The transfer of a gene for glutinous endosperm to Oryza glaberrima Steud. From a japonica variety of O. sativa L.

Summary In common rice, Oryza sativa L. (n=12), the gene Am for non-glutinous is dominant over the gene am for glutinous. In African rice, O. glaberrima Steud. (n=12), no spontaneous glutinous strain has been found, but recently a glutinous strain of glaberrima was induced by EMS-treatment.The interspecific cytoplasm substitution line with sativa cytoplasm and glaberrima nucleus is male sterile. It has been confirmed that the complete restoration of pollen fertility in this male sterile line is attributed to a single dominant nuclear gene Rf _j.Trial to transfer gene am from sativa to glaberrima was commenced with backcrosses of the F₁ hybrid (glutinous sativa cv. Iwai-mochi × glaberrima ) to glaberrima type plants of the substitution line homozygous for Rf _j,using the latter as the pollen parent. At the B₁ step, highly fertile glaberrima type Am/am plants were obtained. Thereafter plants of this type were backcrossed to normal glaberrima as the recurrent pollen parent to complete the nuclear substitution. It was confirmed that the EMS-induced glutinous character of glaberrima was a monogenic recessive and that the same gene controls the expression of glutinous character in the different rice species, sativa and glaberrima.     

Genetic studies on the interspecific cytoplasm substitution lines of an Asian perennial strain of Oryza rufipogon Griff. and O. glaberrima Steud.

Summary It is shown that the restorer gene Rf _j extracted from the Japanese rice variety Akebono is effective on pollen restoration in the cytoplasm substitution line having the nucleus of Oryza glaberrima and japonica or indica cytoplasm of O. sativa, and is of the sporophytic type.The Asian perennial type of the wild rice species O. rufipogon is considered to be the progenitor of O. sativa. Two substitution lines having the cytoplasm of a perennial strain of O. rufipogon from Sri Lanka and the nucleus of O. glaberrima with or without the gene Rf _j in homozygous condition have been bred by means of successive backcrosses. These lines have now reached the BC₅ generation. Plants of the lines resemble morphologically the recurrent parent, but do not show pollen restoration, indicating that the cytoplasm of the rufipogon strain induced male sterility and that the gene Rf _j does not act as the restorer.     

Genetic studies on the interspecific cytoplasm substitution lines of japonica varieties of Oryza sativa L. and O. glaberrima Steud.

Summary Interspecific cytoplasm substitution lines of Oryza sativa and O. glaberrima, i.e. (sativa)-glaberrima and (glaberrima)-sativa, have been bred by means of successive backcrosses, using three japonica varieties of sativa and two glaberrima strains.In all the six substitution lines with the cytoplasm of the glaberrima strains, the fertility increased with succeeding backcrosses, and eventually completely fertile plants whith the characteristics of the parental japonica variety appeared. This indicates that the glaberrima cytoplasm exerted no effect on the genome manifestation of these japonica varieties. Of the five substitution lines with the cytoplasm of each of the japonica varieties, four lines produced male sterile (M.S.) plants only in the backcross generations. In the remaining substitution line with the cytoplasm of the japonica variety Akebono, there was simultaneous segregation for male sterile (M.S.) and pollen fertile plants bearing indehiscent anthers (ID.M.F.) in the backcross generations. In the compulsively selfed progeny of ID.M.F. plants, pollen fertile plants with dehiscent anthers (D.M.F.) occurred with M.S- and ID.M.F. plants. Morphologically, these three types were supposed to have the same genetic background as the glaberrima parent. It was established that D.M.F.-and ID.M.F. plants were homozygous and heterozygous for a dominant nuclear gene restoring pollen fertility, respectively, and the M.S. plants and the two glaberrima strains used in this study carried a recessive gene for pollen sterility in homozygous condition. The restorer gene was assumed to derive from the japonica variety Akebono. The expression of the restorer gene was of the sporophytic type. The pollen sterility of the substitution lines that possessed the cytoplasm of the japonica varieties was of cytoplasmon-genic nature.     

