Genetic analysis for resistance to the green leafhopper, Nephotettix virescens (Distant), in some cultivars of rice, Oryza sativa L.

The genetics of resistance to green leafhopper Nephotettix virescens (Distant) was studied in 17 cultivars of rice (Oryza sativa L.). Seedlings at the one-leaf stage were infested with second- and third-instar nymphs of green leafhopper. Reactions to seedling injury were recorded 7–8 days after infestation. The reactions of F₁, F₂, and F₃ populations from the crosses of resistant varieties with susceptible parent TN1 revealed that resistance of Tilakkachray, Kalimekri 77-5, and Tilockkachari was governed by two dominant genes and resistance of IR42 was conveyed by a single recessive gene. Single dominant genes govern resistance in the remaining 13 cultivars. Allele tests revealed that a single dominant gene of Segon Perak and one of the two genes of Kalimekri 77-5 are allelic to Glh 1. The single dominant gene of Ernest, Bignou and ARC614 and one of the two genes of each of Tilakkachray, Kalimekri 77-5, and Tilockkachari are allelic to Glh 2. A single dominant gene, which is allelic to Glh 3, conditions resistance in Arai and IR30. The single recessive gene which conveys resistance in IR42 appears to be allelic to glh 4. The allelic relationships of one of the two genes of Tilakkachray and Tilockkachari and single dominant genes of Fulkari 653, Chao Pho Kha, Amoule Borome, Kabero, Aus Murali, IR28 and IR34, with each other and with Glh 5 are not known.     

Orientation and integration of the classical and molecular genetic maps of chromosome 11 in rice

Summary The classical genetic map and molecular map of rice chromosome 11 were oriented to facilitate the use of these maps for genetic studies and rice improvement. Three morphological markers (d-27, z-2, and la) were crossed to a rice breeding line, IRBB21, which has the Xa-21 gene for bacterial blight resistance. Three F₂ populations were analyzed with RFLP markers known to be located on chromosome 11. Segregation analysis of molecular markers and morphological markers was used to construct an RFLP map for each population. The recombination frequency between markers varied from population to population although the marker order on the maps was the same for all three populations. Based on a common set of markers mapped in the three populations, an integrated map was generated consisting of both RFLP and morphological markers. The genetic distance between markers on this map was determined by taking a weighted average of the data from the three populations. The oriented map serves as a bridge to understand the relationship between the classical and molecular linkage maps. Based on this information, the location of several genes on the classical map can be approximated with respect to RFLP markers without having to map them directly.     

Chromosomal location of fertility restoring genes for ‘wild abortive’ cytoplasmic male sterility using primary trisomics in rice

Summary Identification and location of fertility restoring genes facilitates their deployment in a hybrid breeding program involving cytoplasmic male sterility (CMS) system. The study aimed to locate fertility restorer genes of CMSWA system on specific chromosomes of rice using primary trisomics of IR36 (restorer), CMS (IR58025A) and maintainer (IR58025B) lines. Primary trisomic series (Triplo 1 to 12) was crossed as maternal parent with the maintainer line IR58025B. The selected trisomic and disomic F₁ plants were testcrossed as male parents with the CMS line IR58025A. Plants in testcross families derived from disomic F₁ plants (Group I crosses) were all diploid; however, in the testcross families derived from trisomic F₁ plants (Group II crosses), some trisomic plants were observed. Diploid plants in all testcross families were analyzed for pollen fertility using 1% IKI stain. All testeross families from Group I crosses segregated in the ratio of 2 fertile: 1 partially fertile+partially sterile: 1 sterile plants indicating that fertility restoration was controlled by two independent dominant genes: one of the genes was stronger than the other. Testcross families from Group II crosses segregated in 2 fertile: 1 partially fertile+ partially sterile: 1 sterile plants in crosses involving Triplo 1, 4, 5, 6, 8, 9, 11 and 12, but families involving triplo 7 and triplo 10 showed significantly higher X² values, indicating that the two fertility restorer genes were located on chromosome 7 and 10. Stronger restorer gene (Rf-WA-1) was located on chromosome 7 and weaker restorer gene (Rf-WA-2) was located on chromosome 10. These findings should facilitate tagging of these genes with molecular markers with the ultimate aim to practice marker-aided selection for fertility restoration ability.     

