Digitaria Didactyla Research Articles

Biomassa dan Cadangan Karbon Tiga Jenis (Cyclosorus interruptus, Nephrolepis biserrata, dan Digitaria didactyla) Tumbuhan Herba Pada Periode Penyiangan Berbeda

The weeding duration influencing biomass and carbon content of herbaceaous species. The objective of this study were to analyze biomass and carbon content of three herbaceaous species (Cyclosorus interruptus, Nephrolepis biserrata, and Digitaria didactyla) in terms of different wedding durations. The biomass of Cyclosorus interruptus that weeded for 2, 3, and 4 weeks were 26.50 gram, 35.50 gram, and 27.00 gram in study plot sized 12 m2. Nephrolepis biserrata had biomass 15.38 gram (weeding period of 2 weeks), 15.28 gram (weeding period of 3 weeks), and 19.90 gram (weeding period of 4 weeks). Biomass content of Digitaria didactyla were 76.67 gram, 74.00 gram, and 190.00 gram for weeding periods 2, 3, and 4 weeks, respectively. The carbon content of Cyclosorus interruptus with weeding periods of 2, 3, and 4 weeks were 0,062 ton/ha, 0,056 ton/ha, and 0,032 ton/ha, respectively. Nephrolepis biserrata had carbon contents of 0,067 ton/ha, 0,051 ton/ha, and 0,050 ton/ha in weeding periods 2, 3, and 4 weeks. The highest carbon content of Digitaria didactyla were that weeded every 4 weeks (0,223 ton/ha) compared than weeding periods 2 weeks (0,180 ton/ha) and 3 weeks (0,116 ton/ha).

Genome sequence and geographic distribution of a new nepovirus infecting Stenotaphrum secundatum in Australia

The genome sequence of a new subgroup C nepovirus from Stenotaphrum secundatum in Australia is described. This virus, tentatively named Stenotaphrum nepovirus (SteNV), was present in separate plants as a mixed infection with either sugarcane mosaic virus or Panicum mosaic virus. The virus genome was divided between two RNA segments, 7,824 and 7,104 nucleotides (nt) in length, which each encode a single long polyprotein with putative 3C-like cysteine protease sites of the type H/G, H/S or L/S. The 3ʹ untranslated region of RNA2, at 2,155 nt, is the longest observed for any subgroup C nepovirus. Phylogenetic analyses using protease-polymerase and coat protein amino acid alignments suggest that SteNV is most closely related to cherry leaf roll virus. Using a newly developed RT-PCR assay, this virus was detected at multiple localities in New South Wales, Queensland and Western Australia, and in a second host species, Digitaria didactyla. No consistent association between virus infection and symptoms could be established. The economic importance, pathogenicity and transmission of this novel virus species warrant further investigation.

Salinity tolerance among a large range of bermudagrasses (Cynodon spp.) relative to other halophytic and non-halophytic perennial C4 grasses

The increasing demand on potable water has resulted in a greater reliance on poorer quality water, including saline sources, for maintaining forage and turfgrasses in agricultural and urban landscapes. Consequently, it will be crucial to identify grasses that can tolerate saline irrigation water. This study aimed to determine salinity tolerance among a large range of bermudagrasses relative to other perennial C4 grasses and test the relationship between salt tolerance and drought resistance. We report the salinity tolerance of 70 genotypes of mostly Australian bermudagrass ecotypes that were compared to halophytic cultivars of seashore paspalum (Paspalum vaginatum Swartz) and a non-halophytic cultivar of Queensland blue couch (Digitaria didactyla Willd) using a flood and drain sand culture system with salt treatments 1–40dSm−1. For the first time for C4 grasses, salt tolerance was determined by comparing total biomass of the grasses with and without salt treatment. Large genetic variation in salinity tolerance was identified and six bermudagrasses collected from saline habitats had salinity tolerance equal to that of seashore paspalum under the salinity treatments used in this study. There was no correlation between salt tolerance and drought resistance phenotypes determined from our previous research. Canopy temperature differential during salt stress was negatively correlated (r=−0.71 to −0.91, P<0.001) to salt tolerance and has potential to be used for screening bermudagrasses for salt tolerance using flood and drain sand culture. Salinity levels above 20dSm−1 for 8 weeks appeared to be effective for detecting large variation for salt tolerance in bermudagrass.

