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.     

Partial resistance to Erysiphe graminis hordei in old European barley varieties

Summary A collection of 133 genotypes consisting mainly of old European barleys and land varieties was assessed for level of partial resistance to barley mildew at the adult plant stage. Identification of any known resistance factors conferring hypersensitive reactions to the mildew races present at various frequencies in N.W. Europe was ensured through seedling tests with an appropriate AO mildew isolate.Thirty-nine varieties with relatively high levels of adult (partial) resistance and lacking known race-specific resistance genes were tested over a period of three years in field disease nurseries. At least thirteen varieties showed significantly less percentage leaf area infected than the control variety Proctor. These constitute a useful reserve of non-hypersensitive resistance, probably under the control of genes with mainly additive effects. In combination, these genes give enhanced levels of resistance, which could be of a more stable nature.     

Segregation distortion in doubled haploid lines of barley (Hordeum vulgare L.) detected by simple sequence repeat (SSR) markers

A total of 147 simple sequence repeat (SSR) markers (including86 barley and 61 wheat microsatellite markers) were tested for their segregation in a doubled haploid (DH) and an F₂ population of barley. The DH population consisted of 71 doubled haploid lines, developed from F₁ plants of a cross between Tadmor and WI2291using isolated microspore culture technique. A genetic linkage map consisting of 43 microsatellite markers was constructed using the DH population. Particularly on chromosome 4H microsatellite markers showed distorted segregation ratios. Segregation of DH lines based on molecular markers were compared with segregation of 92 F₂ lines from the same cross. The proportion of loci deviating from the expected monogenic segregation ratios in the DH population was significantly higher (19/43loci, 44%) than in the F₂ population (7/43 loci, 16%). The deviation was biased towards the WI2291 parent alleles. In line with this observation, WI2291 was found to perform better than Tadmor in regenerating green plantlets with the isolated microspore-culture technique. This revised version was published online in July 2006 with corrections to the Cover Date.     

Improved doubled haploid production protocol for Brassica napus using microspore colchicine treatment in vitro and ploidy determination by flow cytometry

A rapid and efficient microspore culture protocol was applied to produce homozygous progeny of crosses between low erucic canola and high erucic resynthesized rapeseed (Brassica napus L.). Microspores of Canadian cultivars ‘Excel’ and ‘Profit’ as well as three F₁ hybrids with the resynthetic line ‘RS239’ were treated with colchicine immediately after isolation. Flow cytometry was applied for early identification of doubled haploid (DH) regenerants. The diploidization rate was subsequently verified by scoring flower morphology. In vitro colchicine treatment had a positive effect on induced diploidization, and was associated with the frequency of preliminary spontaneous diploidization which was, however, determined by the genotype. In addition, the effects of colchicine treatment on embryoid formation and regeneration have been evaluated. The method presented is feasible for commercial large‐scale production of DHs in rapeseed as the genotype‐specific diploidization can be efficiently balanced by in vitro colchicine treatment. In addition, the use of flow cytometry immediately after in vitro culture allows efficient selection for DHs, thus saving labour and cost and in the laboratory and subsequent greenhouse phase.     

Allelic variation in linolenic acid content of high erucic acid Ethiopian mustard and incorporation of the low linolenic acid trait into zero erucic acid germplasm

Zero erucic acid germplasm of Ethiopian mustard is characterized by high levels of linolenic acid (about 21%). Two genetic sources of low linolenic acid (N2‐4961 and HF‐186, about 5%), have been developed in a high erucic acid background. The objectives of this research were to study the genetic relationship between the two low linolenic acid lines and to transfer the trait to zero erucic acid germplasm. F1 seed generations from crosses between both lines had higher average linolenic acid concentration than both parents. F2 seeds segregated for linolenic acid content following a continuous variation from 1.8 to 7.4%, exceeding the limits of the parental distribution ranges. Transgressive recombinants with very low linolenic acid concentration (0.7‐2.7%) were confirmed in the F3 seed generation. The results suggested that N2‐4961 and HF‐186 possess alleles for low linolenic acid at different loci. Transgressive low linolenic acid F3 plants were crossed with plants of a zero erucic acid line and a selection for zero erucic, low linolenic acid was conducted. As a result, a zero erucic acid F3:4 line containing 1.5 ± 0.7% linolenic acid was developed.     

Ploidy analysis in water yam, Dioscorea alata L. germplasm

Poor reproductive development in yams (Dioscorea spp.) has often been attributed to the polyploid nature of the crop. In this study, flow cytometry was used to determine the ploidy level of 53 accessions of Dioscorea alata, mostly from West African countries, Chad and Puerto Rico. Nuclei were isolated from young leaf material and stained with DAPI(4,6-diamidino-2-phenylindole). The nuclear genome size (2C) was measured as an indicator of the ploidy level. Dioscorea rotundata genotypes with known ploidy levels were used as standards. The results showed that the majority of plants were hexaploid (84.9%) with a smaller percentage of tetraploids (15.1%). A higher number of male plants were hexaploid than tetraploids. This is at variance with earlier findings, which reported that hexaploid male plants are rare. Higher ploidy levels were not directly related to sparse or erratic flowering as previously reported as profuse flowering occurred in some male hexaploid accessions. These findings have important implications for yam breeding in relation to yam genetic resources. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic control of alcohol dehydrogenase, malate dehydrogenase, and phosphoglucomutase isozymes in lima bean (Phaseolus lunatus L.)

A suitable electrophoretic separation method for alcohol dehydrogenase (ADH). malate dehydrogenase (MDH). and phosphoglucomutase (PGM) from P. lunatus has been developed. Two loci (Adh-2 and Pgm-2) showed codominant inheritance and fitted Mendelian ratio. ADH isozyme banding patterns indicate a dimeric quaternary structure. while those of PGM were in agreement with a monomeric nature. The cytoplasmic location of two MDH isozymes (Mdh-1 and Mdh-2) selectively inactivated by homogenization in an ascorbic acid solution was demonstrated. However. distorted ratios were observed for Mdh-2 segregation. On the basis of MDH isozyme banding patterns observed in five progeny families, il is suggested that this enzyme system is a dimeric protein encoded by at least three codominant genes (Mdh-1 .Mdh-2 and Mdh-3). Joint segregation tests between pairs of segregating loci (Adh-2, Mdh-2, and Pgm-2) indicated that each of them is inherited independently.     

玉米显性高油基因存在的若干证据

通过来源不同的20个高油系和5个普通系杂交当代和后代籽粒油分花粉直感效应及遗传分离特点分析，发现N1680高油系的杂交当代籽粒和F2籽粒油分含量接近于高油亲本，表现出显性基因的遗传特征；同时，F2籽粒油分还存在明显的超高亲优势。因此推测该系可能存在显性高油基因，并与其他基因存在互作效应。     

仙居雄性不育大麦的研究——雄性不育性状的遗传

本研究以仙居雄性不育大麦为材料,对其后代的育性作了遗传基因分析.雄性不育材料与正常品种的杂种一代为可育,杂种二代的可育株与不育株的分离比例,大多数供试品种符合3:1的理论值.以不育材料为母本,杂种F_1为父本回交,可育与不育的分离比接近1:1.以品种为母本,以杂种F_1为父本回交,其第一代为可育,第二代出现育性分离.证明仙居雄性不育大麦是受一对隐性基因控制的核不育材料.