The origin,evolution, cultivation,dissemination, and diversification of Asian and African rices

Summary Available evidences drawn from biosystematics, evolutionary biology, biogeography, archaeology, history, anthropology, paleo-geology and paleo-meteorology are pooled to reconstruct the series of events that led to the cosmopolitan cultivation of the Asian cultivated rice (O. sativa) and the regionalized planting of the African cultigen (O. glaberrima) in West Africa. The genus Oryza originated in the Gondwanaland continents and, following the fracture of the supercontinent, became widely distributed in the humid tropics of Africa, South America, South and Southeast Asia, and Oceania. The two cultivated species have had a common progenitor in the distant past. Parallel and independent evolutionary processes occurred in Africa and in Asia, following the sequence of: wild perennialwild annualcultivated annual. The weed races also contributed to the differentiation of the cultivated annuals. The corresponding members of the above series are O. longistaminata Chev. et Roehr., O. barthii A. Chev., O. glaberrima Steud., and the stapfii forms of O. glaberrima in Africa; O. rufipogon Griff., O. nivara Sharma et Shastry, O. sativa L., and the spontanea forms of O. sativa in Asia.The differentiation and diversification of the annuals in South Asia were accelerated by marked climatic changes following the last glacial age, dispersal of plants over latitude or altitude, human selection, and manipulation of the cultural environment.Cultivation of rice began in many parts of South and Southeast Asia, probably first in Ancient India. Cultural techniques such as puddling and transplanting were first developed in north and central China and later transmitted to Southeast Asia. Wetland culture preceded dryland culture in China, but in hilly areas of Southeast Asia, dryland cultivation is older than lowland culture. The planting method progressed from shifting cultivation to direct sowing in permanent fields, then to transplanting in bunded fields.Widespread dispersal of the Asian cultigen led to the formation of three eco-geographic races (Indica. Sinica or Japonica, and Javanica) and distinct cultural types in monsoon Asia (upland, lowland, and deep water). Varietal types changed readily within the span of a millenium, largely due to cultivators' preferences, socio-religious traditions, and population pressure. Genetic differentiation developed parallel to the ecologic diversification process.The African cultigen developed later than the Asian cultigen and has undergone less diversification. The wild races in South America and Oceania retain their primitive features mainly due to lack of cultivation pressure or dispersal.Both the African and Asian rices are still undergoing evolutionary changes at habitats where the wild, weed, and cultivated races co-exist.     

Molecular Mapping of a Pollen Killer Gene S29(t) in Oryza Glaberrima and Co-Linear Analysis with S22 in O. Glumaepatula

Two species in genus Oryza, O. glaberrima and O. glumaepatula, are valuable and potential sources of useful genes of interest for rice improvement. However, the hybrid sterility between O. sativa and these two species is a main reproduction barrier when transferring the favorable traits/genes to mbox{O. sativa.} To overcome it, the nature of hybrid sterility should be understood further. The objective in the report is to map a new hybrid sterility gene as a Mendelian factor from O. glaberrima and analyze the co-linear of hybrid sterility S loci mbox{between} mbox{O. glaberrima} and mbox{O. glumaepatula} via comparative mapping approach. A BC₂F₂ population, derived from a single semi-sterility plant of BC₂F₁ of WAB56-104/ WAB450-11-1-2-P41-HB (WAB450-6) //WAB56-104///WAB56-104 was employed to map this pollen killer in O. glaberrima since WAB450-6 is a progeny of interspecific hybrid between O. sativa and O. glaberrima. A new pollen killer locus, S29(t) in O. glaberrima, was identified and mapped to interval between SSR marker RM7033 (1.1 cM) and RM7562 (1.3 cM) on rice chromosome 2. Comparative mapping indicated that S29(t) closely corresponded to S22 which is also a pollen killer gene in O. glumaepatula and is tightly linked with RFLP marker S910 on the short arm of rice chromosome 2. The good co-linear between S29(t) and S22 implied that there might exist common (orthologous) hybrid sterility loci controlled the reproduction barrier among AA genome species of genus Oryza, which will contribute significantly to our understanding of speciation and operation of hybrid sterility between O. sativa and its AA genome relatives.     

A gametocidal factor of Oryza glaberrima Steud. in O. sativa L.

Summary Recurrent backcrossing has been carried out with a view to transfer a gene for non-glutinous endosperm from two strains of O. glaberrima (Wx _g /Wx _g ) to glutinous japonica and indica varieties (wx/wx) of Oryza sativa. In the course of backcrosses Wx _g /wx segregants were crossed with each of the two glutinous varieties of sativa as the respective recurrent male parent. The wx/wx and Wx _g /wx segregants in the successive generations were consistently fully fertile and semi-sterile, respectively. The semi-sterility of Wx _g /wx plants was attributable to abortion of most of the pollen grains carrying the gene wx. The nucleus but not cytoplasm was related to the semi-sterility. The Wx _g /Wx plants having the gene for non-glutinous endosperm of a glaberrima strain and a japonica variety of sativa were also semi-sterile. Both wx- and Wx-megaspores in the plants heterozygous for the gene Wx _g were deleteriously affected. The results could be explained by assuming that a factor tightly linked with the gene Wx _g of glaberrima sterilizes gametes not carrying it in the heterozygotes and that the gametocidal action is exerted when combined with the sativa nucleus by the recurrent backcross method.     

