Wide compatibility in rice (Oryza sativa L.)

Summary Wide compatible varieties (WCVs) show normal spikelet fertility in crosses with Indica and Japonica rice varieties. Crosses of Indica and Japonica varieties frequently show high spikelet sterility which prevents exploitation of heterosis for grain yield. We screened 41 rice varieties for the wide compatibility trait by crossing each with three Indica and three Japonica testers. Varieties giving fertile F₁ hybrids with both groups of testers were classified as WCVs. Seven varieties viz., BPI-76 (Indica); N 22; Lambayeque-1 and Dular (Aus); Moroberekan, Palawan and Fossa HV (Japonicas), were identified as WCVs. The frequency of WCVs was higher among Aus and Japonicas. The wide compatibility trait in varieties: Dular and Moroberekan was controlled by a single dominant gene linked with the Est-2 and Amp-3 loci (mean recombination 32.0%). Est-2 and Amp-3 showed complete linkage. Pgi-2 was found to be linked with Est-2 and Amp-3 (mean recombination 16.1%). Est-2 and Amp-3, showed a tighter linkage with C ⁺ (mean recombination 4.1%). Pgi-2 showed a lower linkage with C ⁺ (mean recombination 17.3%). The recombination values between the WC gene in Dular and C ⁺ was much higher than those reported in Japan for the WC gene (S₅ ⁿ) from Ketan Nangka. It is possible that the WC gene from Dular is different from that in Ketan Nangka. Linkage intensities with the WC gene were not strong enough to be of use for indirect selection for the wide compatibility trait. A search for a more closely linked isozyme or DNA marker was proposed.     

Linkage studies in rice (Oryza sativa L.)

Summary In an intervarietal cross between IR 8 and Wanar 1, inheritance of pigmentation in coleoptile, leaf-sheath, auricle, node, internode, septum and glume was studied. A pleiotropic gene conditioning pigment in all these parts has been identified which may probably be one of the basic genes for anthocyanin pigmentation. A linkage group consisting of genes causing pigment in these seven organs has been indicated in this sequence: Pau-Pc-Pn-Psh-Pin-Pg-Pm. This group may form part of the III Sp group of Misro et al. (1966) (corresponding to the A linkage group of japonica) in which case Pau, Pc, Pn and Pg are additions to this group. Linkage relationship of genes for coleoptile colour is reported for the first time.     

Linkage studies in rice (Oryza sativa,L.)

Linkage studies in rice up to 1959 have been briefly reviewed with a special reference to the work carried out at the Central Rice Research Institute, Cuttack, India. The crossover values for several genes have been furnished. Instances have been cited wherein two or more genes appear to be involved in determining the expression of anthocyanin pigmentation in different plant parts.

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Samenvatting Een overzicht wordt gegeven van de literatuur tot en met 1959 over de koppeling van genen bij rijst, in het bijzonder het koppelingsonderzoek uitgevoerd door het Central Rice Research Institute, Cuttack, India.De crossover-waarden voor vele genen worden vermeld. Enkele gevallen zijn genoemd waarbij 2 of meer genen een pleiotrope werking hebben bij de vorming van anthocyaan in verschillende delen van de plant.

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Paper read in the meeting of the Working Party on Rice Production and Protection of the International Rice Commission, held in Ceylon during December, 1959.     

Inheritance of amylose content in rice (Oryza sativa L.)

Summary The inheritance of low and very low amylose contents in six rice crosses and their reciprocals was studied by single grain analysis of parents F₁, F₂, B₁ and B₂ seeds. To minimize the environmental effects, the seeds of all generations of all crosses were produced in a single season. The results indicated different dosage effects in different crosses. One major gene was found to govern a difference of 6–12% in amylose content in low and intermediate amylose parents. Very low amylose content was similarly found to be governed by one major gene in crosses between very low- and low-amylose content parents. Minor genes and modifiers also seem to play some role. In the cross between two low amylose parents differing by about 2.5% in amylose content, the differences appeared to be controlled by some minor genes and modifiers. The selection program in different crosses has been suggested.     

A study on heterosis in rice (Oryza sativa L.)

