Tunisian Potato virus Y isolates with unnecessary pathogenicity towards pepper: support for the matching allele model in eIF4E resistance–potyvirus interactions

The pathogenic properties of Potato virus Y (PVY; genus Potyvirus, family Potyviridae) isolates collected in naturally infected pepper (Capsicum annuum) fields in Tunisia were evaluated against recessive resistance alleles at the pvr2 locus of pepper. Two pathotypes were observed. Pathotype (0,1,3) isolates were able to infect plants carrying the susceptibility allele pvr2⁺, together with pvr2¹/pvr2¹ and pvr2³/pvr2³ plants, but not pvr2²/pvr2² plants. Pathotype (0) isolates were only able to infect pvr2⁺/pvr2⁺ plants. On the other hand, sequence data and phylogenetic analyses revealed three major groups of isolates, each characterized by particular amino acid residues in the central part of the VPg, the pathogenicity factor towards pvr2. Correspondence between pathogenic properties and phylogeny suggested a single evolutionary step for pathogenicity towards the pvr2¹ and pvr2³ resistances, possibly under the selective pressure of pvr2¹. Indeed, 23% of the pepper plants in this area were shown to carry the pvr2¹ resistance, while pvr2³ was not detected. The data suggested that pathogenicity towards pvr2¹ and pvr2³ were not costly for PVY to infect susceptible pepper genotypes and supported the matching allele model for pepper–PVY interactions.     

Estimating allelic richness and its diversity

Assessing allelic richness in a set of populations requires that variations of sample size be taken into account. One way of doing this is to estimate the number of alleles expected in samples of specified size, using the rarefaction method applied in ecology. An alternative method, based on extrapolation, consists of adding to the number of alleles actually seen in a population the expected number of alleles missing, given the number of genes examined in the population and the allelic frequencies observed over the whole set of populations. Heterogeneity of allelic richness across populations and across loci can also be tested in this framework by numerical re-sampling. Both methods provide a measure of “private” allelic richness, a useful criterion in genetic diversity preservation, by allowing evaluation of the uniqueness of each population in terms of allele numbers. The two methods are compared on isozyme loci in the argan tree of Morocco and on microsatellite genotypes in the European pig. In both species, allelic richness and gene diversity behave quasi-independently over the populations compared and a higher differentiation is observed in allelic richness compared to gene diversity. In general, the rarefaction technique is sensitive to the sample size of reference and may lack sensitivity to rare alleles when the sample size of reference is small. Extrapolation may thus be recommended especially when the sample sizes of the populations are either low on average or highly unbalanced among populations.     

乐都本地山羊血清运铁蛋白多态性

采用聚丙烯酰胺凝胶电泳对８０只乐都本地山羊血清运铁蛋白的多态性进行研究。结果：被检山羊中有ＴＦＡＡ和ＴＦＡＢ两种基因型，以ＴＦＡＡ型为优势基因型（８６．３％）；ＴＦＡ和ＴＦＢ等位基因频率分别为０．９３１和０．０６９；基因杂合度和有效等位基因数分别为０．１２８和１．１４７。聚类分析表明，乐都本地山羊与藏山羊、英国阿尔卑山羊有较紧密的遗传联系。     

Effects of a photoperiod-response gene Ppd-D1 on yield potential and drought resistance in UK winter wheat

