Scabra Cv Research Articles

Responses of selected tropical forage legumes to imposed drought

Drought tolerance is an important attribute for the establishment of forage legumes in the rangelands of the seasonal semi-arid tropics. This experiment examined the seedling rooting depth, plant biomass, and other growth parameters of 5 perennial tropical legumes in response to different watering and drying regimes. Centrosema brasilianum cv. Oolloo and Macroptilium bracteatum (CPI 55770) produced deeper roots, greater root biomass, and more root nodules than Stylosanthes scabra cv. Seca and Desmanthus virgatus (CPI 79653), however only D. virgatus produced deeper roots and increased biomass in response to the drought treatment. Arachis triseminalis (CPI 91423), C. brasilianum and M. bracteatum flowered during the 9-week course of the experiment, with the latter two species producing pods. Seca, A. triseminalis and D. virgatus show adaptations of drought-tolerance, whilst C. brasilianum and M. bracteatum are adapted to drought avoidance.

QUALITY OF SEED PRODUCED BY TROPICAL FORAGE LEGUMES ON LOW FERTILITY SOILS

Soil fertility can influence seed production and seedling growth. This study compared seed yields, seed and seedling characteristics of eight forage legumes (Stylosanthesscabra, S. hamata, Centrosemabrasilianum, C. pascuorum, Desmanthuspubescens, D. Virgatus, Macroptiliumbracteatum and M. martii) grown on two soil types (red and yellow kandosols), of low fertility, that are widespread in the Australian tropical rangelands. Seeds of the Desmanthus species germinated most rapidly and, with M. bracteatum, produced the highest proportion of readily germinable seed. M. bracteatum seed produced on the Yellow Kandosol germinated significantly faster, as did the S. hamata from the Red Kandosol than the other species. S. scabra cv. Seca and C. brasilianum produced more readily germinable seeds from plants grown on the Red Kandosol. C. pascuorum, D. pubescens and M. bracteatum produced a higher percentage of readily germinable seeds and fewer hard seeds when grown on the Yellow Kandosol. No significant differences were found in seedling vigour or biomass allocation from seeds produced on the different soil types

Evaluation of forage legumes for introduction into natural pastures of semi‐arid rangelands of Kenya

AbstractTo address the potential of legumes to contribute to improved quality and quantity of natural pastures in the semi‐arid rangelands of Kenya, five legume species were introduced and evaluated in a small‐plot field experiment over three growing seasons. The investigated species were glycine (Neonotonia wightii), siratro (Macroptilium atropurpureum), dolichos (Lablab purpureus cv. Rongai), velvet bean (Mucuna pruriens) and shrubby stylo (Stylosanthes scabra cv. seca). Treatments included two cutting heights (ground level and 15 cm) and two cutting intervals (at 2 and 4 months). The mean dry matter (DM) yields of glycine and siratro were highest when the legumes were harvested at ground level at 2‐month intervals (10·31 and 7·81 t ha−1 year−1 respectively). Mean DM yield of stylo was highest when the legume was harvested at 15 cm after 4 months (3·52 t ha−1 year−1). These three legumes also produced high organic matter through litter fall, which contributed to soil fertility. Evidence from a supporting pot experiment showed effective nodulation and potential for N fixation. These legumes also possessed deep tap roots and withstood heavy defoliation. These three legumes were selected for further integration with grasses in natural pastures. The DM yields of dolichos and velvet bean when harvested at 15 cm after 2 or 4 months were low (2·48 and 1·91 t ha−1 year−1), and these species were considered inappropriate for further investigation.

