was governed by the Glh2 gene which was independent of Glh1. The test cultivars ‘IR36’;. ‘MRC603-303’, ‘RD4’. and Irat104 ’ had a dominant gene for resistance which was nonallelic to Glb1 and Glb2. The recessive gene which conditioned the resistance in ‘Ptb8’, ‘IR9805-97-1’, and ‘BG367-1’ segregated independently of Glh1 and Glh2. Eleven trisomics in an ‘TR36’ background were crossed with ‘Java’, a cultivar susceptible to green leafhopper. The segregation pattern of the F₂ and backcross generations revealed that the Glb6 gene was located on chromosome 5.     

Genetic Analysis of Resistance to Gall Midge (Orseolia oryzae Wood Mason) in Rice

The inheritance of resistance to rice gall midge (Ranchi biotype) was studied in 12 resistant cultivars by crossing with susceptible cultivars. By the study of F₁, F₂, F₃, B₁ and B₂ generations, it was found that resistance was governed by a single dominant gene in ‘Surekha’, ‘Phalguna’, ‘Rajendra Dhan 202’, ‘IET 7918’‘IET 6187’, ‘BG 404-1’; by duplicate dominant genes in ‘W 1263’, ‘RPW 6-17’ and ‘WGL 48684’ and a monogenic recessive gene in ‘OB 677’ and ‘BKNBR 1008-21’. The allelism test of the resistant genes in the test cultivars with already known genes Gm1 and Gm2 was carried out. A single dominant gene that conveyed the resistance in ‘RPW 6–17’, ‘IET 7918’ and ‘IET 6187’ was allelic to Gm1 and segregated independently of Gm2. The resistance in ‘Phalguna’, ‘Rajendra Dhan 202’, ‘W 1263’ and ‘RPW 6–17’, ‘IR 36’ and ‘WGL 48684’ was governed by Gm2 gene which was independent of Gm1. Two additional genes were identified and designated as Gm3 and gm4. Three test cultivars ‘BG 404-1’, ‘W 1263’ and ‘WGL 48684’ were found to have Gm3 gene for resistance which was non-allelic and segregated independently of Gm1 and Gm2. Thus the cultivars ‘W 1263’ and ‘WGL 48684’ had two resistance genes Gw2 and Gm3 together. The cultivar ‘RPW 6–17’ also had two resistance genes Gm1 and Gm2 together. The recessive gene gm4 which conditioned the resistance in ‘OB 677’ and ‘BKNBR 1008-21’ was nonallelic to and segregated independently of Gm1, Gm2 and Gm3 genes. Linkage studies of the resistance gene with pigment characters were carried out in ‘Purple gora/IR 36’ cross. The resistance gene Gm2 was found to be linked with the genes governing the pigmentation in node, apiculus and stigma with crossover values of 15.78, 31.57 and 35.78 % respectively. By the trisomic analysis, it was found that the Gm2 gene was located on chromosome 3.     

Inheritance of resistance to whitebacked planthopper,Sogatella furcifera (Horvath) in some rice cultivars

Summary The genetics of resistance to whitebacked planthopper, Sogatella furcifera (Horvath) in ten resistant cultivars was studied. The reactions of the F₁, F₂ and F₃ populations of resistant varieties with Taichung Native 1, a suspectible check, showed that WBPH resistance is monogenic in nature and governed by dominant gene(s) in Ptb 19 and IET 6288 and recessive gene in eight cultivars viz. ARC 5838, ARC 6579, ARC 6624, ARC 10464, ACR 11321, ARC 11320, Balamawee and IR 2415-90-4-3. Allelic relationship of resistance gene(s) in the test cultivars revealed recessive gene in IR 2415-90-4-3, ARC 5838 and ARC 11324 to be allelic but it was non allelic to the resistance gene in ARC 6624. Cultivars ARC 6579, ARC 11321 and Balamawee have identical gene among themselves but their relationship with IR 2415-90-4-3, ARC 5838, ARC 11324 and ARC 6624 is unknown. The recessive gene in ARC 10464 is non-identical to all other cultivars having the recessive gene except ARC 6624 with which its relationship needs further investigation.     