Increasing biodiversity of irrigated rice in Africa by interspecific crossing of Oryza glaberrima (Steud.) × O. sativa indica (L.)

The African rice Oryza glaberrima, traditionally cultivated since more than 3.500 years, is of poor agronomic performance but resistant/tolerant to various stresses and diseases. The introduction of these characters into O. sativa cultivars is difficult since crossing barriers cause spikelet sterility in F1. Backcrossing can restore fertility and recently facilitated the development of fertile O. glaberrima × O. sativa ssp. japonica hybrid progenies for rain fed systems. With the objective to gain access to African rice germplasm for improvement of irrigated rice, crosses were performed with eighteen O. glaberrima and twenty O. sativa ssp. indica accessions. In total about one hundred F1-hybrid grains were obtained. The F1 plants were all completely sterile and backcrossing (BC) to O. sativa was performed in order to restore spikelet fertility. Monitoring of Tog5681 × IR64 hybrid progenies under field conditions revealed a broad genetic diversity within the BC₁ and BC₂ populations. Some BC₁ and BC₂ progeny plants outperformed the O. sativa parent, indicating that the heterozygocity level and complementary gene action after two backcrosses are still sufficient to positively influence plant vigor. Spikelet fertility of progenies was highly variable, but almost complete fertility was already observed within the BC₁F₂ population. High spikelet fertility was preserved in one out of two analyzed BC₁F₃ families and inmost of the BC₂F₃ families. The ability to restore spikelet fertility within few generations and the potential of the genetic diversity present in interspecific progenies facilitates the development of plant types specifically designed for the African irrigated and lowland environment. This revised version was published online in August 2006 with corrections to the Cover Date.     

Identification of four genes for stable hybrid sterility and an epistatic QTL from a cross between Oryza sativa and Oryza glaberrima

To further understand the nature of hybrid sterility between Oryza sativa and Oryza glaberrima, quantitative trait loci (QTL) controlling hybrid sterility between the two cultivated rice species were detected in BC₁F₁ and advanced backcross populations. A genetic map was constructed using the BC₁F₁ population derived from a cross between WAB450-16, an O. sativa cultivar, and CG14, an O. glaberrima cultivar. Seven main-effect QTLs for pollen and spikelet sterility were detected in the BC₁F₁. Forty-four sterility NILs (BC₆F₁) were developed via successive backcrosses using pollen sterility plants as female and WAB450-16 as the recurrent parent. Seven NILs, in which the target QTL regions were heterozygous while the other QTL regions as well as most of the reminder of the genome were homozygous for the WAB450-16 allele, were selected as the QTL identification materials. BC₇F₁ for the seven NILs showed a continuous variation in pollen and spikelet fertility. The four identified pollen sterility QTLs were located one each on chromosomes 1, 3, 7 and 7. Pollen sterility loci qSS-3 and qSS-7a were on chromosomes 3 and 7, respectively, which coincides with the previously identified S19, and S20, while loci qSS-1 and qSS-7b on chromosomes 1 and 7L appear distinct from all previously reported loci. An epistatic interaction controlling the hybrid sterility was detected between qSS-1 and qSS-7a.     

Cytological observations in some hybrids between the rice species Oryza sativa L. and O. glaberrima Steud.

Summary Several hybrids between Oryza sativa and O. glaberrima and their backcrosses with O. sativa were studied. Their seed sterility was very different; large differences were also observed in the level of pollen sterility and in the earliness of microspore failure. The proportion of aborted embryo sacs was much lower than the rate of sterile male gametophytes. The backcross populations were much more sterile than the corresponding F₁ hybrids. On the base of our observations and according to the literature, we may conclude that genic unbalance is the main cause of sterility of these hybrids, but that physiological factors may also be involved. Thus a restoration of fertility is generally possible by selection. On the other hand, male-sterile lines could be bred from some of these hybrids.     

Effects of low temperature storage on the pollen of Brassica campestris,B. oleracea and B. napus

Summary Four indica cultivars viz. Kalinga-I, Ptb. 10, IR 27280-13-3-3-3 and Co. 41 were found to possess male sterile cytoplasm with fertility restoring genes while the cultivar Krishna was found to maintain the male sterility in all the cases. All the plants in the F₁ of Kalinga-I × Krishna were observed to be completely male sterile and continued to show complete pollen sterility in subsequent backcross generations when backcrossed with recurring pollen parent, Krishna. Thus, it was posible to develop a new cytoplasmic-genetic male sterile line in indica rice (Krishna A) with Kalinga-I male sterile cytoplasm and this male sterile cytoplasm was found to be genetically different from others. Further, the newly developed male sterile line (Krishna A) was observed to be tolerant for low temperature at seedling stage.     