Early recovery signs of an Australian grassland following the management of Parthenium hysterophorus L.

Parthenium weed (Parthenium hysterophorus L.) is believed to reduce the above- and below-ground plant species diversity and the above-ground productivity in several ecosystems. We quantified the impact of this invasive weed upon species diversity in an Australian grassland and assessed the resulting shifts in plant community composition following management using two traditional approaches. A baseline plant community survey, prior to management, showed that the above-ground community was dominated by P. hysterophorus, stoloniferous grasses, with a further high frequency of species from Malvaceae, Chenopodiaceae and Amaranthaceae. In heavily invaded areas, P. hysterophorus abundance and biomass was found to negatively correlate with species diversity and native species abundance. Digitaria didactyla Willd. was present in high abundance when P. hysterophorus was not, with these two species, contributing most to the dissimilarity seen between areas. The application of selective broad leaf weed herbicides significantly reduced P. hysterophorus biomass under ungrazed conditions, but this management did not yet result in an increase in species diversity. In the above-ground community, P. hysterophorus was partly replaced by the introduced grass species Cynodon dactylon L. (Pers.) 1 year after management began, increasing the above-ground forage biomass production, while D. didactyla replaced P. hysterophorus in the below-ground community. This improvement in forage availability continued to strengthen over the time of the study resulting in a total increase of 80% after 2 years in the ungrazed treatment, demonstrating the stress that grazing was imposing upon this grassland-based agro-ecosystem and showing that it is necessary to remove grazing to obtain the best results from the chemical management approach.

Performances of Some Perennial Warm Season Grasses Alfalfa (Medicago sativa L.) Mixtures under Mediterranean Conditions

This research was conducted to determine forage yield and botanical composition of duo (alfalfa + one grass) and trio ( alfalfa + two grasses) mixtures of some warm season perennial grass species such as dallis grass (Paspalum dilatatum Poir.), Rhodes grass (Chloris gayana L.), Bermuda grass (Cynodon dactylon (L.) Pers.) Guineae grass (Panicum maximum Jacq.), blue couch grass (Digitaria didactyla Willd) and finger grass (Digitaria milanjiana (Rendle) Stapf) with alfalfa (Medicago sativa L.) as well as their pure sowings under irrigated conditions of Mediterranean during the years of 2011 and 2012. In the study, green herbage yield, dry matter yield, alfalfa proportion in dry matter yields and land equivalent ratio (LER) were determined. The experimental design was completely randomized block design with three replications. According to the results, it was determined that the ratios of warm season grasses in the botanical composition of the mixtures declined with the establishment age while rate of alfalfa in the botanical composition of the mixtures increased. Increasing the rate of alfalfa in the botanical composition of the mixtures also increased hay quality of the mixtures. The mixtures gave higher dry matter yield than pure sowings of the species. The highest green herbage yield (98.14 t ha1) was obtained from the mixture of Rhodes grass + alfalfa. The highest dry matter yield (22.46 t ha1) was obtained from the mixture of dallis grass + Guinea grass + alfalfa. The highest value of land equivalent ratio (LER) (1.49) was obtained from the mixture of bermuda grass +Rhodes grass + alfalfa. From the results of the study, it was concluded that Guinea grass and finger grass did not show good adaptaion to the Cukurova conditions due to low temperatures during the winter season. Bermuda grass, Rhodes grass, blue couch grass and dallis grass could be used to establish pasture mixtures with alfalfa, having long grazing season and giving high hay yield and quality. Before the establishment of such pasture mixtures, it was needed to research proper mixture ratios and proper management techniques of the mixtures

Water use, water use efficiency and drought resistance among warm-season turfgrasses in shallow soil profiles.