Homozygous transgenic rice lines expressing GNA with enhanced resistance to the rice sap-sucking pest Laodelphax striatellus

Homozygous transgenic rice lines expressing snowdrop lectin, Galanthus nivalis agglutinin (GNA), were investigated for resistance to the rice small brown planthopper (SBPH), Laodelphax striatellus, an important rice sap‐sucking pest causing yield losses and serving as vector for some important rice viruses. Insect bioassay results revealed that both the GNA‐expressing homozygous lines tested significantly inhibited SBPH by decreasing its survival, its overall fecundity and retarding development. This is the first report on homozygous transgenic rice lines expressing GNA conferring enhanced resistance to SBPH. This result suggests that transgenic rice expressing GNA will be useful in rice pest resistance breeding, as an alternative to conventional breeding for the control of SBPH, and potentially alleviating damage caused by the viruses it transmits.     

Genetic analysis of semidwarf mutants induced in indica rice (Oryza sativa L.)

The mode of inheritance of five semidwarf (SD) mutants and allelic relationship with DGWG (sd1) locus was studied. The five SD mutants viz., Basmati 370 (SD1), Basmati 370 (SD2), Basmati 370 (SD3), TCA 2 (SD) and TCA P2-5 (SD) when crossed with their tall parents exhibited monogenic inheritance of 3 tall: 1 semidwarf in the F2 progenies. The SD mutants were also crossed with semidwarf varieties (DGWG and Bala) possessing sd1 gene. Crosses between Basmati 370 (SD1) × Bala, Basmati 370 (SD3) × Bala and TCA 2 (SD) × DGWG produced tall F1 hybrids and in F2 generation, modified dihybrid ratios (9 : 6 : 1 and 9 : 7) were observed indicating that the mutants Basmati 370 (SD1), Basmati 370 (SD3) and TCA 2 (SD) are non-allelic to sd1 gene. Whereas, the mutants Basmati 370 (SD2) and TCA P2-5 (SD) when crossed with Bala produced semidwarf F1 hybrids and in F2 generation, segregation for plant height was not observed indicating that these mutants are allelic to sd1 gene. The three non-allelic SD mutants identified in the present study can be used in rice breeding as alternative gene sources for semidwarfism. This revised version was published online in July 2006 with corrections to the Cover Date.     

Trisomic genetic analysis of aroma in three Japanese native rice varieties (Oryza sativa L.)

Information on the genetics of aroma in rice facilitates breeding and selection of new aromatic varieties with high yield and good quality. Objective of the present study was to make clear the number of genes controlling aroma, and the allelism of aroma genes and the location of aroma gene(s) on the chromosome in three Japanese native aromatic rice varieties (Kabashiko, Shiroikichi and Henroyori). Lack of leaf aroma in all F₁ plants of non-aromatic/aromatic crosses indicated the recessive nature of aroma, and the segregation ratios (3:1) of non-aromatic to aromatic plants in its F₂ populations from Nipponbare/aromatic varieties crosses revealed that each of the three aromatic varieties contains a single recessive gene for aroma. Through trisomic analysis, the segregation of non-aromatic and aromatic plants in all F₂ populations from the crosses between trisomics lines NT8, with an extra chromosome 8, and aromatic varieties deviated significantly from disomic segregation of 3:1 ratios, and fitted to trisomic segregation, however, in other F₂ populations derived from other 7 types of trisomic F₁ plants, the segregation ratios of non-aromatic to aromatic were 3:1, indicating that the single recessive aroma gene was located on chromosome 8 in three aromatic varieties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic Analysis of Resistance to Brown Planthopper in Rice (Oryza sativa L.)

Seventeen rice cultivate resistant to brown planthoppers were genetically analyzed using the Bangladesh insect population. Seven cultivars were found to have a single dominant gene for resistance. These genes segregated independently of the recessive resistance gene bph-5. Tae dominant resistance gene of ‘Swarnalata’ was designated Bph-6. In ten cultivars, resistance is conferred by single recessive genes. In eight cultivars, the resistance genes are allelic to bph-5. However, the recessive genes o: two cultivars are non-allelic to bph-5. The recessive gene of T12 is designated bph-7.     