QTLs for phosphorus deficiency tolerance detected in upland NERICA varieties

Phosphorous (P) deficiency is a major yield limiting factor in rice (Oryza sativa L.) production. The interspecific New Rice for Africa (NERICA) varieties combine general stress tolerance from African cultivated rice (Oryza glaberrima Steud) with characteristics associated with high yield from O. sativa. However, little is known about their ability to tolerate P deficiency. Here, we examined the variation for tolerance to P deficiency among the 18 upland NERICAs and their parents in multi‐year field experiments. The good performance under P deficiency of the O. glaberrima parent CG 14 and some NERICAs suggested that these tolerant NERICAs contain loci associated with P deficiency tolerance inherited from CG 14. Additionally, four QTL clusters for P deficiency tolerance were detected on chromosomes 4, 6 and 11 using F₃ lines derived from the cross between the P deficiency tolerant variety NERICA10 and a Japonica‐type sensitive variety ‘Hitomebore’. These QTLs represent the first step in identifying stress tolerance genes from O. glaberrima that could subsequently be used to enhance P deficiency tolerance in O. sativa.     

Genetic base of Japonica rice varieties released in Taiwan

Summary The pedigrees of 99 Japonica rice (Oryza sativa L.) varieties released between 1940 and 1987 were traced back to 65 ancestors, of which 44 were plant introductions from Japan and only 11 from Taiwan. Japanese introductions collectively contributed more than 85% of the parentage of the varieties. Although more ancestors were integrated into recent breeding programs, as few as 10 ancestors comprised 66% of the genetic background. Extensive use of superior genotypes from the same sources explained why the integration of new germplasm did not result in the diversification of the released varieties. The 10 most important ancestral contributors of the 99 varieties were from Japan except Oloan-chu from Taiwan. Two introductions, Sinriki and Kameji, had the highest mean relative genetic contributions of the genes with 21.3% and 16.7%, respectively. Shinriki was the most frequently used ancestor and occurred in 83 of the 99 pedigrees. These results clearly revealed the narrow genetic base in current Japonica rice varieties of Taiwan.     

Mapping three new interspecific hybrid sterile loci between Oryza sativa and O. glaberrima

Hybrid sterility hinders the transfer of useful traits between Oryza sativa and O. glaberrima. In order to further understand the nature of interspecific hybrid sterility between these two species, a strategy of multi-donors was used to elucidate the range of interspecific hybrid sterility in this study. Fifty-nine accessions of O. glaberrima were used as female parents for hybridization with japonica cultivar Dianjingyou 1, after several backcrossings using Dianjingyou 1 as the recurrent parent and 135 BC₆F₁ sterile plants were selected for genotyping and deducing hybrid sterility QTLs. BC₆F₁ plants containing heterozygous target markers were selected and used to raise BC₇F₁ mapping populations for QTL confirmation and as a result, one locus for gamete elimination on chromosome 1 and two loci for pollen sterility on chromosome 4 and 12, which were distinguished from previous reports, were confirmed and designated as S37(t), S38(t) and S39(t), respectively. These results will be valuable for understanding the range of interspecific hybrid sterility, cloning these genes and improving rice breeding through gene introgression.     

Inheritance studies of characters associated with floating habit and their linkage relationship in rice

Summary Deep water rice varieties in general have certain peculiar characters which are associated with floating habit. These characters are (i) early nodal differentiation, (ii) nodal rooting, (iii) spreading habit, (iv) awned grains, (v) brown hull colour, (vi) red pericarp (red rice), and (vii) seed dormancy. Inheritance of these characters and linkage relationship of genes governing these characters were studied in a cross between Pankaj (non floating) and Nageribao (floating) rice varieties. Nageribao, a cultivar from Assam possesses these characters.Early nodal differentiation was observed to be controlled by a single dominant gene, designated as Nd. Nodal rooting was controlled by two dominant complementary genes, designated as Nr ₁ and Nr ₂. We found an inhibitory factor for spreading habit and one for brown hull colour in Pankaj; the operation of two dominant duplicate genes An ₁ and An ₂ for controlling awning characters, a single dominant gene Rd for red pericarp colour and a single dominant gene Gd for grain dormancy. Joint segregations between these characters resulted in the assignment of genes in the X linkage group of indica rices with estimated map distances based on the cross-over values. The genes An (awning), Es (spreading habit), Nr (nodal rooting) and Nd (nodal differentiation) were observed to be associated with each other. The gene for red pericarp (Rd) was observed to be linked with the grain dormaney gene Gd.     