As the available water supply for urban turfgrass management is becoming limited in Australia, it will be crucial to identify drought-resistant turfgrass species and water-saving management strategies. Eight (pre-)commercial turfgrasses grown in Australia, two each of four species including the bermudagrasses (Cynodon dactylon L.), the Queensland blue couches (Digitaria didactyla Willd), the seashore paspalums (Paspalum vaginatum Swartz.) and St Augustinegrasses (Stenotaphrum secundatum (Walt.) Kuntze) were evaluated in two lysimeter experiments. Shallow lysimeters (28 and 40cm) were used to represent shallow soil profiles typical of urban environments. We measured gravimetric water use for the eight cultivars and calculated water use efficiency (WUE, clipping yield to water use ratio) and WUEr (ratio of WUE under drought to that under irrigated conditions). WUEr measured in both experiments correlated strongly with survival period and this relationship was not affected by soil type or cutting height. Using survival period as the criterion for drought resistance, the best were the bermudagrasses and the worst were the seashore paspalums and Queensland blue couches. The bermudagrass genotypes had the lowest water use, highest WUE and WUEr and the Queensland blue couches and seashore paspalums had the greatest water use, lowest WUE and WUEr. The possible mechanisms of drought resistance included lower water use and lower stomatal conductance as indicated by higher canopy temperature in the early stage of water deficit.

Paspalum striate mosaic virus: an Australian mastrevirus from Paspalum dilatatum

Three monocot-infecting mastreviruses from Australia, all found primarily in pasture and naturalised grasses, have been characterised at the molecular level. Here, we present the full genome sequence of a fourth, Paspalum striate mosaic virus (PSMV), isolated from Paspalum dilatatum from south-east Queensland. The genome was 2816 nt long and had an organisation typical of other monocot-infecting mastreviruses. Its nearest relative is Bromus cartharticus striate mosaic virus (BCSMV), with which it shares an overall genome identity of 75%. Phylogenetic analysis of the complete genome and each of the putative viral proteins places PSMV in a group with the other three Australian striate mosaic viruses. PSMV, BCSMV and Digitaria didactyla striate mosaic virus all contain a similar, small recombinant sequence in the small intergenic region.

Bromus catharticus striate mosaic virus: a new mastrevirus infecting Bromus catharticus from Australia

Although monocotyledonous-plant-infecting mastreviruses (in the family Geminiviridae) are known to cause economically significant crop losses in certain areas of the world, in Australia, they pose no obvious threat to agriculture. Consequently, only a few Australian monocot-infecting mastreviruses have been described, and only two have had their genomes fully sequenced. Here, we present the third full-genome sequence of an Australian monocot-infecting mastrevirus from Bromus catharticus belonging to a distinct species, which we have tentatively named Bromus catharticus striate mosaic virus (BCSMV). Although the genome of this new virus shares only 57.7% sequence similarity with that of its nearest known relative, Digitaria didactyla striate mosaic virus (DDSMV; also from Australia), it has features typical of all other known mastrevirus genomes. Phylogenetic analysis showed that both the full genome and each of its probable expressed proteins group with the two other characterised Australian monocot-infecting mastreviruses. Besides the BCSMV genome sequence revealing that Australian monocot-infecting mastrevirus diversity rivals that seen in Africa, it has enabled us, for the first, to time detect evidence of recombination amongst the Australian viruses. Specifically, it appears that DDSMV possesses a short intergenic region sequence that has been recombinationally derived from either BCSMV or a close relative that has not yet been identified.

A novel species of mastrevirus (family Geminiviridae) isolated from Digitaria didactyla grass from Australia

Mastreviruses (family Geminiviridae) that infect monocotyledonous plants occur throughout the temperate and tropical regions of Asia, Africa, Europe and Australia. Despite the identification of a very diverse array of mastrevirus species whose members infect African monocots, few such species have been discovered in other parts of the world. For example, the sequence of only a single monocot-infecting mastrevirus, Chloris striate mosaic virus (CSMV), has been reported so far from Australia, even though earlier biological and serological studies suggested that other distinct mastreviruses were present. Here, we have obtained the complete nucleotide sequence of a virus from the grass Digitaria didactyla originating from Australia. Analysis of the sequence shows the virus to be a typical mastrevirus, with four open reading frames, two in each orientation, separated by two non-coding intergenic regions. Although it showed the highest levels of sequence identity to CSMV (68.7%), their sequences are sufficiently diverse for the virus to be considered a member of a new species in the genus Mastrevirus, based on the present species demarcation criteria. We propose that the name first used during the 1980s be used for this species, Digitaria didactyla striate mosaic virus (DDSMV).

