Salinity tolerance of twelve hybrid Bermudagrass (Cynodon Dactylon (L.) Pers. x C. Transvaalensis Burtt Davy) genotypes

Salinity is an increasingly important issue in both rural and urban areas throughout much of Australia. The use of recycled/reclaimed water and other sources of poorer quality water to irrigate turf is also increasing. Hybrid Bermudagrass (Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt Davey), together with the parent species C. dactylon, are amongst the most widely used warm-season turf grass groups. Twelve hybrid Bermudagrass genotypes and one accession each of Bermudagrass (C. dactylon), African Bermudagrass (C. transvaalensis) and seashore paspalum (Paspalum vaginatum Sw.) were grown in a glasshouse experiment with six different salinity treatments applied hydroponically through the irrigation water (ECW = <0.1, 6, 12, 18, 24 or 30 dSm-1) in a flood-and-drain system. Each pot was clipped progressively at 2-weekly intervals over the 12-week experimental period to determine dry matter production; leaf firing was rated visually on 3 occasions during the last 6 weeks of salinity treatment. At the end of the experiment, dry weights of roots and crowns below clipping height were also determined. Clipping yields declined sharply after about the first 6 weeks of salinity treatment, but then remained stable at substantially lower levels of dry matter production from weeks 8 to 12. Growth data over this final 4-week experimental period is therefore a more accurate guide to the relative salinity tolerance of the 15 entries than data from the preceding 8 weeks. Based on these data, the 12 hybrid Bermudagrass genotypes showed moderate salinity tolerance, with FloraDwarfM, 'Champion Dwarf', NovotekM and 'TifEagle' ranking as the most salt tolerant and 'Patriot', 'Santa Ana', 'Tifgreen' and TifSport M the least tolerant within the hybrid group. Nevertheless, Santa Ana, for example, maintained relatively strong root growth as salinity increased, and so may show better salt tolerance in practice than predicted from the growth data alone. The 12 hybrid Bermudagrasses and the single African Bermudagrass genotype were all ranked above FloraTeXM Bermudagrass in terms of salt tolerance. However, seashore paspalum, which is widely acknowledged as a halophytic species showing high salt tolerance, ranked well above all 14 Cynodon genotypes in terms of salinity tolerance.

Factors contributing to wear tolerance of Bermudagrass (Cynodon dactylon (L.) Pers., C. dactylon x C. transvaalensis Burtt-Davey) on a sand-based profile under simulated sports field conditions

Wear resistance and recovery of 8 Bermudagrass (Cynodon dactylon (L.) Pers.) and hybrid Bermudagrass (C. Dactylon x C. transvaalensis Burtt-Davey) cultivars grown on a sandbased soil profile near Brisbane, Australia, were assessed in 4 wear trials conducted over a two year period. Wear was applied on a 7-day or a 14-day schedule by a modified Brinkman Traffic Simulator for 6-14 weeks at a time, either during winter-early spring or during summer-early autumn. The more frequent wear under the 7-day treatment was more damaging to the turf than the 14-day wear treatment, particularly during winter when its capacity for recovery from wear was severely restricted. There were substantial differences in wear tolerance among the 8 cultivars investigated, and the wear tolerance rankings of some cultivars changed between years. Wear tolerance was associated with high shoot density, a dense stolon mat strongly rooted to the ground surface, high cell wall strength as indicated by high total cell wall content, and high levels of lignin and neutral detergent fiber. Wear tolerance was also affected by turf age, planting sod quality, and wet weather. Resistance to wear and recovery from wear are both important components of wear tolerance, but the relative importance of their contributions to overall wear tolerance varies seasonally with turf growth rate.

Morphological and developmental comparisons of seven greens quality hybrid bermudagrass (Cynodon dactylon (L.)Pers.x C transvaalensis Burtt-Davy

Fine-textured hybrid bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy] cultivars have been widely used for golf putting greens and lawn bowls greens in warm-climate areas for more than 40 years. During the past decade, the choice of cultivar for professional turfgrass managers has been expanded by a range of secondgeneration hybrid bermudagrasses, which differ from the first-generation cultivars ‘Tifgreen’ and ‘Tifdwarf ’ in their management requirements. In this paper, we present comparative morphological and developmental data for seven cultivars (Champion Dwarf, FloraDwarf, MS-Supreme, Novotek, Tifdwarf, TifEagle, Tifgreen) grown in spaced plant and sward experiments at Cleveland, Australia (27º32’S lat, 153º15’E long, 25 masl). The four ‘ultradwarf ’ cultivars (Champion Dwarf, MS-Supreme, FloraDwarf, TifEagle) showed slower vertical extension and produced fewer inflorescences than Tifdwarf, Tifgreen, and Novotek. However, in terms of the length of stolon internodes and their overall rate of lateral spread, Champion Dwarf, FloraDwarf, and TifEagle were comparable to Tifdwarf; MS-Supreme (with longer internodes) spread faster laterally, though slower than Tifgreen (which had the longest stolon internodes). In unmown swards, the four ultradwarfs produced shorter leaves than Tifgreen, Tifdwarf, and Novotek, but only Champion Dwarf produced significantly narrower leaves than Tifgreen, Tifdwarf, and Novotek, with TifEagle leaves also significantly narrower than those of Tifgreen and Novotek. Minimum threshold temperatures for growth were approximately 9° to 10°C (air temperature) and 15° to 16°C at 10 cm soil depth.