Summary Heterosis for yield and four yield components, viz. panicle number per plant, panicle length, spikelet per panicle and 1000-grain weight, was studied in fifteen crosses involving six varieties of rice, Oryza sativa L. Positive and significant heterosis for yield was observed in 11 and 8 crosses, over the mid-parent and the better parent, respectively. Hamsa x Hybrid 27 gave the highest heterosis both over the mid-parent (156.23%) and the better parent (136.38%) followed by Jaya x Norin 18 with respective values of 155.18 and 56.29%.As compared with the average yield of 36.54 g per plant of the high yielding commercial variety, viz. Jaya hybrids in 8 crosses gave significant higher yield and four crosses, viz. Hamsa x Hybrid 27, Hybrid 27 x Jhona 349, Jaya x Palman 579 and Jaya x Hybrid 27, gave 80.51, 66.56, 57.11 and 56.30 g per plant, recording an increase of 120.33, 82.13, 56.29 and 54.08%, respectively. The heterosis for yield was due to simultaneous heterosis for a number of yield components. The possibility of hybrid crop production as compared with the recently developed high yielding rice varieties has also been discussed.Contribution No. 73.15 from the Department of Plant Breeding, Punjab Agricultural University, Ludhiana, India.     

Linkage of genes for anthocyanin pigmentation in rice (Oryza sativa L.)

Summary The inheritance of anthocyanin pigmentation and the interrelationship between genes governing anthocyanin pigmentation in different parts of the rice plant and genes governing panicle density were studied in the cross Suma × Wanar-1. A ratio of 45 pigmented: 19 non pigmented was realised for anthocyanin accumulation in sheath, nodal ring, internode, leaf tip, leaf margin and apiculus whereas a ratio of 3 normal:1 laxy was observed for panicle density. Pleiotropic action of a basic gene (A) and each of the two complementary duplicate genes (P _a or P _b) was detected. A linkage group of genes localising pigment in six plant parts was identified, the sequence of genes being P _nr-P _lm-P _la-P _a-P _sh-P _in. This may form part of the III S _p group of Misro et al. (1966), in which case the genes P _nr and P _la are proposed to be additions to this group.     

Genetic analysis of ratooning ability of rice (Oryza sativa L.)

Summary Genetic analysis of generation means of F₁, F₂, F₃, F₄, and the parental populations of the cross IR10154-23-3-3A/IR15795-232-3-3-2 for ratooning ability was conducted. Good ratooning ability is a recessive trait. The parents differed by at least two pairs of major genes for ratooning ability. A large proportion of transgressive segregants in F₂ suggested that the expression of ratooning ability is influenced not only by major genes but also by modifiers. Broad-sense heritability estimates computed by different methods ranged from 0.66 to 0.88. Narrow-sense heritability by the F₄–F₃ regression method was 0.39. The heritability estimates were 0.42 and 0.33 by the variance component method. The prevalence of additive x additive type of gene effects along with prominent additive effects imply some scope for selection in the segregating generations. However, non-additive type of gene action also affects the expression of ratooning ability.     

QTL analysis of seed dormancy in rice (Oryza sativa L.)

Effective cumulative temperature (ECT) after heading would be a more reasonable parameter for seed sampling of pre-harvest sprouting/seed dormancy (SD) tests in segregating populations than the days after flowering. SD is an important agronomic trait associated with grain yielding, eating quality and seed quality. To identify genomic regions affecting SD at different grain-filling temperatures, and to further examine the association between SD and ECT during grain-filling, 127 double haploid (DH) lines derived from a cross between ZYQ8 (indica)/JX17 (japonica) by anther culture were analyzed. The quantitative trait loci (QTLs) and their digenic epistasis for SD were identified using a molecular linkage map of this population. A total of four putative QTLs for SD (qSD-3, qSD-5, 6 and 11) were detected on chromosomes 3, 5, 6 and 11, together explaining 41.4% of the phenotypic variation. Nine pairs of digenic epistatic loci were associated with SD on all but chromosome 9, and their contributions to phenotypic variation varied from 2.87%–8.73%. The SD QTL on chromosome 3 was identical to the QTLs found in other mapping populations with different genetic backgrounds, which could be a desirable candidate for gene cloning and marker-assisted selection in rice breeding.     

Anther and pollen grain culture of rice (Oryza sativa L.)

Summary Factors favouring callus proliferation and subsequent regeneration of plants from pollen grains of rice anthers (Oryza sativa L., cvx. Bahia, Girona, Balilla × Sollana and Sequial) were determined. Cultivar differences in response were found, such as a high rate of haploid plant regeneration.In addition, isolated pollen grain culture was used to induce tissue proliferation outside the anther walls. The frequency of callus formation from isolated pollen grains was very low. It was necessary to preculture the anthers before pollen grain separation, in order to accomplish a successful development later. Root differentiation was observed in some of the obtained callus.     

Genetics of stem elongation ability in rice (Oryza sativa L.)