Impacts of grazing management options on pasture and animal productivity in a Heteropogon contortus (black speargrass) pasture in central Queensland. 2. Population dynamics of Heteropogon contortus and Stylosanthes scabra cv. Seca

The dynamics of Heteropogon contortus and Stylosanthes scabra cv. Seca populations were studied in a subset of treatments in an extensive grazing study conducted in central Queensland between 1988 and 2001. These treatments were 4 stocking rates in native pasture and 2 of these stocking rates in legume oversown and supplement/spring burning treatments. For the 1999–2000 summer, population data for H. contortus in 5 of these native pasture and supplement/burning treatments were compared with those for an additional burnt treatment. Seasonal rainfall throughout this study was below the long-term mean and mean annual pasture utilisation ranged from 24 to 61%. Increasing stocking rate from 5 to 2 ha/steer in native pasture reduced H. contortus plant density. Increasing stocking rate reduced seedling recruitment as a result of its effect on soil seedbanks. Seedling recruitment was the major determinant of change in plant density, although some individual H. contortus plants did survive throughout the study. Burning in spring 1999, particularly at light stocking rate, promoted seedling recruitment above that in both unburnt native and legume oversown pasture and resulted in increased H. contortus plant density. In the legume oversown treatments, S. scabra cv. Seca density increased rapidly from 15 plants/m2 in 1988 to 140 plants/m2 in 2001 following a lag phase between 1988 and 1993. This increased S. scabra density was associated with an eventual decline in H. contortus plant density through reduced seedling recruitment. It was concluded that H. contortus population density is sustainable at stocking rates of 4 and 5 ha/steer (30% pasture utilisation) and that spring burning at light stocking rate can promote H. contortus populations. Increasing densities of S. scabra need to be managed to prevent its dominance.

Impacts of grazing management options on pasture and animal productivity in a Heteropogon contortus (black speargrass) pasture in central Queensland. 1. Pasture yield and composition

An extensive grazing study was conducted between 1988 and 2001 in a Heteropogon contortus (black speargrass) pasture in central Queensland. The study was designed to measure the effects of stocking rate on native pasture, native pasture with legume oversown, and native pasture with animal diet supplement/spring burning on pasture and animal production. Summer rainfall throughout the study was below the long-term mean. Mean annual pasture utilisation ranged from 13% at 8 ha/steer up to 61% at 2 ha/steer. Increasing stocking rate treatments reduced total pasture yields while total yields in legume oversown treatments were similar to those in native pasture at the same stocking rate. When spring burning was possible, total yields were reduced in the subsequent autumn. Increasing stocking rate in native pasture tended to reduce H. contortus and Bothriochloa bladhii, increased the composition of intermediate species, such as B. decipiens and Chloris divaricata, and also changed the frequencies of a range of minor species. Oversowing legumes resulted in Stylosanthes scabra cv. Seca increasing from <1% of pasture composition in 1988 to 50% in 2000 and was associated with a reduction in H. contortus and changes in the frequencies of some minor species. Stocking rates heavier than 4 ha/steer resulted in annual pasture utilisation greater than 30% and were unsustainable because they reduced total yield and resulted in undesirable changes in species composition. It was concluded that pasture production was sustainable when stocking rates were maintained at 4 ha/steer, which equates to 30% annual pasture utilisation, and through the judicious use of spring burning.

Molecular Assessment of Variation in Stylosanthes fruticosa Accessions Employing STS and RAPD Markers

Genetic variations in two accessions of S. fruticosa (41117 and 41117A) was carried out employing random amplified polymorphic DNA (RAPD) and sequence-tagged-sites (STS) markers to establish the accession closely resembles to the mapping population developed using one of these as a anthracnose susceptible parent along with S. scabra cv Seca as resistant source. Sixty-four RAPD and 15 STS primers generated 469 and 59 fragments respectively. Of these, 90 (19.2%) RAPD and 6 (10.2%) STS fragments showed polymorphism between two accessions of S. fruticosa. When same primers sets were used with F2 progeny, the segregated RAPD fragments showed patterns belonging to S. scabra cv Seca×S. fruticosa 41117A rather S. scabra cv Seca×S. fruticosa 41117 cross. Of 15 STS primers pairs, SHPALF2/R2, SHST2F3/T2R16 and SHST1F3/T1R3 clearly demonstrated that 41117A line was closer to population as SHPALF2/R2 showed absence of a 480-bp fragment in S. fruticosa 41117 and present in other two parents i.e., S. scabra cv Seca and S. fruticosa 41117A and 78 F2 plants tested whereas rest two primer pairs amplified a fragment of smaller size in 41117 only. Though most of the STS primer sequences used were derived from S. scabra cv Fitzroy and S. hamata cv Verano, the level of reaction in S. fruticosa accessions indicated low genome specificity of STS primers and hence low level of genetic divergence in different species of Stylosanthes. Results also provided the list of potential STS and RAPD primers could be used in studying the genetic relationships among S. fruticosa accessions, which is the only species of the genus Stylosanthes native and endemic to the southern peninsular regions of India, for plant conservation and breeding programs.