Nutrient uptake in tropical turfgrasses growing in winter in southern Queensland

The effects of fertilisers on 8 tropical turfgrasses growing in 100-L bags of sand were studied over winter in Murrumba Downs, just north of Brisbane in southern Queensland (latitude 27.4°S, longitude 153.1°E). The species used were: Axonopus compressus (broad-leaf carpetgrass), Cynodon dactylon (bermudagrass ‘Winter Green’) and C. dactylon × C. transvaalensis hybrid (‘Tifgreen’), Digitaria didactyla (Queensland blue couch), Paspalum notatum (bahiagrass ‘38824’), Stenotaphrum secundatum (buffalograss ‘Palmetto’), Eremochloa ophiuroides (centipedegrass ‘Centec’) and Zoysia japonica (zoysiagrass ‘ZT-11’). Control plots were fertilised with complete fertilisers every month from May to September (72 kg N/ha, 31 kg P/ha, 84 kg K/ha, 48 kg S/ha, 30 kg Ca/ha and 7.2 kg Mg/ha), and unfertilised plots received no fertiliser. Carpetgrass and standard bermudagrass were the most sensitive species to nutrient supply, with lower shoot dry weights in the unfertilised plots (shoots mowed to thatch level) compared with the fertilised plots in June. There were lower shoot dry weights in the unfertilised plots in July for all species, except for buffalograss, centipedegrass and zoysiagrass, and lower shoot dry weights in the unfertilised plots in August for all species, except for centipedegrass. At the end of the experiment in September, unfertilised plots were 11% of the shoot dry weights of fertilised plots, with all species affected. Mean shoot nitrogen concentrations fell from 3.2 to 1.7% in the unfertilised plots from May to August, below the sufficiency range for turfgrasses (2.8–3.5%). There were also declines in P (0.45–0.36%), K (2.4–1.5%), S (0.35–0.25%), Mg (0.24–0.18%) and B (9–6 mg/kg), which were all in the sufficiency range. The shoots in the control plots took up the following levels (kg/ha.month) of nutrients: N, 10.0–27.0; P, 1.6–4.0; K, 8.2–19.8; S, 1.0–4.2; Ca, 1.1–3.3; and Mg, 0.8–2.2, compared with applications (kg/ha.month) of: N, 72; P, 31; K, 84; S, 48; Ca, 30; and Mg, 7.2, indicating a recovery of 14–38% for N, 5–13% for P, 10–24% for K, 2–9% for S, 4–11% for Ca and 11–30% for Mg. These results suggest that buffalograss, centipedegrass and zoysiagrass are less sensitive to low nutrient supply than carpetgrass, bermudagrass, blue couch and bahiagrass. Data on nutrient uptake showed that the less sensitive species required only half or less of the nitrogen required to maintain the growth of the other grasses, indicating potential savings for turf managers in fertiliser costs and the environment in terms of nutrients entering waterways.