Summary The genetics of stem elongation ability in rice was studied in parents, F₁, F₂ and backcross generations of six crosses. Segregation analysis indicated dominance for stem elongation ability. Estimation of genetic parameters under epistatic model indicated more than one locus control stem elongation ability and both additive and nonadditive gene effects were important. Epistatic effects were predominant over additive and dominance effects with an important role of duplicate type of epistasis. The occurrence of significant additive and additive x additive types of genetic variation and the moderately high broad sense heritability indicated the possibility of selection for an increased manifestation of stem elongation ability.     

Chromosomal regions controlling anther culturability in rice (Oryza sativa L.)

Diallel analysis has revealed that anther culturability in rice (Oryza sativa L.) is a quantitative trait controlled by the nuclear genome. Mapping of anther culturability is important to increase the efficiency for green plant regeneration from microspores. In the previous study, we detected distorted segregation of RFLP markers in rice populations derived from the anther culture of an F₁ hybrid between a japonica cultivar ‘Nipponbare’ and an indica cultivar ‘Milyang 23’. To clarify the association between chromosomal regions showing distorted segregation and anther culturability, the anther culturability of doubled haploid lines derived from the same cross combination was examined, and the association between alleles of the RFLP markers, which exhibiting the most distorted segregation on chromosomes 1, 3, 7, 10 and 11, and the anther culturability was evaluated. One region on chromosome 1 was found to control callus formation from microspores, and one region on chromosome 10 appeared to control the ratio of green to albino regenerated plants. In both regions, the Nipponbare allele had positive effects. Three regions on chromosomes 3, 7 and 11, however, showed no significant effect on anther culturability. This revised version was published online in August 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.     

Mapping of QTLs for leaf developmental behavior in rice (Oryza sativa L.)

Leaf developmental behavior in rice (Oryza sativa L.) is one of the important agronomic characteristics, which not only determines vegetative growth but also influences grain yield. This study was conducted to identify quantitative trait loci (QTLs) for total number of leaves (TNL), days to the emergence of flag-leaf (DEF) and the leaf emergence rates (LER) on main stem, which mainly represent leaf developmental behavior, using recombinant inbred lines (RILs) derived from a cross between a japonica variety, Asominori and an indica variety, IR24, cultivated in 2001 and 2002. The transgressive segregations in both parental directions and continuous variations of all three tested traits were observed. Significant correlations among these traits were detected. A total of fourteen QTLs for leaf development behavior were detected with 289 RFLP markers. Six QTLs controlling TNL were mapped to chromosomes 3, 5, 6, 8, 9, 12, and accounted for 5.615.7% of the total phenotypic variations, and three QTLs for DEF were mapped to chromosome 3, 6, 8 and accounted for 10.735.4% of total phenotype variation and five QTLs for LER were mapped to chromosome 1(two QTLs), 2, 4, 9 and explained 6.217.5% of phenotype variation. The identification of QTLs for leaf developmental behavior in rice may be useful for selection of fast growing genotype before heading using maker-assisted selection.     

A major gene for low temperature germinability in rice (Oryza sativa L.)

Low temperature-induced retardation of seedling growth is a common problem in temperate rice-growing areas, at high altitudes of tropical and sub-tropical areas, and in areas with a cold irrigation water supply. Studies on low temperature germinability have revealed complex inheritance of the trait. The purpose of this study was to identify the gene(s) for low temperature germinability using Italica Livorno as a donor parent. The frequency distributions for the germination rate at 15 °C in the F₂ and BC₁F₁ populations showed continuous segregation, suggesting that low temperature germinability was under polygenic control. Since some lines in the BC₁F₁ population showed vigorous low temperature germinability similar to that of Italica Livorno, backcrosses until the BC₅F₁ generation was carried out using Hayamasari as the recurrent parent. Clear segregations of low temperature germinability were observed in the BC₅F₁ and BC₅F₂ populations. The distribution of low temperature germinability fitted a single-gene segregation, indicating that a single dominant gene with a large effect was transferred to Hayamasari. This gene is tentatively symbolized as Ltg(t). Low temperature germinability of near isogenic lines for Ltg(t) was similar to that of Italica Livorno. Ltg(t) should greatly contribute to the improvement and manipulation of low temperature germinability in rice breeding programs. This revised version was published online in August 2006 with corrections to the Cover Date.     

Agro-morphological characterization of ovary culture-derived plants of rice (Oryza sativa L.)