A new gene for resistance in rice to Asian rice gall midge (Orseolia oryzae Wood Mason) biotype 1 population at Raipur, India

The Asian rice gall midge, Orseolia oryzae Wood Mason (Diptera: Cecidomyiidae), is a major pest of rice in several South and South East Asian countries. The maggots feed internally on the growing tips of the tillers and transform them into tubular galls, onion leaf-like structures called ‘silver shoots’ resulting into severe yield loss to the rice crop. We studied the mode of inheritance and allelic relationships of the resistance genes involved in resistant donor Line 9, a sib of a susceptible cultivar ‘Madhuri’. The segregation behaviour of F₁, F₂ and F₃ populations of the cross between Line 9 and susceptible cultivar MW10 confirmed the presence of a single dominant gene for resistance. Tests of allelism with all the known genes giving resistance to this population indicated that Line 9 possessed a new gene which was designated Gm 9 This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic Analysis of Resistance to Xanthomonas campestris pv. oryzae (Ishiyama) Dye in a Rice Breeding Line ARC 10464

The genetics of resistance to three Indian pathotypes of Xanthomonas campestris pv. oryzae, namely, IX01, IX08 and IX09, was studied in a landrace of Indica rice ‘ARC 10464’. Resistance to each of the two pathotypes IX01 and IX09 was governed by two independently-inherited dominant genes while a single dominant gene was operative against patho-type 1X08. The joint segregation tests conducted on F₂ plant progenies (F₃ families) using pathotypes IX01, IX08 and IX09 suggested that the gene/(s) effective against each of the pathotypes are different.     

Mapping of a blast field resistance gene Pi39(t) of elite rice strain Chubu 111

We investigated the mode of inheritance and map location of field resistance to rice blast in the elite rice strain Chubu 111, and yield under severe blast conditions. Chubu 111 carries the complete resistance gene Pii, although field testing showed this strain to be susceptible to infection. The level of field resistance of Chubu 111 was so high that chemicals used to control blast were not required, even in an epiphytotic area. Genetic analysis of field resistance to blast in 149 F₃ lines derived from a cross between Chubu 111 and the susceptible cultivar ‘Mineasahi’ suggested that field resistance is controlled by a dominant gene, designated Pi39(t), that cosegregates with the single sequence repeat marker loci RM3843 and RM5473 on chromosome 4. Comparative studies of polymorphism at RM3843 among Chubu 111 and six cultivars or lines in its pedigree suggested that the donor of the resistance gene was the Chinese cultivar ‘Haonaihuan’. Marker‐assisted selection of Pi39(t) should be useful in rice‐breeding programmes for field resistance to blast.     

QTL analysis for resistance to preharvest sprouting in rice (Oryza sativa)

Preharvest sprouting (PHS) is caused by early breaking of seed dormancy. In Sichuan, a major hybrid rice seed production area of China, PHS in hybrid seeds originated from ‘G46A’ parent may lead to severe yield loss, causing serious damage to agricultural production. To detect quantitative trait loci (QTLs) governing PHS, we developed an F₂ population of 164 plants derived from ‘G46B’ and ‘K81’, a near‐isogenic introgression line of G46B, with high level of resistance to PHS. PHS was evaluated under controlled field and laboratory conditions. Using simple sequence repeat markers, we constructed a linkage map from this population and identified three QTLs for PHS, namely qPSR2, qPSR5 and qPSR8, which were located on chromosomes 2, 5 and 8, respectively. Among these QTLs, qPSR8, residing in the interval between RM447 and RM3754 on chromosome 8, was the major QTL controlling PHS, for it had a relative high logarithm of the odds (LOD) score and explained 43.04% of the phenotypic variation. These results were correspondent to those identified in extreme low germination rate plants (ELGP) using linkage and linkage disequilibrium. At all loci, ‘K81’ was responsible for enhancing the resistance to PHS.     

Genetic control of seedling tolerance to aluminum toxicity in rice

An uncomplete diallel analysis was conducted for 56 F1 progenies derived from 8 male × 7 female parents with differential Al tolerance based on root tolerance index (RTI) in a solution culture with Al concentration of 1 mM Al. Remarkable variation in RTI among the parents was observed after 6 weeks in culture. Significant (P < 0.001) general combine ability (GCA) variance for both male and female parents and specific combine ability (SCA) variance were observed. The variance of GCA was much higher than that of SCA, indicating greater additive expression of the tolerant trait. Higher narrow-sense heritability (48%) was detected, indicating the possibility of a genetic gain in selection for Al tolerance based on RTI. The tolerant performance of F1 progenies appeared to be influenced by the susceptible genotype. suggesting the inconsistent dominance effect. The possible mechanisms of the apparent inconsistent dominance was discussed in terms of the genetic background in wheat. Two restore lines, Pedel and 02428, and one sterile variety, XieqinzaoA, were found to be high in the GCA effect and SCA variance in this case. These genotypes may be useful in development of hybrid rice production on acid soils. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic progress of upland rice (Oryza sativa L.) lines for disease resistance

