Adventitious root formation (ARF) at the soil surface is one of the most important adaptations to soil flooding or waterlogging. Quantitative trait loci (QTL) controlling ARF under flooding condition were identified in a 94 F 2 individual population by crossing maize (Zea mays L., B64) × teosinte (Z. mays ssp. huehuetenangensis). A base-map was constructed using 66 SSR and 42 AFLP markers, covering 1,378 cM throughout all ten maize chromosomes. The ARF capacity for seedlings was determined by evaluating the degree of root formation at the soil surface following flooding for 2 weeks. ARF showed continuous variation in the F 2 population. Interval mapping and composite interval mapping analyses revealed that the QTL for ARF was located on chromosome 8 (bin 8.05). Utilising a selective genotyping strategy with an additional 186 F 2 population derived from the same cross combination and 32 AFLP primer combinations, regions on chromosomes 4 (bin 4.07) and 8 (bin 8.03) were found to be associated with ARF. Z. mays ssp. huehuetenangensis contributed all of the QTL detected in this study. Results of the study suggest a potential for transferring waterlogging tolerance to maize from Z. mays ssp. huehuetenangensis.
In order to develop simple sequence repeat (SSR) markers in Italian ryegrass, we constructed a genomic library enriched for (CA)n-containing SSR repeats. A total of 1,544 clones were sequenced, of which 1,044 (67.6%) contained SSR motifs, and 395 unique clones were chosen for primer design. Three hundred and fifty-seven of these clones amplified products of the expected size in both parents of a two-way pseudo-testcross F(1) mapping population, and 260 primer pairs detected genetic polymorphism in the F(1) population. Genetic loci detected by a total of 218 primer pairs were assigned to locations on seven linkage groups, representing the seven chromosomes of the haploid Italian ryegrass karyotype. The SSR markers covered 887.8 cM of the female map and 795.8 cM of the male map. The average distance between two flanking SSR markers was 3.2 cM. The SSR markers developed in this study will be useful in cultivar discrimination, linkage analysis, and marker-assisted selection of Italian ryegrass and closely related species.
We introduced the rice chitinase (Cht-2; RCC2) gene into calli of Italian ryegrass (Lolium multiflorum Lam.), with a hygromycin phosphotransferase (HPT) gene as a selectable marker, by particle bombardment. Hygromycin-resistant calli were selected and transferred to regeneration medium for shoot formation. Polymerase chain reaction (PCR) analysis revealed regenerants containing the HPT gene. The RCC2 gene was detected in 65.5% of those regenerants. Southern hybridization detected both HPT and RCC2 genes and indicated that the transgenic plants were independently transformed. Expression of the RCC2 gene in the transgenic plants was confirmed by Northern hybridization, reverse transcription-PCR and Western blotting. Bioassay of detached leaves indicated increased resistance to crown rust (Puccinia coronata) in transgenic plants, which exhibited higher chitinase activity than a nontransgenic plant.
To construct a high-density molecular linkage map of Italian ryegrass (Lolium multiflorum Lam), we used a two-way pseudo-testcross F1 population consisting of 82 individuals to analyze three types of markers: restriction fragment length polymorphism markers, which we detected by using genomic probes from Italian ryegrass as well as heterologous anchor probes from other species belonging to the Poaceae family, amplified fragment length polymorphism markers, which we detected by using PstI/MseI primer combinations, and telomeric repeat associated sequence markers. Of the restriction fragment length polymorphism probes that we generated from a PstI genomic library, 74% (239 of 323) of randomly selected probes detected hybridization patterns consistent with single-copy or low-copy genetic locus status in the screening. The 385 (mostly restriction fragment length polymorphism) markers that we selected from the 1226 original markers were grouped into seven linkage groups. The maps cover 1244.4 cM, with an average of 3.7 cM between markers. This information will prove useful for gene targeting, quantitative trait loci mapping, and marker-assisted selection in Italian ryegrass.
cal forage grasses such as guinea grass (Panicum maximum Jacq.) (Nakagawa and Momonoki, 2000). To meet Rhodesgrass (Chloris gayana Kunth) is a highly variable, perennial growers' needs, many cultivars improved for traits such forage grass widely cultivated in all tropical and subtropical regions of the world. Despite its economic importance, there is a lack of as nutritive value, yield potential, and persistence have information on the genetic diversity within and among rhodesgrass been developed mainly in Africa (Boonman, 1978), cultivars, which are all based on genetic resources initially introduced Australia (Lambert and Graham, 1996), and Japan (Nafrom East and South Africa. The objective of this study was to assess kagawa et al., 1993). All breeding efforts were based genetic diversity within and among 13 cultivars of diploid rhodesgrass on genetic resources initially introduced from East and and to determine whether recent breeding efforts have resulted in South Africa (Duke, 1978). cultivars distinct from the African source populations. For each culti-Despite its economic importance, little research has var, 15 individuals were examined for 237 amplified fragment length been undertaken on genetic characterization of rhodespolymorphism (AFLP) markers generated from three EcoRI/MseI grass germplasm and cultivars. Information about geprimer pairs. Partition of the variation revealed that the major propornetic diversity and germplasm characterization is importion of the total genetic variation occurred within cultivars and with only 12 to 13% attributed to geographical origin or breeding history. tant for any breeding program. In particular, it is often Cluster analysis revealed three distinct groups among the cultivars useful to identify diverse parental combinations to creinvestigated. Group one consisted mainly of recent Japanese cultivars ate segregating progenies with genetic variability that and their African source population, group two contained mostly would provide further gain from selection. African cultivars, and group three contained one African cultivar. Molecular markers offer an efficient tool to investi-However, the genetic diversity within recent Japanese cultivars was gate genetic diversity in plant populations. They have comparable to the diversity within old African cultivars and there been successfully used to differentiate cultivars of outwas no evidence of a reduced genetic base because of breeding efforts. Published in Crop SciA African cultivar introduced into Australia in 1905 and registered as cv. Pioneer in 1973. Previously known as cv. Commercial Rhodesia local (RHO) A Ecotype from Rhodesia Tochirakukei (TOC) J Japanese local strain bred from a few selected African strains † Location where cultivars were bred or where ecotypes were collected-J ϭ Japan, A ϭ Africa.to a final volume of 5.5 L with purified water (Milli-Q Labo, MATERIALS AND METHODSMillipore Corp., Bedford, MA). AFLP analysis was performed
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