The effect of aluminium concentration on root hairs in white clover (Trifolium repens L.)

The effect of aluminium (Al) on root hair length and number is quantified using solution culture techniques with genotypes from white clover cultivar Tamar, that had previously been selected for long and short root hairs. The population differences were maintained in control (0 Al) treatments, with the long-haired population having hairs three times longer than the short-haired population. At an activity of 2.2 µM Al³⁺, root hair length decreased in both populations, the magnitude of the decrease being greater for the long-haired population. Root hair numbers decreased in a similar manner for both populations. At an activity of 4.4 µM Al³⁺ or higher, root hairs virtually disappeared and root growth was very stunted. The effect of Al on root hair development has not been previously quantified, however other workers have observed reduced root hair development in other species at activities of Al greater than 2.5 µM Al³⁺.     

表达马铃薯Y病毒外壳蛋白的转基因烟草的抗病性研究

将马铃薯Ｙ病毒中国分离物（ＰＶＴ－Ｃ）的外壳蛋白（ＣＰ）基因,在土壤农杆菌ＬＢＡ４４０４的介导下,转化烟草生产品种ＮＣ８９,获得了６个烟草株系。通过抗性分析发现,６个株系中有一个株系在２００μｇ／ｍｌＰＶＹ－Ｃ的攻毒下,仍未发病,分子检测发现,转基因植物中抗性产生的程度并不是同ＰＶＹ－Ｃ外壳蛋白的表达水平成正相关。     

Improvement of transgenic alfalfa by backcrossing

Summary Two regenerative alfalfa genotypes were transformed withAgrobacterium tumefaciens with binary vectors containing the coding sequences for ?-glucuronidase (GUS) and npt II (kanamycin resistance). The regenerative genotypes and their transgenic populations were agronomically inferior, and one was a somaclonal variant for flower color. GUS was used as a dominant genetic marker in a model system for studying backcrossing to improve transgenic alfalfa. Agronomic yield deficiencies and somaclonal changes were corrected by one to three backcrosses to cultivar genotypes, depending on the vigor of the original transformant. Three backcrosses were considered optimal because progeny contain 94% cultivar germplasm and could be used as parents of a new cultivar. Use of different cultivar genotypes each generation of backcrossing minimized inbreeding and maximized the heterotic potential of backcross derivatives. The improvement of transgenic alfalfa by backcrossing using a dominant marker required only as much time as the original transformation experiment.     

采用竹管蜂巢繁育苜蓿切叶蜂

对5种繁育苜蓿切叶蜂的蜂巢材料进行了筛选测定,结果表明,竹管的繁蜂效果较好,子代蜂的雌雄性比为1：1,而且竹管内的蜂茧均未被寄生蜂寄生。     

Molecular cloning and characterization of novel isoforms of potato ADP-glucose pyrophosphorylase

ADP-glucose pyrophosphorylase (AGPase) is one of the major enzymes involved in starch biosynthesis in higher plants. We report here the molecular cloning of two cDNAs encoding so far uncharacterized isoforms (AGP S2 and AGP S3) of the potato enzyme. Sequence analysis shows that the two polypeptides are more homologous to previously identified large subunit polypeptides from potato and other plant species than to small subunit isoforms. This observation suggests that AGP S2 and AGP S3 represent novel large subunit polypeptides. agpS2 is expressed in several tissues of the potato plant, including leaves and tubers. Expression was stronger in sink leaves than in source leaves, indicating developmental regulation. In leaves, agpS2 expression was induced 2- to 3-fold by exogenous sucrose; therefore, agpS2 represents a new sucrose-responsive gene of starch metabolism. Expression of agpS3 was restricted to tubers: no agpS3 expression could be seen in leaves of different developmental stages, or when leaves were incubated in sucrose. Therefore, agpS3 represents the only AGPase gene so far characterized from potato, which is not expressed in leaves. Conversely, all four AGPase isoforms known from potato are expressed in tubers.     

Cytological,morphological and molecular analyses of controlled progenies from meiotic mutants of alfalfa producing unreduced gametes

A program of sexual polyploidization was carried out in alfalfa using plants from wild diploid species that produced male or female unreduced gametes. Sixteen progenies from 2x-4x and 2x-2x crosses were examined with a combination of morphological, cytological and molecular analyses. The chromosome counts revealed diploid, tetraploid and aneuploid plants. Plants with B chromosomes were also detected. The leaf area of the plants was a useful characteristic for distinguishing tetraploid from diploid plants obtained by unilateral or bilateral sexual polyploidization. Leaf shape and leaf margin were not correlated with the ploidy levels. Plants with supernumerary chromosomes displayed obovate or elliptic leaves which differed markedly from the range of forms typical of diploid and tetraploid alfalfa plants. RAPD markers were investigated in all progeny plants to determine maternal and paternal amplification products. Three alfalfa-specific primers proved to be effective in revealing the hybrid origin of the plants. A combination of cytological, morphological and molecular analyses is essential for a detailed genetic characterization of progenies in programs of sexual polyploidization.     