Using a pair of near-isogenic lines(NILs) of winter wheat (Triticumaestivum L.) contrasting for the Ppd-D1 and ppd-D1 alleles, in eachof Mercia and Cappelle-Desprez, experimentsin two seasons (1997/8 and 1998/9) on aloamy medium sand examined differences inflowering date, resource capture, biomassproduction and grain yield responses toirrigation. Drought did not occur for anysustained period in unirrigated conditionsin 1998 due to high seasonal rainfall. In1999, drought developed post-floweringunder unirrigated conditions. Ppd-D1on average advanced flowering by 12 days inMercia and 9 days in Cappelle-Desprez.Earlier flowering with Ppd-D1 was dueto a shorter thermal duration from cropemergence to GS31, with no effect on thethermal duration from GS31 to GS61. In bothgenetic backgrounds, Ppd-D1 decreasedabove-ground dry matter (AGDM) at harvestin irrigated conditions by 0.3–0.9 tha^-1 (p< 0.05), but thiswas compensated for by increases inharvest index (HI), so that grain yield wasconserved. Although Ppd-D1 decreasedmaximum green area index (GAI) by 0.8–1.9this was countered by greater maintenanceof green area after flowering, so thatradiation interception during grain fillingwas conserved. The Ppd-D1 alleledecreased season-long crop water uptake inthe Mercia NILs in irrigated conditions by39 mm. Effects of drought in 1999,averaging across NILs, were todecrease machine-harvested grain yield by 0.6 t ha^-1 in Mercia and by 1.8 tha^-1 in Cappelle-Desprez (p<0.05). The Ppd-D1 and ppd-D1NILs, though, responded similarly todrought in both genetic backgrounds. Earlyflowering with Ppd-D1 decreasedpre-flowering water uptake underunirrigated conditions by ca. 25 mm,but increased post-flowering uptake by only10 mm, compared to ppd-D1. This was aresult of smaller season-long water uptakefor Ppd-D1 compared to ppd-D1.Ppd-D1 decreased stem solublecarbohydrate measured shortly afterflowering under drought by ca. 0.3 tha^-1. Effects of Ppd-D1 onother drought-resistance traits, such aswater-use efficiency (WUE; AGDM per unitcrop evapotranspiration) and maximumrooting depth, appeared to be neutral. Itis concluded that the effects of the Ppd-D1 allele appeared to be largelyneutral on yield potential and late-seasondrought resistance in the UK's temperateenvironment in these genetic backgrounds.However, there were indications that Ppd-D1 may offer scope for breeding winterwheat cultivars with more efficientproduction of grain DM per unit seasonalcrop evapotranspiration, associated withimproved HI, compared to currentlycommercial UK genotypes.     

Inheritance of dwarfism in plantain (Musa spp., AAB group)

Plantain (Musa spp., AAB group) is a major food crop in the humid lowland tropics of Africa, the Caribbean and Latin America. Lodging, caused by strong winds occurs periodically in these areas. Therefore, development of dwarf plantain cultivars and elucidation of the inheritance of dwarfism is desirable. A heterozygous normal plantain cultivar (2n= 2x) with long false-internodes (19.4 ± 0.9 cm) was crossed with a homozygous wild banana (2n= 2x) with short false-internodes (6.9 ± 0.4 cm) to develop a test-cross segregating population. A total of 74 euploids (2x, 3x and 4x) were produced. Forty-one normal and 24 dwarf diploids were obtained, which fits a 2: 1 trisomic test-cross segregation ratio for one locus. Dwarfism is controlled by a single recessive gene, dw. At the tetraploid level, two normal and six dwarf hybrids were produced, suggesting that the dw locus is close to the centromere and that there is a dosage effect of the dw allele at the tetraploid level.     

Effect of VRN‐1 and PPD‐D1 genes on heading time in European bread wheat cultivars

The variation of the vernalization (VRN‐1) and photoperiod (PPD‐1) genes offers opportunities to adjust heading time and to maximize yield in crop species. The effect of these genes on heading time was studied based on a set of 245 predominantly spring cultivars of bread wheat from the main eco‐geographical regions of Europe. The genotypes were screened using previously published diagnostic molecular markers for detecting the dominant or recessive alleles of the major VRN‐1 loci such as: VRN‐A1, VRN‐B1, VRN‐D1 as well as PPD‐D1. We found that 91% of spring wheat cultivars contain the photoperiod sensitive PPD‐D1b allele. Photoperiod insensitive PPD‐D1a allele has been found mainly in southern region of Europe. For this region the monogenic control of vernalization by VRN‐B1 or VRN‐D1 dominant alleles is common, whereas in the remaining part of Europe, the combination of photoperiod sensitive PPD‐D1b allele with dominant VRN‐A1, VRN‐B1 and recessive vrn‐D1 alleles represents the most frequent genotype. Also, we revealed a significantly later (5–8 days) heading of the monogenically dominant genotypes at VRN‐B1 as compared to the digenic VRN‐A1 VRN‐B1 genotypes.     