Floral reward and insect visitation in ornamental deutzias (Deutzia spp.), Saxifragaceae sensu lato

SummaryOrnamental plants cultivated in urban regions may help to sustain local pollinator populations as well as broaden food source for honey bees. This 3–year study examined the abundance of flowering, nectar and pollen production as well as insect visitation to six ornamental Deutzia species and cultivars. In Poland, the blooming of the observed taxa lasted from early June to the end of July. The number of developed florets strongly depended on the weather conditions before and during the flowering period. All deutzias showed abundant secretion of highly concentrated nectar. The mean amount of sugars secreted in nectar per 10 flowers ranged from 11.8 mg (D. scabra) to 18.7 mg (D. gracilis). Average pollen mass produced by the same number of florets was similar in all species and reached 17.8 mg. The highest estimated nectar (71.1 g) and pollen (74.1 g) crop per plant was obtained from D. scabra cv. Watereri. Deutzia flowers attracted numerous insects, mainly honey bees, bumble bees and solitary bees.The species and cultivars investigated are highly valuable honey plants. Increased use of these shrubs in gardens and parks should be encouraged in order to enrich nectar and pollen pasture for honey bees and wild Apoidea. However, their use is limited to areas of mild climate and adequate water supply.

A Partial Genetic Map of Stylosanthes Developed Using Inter-Specific F2 Cross

Low polymorphism in Stylosanthes emphasizes use of inter-specific crosses for the development of mapping population for genetic linkage map. Using 78 F2 individuals of the cross of S. scabra cv. Seca and S. fruticosa, 7 linkage groups were obtained when 81 polymorphic RAPD (Random Amplified Polymorphic DNA) markers were processed. Of these, 53 segregated in expected ratio of 3 : 1 for dominant marker in the F2 generation, 11 markers in 1 : 1 while 17 deviated from the expected ratio. Thirty markers remain unlinked. Total genome length covered by markers in the present partial map is 630.4 cM (centi Morgan) with an average interval of 39.4 cM. The skeleton map developed is being used to place reasonable numbers of RAPD and STS (Sequence Tagged Sites) markers and to identify QTLs (Quantitative Trait Loci) for anthracnose disease, one of the most important disease of the genus Stylosanthes.

Assessment of Stylosanthes seed yield reduction caused by phytoplasma-associated diseases

The effect of Stylosanthes little leaf disease on Stylosanthes scabra cv. Seca seed yield was monitored over 2 consecutive seasons at Southedge Research Station in northern Queensland. The time of initial symptom expression was recorded during weekly assessments to determine what effect time of infection after planting had on seed yield. First flowering date was recorded to establish whether the developmental stage of the plant, as indicated by the onset of reproductive activity, at the time of symptom expression influenced the effect of Stylosanthes little leaf disease on yield. At the end of each season, both diseased and asymptomatic plants were harvested and seed yield determined. Seed yield data from the 1999 season showed that there was no significant difference between the mean yield of symptomatic plants, regardless of when they first showed symptoms, and that of asymptomatic plants. However, during the 2000 season plants that showed symptoms early in the season had a significantly lower seed yield than both asymptomatic plants and plants that became diseased later in the season. This decrease in productivity amounted to a yield loss of 98.8 and 56.5% when the plants showed symptoms at 79�and 110 days, respectively, after planting. If plants became diseased within 30 days of first flowering, they did not produce significant amounts of seed. Yield remained low even when the time between first flowering and initial symptom expression increased up to 60 days, after which yield was extremely variable but within the range of that observed for individual asymptomatic plants. It is concluded that Stylosanthes little leaf disease has little or no effect on seed yield if plants have been flowering for about 8 weeks before symptom expression.