Response of tropical turfgrasses to recycled water in southern Queensland

The effects of recycled water (effluent) on 8 tropical grasses growing in 100-L bags of sand were studied in Murrumba Downs, just north of Brisbane in southern Queensland (27.4°S, 153.1°E). The species used were: Axonopus compressus (broad-leaf carpetgrass), Cynodon dactylon (bermudagrass ‘Winter Green’) and C. dactylon × C. transvaalensis hybrid (‘Tifgreen’), Digitaria didactyla (Queensland blue couch), Paspalum notatum (bahiagrass ‘38824’), Stenotaphrum secundatum (buffalograss ‘Palmetto’), Eremochloa ophiuroides (centipedegrass ‘Centec’) and Zoysia japonica (zoysiagrass ‘ZT-11’). From May 2002 to June 2003, control plots were irrigated with potable water and fertilised monthly. Plots irrigated with effluent received no fertiliser from May to August 2002 (deficient phase), complete fertilisers at control rates from September to December 2002 (recovery phase) and nitrogen (N) only at control rates from January to June 2003 (supplementary phase). In October 2002, the average shoot weight of plants from the effluent plots was 4% of that from potable plots, with centipedegrass less affected than the other species (relative growth of 20%). Shoot N concentrations declined by 40% in the effluent plots from May to August 2002 (1.8 ± 0.1%) along with phosphorus (P, 0.46 ± 0.02%), potassium (K, 1.6 ± 0.2%), sulfur (S, 0.28 ± 0.02%) and manganese (Mn, 19 ± 2 mg/kg) concentrations. Only the N and Mn concentrations were below the optimum for grasses. The grasses grew satisfactorily when irrigated with effluent if it was supplemented with N. Between January and June 2003 the average weight of shoots from the effluent plots was 116% of the weight of shoots from the control plots. Shoot nutrient concentrations were also similar in the 2 regimes at this time. The recycled water supplied 23% of the N required for maximum shoot growth, 80–100% of the P and K, and 500–880% of the S, calcium and magnesium. The use of recycled water represents savings in irrigation and fertiliser costs, and reductions in the discharge of N and P to local waterways. Effluent is currently about 50% of the cost of potable water with a saving of about AU$8000/ha.year for a typical sporting field.

Serological relationships of geminivirus isolates from Gramineae in Australia

Three distinct viruses, named chloris striate mosaic virus (CSMV), paspalum striate mosaic virus (PaSMV) and digitaria didactyla striate mosaic virus (DDSMV), have been identified among the five Gramineae‐infecting geminiviruses from Australia using polyclonal antisera. An isolate from Microlaena was confirmed as a strain of CSMV, and an isolate from Bromus catharticus was identified as PaSMV‐BC. Enzyme‐linked immunosorbent assay (ELISA) detected relationships between all but one of the viruses tested, the exception being miscanthus streak virus (MiSV) from Japan. The Australian viruses proved to be distantly related to similar viruses from Africa, digitaria streak virus (DSV) from Vanuatu, and wheat dwarf virus (WDV) from Europe. Three distinct groups of viruses from Africa, Australia and Europe were distinguished by phylogenetic analysis.

Susceptibility of Pearl Millet Accessions and Cultivars to Johnsongrass Mosaic and Sugarcane Mosaic Viruses in Queensland.

When 23 accessions of pearl millet growing in 1990 at Gatton, south-eastern Queensland, were examined for virus infection, all accessions had plants with mosaic symptoms. Using sorghum differential test plants, it was shown that Johnsongrass mosaic virus (JGMV) was commonly associated, but one isolate of the sabi grass strain of sugarcane mosaic virus (SCMV) was also obtained. In glasshouse tests where 15 accessions of pearl millet were each inoculated with JGMV and the three Australian strains of SCMV 17 days after sowing, all 15 were infected by JGMV and the sabi grass strain of SCMV. However, only two pearl millet accessions were infected by the Queensland blue couch grass strain of SCMV and 14 with the sugarcane strain of SCMV. JGMV caused an average of 60% decrease in dry matter yield 83 days after sowing, whereas strains of SCMV caused less stunting.

Levels of germinable seed in topsoil and cattle faeces in legume-grass and nitrogen-fertilized pastures in south-east Queensland