The rice crop is affected by diseases throughout its cycle, impacting negatively on grain yield and quality. The control of the disease impact can be accomplished via crop breeding, using highly multiple resistant genotypes. This study aimed to evaluate the efficiency of multiple-character and specific selection of multiple resistance to major culture-associated diseases (neck blast, leaf scald and grain discoloration) in rice lines of the Upland Rice Genetic Breeding Program. The experiments were conducted in 35 sites during 12 agricultural years, where 124 lines were evaluated for the severity of fungal diseases, under natural field conditions. Multiple parameters were calculated based on the diseases´ scores: genetic, phenotypic and environmental variances, heritability, selection gain, renewal rate, and genetic and renewal progress. Genetic variance for the disease resistance was identified in the population, and the selection gain for multiple-character selection was of 3.16 year⁻¹ throughout the breeding process with a renewal rate of over 35%. The programme has showed efficiency in selecting multiple resistant genotypes to the mentioned diseases, highlighting genotypes with high potential for market release.     

Crosses between cultivars and tissue culture-selected plants for salt resistance improvement in rice, Oryza sativa

Several R₂ somaclonal families were derived from plants regenerated from a salt‐resistant callus of the salt‐sensitive rice cultivar ‘I Kong Pao’ (IKP). The family R₂‐1‐23, in the presence of NaCl exhibited higher yield performances than the initial cultivar. This improvement in salinity resistance, however, was not transmitted to following generations; despite a higher number of spikelets per plant, family R₃‐1‐23 did not perform better than the initial cultivar because of a very low seed set. This somaclonal family, its initial being the cultivar IKP, the breeding line IR₃1785 (extremely salt‐sensitive) and the cultivar ‘Aiwu’ (moderately salt‐resistant), were used as parents for production ofhybrids. Four crosses, IKP×R3‐1‐23, IR31785 ×R3‐1‐23, IR31785× IKP and IKP בAiwu’, were performed. Most of the F₁ hybrids cultivated in the absence of salt exhibited increased performances compared with the mid‐parent, suggesting an heterosis effect for yield‐related parameters. F₂ populations were screened for salinity resistance and a clear improvement for yield in stress conditions was recorded for populations derived from IK×R3‐1‐23, IR31785×R3‐1‐23 and IR31785×IKP, although the mean level of increase over the mid‐parent (RIMP) varied depending on the population, the presence or absence of stress, and the quantified parameters. The results are discussed in relation to the usefulness of in vitro selection for obtaining interesting somaclonal variants useful to be integrated in classical breeding programmes for salinity resistance in rice.     

Pyramiding of Xa7 and Xa21 for the improvement of disease resistance to bacterial blight in hybrid rice

‘Minghui 63’ is a restorer line widely used in hybrid rice production in China for the last two decades. This line and its derived hybrids, including ‘Shanyou 63’, are susceptible to bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae (Xoo). To improve the bacterial blight resistance of hybrid rice, two resistance genes Xa21 and Xa7, have been introgressed into ‘Minghui 63’ by marker‐assisted selection and conventional backcrossing, respectively. The single resistance gene‐introgressed lines, Minghui 63 (Xa21) and Minghui 63 (Xa7) had higher levels of resistance to bacterial blight than their derived hybrids, Shanyou 63 (Xa21) or Shanyou 63 (Xa7). Both Xa21 and Xa7 showed incomplete dominance in the heterozygous background of rice hybrids by infection with GX325 and KS‐1‐21. The improved restorer lines, with the homozygous genotypes, Xa21Xa21 or Xa7Xa7, were more resistant than their hybrids with the heterozygous genotypes Xa21xa21 or Xa7xa7. To further enhance the bacterial blight resistance of ‘Minghui 63’ and its hybrids, Xa21 and Xa7 were pyramided into the same background using molecular marker‐aided selection. The restorer lines developed with the resistance genes Xa21 and Xa7, and their derived hybrids were evaluated for resistance after inoculation with 10 isolates of pathogens from China, Japan and the Philippines, and showed a higher level of resistance to BB than the restorer lines and derived hybrids having only one of the resistance genes. The pyramided double resistance lines and their derived hybrids have the same high level of resistance to BB. These results clearly indicate that pyramiding of dominant genes is a useful approach for improving BB resistance in hybrid rice.     