Promising tropical grasses and legumes as feed resources in Central Tanzania: VI. Nitrogen balance in growing bulls consuming tropical herbaceous forage legumes

Nitrogen balance was measured in six growing Mpwapwa bulls (mean age 1.5 years, weight 131 kg) fed Cenchrus ciliaris hay and cassava as basal diet (negative control) supplemented with dried leaves from four herbaceous legumes: Macrotyloma axillare cv. Archer (MAA), Stylosanthes scabra cv. Seca (SSS) and Neonotonia wightii cv. Mpwapwa (NWM); or with Fish meal (FM) as positive control in a 6×6 Latin square design. All treatments with protein were formulated to provide the same energy and protein levels of intake. The digestible organic matter intakes were 13.9, 13.6, 14.2, 13.8 and 13.6 g per kg body weight (BW) per day in treatments supplemented with MAA, SSS, FM and NWM respectively and these were similar ( P>0.05) but significantly higher ( P<0.05) compared to the negative control. The crude protein contents of the DM consumed ranged from 8.6 to 9.5% among the supplemented diets and these were higher than the unsupplemented treatment of only 3.9%. Nitrogen intake, faecal nitrogen output, urinary nitrogen output and nitrogen balance were significantly higher ( P<0.001) in the supplemented diets compared with the negative control. For the negative control treatment, nitrogen balance was 0.09 g per kg W 0.75 whereas N balance ranged from 0.19–0.32 g per kg W 0.75 in the other treatments. The ranking was: FM>SSS>MAS>MAA>NWM but they were not significantly different from each other. Only when calculated as percent N retained, was FM superior to NWM ( P<0.05). It is concluded that using leaves from these legumes as protein supplements will have an effect on N balance in growing Mpwapwa bulls comparable to fish meal.

Population dynamics of Stylosanthes hamata and S. scabra in north-eastern Queensland: effects of superphosphate application, timber treatment, and stocking rate

The effects of pasture management (superphosphate application, timber treatment, stocking rate) on the herbage yields and population dynamics (seed production, seedling numbers, plant longevity) of Stylosanthes hamata cv. Verano and S. scabra cv. Seca grown in grass-legume mixtures were measured from 1982 to 1992 at 2 sites, Hillgrove (extractable phosphorus, 50 mg/kg) and Cardigan (extractable phosphorus, 6 mg/kg), near Charters Towers, north-eastern Queensland. Stylosanthes hamata was higher yielding during the first 3 years at both sites but subsequently S. scabra produced the larger yields. This resulted in S. hamata dominating the legume component in the early years but the proportion of S. hamata then declined, so that by the final year, S. hamata contributed &lt;20% of the legume mixture at both sites. Both seed yields and seedling numbers varied widely between years for both species at both sites. In the early years there were more S. hamata seedlings but in the later years S. scabra had greater seedling numbers. Seed yield and seedling numbers were not significantly affected by superphosphate but both were higher for S. hamata on plots with live trees than on plots with killed trees; numbers of seeds and seedlings of S. scabra were not affected by tree killing. Seed and seedling numbers of both species tended to be greatest at the intermediate stocking rates. Survival of both S. hamata and S. scabra at both sites conformed to Deevey"s Type II curve (i.e. death rate was constant with age). The S. scabra plants lived considerably longer than the S. hamata plants. Pasture treatments had less influence on longevity than on seed production and seedling numbers. Seed production and seedling establishment of both species were marginal for their persistence in the region, and management should aim for seed set and subsequent seedling establishment to occur sufficiently frequently to allow the legumes to persist.