Cytoplasmically controlled cold tolerance in a cytoplasmic-genetic male sterile line of rice

Summary The cytoplasmic-genetic male sterile line, Krishna-A with Kalinga-I cytoplasm was developed in rice through repeated backcrossing the completely pollen sterile F₁ of the cross Kalinga-I/Krishna with the recurrent male parent cv. Krishna. The germination percentage and root-shoot length in Krishna-A at 12°C and 9°C indicated a higher degree of tolerance to low temperature than the cold tolerant female parent Kalinga-I. The high yielding cold tolerant variety Kalinga-I was developed from a cross involving the cold tolerant variety Dunghansali and the high yielding variety IR 8. It is inferred that tolerance to low temperature during germination in Krishna-A was inherited from the cytoplasm of cv. Dunghansali through Kalinga-I besides male sterility. The cytoplasmic control of cold tolerance is reported here for the first time in rice literature. The male sterile line Krishna-A because of its tolerance to low temperature would be suitable for the development of hybrid rice especially for areas where low temperature is a problem during germination.     

Photosynthetic ability,grain yield and an esterase band in rice genotypes

Summary Four Indica and one Japonica (Tainung 67) of rice (Oryza sativa L.) varieties had an esterase band (tentatively designated as E₁), and also had higher photosynthetic ability than other five Japonica varieties without E₁ band. The F₁ plants of Tainung 67 × Mineyutaka (low photosynthetic ability, no E₁ band) showed E₁ band and a low photosynthetic ability. Of 34 F₂ plants, 28 had E₁ band, but 6 had no E₁ band of which 5 plants showed a low photosynthetic ability. These results suggest that an esterase gene and one of the photosynthesis gene are linked, and the gene for low photosynthetic ability is dominant.Among 42 new Japonica strains and 2 control varieties bred in Taiwan, most genotypes with E₁ band showed higher grain yield potential (grain field/growth days) in local test.Esterase band may be used as a marker for high photosynthesis and grain yield ability in breeding.     

Variation of <Emphasis Type="Italic">Wx</Emphasis> microsatellite allele,waxy allele distribution and differentiation of chloroplast DNA in a collection of Thai rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Eighty-two varieties of rice from different regions in Thailand were selected to explore the Waxy (Wx)gene diversity and indica-japonica differentiation of chloroplast DNA. A comparison of the 5 splice site in the first intron was made between glutinous and nonglutinous rice. It revealed that non-glutinous with low-amylose content and glutinous rice were characterized as the Wx^b allele based on the G-to-T base substitution, whereas non-glutinous rice with intermediate and high amylose carried the Wx^a allele. Four Wx microsatellite alleles, (CT)_n repeat, (n = 16,17,18 and 19) were found in glutinous rice. In contrast, non-glutinous rice showed five Wx microsatellite alleles (n = 11, 16, 17, 18 and 19). The (CT)₁₇ allele was prominent allele in Thai population, while the (CT)₁₁ allele was found only in intermediate and high amylose rice varieties from southern Thailand. Almost all of upland rice grown by various ethnic groups in northern Thailand were characterized as japonica type based on their having the PstI-12 fragment in their cpDNA, whereas most of rainfed lowland varieties from other regions of Thailand were indica. This exploration of DNA-based genetic markers is important, as it enhances our ability to describe and manipulate sources of genetic variation for rice breeding programs.     

Inheritance of aroma in rice

Summary Inheritance of an aroma was worked out in crosses between Brimful from Nepal as an aromatic rice and leading Japanese varieties Koshihikari and Nipponbare as non-aromatic ones. The F₂ pattern of segregation for aroma to non-aroma was 3:13 indicating one dose gene for aroma and one dose inhibitor gene in two crosses. This ratio was confirmed by genetic behavior of F₃ populations.     

Increased regeneration from NaCl-tolerant callus in rice

Summary NaCl-tolerant calli were selected from two Japonica and two Indica rice (Oryza sativa L.) cultivars on basal media containing 6,000, 9,000, 12,000 or 15,000 ppm NaCl. Frequency of callus formation decreased with the increase of NaCl in the medium, especially in Indica. About half of the calli of Japonica cultivars selected on NaCl-ammended media survived 20,000 ppm NaCl but none of the Indica callus survived. In Japonica, more plants were regenerated from calli selected on all concentrations of NaCl media than from NaCl-free medium. Concentration of Cl^- in callus increased dramatically with increased NaCl content but peroxidase activity decreased.