Measurements were made of germinable seed of all species in the top 5 cm of soil beneath 9 paddocks in an 11-year-old pasture experiment in south-east Queensland. The experiment comprised two pasture types grazed by cattle: legume-grass (Macroptilium atropurpureum- Setaria sphacelata) pastures grazed at four stocking rates and nitrogen fertilized S. sphacelata pastures grazed at five stocking rates. Levels of germinable seed in the soil varied with pasture type and stocking rate and ranged from 6760 to 45480 seeds/m2. Seed reserves increased on the legume-grass pastures as stocking rate increased. Fifty-seven different plant species were identified from the seedlings grown from the soil seed reserve. For 11 of these species, which contributed 70% of the seed reserves, there were significant trends in relation to pasture type and/or stocking rate. The only species where seed reserves significantly decreased with increasing stocking rate were the two sown species. Cattle faeces were also collected from lightly and heavily stocked legume-grass and nitrogen-fertilized pastures in spring, summer, autumn and winter. Germinable seed contents of all species were measured. Seed content of faeces was higher in the summer and autumn than in the winter and spring samplings, and in the heavily stocked than in the lightly stocked pastures. The highest content recorded was 20.5 germinable seeds g-1 faecal dry matter. The species with the highest germinable seed content in faeces were Digitaria didactyla, Axonopus affinis and Eleusine indica, the latter being restricted to nitrogen-fertilized pastures. Seed dissemination in faeces is a factor contributing to the invasiveness of prostrate perennial grasses such as D. didactyla and A. affinis under heavy grazing.

Biological characteristics of grass geminiviruses from eastern Australia

SummaryTwo serotypes of chloris striate mosaic virus (CSMV), paspalum striate mosaic virus (PSMV) and geminiviruses infecting Bromus catharticus and Digitaria didactyla were investigated. Their field occurrence and experimental hosts are listed. Serial transmission data for CSMV by single Nesoclutha pallida show a minimum latent period of 12–14 h, and regular transmission with occasional breaks for up to 50 days. Cicadulina bimaculata did not transmit any isolates after plant feeding acquisition, but transmitted CSMV inefficiently after insect injection. The vector of PSMV was found to be a specific biotype of N. pallida which bred only on Paspalum spp. The rate of transmission of CSMV with the Chloris biotype of N. pallida and of PSMV with the Paspalum biotype reached c. 50% with single insects, but only when freshly‐infected source plants were used. Geminate particles were found in thin sections of leaf tissue infected with all four viruses, and partially purified preparations were made of three of these. In gel diffusion tests, the virus from Microlaena stipoides produced a spur reaction with CSMV, when reacted with CSMV antiserum. The B. catharticus and D. didactyla isolates failed to react serologically with CSMV, maize streak or Vanuatu digitaria streak viruses.

Coat protein of potyviruses

The amino acid sequence of the coat protein of the Johnsongrass (JG) strain of sugarcane mosaic virus (SCMV) has been determined by protein sequencing techniques. The protein contains 303 amino acid residues corresponding to a molecular weight of 33,510 and when compared to the coat proteins of other potyviruses that have been characterized (263–267 residues) is found to have additional residues at its N-terminus. The N-terminus is acetylated as shown by fast atom bombardment mass spectrometry. Partial amino acid sequences of the coat proteins of the other three Australian SCMV strains, sugarcane (SC), Queensland blue couch grass (BC) and sabi grass (Sabi) have also been obtained. The sequence data and the comparative tryptic peptide HPLC profiles showed that the JG coat protein was substantially different from those of the other three SCMV strains, the sequence homology being around 66 per cent. This is in marked contrast to the high sequence homology between SC, BC and Sabi strains (95–100 per cent) but similar to that (51–62 per cent) found between coat proteins of distinct members of the potyvirus group. On the basis of these structural findings and other information on major differences in serological, biological and biochemical properties we believe that the present JG strain should not be considered a strain of SCMV but should be regarded as an independent member of the potyvirus group. The name “Johnsongrass mosaic virus” is proposed for this new member.

FEEDING PREFERENCES OF LARVAE OF HERPETOGRAMMA LICARSISALIS (WALKER) (LEPIDOPTERA: PYRALIDAE) AND SPODOPTERA MAURITIA (BOISDUVAL) (LEPIDOPTERA: NOCTUIDAE), TWO LAWN PESTS COMMON ABOUT BRISBANE

AbstractLarvae of 2 species of moth, Herpetogramma licarsisalis and Spodoptera mauritia were fed 25 species of lawn and pasture grasses and 32 other wild and cultivated plants. Leaves of few plants except grasses and sedges were ingested, but of these almost any species was eaten. No dicotyledons were eaten by H. licarsisalis while S. mauritia consumed 4 out of 17 dicotyledons. The preference of the larvae for Digitaria didactyla or each of 24 species of grasses and sedges was determined. It appears from the results of tests that there is no connection between the observations that these larvae are now of less concern around Brisbane than formerly and that Axonopus compressus, carpet grass, is becoming increasingly acceptable in lawns.