Diet composition of cattle grazing Stylosanthes - grass pastures in the seasonally dry tropics: the effect of phosphorus as fertiliser or supplement

Summary. The effect of phosphorus (P) on diet selection in cattle grazing pastures based on Stylosanthes hamata cv. Verano andS. scabra cv. Seca in the seasonally dry tropics was studied in 3 grazing trials on soils with inherently low P status ( 5 µg/g bicarbonate-extractable P). The contribution of Stylosanthes (stylo) to diets was estimated at regular intervals (approximately monthly) using carbon isotope analysis of faeces. Feeding P supplement increased the proportion of stylo in the diet but the effect was seasonal and variable, being most pronounced during the late wet and early dry seasons when dietary stylo proportions are usually highest. The results indicated that P supplement influenced diet selection through its effect on dietary P status such that cattle with a deficiency of dietary P select a lower proportion of stylo than those with higher P intakes. The effect of fertiliser P on dietary stylo content was also variable. The dominant effect was via fertiliser-induced changes in pasture botanical composition. Higher stylo proportions in the diet of heifers grazing unfertilised pasture compared with those grazing fertilised pasture were associated with increasing stylo dominance in unfertilised pastures as opposed to grass dominance in fertilised pastures. At the same time there was evidence of a fertiliser treatment effect that was consistent with dietary P status influencing diet composition. In the grass-dominant pastures, unsupplemented cattle on low P pasture selected less stylo than those grazing pastures of higher P status due to more frequent fertilising but there was no difference where P supplement was fed. A strong seasonal preference for grass early in the wet season, reinforced by a generally reduced preference for stylo in cattle with diets deficient in P, probably hastened the development of stylo dominance in unfertilised pasture where P supplement was not fed.

Promising tropical grasses and legumes as feed resources in Central Tanzania IV. Effect of feeding level on digestibility and voluntary intake of four herbaceous legumes by sheep

An experiment involving comparison of 4 legumes fed at 5 levels was conducted to study the effect of the level of feeding on digestibility and voluntary intake by Blackhead persian rams. The legumes were Neonotonia wightii cv. Mpwapwa (NWM), Stylosanthes scabra cv. Seca (SSS), Macrotyloma axillare cv. Archer (MAA) and Macroptilium atropurpureum cv. Siratro (MAS). The forages were cut at 8 weeks and dried in the sun. Sixteen sheep were used and fed 600, 900, 1200, 1500 and 1800 g/day in a split plot design. Among the species compared, SSS and NWM had higher ( P < 0.05) organic matter (OM) digestibility than MAA and MAS. Differences in intakes among species were observed, with MAS having lower OM intakes ( P < 0.05) than the other species. Increasing feeding level allowed the selection of more leafy diet with significant improvement ( P < 0.05) in OMD in SSS, and MAA, but not of MAS and NWM. Significant improvement ( P < 0.05) in intakes of OM and digestible OM were observed in all species, as feeding level was raised from 600–1800 g per day, to allow for the selection. The level of feeding allowing maximum intakes of OM with the least refusal was, on the average, 1200 g with 19.6% refusals, ranging from 900 g per day with refusals of 10.3% for MAS, to 1500 g per day with refusals of 29.4% for SSS. The maximum OM intakes were 20.5 g kgW −1 d −1 and 25.5 g/kg BW/day for MAS and SSS, respectively. Estimated maximum intake at infinite feeding level was, on the average, 26 g/kg BW/day. A realistic value for SSS could not be obtained, but was, probably, considerably higher than that for the others. To obtain a maximum value for animal production, refusals of approximately 40% would be required. Among the legumes studied, SSS seems to be the most promising species for the semiarid areas of Central Tanzania.