玉米突变自交系“原辐17”的遗传鉴定

用γ射线辐照玉米自交系“公70”花粉诱发突变,获得突变自交系“原辐17”。用淀粉凝胶电泳分析“原辐17”与原亲本“公70”杂交和回交后代的酯酶同工酶,并观察苗期叶鞘色泽,证明“原辐17”的酯酶同工酶和叶鞘色泽的变异是分别由一对等位基因突变的结果。用“P×Q“杂交模式测验,经方差分析证明。“原辐17”的株高、穗位、穗长、千粒重、产量以及配合力等,与原亲本“公70”的这些性状之间发生了明显变异。说明突变自交系“原辐17”在一系列基因位点上发生了变异。     

Persistence of Florida largemouth bass alleles in a northern Arkansas population of largemouth bass, Micropterus salmoides Lacèpéde

Abstract– Lake Ashbaugh, located in northeast Arkansas, was constructed in 1981, and initially stocked with Florida largemouth bass followed by supplemental stockings of northern largemouth bass. Allele frequencies of three discriminant allozyme loci (sAAT-B, sIDH-B, sMDH-B) between Florida and northern largemouth bass were determined for 414 largemouth bass collected between 1994 and 1996. F_x bass dominated our sample, with 62.3% possessing Florida largemouth bass alleles. A high incidence of Hardy-Weinberg disequilibrium was observed, indicative of genetic change within the population. No significant differences were identified for frequency of age classes, relative weight, and length at age between the northern, F₁ and F_x phenotypes. Despite being located north of what is generally considered suitable for stocking Florida largemouth bass, it was demonstrated that temperature is not selective at present against bass possessing Florida largemouth bass alleles. However, caution should prevail when introducing non-native stock into native gene complexes, as introduced genes persist through many generations.     

Variation in Friabilin Composition as Determined by A-PAGE Fractionation and PCR Amplification, and its Relationship to Grain Hardness in Bread Wheat

A-PAGE fractionation of starch granule proteins from 63 bread wheat cultivars with contrasting grain texture characteristics revealed two prominent polypeptides and three minor ones, approximately 15 kDa in size. These proteins were found to be encoded by genes on the short arm of chromosome 5D. The two major friabilin components were assumed to correspond to puroindolines a and b (pinA and pinB), as suggested by PCR amplification of genes coding for pinA, glycine-type or serine-type pinB. Two electrophoretic patterns for pinA (presence vs absence) and three patterns for pinB were obtained by A-PAGE. In cultivars with pinA (allele Pina-D1a), pinB was found to be encoded by wild-type Pinb-D1a, serine-type Pinb-D1b or by the novel glycine-type b1 allele. Cultivars lacking pinA (allele Pina-D1b) were shown to contain eitherPinb-D1a or the novel b2 allele, both alleles coding for glycine-type pinB. The intensity of pinB in A-PAGE gels was found to be associated with grain hardness as determined by the SKCS method. Cultivars lacking pinA had the highest SKCS values, suggesting that both pinA and pinB may affect grain texture. In the presence of pinA, cultivars with wild-type allelePinb-D1a had soft grain texture, whereas those with alleles Pinb-D1b or b1 showed increased grain hardness. It is suggested that allele b1 affects the interaction of pinB with starch granules because of a sequence mutation different from the glycine-to-serine change.     

Allele frequencies of gene polymorphisms related to economic traits in Bos taurus and Bos indicus cattle breeds

Allele frequencies of 10 representative polymorphisms for beef and milk traits were investigated for a total of 240 animals from Bos taurus and Bos indicus breeds, including two Japanese groups (Japanese Black and Japanese Brown), two East Asian groups (Korean and Mongolian), three European groups (Holstein, Angus and Hereford) and a Bos indicus group in South Asia (Myanmar, Laos and Cambodia). The Japanese Black revealed unique genetic construction in GH, FASN and SREBP‐1 and the other Asian populations show intermediate frequencies between European and Japanese populations. The Bos indicus group showed low favorable allele frequencies in most of the genes. The study showed the variability and distribution of 10 genes affecting economic traits among world representative cattle breeds. The genetic information would contribute to elucidating the genetic background for worldwide cattle breeds and the possibility of improvement using the markers.