Successive domestication and evolution of the Andean potatoes as revealed by chloroplast DNA restriction endonuclease analysis

Five chloroplast DNA (ctDNA) types (W, T, C, S, and A) have previously been identified in the Andean tetraploid cultivated potatoes (Solanum tuberosum ssp. andigena) and three types (C, S, and A) in diploid cultivated potatoes (S. stenotomum). In this study, ctDNA types were determined for an additional 35 accessions of S. stenotomum and 97 accessions of putative ancestral wild species (15 of S. brevicaule, 26 of S. bukasovii, 4 of S. candolleanum, 25 of S. canasense, 17 of S. leptophyes, and 10 of S. multidissectum). The first five ctDNA types were also identified in S. stenotomum. The wild species were also polymorphic for ctDNA types except for S. brevicaule, which had only W-type ctDNA. T-type ctDNA was not found in any of the wild species and could have originated from W-type ctDNA after S. stenotomum arose. The other types of ctDNA evolved in wild species. The geographical distribution of each ctDNA type indicated that A-type ctDNA arose in central Peru and T-type ctDNA in the Bolivia-Argentine boundary. It is implied that potatoes were successively domesticated and that, in parallel, several wild species were differentiated from time to time and place to place from the ancestral species complex. Subsequent sexual polyploidization formed a wide ctDNA diversity among the Andean tetraploid potatoes, and selection from them formed the limited ctDNA diversity found in Chilean tetraploid potatoes (ssp. tuberosum).Hawkes' (1990) classification system is tentatively adopted throughout this text. Synonyms indicated by Hawkes (1990) for the species names described by various authors are presented in parentheses.     

Assessment of genetic diversity in dent and popcorn (Zea mays L.) inbred lines using inter-simple sequence repeat (ISSR) amplification

Popcorn (Zea mays L.) hybrids grown in the United States are derived from narrow-based germplasm, and standard RFLP analysis detects relatively little polymorphism. Inter-simple sequence repeat (ISSR) amplification, a novel technique based on PCR amplification of inter-microsatellite sequences to target multiple loci in the genome, was employed to investigate its potential for detection of polymorphism among nineteen popcorn and eight dent corn inbred lines. ISSR yielded an average of 54 bands/primer/inbred line, with over 98% of the bands repeatable across DNA extractions and separate PCR runs. Ten primers based on di- and tri-nucleotide tandem repeats revealed 73% and 87% polymorphism among popcorn and dent corn lines, respectively, with an overall 95% polymorphism rate. Principal component and cluster analyses resulted in grouping of dent and popcorn lines corresponding to their heterotic breeding pools. ISSR amplification, in addition to being both simple and cost and time efficient, provides for rapid production of highly polymorphic markers which appear to correspond to known pedigree information. Therefore, the ISSR technique may have great potential for identifying polymorphism in species with narrow-based germplasm, and for use in DNA marker-assisted breeding approaches.     

Distribution of Races of Heterodera glycines in the Central United States

A total of 62 populations of Heterodera glycines were collected in 10 states along the Mississippi and Missouri rivers, and 206 populations were collected in Arkansas. Among the 62 populations, races 2, 3, 4, 5, 6, 9, and 14 were found south of 37°N latitude, and races 1 and 3 were found north of 37°N latitude. In Arkansas samples, races 2, 4, 5, 6, 9, and 14 comprised 87% of the populations. In both groups of samples, H. glycines populations with genes that enabled the population to parasitize cv. Pickett occurred the most frequently, followed by those with genes for parasitism of cv. Peking, then PI88.788, and the fewest with genes for parasitism of PI90.763. The diversity of races in this study raises questions about the effectiveness of race-specific cultivars for the management of soybean cyst nematodes. The greater diversity of races of H. glycines in the southern United States may be because of a longer history of planting resistant cultivars.     

Mapping and marker-assisted selection for a gene for extreme resistance to potato virus Y

The chromosomal location of the major gene Ry _adg controlling extreme resistance to potato virus Y (PVY) in Solanum tuberosum subsp. andigena was identified by RFLP analysis of a diploid potato population. A total of 64 tomato and potato RFLP markers were screened with the bulked segregant analysis (BSA) on segregants extremely resistant, hypersensitive or susceptible to PVY. Four markers TG508, GP125, CD17 and CT168 at the proximal end of chromosome XI showed close linkage with extremely resistant phenotypes. TG508 was identified as the closest marker linked with the Ry _adg locus with the maximum map distance estimated as 2.0 cM. The 4 markers linked with the Ry _adg locus were tested on independent tetraploid and diploid potato clones and were subsequently found useful for marker-assisted selection for plants containing Ry _adg . Received: 5 July 1996 / Accepted: 19 July 1996