Transpiration effciency and its relationship with carbon isotope discrimination under well-watered and water-stressed conditions in Stylosanthes scabra

Stylosanthes scabra cv. Seca is a widely sown tropical pasture legume in northern Australia and has a high degree of drought resistance. Identification of traits contributing to the drought resistance of Seca may be valuable for use in breeding programs. Transpiration efficiency (TE) has been suggested as one such trait contributing to drought resistance. Carbon isotope discrimination (Δ) has been proposed for estimating TE indirectly in C3 plants. A glasshouse experiment was conducted using 8 accessions of S. scabra to identify whether Seca differs in TE from other accessions of S. scabra and to determine the relationship between TE and Δ under both well-watered and water-stressed treatments. Seca maintained the highest TE (lowest Δ) under both control and stress treatments, and leaf Δ was significantly and negatively correlated with TE under both control and stress conditions. A significant and negative relationship was found between Δ and dry matter production under stress treatment. The interaction between accession and watering treatment was not significant for either TE or Δ. We also found a signirficant agreement between the performance in the field and in the laboratory for these 8 accessions. These results indicate that TE could be one of the significant factors contributing to drought resistance of Seca. Furthermore, Δ and/or specific leaf area may be useful as selection criteria in breeding programs to identify the lines with high TE.

Promising tropical grasses and legumes as feed resources in Central Tanzania V. Effect of supplementing Cenchrus ciliaris hay with leaves from four legumes on intake and digestibility by growing Mpwapwa bulls

In Trial 1, six growing Mpwapwa bulls (mean age 1.5 years, mean body weight 158 kg) were used in a 6 × 6 Latin square design to study the effect on intake and digestion of supplementing Cenchrus ciliaris cv. Kongwa hay with four different legume leaf proteins. Hay alone and fish meal (FM) treatments were included as negative and positive control treatments, respectively. The grass hay was fed allowing above 40% refusal to maximize selectivity and contained 5.1% crude protein (CP), 76.1% neutral detergent fibre (NDF), 9.9% lignin and 3.1% silica. The protein sources were dried leaves of Macroptilium atropurpureum cv. Siratro (MAS), Macrotyloma axillare (MAA), Neonotonia wightii cv. Mpwapwa (NWM), Stylosanthes scabra cv. Seca (SSS) and FM. The protein sources were fed aiming at supplying approximately 150 g CP/day. The legume CP contents varied from 18.6–20.6% and the FM contained 54.7%. In Trial 2 in a completely randomised block design, 8 bulls were used to measure the digestibility of the legumes alone. Selective feeding resulted in consumption of hay containing 6.2% CP. The apparent digestibility of organic matter (OM) and NDF were 58.3 and 62.5%, respectively. Supplementing the hay resulted in intake of a diet with CP ranging from 8.0–8.5%. Despite the increased CP intake, neither the digestibility of OM nor NDF increased significantly, implying that the protein was not a first limiting factor for fibre digestion. The grass hay OM intakes varied between 21.0 and 22.2 g/kg body weight (BW) per day (77.3–86.0 g/kg BW 0.75/d) and were not improved by protein supplementation. Significant improvements ( P < 0.001) in daily intakes of total OM and CP were observed by supplementation, although total NDF was not improved. All protein supplements except MAS improved ( P < 0.05) digestible OM intakes compared to the unsupplemented hay. Calculated digestible and metabolizable energy values for the diets were not improved by supplementation. However, an improvement in total energy and protein intake may be obtained as a result of supplementation. It is concluded that it is beneficial to use MAA, NWM, SSS and also FM in C. ciliaris-based diets to improve total intake of CP by growing bulls. Total intake of OM and digestible OM may also be improved, but the levels are only on the order of 10%. The use of legume supplements and allowing ample feed refusals may result in an estimated daily BW gain of 200–400 g.