High-resolution DNA fingerprinting of Indian rice (Oryza sativa L) varieties by amplified fragment length polymorphism

To assess diversification of indica rice, fingerprinting of 42 Indian rice varieties (Oryza sativa L) and one accession of O. brachyantha Chev. et Roehr. was taken up using amplified fragment length polymorphism (AFLP). Six primer combinations of PstI and MseI were used for this purpose. On denaturing polyacrylamide sequencing gel, on average 41 scorable AFLP bands were obtained of which 81% were polymorphic. Each variety revealed a distinct fingerprint. Data were scored on the basis of presence and absence of bands and cluster analysis was performed using Dice similarity coefficients. The resultant dendrogram showed four major clusters and traits. Some varieties especially landraces revealed more polymorphism and unique loci. Such study will be a valuable tool for proper choice of parents in mapping populations or breeding programs to produce heterotic several inexplicable minor clusters. Some varieties were grouped according to parentages of the cross while some were grouped according to physiological combinations apart from providing a characteristic fingerprint.     

Genetic analysis of resistance to whitebacked planthopper, Sogatella furcifera (Horvath), in some rice varieties

For genetic analysis of resistance to the whitebacked planthopper, Sogatella furcifera (Horvath) (Homoptera: Delphacidae), in 13 rice varieties, seedlings at the one-leaf stage were artificially infested in the greenhouse with second; and third-instar nymphs of this planthopper. Reactions of the seedlings were recorded 7–10 days after infestation when the susceptible check (control variety) TN1 was completely killed. The reactions of the F₁, F₂, and F₃ populations from the crosses of resistant varieties with TN1 revealed that single dominant genes condition resistance in the varieties Sinnanayam, ARC 13349, MGL 1, Sukhwel 20, Bam 3, Hornamawee, Senawee, A1, T1432, W128, and Chuvanna Kumbolum. The resistance in NP130 and CI-5662-2 was conditioned by two independent dominant genes. The allelic relationships of the latter genes for resistance in the test varieties to resistance genes Wbph 1 and Wbph 2 were determined. Reactions of the F₂ and F₃ progenies from the crosses of test varieties with IR13475-7-3-2 which is homozygous for Wbph 1, and with IR30659-2-165, which is homozygous for Wbph 2, showed that the resistance genes in Sukhwel 20, Senawee, T1432, and W128 are allelic to Wbph 1. The resistance genes in Sinnanayam, ARC 13349, MGL 1, Bam 3, A1, and Chuvanna Kumbolum are allelic to Wbph 2. The two independent dominant genes for resistance in NP130 and CI-5662-2 are Wpbh 1 and Wbph 2. However, there is a single dominant gene for resistance in Hornamawee which is independent and non-allelic to Wbph 1 and Wpbh 2.     

Chromosomal localization of five mutant genes in rice, Oryza sativa, using primary trisomics

The chromosomal locations of five mutant genes in rice were determined by crossing the marker stocks with the 12 primary trisomics. Genetic segregation of each gene was studied in the F₂ or backcross populations. Out of the 60 possible cross combinations, 43 F₂ or BC₁ populations were studied. Segregation data indicated that spl11 was located on chromosome 12 while wp2 and eg2_(t) were located on chromosome 6. The genes v12_(t) and Bc₆ were located on chromosomes 8 and 9, respectively, which are sparsely populated with genetic markers.     

抗稻瘿蚊品种多抗1的抗性遗传分析及抗性基因定位

稻瘿蚊是亚洲稻区主要害虫,采用抗虫品种进行防治是最理想的方法。1993～1995年,广东省农科院与国际水稻研究所有关专家紧密合作,对能抗华南4个稻瘿蚊生物型的品种多抗1作进一步抗性遗传分析,确认多抗1对中国稻瘿蚊生物型1和4的抗性受显性单基因控制,这个基因暂定名为GM—6(t)。以多抗1×丰银占1组合的F3代160个家系作基因标记,据DNA库分离个体分析(BSA)原理,用随机扩增多态性DNA(RAPD)标记物OPM6(1.4kb),首次成功地标记了这个抗性基因。随后多态性扩增产物经~(32)p标记,用作探针,检测另一个参考作图群体IR64×Azucena,将这个抗性基因定位在水稻第4条染色体上,位于RG214和RG163两个DNA限制性片段长度多态性(RFLP)标记之间。应用这些分子标记辅助选择有可能不必通过稻瘿蚊的直接筛选,快速准确地选育抗稻瘿蚊品种或进行抗性基因累加。     

稻米胶稠度单籽粒分析法

胶稠度是重要的稻米蒸煮和食用品质性状,然而前人对该性状的遗传研究甚少。主要原因是Cagampang(1973)的大样品(100mg)方法不适合遗传分析。实际上,F_2植株上结的种子即为F_3,因而,采用该法对F_2及回交世代的分离了解只能依