Plants derived from unpollinated ovary culture of ten rice genotypes showed significant variability in agro-morphological characteristics. The ovary-derived plant (H1) populations were completely haploid, doubled haploid or haploid-doubled haploid mixture. Haploids had very drastic reduction in plant height, panicle length, grain length, breadth and number and spikelet fertility (0.0%–2.1%). Doubled haploids from the hybrid of UPRI 95–121 × UPRI 95–165 were normal with fertility ranging between 69.6% and 97.7%. A genetic segregation in ratio of 1:1 was observed for five pigmentation characters in the H1 population derived from hybrid UPRI 95–122 × UPRI 95–165. Plant height showed the largest coefficient of variability (28.5%) followed by the number of spikelets per panicle (24.2%), number of grains per panicle (22.0%), percent seed set (9.2%) and panicle length (9.0%). The range of variation in the H1 population from fully fertile hybrid PMS 2A (CMS) × IR 31802 (restorer) was similar to its corresponding F2 population for plant height, spikelet fertility and number of grains/panicle. A single clone of plants from the cultivar BG 1321 exhibited complete male sterility but normal female fertility when pollinated with other varieties. Ovary-derived plants from the CMS lines PMS 2A and IR 58025A showed stable male sterility and those from thermosensitive genetic male sterile line UPRI 95–140 showed thermosensitive genetic male sterility. These lines have potential in the hybrid breeding program and are being currently exploited. This revised version was published online in July 2006 with corrections to the Cover Date.     

A linkage group in rice (Oryza sativa L.) involving anti-inhibitory genes

Summary Inheritance studies of purple pigmentation in T-160 x AC-177 revealed that purple colour in the coleoptile is based on four genes (Pc ₁ , Pc₂, I-Pc, Ai-Pc), in the internode on two genes (Pin _a1 , Pin _a2 ), in the junctura on three genes (Pja, Pjb ₁ , Pjb ₂ ) and in the apiculus on three genes (Pa, I-P, Ai-P). For panicle density monogenic segregation (Lx) was obtained. Linkage was established between the genes for the apiculus (Pa and Ai-P), panicle density (Lx), the internode (Pin _a ), the coleoptile (Ai-Pc) and the junctura (Pja), in that sequence. This linkage group forms part of the IV mp group of Misro et al. (1966) which corresponds to the g group of japonica.The two anti-inhibitory genes Ai-Pg and Ai-Pau of the linkage group Ai-Pg=Ai-Pc=Ai-Pau reported earlier (Dhullappanavar et al., 1975) are also allotted to the IV linkage group of Misro et al. (1966) since Ai-Pc is placed in that group in the present studies.     

Calcium silicate slag reduces drought stress in rice (Oryza sativa L.)

Silicon has been reported to reduce drought stress on many crops, but limited studies have evaluated this effect with rice using calcium silicate slag from the phosphorus fertilizer industry as a source of Si. A greenhouse study was performed to address this issue. Four slag rates (0, 1,000, 2,000 and 4,000 mg/kg) and two application methods (surface application and incorporation) were evaluated under two moisture regimes (flood and 50% field capacity) for drought stress mitigation in a mineral soil that is typical for rice production. Slag application significantly elevated plant‐available Si in the soil and Si accumulation in plant tissues, and tended to improve rice shoot and root biomass relative to the untreated control under both flooding and drought stress. Increased carbon isotope discrimination (△¹³C) and decreased proline in rice leaves subjected to drought stress indicate that this slag may reduce drought stress in rice, which was supported by restoration of foliage density, transpiration, photosynthesis rate and sugar accumulation to at or near flooded levels following the highest slag application. This study supports the usage of calcium silicate slag in rice production as it could improve Si availability and reduce drought stress.     

A new gene controlling hybrid sterility in rice (Oryza sativa L.)

Hybrids between rice subspecies indica and japonica display strong heterosis. However, semi-sterility of inter-subspecific hybrids between indica and japonica varieties is a major obstacle for application of hybrid vigor in rice production. Semi-sterility was previously ascribed to allelic interaction at a number of different loci, whereas, wide-compatibility varieties can overcome hybrid sterility. Variety Nekken 2, which is a source of wide compatibility genes, showed sterility when crossed to the Korean variety Yeong Pung. Genetic and cytological analyses revealed that the semi-sterility was caused by partial abortion of the embryo sac. Genome-wide analysis of the backcross population, Nekken 2/Yeong Pung//Nekken 2 identified two independent loci for hybrid sterility on chromosomes 1 and 12, explaining 18.99 and 18.03% of the phenotypic variance, respectively. To confirm this result, another population of the same backcross containing 216 individuals was tested at a different site in a different year. The locus on chromosome 12 was detected again. Based on the study, the stable QTL on chromosome 12 appeared to be different from previously reported genes for this trait, and was designated as S35(t).