Effects of plant extracts of Bothriochloa pertusa and Urochloa mosambicensis on seed germination and seedling growth of Stylosanthes hamata cv. Verano and Stylosanthes scabra cv. Seca

Effects of osmotic stress and of aqueous plant extracts from 4 pasture species on seed germination and seedling growth of the tropical legumes S. hamata (L.) Taub cv. Verano and S. scabra Vog. cv. Seca were investigated. Allelopathic effects of plant extracts from B. pertusa (L.) A. Camus were measured on S. scabra cv. Seca in terms of lower germination (35%) and shorter root length (35%). Extracts from Urochloa mosambicensis(Hack.) Dandy cv. Nixon had no adverse effect on Seca germination, but also reduced Seca root length. There was no evidence to support the hypothesis that B. pertusa had allelopathic effects on Verano germination or seedling growth. Extracts from Verano and Seca also reduced germination, seedling weight, and root length of Seca as well as root length of Verano. Root length was more sensitive than seedling length for ascertaining allelopathic effects, as there was no osmotic potential effect on root length up to 300 mmol/kg, whereas seedling weight and shoot length declined linearly with increasing osmotic potential (r = -0·92 and -0·99, respectively). Germination responses of Verano and Seca in solutions of both mannitol and polyethylene glycol-600 (PEG) were similar up to 300 mmol/kg, but at 600 mmol/kg Verano had a significantly higher germination in mannitol. Since the osmotic potential of the plant extracts did not exceed 78 mmol/kg, the use of osmotically adjusted control treatments had little effect on the conclusions drawn from using a distilled water control treatment.

Spatial Dependence in Anthracnose Development in Mixtures of Stylosanthes scabra

AbstractDevelopment of anthracnose caused by Cotletotrichum gloeosporioides in mixtures of the tropical pasture legume Stylosanthes was studied in 3 successive years. The performance of three accessions of Stylosanthes sp., 36260, QiaO42 and 55860 and cv. Seca were evaluated by growing these in three different mixtures with other susceptible or resistant components. Small test plots of these mixtures were established within large grazed background paddocks which were sown to a pure stand of S. scabra cv. Seca or a mixture of six S. scabra genotypes, including ‘Seca’, This simulated the widely used practice of oversowing existing pastures with improved cultivars. In all 3 years, 36260, Q10042, 55860 and ‘Seca’ developed more disease when grown in a mixture with the susceptible ‘Fitzroy’. A hexagonal lattice design was used in the test plots to study the influence of nearest neighbours on the partially resistant 55860. At a plant level, the area under the disease‐progress curve, averaged over the six neighbours, NADPC, was used as a covariate to approximate the influence of inoculitm pressure in th e neighbourhood. The partial regression coefficient for this covariate wa s significant (P &lt; 0.05) for mixture with ‘Fitzroy’ in 1989 and 1990, for mixture with the highly resistant 93116 in 1989, and for mixture with the moderately resistant ‘Verano’ in 1990. The NADPC was further subdivided into three components to separate inoculum pressure due to the component unique to a mixture, the resistant component ‘Seca’ and th e three moderately resistant components 36260, 55860 and Q10042. This showed that the NADPC effect was largely due to inoculum pressure from the moderately resistant components. The study demonstrates the lack of any significant protection of susceptible components from resistant components in the immediate neighbourhood. The practical implication of this finding is that only resistant components should be used when oversowing Stylosanthes pastures.

The Relationship between Anthracnose Severity and Populations of Bacteria on the Phylloplane of the Tropical Pasture Legume Stylosanthes Scabra

Populations of gram-negative bacteria, spore-forming bacilli, pseudomonads, and total bacteria were monitored on leaves of the tropical pasture legume Stylosanthes scabra cv. Fitzroy showing different severity levels of anthracnose caused by Colletotrichum gloeosporioides . Leaves were either disease-free or were grouped on the basis of percentage of leaf area visibly diseased into low-, moderate-, and high-severity classes. Data on bacterial populations, collected on nine different occasions during a growing season, were analyzed with the population estimates as dependent variables and anthracnose severity class as the treatment. Meteorological variables were summarized using the maximum likelihood factor analysis and used as covariates. Of the three bacterial groups, only the spore-forming bacilli showed a statistically significant negative relationship between their population density and anthracnose severity. Total bacterial populations were assessed independently and also tended to rise with increasing disease severity. This suggested a possible antagonism of spore forming bacilli toward the anthracnose pathogen. A simple in vitro method for differentiating modes of antagonism was developed. Twenty-four bacterial isolates collected from the leaf surface were tested using this method; of these, 19 showed a degree of antagonism. The method proved incapable of differentiating between modes of antagonism. Further work is necessary to establish the nature and effectiveness of this putative antagonism.