Efficient organogenesis of an Australian passionfruit hybrid (Passiflora edulis x Passiflora edulis var. flavicarpa) suitable for gene delivery

An efficient regeneration protocol based on organogenesis from cotyledon explants and suitable for gene delivery has been developed for an Australian passionfruit hybrid. Multiple shoots were regenerated from 30-day-old cotyledon explants on Murashige and Skoog (MS) medium containing 6-benzylvaminopurine (BAP) and coconut water. Media pulsing experiments were conducted to investigate the effect on organogenesis of exposure time of the explants to MS containing 10 mu M BAP and 10% (v/v) coconut water, i.e. passionfruit regeneration medium (PRM). Continuous exposure of these explants to PRM maximised the number of shoots produced to 12.1 per explant. However, periods on hormone-free medium improved the appearance of the shoots and increased the number of explants with shoots from 75 to 84.6%. Further, shoots exposed for 7 days to half-strength MS supplemented with 10 mu M NAA (1-napthalene acetic acid) produced twice as many plantlets than those on half-strength MS alone. Transient GUS histochemical assays indicated delivery of the uidA gene via Agrobacterium tumefaciens.

Finding genes for economically important traits: Brahman cattle puberty.

Age at puberty is an important component of reproductive performance in beef cattle production systems. Brahman cattle are typically late-pubertal relative to Bos taurus cattle and so it is of economic relevance to select for early age at puberty. To assist selection and elucidate the genes underlying puberty, we performed a genome-wide association study (GWAS) using the BovineSNP50 chip (similar to 54 000 polymorphisms) in Brahman bulls (n = 1105) and heifers (n = 843) and where the heifers were previously analysed in a different study. In a new attempt to generate unbiased estimates of single-nucleotide polymorphism (SNP) effects and proportion of variance explained by each SNP, the available data were halved on the basis of year and month of birth into a calibration and validation set. The traits that defined age at puberty were, in heifers, the age at which the first corpus luteum was detected (AGECL, h(2) = 0.56 +/- 0.11) and in bulls, the age at a scrotal circumference of 26 cm (AGE26, h(2) = 0.78 +/- 0.10). At puberty, heifers were on average older (751 +/- 142 days) than bulls (555 +/- 101 days), but AGECL and AGE26 were genetically correlated (r = 0.20 +/- 0.10). There were 134 SNPs associated with AGECL and 146 SNPs associated with AGE26 (P < 0.0001). From these SNPs, 32 (similar to 22%) were associated (P < 0.0001) with both traits. These top 32 SNPs were all located on Chromosome BTA 14, between 21.95 Mb and 28.4 Mb. These results suggest that the genes located in that region of BTA 14 play a role in pubertal development in Brahman cattle. There are many annotated genes underlying this region of BTA 14 and these are the subject of current research. Further, we identified a region on Chromosome X where markers were associated (P < 1.00E-8) with AGE26, but not with AGECL. Information about specific genes and markers add value to our understanding of puberty and potentially contribute to genomic selection. Therefore, identifying these genes contributing to genetic variation in AGECL and AGE26 can assist with the selection for early onset of puberty.

Correlation between NIRS generated and chemically measured feed quality data in barley (Hordeum vulgare), and potential use in QTL analysis identification

A study was performed to investigate the value of near infrared reflectance spectroscopy (NIRS) as an alternate method to analytical techniques for identifying QTL associated with feed quality traits. Milled samples from an F6-derived recombinant inbred Tallon/Scarlett population were incubated in the rumen of fistulated cattle, recovered, washed and dried to determine the in-situ dry matter digestibility (DMD). Both pre- and post-digestion samples were analysed using NIRS to quantify key quality components relating to acid detergent fibre, starch and protein. This phenotypic data was used to identify trait associated QTL and compare them to previously identified QTL. Though a number of genetic correlations were identified between the phenotypic data sets, the only correlation of most interest was between DMD and starch digested (r = -0.382). The significance of this genetic correlation was that the NIRS data set identified a putative QTL on chromosomes 7H (LOD = 3.3) associated with starch digested. A QTL for DMD occurred in the same region of chromosome 7H, with flanking markers fAG/CAT63 and bPb-0758. The significant correlation and identification of this putative QTL, highlights the potential of technologies like NIRS in QTL analysis.