Coat protein of potyviruses. I. Comparison of the four Australian strains of sugarcane mosaic virus

As an aid to a more rational classification of the potyvirus group, we have examined the molecular weight, amino acid composition, and tryptic peptide map of the coat protein of four Australian sugarcane mosaic virus strains: Johnson grass (JG), sugarcane (SC), Queensland blue couch grass (BC), and sabi grass (Sabi). The proteins migrated as a single band in SDS-polyacrylamide gel electrophoresis with molecular weights of 33,700 (SC), 34,200 (JG), 39,100 (BC), and 40,300 (Sabi). The BC and Sabi strains have identical amino acid compositions and tryptic peptide maps. The SC strain has a similar amino acid composition and tryptic peptide map but these two properties of the JG strain show very little similarity to the three other strains. On the basis of the coat protein properties investigated, we propose that the four sugarcane mosaic virus strains be subdivided into two groups: the sugarcane group containing SC, BC, and the Sabi strains and the Johnson grass group containing the JG strain.

The resistance of maize inbred lines to sugarcane mosaic virus in Australia

Maize inbred lines, derived from both Australian and exotic sources, and used in a breeding programme at Kairi, Qld, were screened for resistance to a Johnson grass strain of sugarcane mosaic virus (SCMV-Jg). There was a good correlation between ratings made following manual inoculation in a glasshouse and those following exposure to natural field infection. Seven lines were highly resistant in both glasshouse and field ratings. A further nine lines showed an intermediate level of resistance following manual inoculation and developed from 0 to 7 % infection under field conditions when a susceptible line developed 99 % infection. Data obtained following the manual inoculation of plants in segregating generations of crosses between resistant KL 57 and susceptible KL 9 were consistent with resistance being controlled by a single dominant gene. Six lines (Pa 405, CI 44, Tx 601, Oh 07, Oh 7B, 38-11) that were used as sources of resistance to maize dwarf mosaic virus, strain A (MDMV-A) in the U.S.A. developed natural infection levels of less than 15% with SCMV-Jg. Only Pa 405 was highly resistant to manual inoculation. Four of 11 SCMV-Jg resistant lines were also highly resistant to manual inoculations with the sugarcane, Sabi grass and Queensland blue couch grass strains.

Effect of stocking rate and grazing frequency on a Siratro (Macroptilium atropurpureum)/Setaria anceps cv. Nandi pasture

Five stocking rates, ranging from 0.8 to 2.8 beasts ha-1, and three frequencies of grazing were imposed on a five-year-old Siratro (Macroptilium atropurpureum)/Setaria anceps cv. Nandi pasture at Samford, south-east Queensland. The three grazing frequencies involved grazing for four days every three, six or nine weeks. Plots were individually grazed from 1972 to 1976 and the residual effect of treatments was measured over a grazing-free period in 1977. Within the three week grazing frequency both Siratro yield and total yield declined markedly with increased stocking rate, with an increased invasion of prostrate species such as blue couch (Digitaria didactyla). The decline in Siratro yield at higher stocking rates was less marked in the nine week system where there was much less invasion of prostrate species. However, it is suggested that the value of rotational grazing with a long rest period as a means of maintaining Siratro productivity could be largely at stocking rates where the pasture is overgrazed in terms of animal performance. Siratro density and seedling regeneration were largely unaffected by treatment and there was a good recovery of Siratro in the heavily grazed treatments during the grazing-free period at the end of the experiment. However, Siratro soil seed reserves declined with increased stocking rate and there was a much greater decline in flowering and seeding. On this basis it is predicted that if grazing treatments had been continued the heavily grazed pastures would eventually have reached the stage where Siratro would not recover with spelling.