Survival of Colletotrichum gloeosporioides on Stylosanthes scabra cv. Fitzroy during the dry season

Infected stems of the tropical pasture legume Stylosanthes scabra cv. Fitzroy were assessed over two consecutive dry seasons to determine if Colletotrichum gloeosporioides survived as conidia on lesions formed during the previous wet season or as hyphae within infected tissue. In the second season, infected stem pieces placed on the soil surface (debris) and in a 15�C incubator at the beginning of the dry season were assessed in addition to the material from living plants. Infective conidia were present in sufficient numbers to be detected in all but the initial sample in each season, and C. gloeosporioides could be isolated from lesions on plant tissue throughout both dry seasons. Conidium density on live stems was variable in the first season, where no rain fell until the onset of the wet season in mid-November. Conidia were present in similar densities on stems throughout the second dry season, when intermittent light rain fell during the assessment period. The mean density of conidia was significantly higher on live stems than on debris or stems stored at 15�C. Large numbers of conidia were produced on stem pieces from living plants and debris after incubation under conditions conducive to sporulation. Conidia were, therefore, present or could be rapidly produced to initiate an epidemic once favourable conditions for dispersal and infection occurred.

Seasonal nutrient intake and phosphorus kinetics of grazing steers in northern Australia

The growth of Bos indicus cross-steers grazing native grass and native grass-legume (Stylosanthes scabra cv. Seca) pastures was monitored for 392 days in five unreplicated experimental paddocks, each grazed by three steers. Two phosphorus (P) fertilizer rates: F1, 4-5 kgP/ha every 2 years and F2, 9.0 kgP/ha annually, together with an unfertilized control, FO, were studied. P supplement was supplied to cattle in two additional paddocks (FOS and F1S) at the rate of 5 gP/ha/day-l. In the dry, wet and late wet seasons, pasture yield and pasture component yield were measured. At the same time, the nutrient intake and P kinetics of resident steers were measured using chromic oxide capsules and intravenous injections of 32P . Additional non-resident steers, fistulated at the oesophagus, grazed the pastures intermittently to provide estimates of dry matter digestibility, fibre, nitrogen (N) and P content of the selected diet. Phosphorus fertilizer increased legume and native grass growth which resulted in more dry matter containing higher concentrations of P and N than unfertilized pastures. Both P fertilizer and supplement increased dry matter intake and liveweight gain of cattle. During the experimental period of 13 months, steers which grazed pastures that received the (F2) fertilizer treatment gained on average 0.43 kg/day compared with 0.19 kg/day for those which grazed unfertilized FO pastures. Supplementation increased wet season liveweight gain from 0.45 to 0.59 kg/day and 0.46 to 0.73 kg/day for FO and F1 treatments respectively. Only cattle which grazed pastures that received the F1S and F2 treatments gained weight in the dry season. Nitrogen was the primary nutrient limiting cattle growth from unfertilized pastures in the dry season, but when pastures were fertilized (4.5 kgP/ha every 2 years) and legumes established, P was the primary limiting nutrient. Intakes of P ranged from 7 to 35 mg/kg LW and were lower than those recommended by recognized authorities for the steer growth rates we recorded. Both the absorption and faecal excretion of dietary P were closely related to P intake. Endogenous faecal P values varied with P intake in the range 9-22 mg/kg liveweight. Endogenous faecal P was also related to dry matter intake and plasma inorganic P. The coefficient of P absorption was lowest (0.65) for steers grazing unfertilized native pasture (FO), but increased with P intake to 0.85 for steers grazing the F1S treatment. We conclude that the P requirements of growing cattle grazing native grass and native grass-legume pastures in northern Australia are about half those recommended by most authorities.