Genetic analysis of resistance of three melon lines to Sphaerotheca fuliginea

Summary The inheritance of resistance of three melon lines to Sphaerotheca fuliginea race 1 has been studied. Negro possesses one dominant gene for resistance. Resistance in Amarillo is mainly controlled by one gene, and resistance in Moscatel Grande seems to be controlled by two genes. These four genes are different from each other and allelism tests showed that the gene present in Negro is different from those described before in PMR5, PI 124111 and PI 124112. The main gene present in Amarillo is different from those carried by PMR5 and PI 124111 and the two genes carried by Moscatel Grande are different from the one present in PMR5.     

Genetic analysis and breeding use of blast resistance in a japonica rice mutant R917

R917, a japonica rice mutant with broad-spectrum of resistance to blast, was selected after treatment of the F₁ seeds from the cross between Chengte 232 and Xiushui 37 with 10 krad of ⁶⁰Co γ-ray. R917 was evaluated for blast resistance in multiple years and locations. It was resistant to 136 of 138 strains of Magnaporthe grisea collected from different regions in China with a resistance frequency of 98.55%, much higher than 86.13% and 10.15% of Chengte 232 and Xiushui 37. To analyze its inheritance of resistance to blast, R917 was crossed with the susceptible cultivar, Nonghu 6, and its two parents. It had a single dominant resistance gene to Chinese races ZB13, ZC15 and ZE3, nonallelic to those of Chengte 232 and Xiushui 37. When inoculated with 7 Japanese differential strains, R917 showed the same reaction pattern as Toride 1 and differed from the other differential varieties. But R917 was different from Toride 1 in its reaction to 7 Chinese strains. Allelism test indicated that the resistance genes between R917 and Toride 1 were nonallelic to Chinese races ZC15 and ZE3. R917 was a semi dwarf with strong stem, narrow and erect leaf, tight plant type and monogenic broad-spectrum resistance to blast. Several lines with desirable agronomic traits newly bred using R917 as a donor of blast resistance had the same broad-spectrum of resistance to blast as R917, indicating there was no linkage drag between the resistance gene and other important agronomic genes in R917. R917 has been used as a donor in rice breeding programs in China. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identification of a major blast resistance gene in the rice cultivar 'Tetep'

Analysis of near‐isogenic lines (NILs) indicated the presence of a novel resistance gene in the indica rice cultivar ‘Tetep’ which was highly resistant to the rice blast fungus Magnaporthe grisea.‘Tetep’ was crossed to the widely used susceptible cultivar ‘CO39’ to generate the mapping population. A Mendelian segregation ratio of 3 : 1 for resistant to susceptible F₂ plants further confirmed the presence of a major dominant locus, in ‘Tetep’, conferring resistance to the blast fungal isolate B157, corresponding to the international race IC9. Simple sequence length polymorphism (SSLP) was used for molecular genetic analysis. The analysis revealed that the SSLP marker RM 246 was linked to a novel blast resistance gene designated Pi‐tp(t) in ‘Tetep’.     

Genetic analysis of resistance to leaf-rust (Puccinia recondita f. sp. tritici) pathotypes in the durum wheats 'PBW 34' and 'DWL 5023'

Genetic analysis of leaf-rust resistance was conducted on two durum wheats. Triticum durum cvs. ‘PBW 34’ and ‘DWL 5023’ were crossed with the leaf-rust-susceptible durum wheat ‘Malvi Local’. The F₁, F₂ and F₃ generations were tested against leaf-rust pathotypes 1, 77A and 108. In ‘PBW 34’, a single dominant gene was effective against each of the pathotypes 1 and 108, whereas two independently inherited dominant genes were effective against pathotype 77A. In ‘DWL 5023’, two independently inherited dominant genes were operative against pathotypes 1 and 77A, whereas a single dominant gene was identified as being operative against pathotype 108. Allelic tests on F₂ generation and joint segregation analysis on F₃ generation seedlings, suggested that two different genes in each cultivar are effective against these three leaf-rust pathotypes. Cultivar ‘PBW 34’ has Lrd1 and Lrd2 genes whereas Lrd1 and Lrd3 genes are present in ‘DWL 5023’.