Grain dormancy QTL identified in a doubled haploid barley population derived from two non-dormant parents

Grain dormancy provides protection against pre-harvest sprouting (PHS) in cereals. Composite interval mapping and association analyses were performed to identify quantitative trait loci (QTL) contributing grain dormancy in a doubled haploid (DH) barley population (ND24260 x Flagship) consisting of 321 lines genotyped with DArT markers. Harvest-ripe grain collected from three field experiments was germinated over a 7-day period to determine a weighted germination index for each line. DH lines displaying moderate to high levels of grain dormancy were identified; however, both parental lines were non-dormant and displayed rapid germination within the first two days of testing. Genetic analysis identified two QTL on chromosome 5H that were expressed consistently in each of the three environments. One QTL (donated by Flagship) was located close to the centromeric region of chromosome 5H (qSDFlag), accounting for up to 15% of the phenotypic variation. A second QTL with a larger effect (from ND24260) was detected on chromosome 5HL (qSDND), accounting for up to 35% of the phenotypic variation. qSDFlag and qSDND displayed an epistatic interaction and DH lines that had the highest levels of grain dormancy carried both genes. We demonstrate that qSDND in the ND24260 9 Flagship DH population is positioned proximal and independent to the well-characterised SD2 region that is associated with both high levels of dormancy and inferior malt quality. This indicates that it should be possible to develop cultivars that combine acceptable malting quality and adequate levels of grain dormancy for protection against PHS by utilizing these alternate QTL.

Analysis of the barley bract suppression gene Trd1

A typical barley (Hordeum vulgare) floret consists of reproductive organs three stamens and a pistil, and non-reproductive organs-lodicules and two floral bracts, abaxial called 'lemma' and adaxial 'palea'. The floret is subtended by two additional bracts called outer or empty glumes. Together these organs form the basic structural unit of the grass inflorescence, a spikelet. There are commonly three spikelets at each rachis (floral stem of the barley spike) node, one central and two lateral spikelets. Rare naturally occurring or induced phenotypic variants that contain a third bract subtending the central spikelets have been described in barley. The gene responsible for this phenotype was called the THIRD OUTER GLUME1 (Trd1). The Trd1 mutants fail to suppress bract growth and as a result produce leaf-like structures that subtend each rachis node in the basal portion of the spike. Also, floral development at the collar is not always suppressed. In rice and maize, recessive mutations in NECK LEAF1 (Nl1) and TASSEL SHEATH1 (Tsh1) genes, respectively, have been shown to be responsible for orthologous phenotypes. Fine mapping of the trd1 phenotype in an F-3 recombinant population enabled us to position on the long arm of chromosome 1H to a 10 cM region. We anchored this to a conserved syntenic region on rice chromosome Os05 and selected a set of candidate genes for validation by resequencing PCR amplicons from a series of independent mutant alleles. This analysis revealed that a GATA transcription factor, recently proposed to be Trd1, contained mutations in 10 out of 14 independent trd1 mutant alleles that would generate non-functional TRD1 proteins. Together with genetic linkage data, we confirm the identity of Trd1 as the GATA transcription factor ortholog of rice Nl1 and maize Tsh1 genes.

High resolution mapping of Dense spike-ar (dsp.ar) to the genetic centromere of barley chromosome 7H

Spike density in barley is under the control of several major genes, as documented previously by genetic analysis of a number of morphological mutants. One such class of mutants affects the rachis internode length leading to dense or compact spikes and the underlying genes were designated dense spike (dsp). We previously delimited two introgressed genomic segments on chromosome 3H (21 SNP loci, 35.5 cM) and 7H (17 SNP loci, 20.34 cM) in BW265, a BC7F3 nearly isogenic line (NIL) of cv. Bowman as potentially containing the dense spike mutant locus dsp.ar, by genotyping 1,536 single nucleotide polymorphism (SNP) markers in both BW265 and its recurrent parent. Here, the gene was allocated by high-resolution bi-parental mapping to a 0.37 cM interval between markers SC57808 (Hv_SPL14)-CAPSK06413 residing on the short and long arm at the genetic centromere of chromosome 7H, respectively. This region putatively contains more than 800 genes as deduced by comparison with the collinear regions of barley, rice, sorghum and Brachypodium, Classical map-based isolation of the gene dsp.ar thus will be complicated due to the infavorable relationship of genetic to physical distances at the target locus.

Inactivation of Aspergillus flavus spores by curcumin-mediated photosensitization

Minimizing fungal infection is essential to the control of mycotoxin contamination of foods and feeds but many potential control methods are not without their own safety concerns for the consumers. Photodynamic inactivation is a novel light-based approach which offers a promising alternative to conventional methods for the control of mycotoxigenic fungi. This study describes the use of curcumin to inactivate spores of Aspergillus flavus, one of the major aflatoxin producing fungi in foods and feeds. Curcumin is a natural polyphenolic compound from the spice turmeric (Curcuma longa). In this study the plant has shown to be an effective photosensitiser when combined with visible light (420 nm). The experiment was conducted in in vitro and in vivo where A. flavus spores were treated with different photosensitiser concentration and light dose both in buffer solution and on maize kernels. Comparison of fungal load from treated and untreated samples was determined, and reductions of fungal spore counts of up to 3 log CFU ml−1 in suspension and 2 log CFU g−1 in maize kernels were obtained using optimal dye concentrations and light dose combinations. The results in this study indicate that curcumin-mediated photosensitization is a potentially effective method to decontaminate A. flavus spores in foods and feeds.