Stay-green Drought Adaptation Trait Enhances Sorghum Production in Sub-tropical Australia, Central-Western India and Sub-Saharan Africa

Drought during grain filling is a common challenge for sorghum production in north-eastern Australia, central-western India, and sub-Saharan Africa. We show that the stay-green drought adaptation trait enhances sorghum grain yield under post-anthesis drought in these three regions. A positive relationship between stay-green and yield was generally found in breeding trials in north-eastern Australia that sampled 1668 unique hybrid combinations and 23 environments. Physiological studies in Australia also found that introgressing four individual stay-green (Stg1–4) quantitative trait loci (QTLs) into a senescent background reduced water demand before flowering and hence increased water supply during grain filling, resulting in higher grain yield relative to the senescent control. Studies in India found that various Stg QTLs affected both transpiration and transpiration efficiency, although these effects depended on the interaction between genetic background (S35 and R16) and individual QTLs. The yield variation unexplained by harvest index was related to transpiration efficiency in S35 (R2 = 0.29) and R16 (R2 = 0.72), and was related to total water extracted in S35 (R2 = 0.41) but not in R16. Finally, sixty-eight stay-green enriched lines were evaluated in six countries in sub-Saharan Africa during the 2013/14 season. Analysis of the data from Kenya indicates that stay-green and grain size were positively correlated at two sites: Kiboko (high yielding, r2=0.25) and Masongaleni (low yielding, r2=0.37). Together, these studies suggest that stay-green is a beneficial trait for sorghum production in the semi-arid tropics and is a consequence of traits altering the plant water budget.

Conversion of sub-tropical native vegetation to introduced conifer forest: Impacts on below-ground and above-ground carbon pools

Land-use change can have a major influence on soil organic carbon (SOC) and above-ground C pools. We assessed a change from native vegetation to introduced Pinus species plantations on C pools using eight paired sites. At each site we determined the impacts on 0–50 cm below-ground (SOC, charcoal C, organic matter C, particulate organic C, humic organic C, resistant organic C) and above-ground (litter, coarse woody debris, standing trees and woody understorey plants) C pools. In an analysis across the different study sites there was no significant difference (P > 0.05) in SOC or above-ground tree C stocks between paired native vegetation and pine plantations, although significant differences did exist at specific sites. SOC (calculated based on an equivalent soil mass basis) was higher in the pine plantations at two sites, higher in the native vegetation at two sites and did not differ for the other four sites. The site to site variation in SOC across the landscape was far greater than the variation observed with a change from native vegetation to introduced Pinus plantation. Differences between sites were not explained by soil type, although tree basal area was positively correlated with 0–50 cm SOC. In fact, in the native vegetation there was a significant linear relationship between above-ground biomass and SOC that explained 88.8% of the variation in the data. Fine litter C (0–25 mm diameter) tended to be higher in the pine forest than in the adjacent native vegetation and was significantly higher in the pine forest at five of the eight paired sites. Total litter C (0–100 mm diameter) increased significantly with plantation age (R2 = 0.64). Carbon stored in understorey woody plants (2.5–10 cm DBH) was higher in the native vegetation than in the adjacent pine forest. Total site C varied greatly across the study area from 58.8 Mg ha−1 at a native heathland site to 497.8 Mg ha−1 at a native eucalypt forest site. Our findings suggest that the effects of change from native vegetation to introduced Pinus sp. forest are highly site-specific and may be positive, negative, or have no influence on various C pools, depending on local site characteristics (e.g. plantation age and type of native vegetation).

The tolerance of steers (Bos taurus) to sorghum ergot (Claviceps africana) in a feedlot during the cooler months in sub-tropical Queensland

Two experiments tested the tolerance of steers (Bos taurus) to sorghum ergot (Claviceps africana) during cooler months in south-east Queensland. Sorghum grain containing 2.8% ergot and 28 mg/kg ergot alkaloids (84% dihydroergosine, 10% dihydroelymoclavine, 6% festuclavine) was incorporated into feedlot rations. In a previous study in summer–autumn, ergot (1.1–4.4 mg alkaloids/kg ration) severely reduced performance in steers when the temperature–humidity index (THI; dry bulb temperature °C + 0.36 dew-point temperature °C + 41.2) was ~70, whereas a THI of ~79 was tolerated by steers fed ergot-free rations. Experiment 1 was conducted in winter–spring, with rations containing 0, 2.8, 5.6, 8.2 or 11.2 mg ergot alkaloids/kg ration. All ergot inclusions depressed feed intake (14% average reduction) and growth rate (34% average reduction), even when the weekly average daily THI was less than 65. Rectal temperatures were occasionally elevated in ergot-fed steers (P < 0.05), primarily when the THI exceeded ~65. All ergot inclusions depressed plasma prolactin concentrations in steers. Experiment 2 was predominantly carried out in winter, with weekly average daily THI <65 throughout the experiment. Rations containing 0, 0.28, 0.55 or 1.1 mg ergot alkaloids/kg were fed for 4 weeks but produced no significant effect on feed intakes and growth rates of steers. Alkaloid concentrations were then changed to 0, 2.1, 4.3 and 1.1 mg/kg, respectively. Subsequently, feed intakes declined by 17.5% (P < 0.05), and growth rates by 28% (P > 0.05) in the group receiving 4.3 mg/kg alkaloid, compared with Controls. Plasma prolactin concentrations were depressed, relative to the Controls, by dietary alkaloid inclusion greater than 1.1 mg/kg, with alkaloid intake of 4.3 mg/kg causing the greatest reduction (P < 0.05). Cattle performance in these studies shows steers can tolerate up to ~2 mg ergot alkaloid/kg (0.2% ergot) in feedlot rations under low THI conditions (< ~60–65), but previous findings indicate a much lower threshold will apply at higher THI (>65).

The tolerance of steers (Bos taurus) to sorghum ergot (Claviceps africana) in a feedlot during the cooler months in sub-tropical Queensland

Two experiments tested the tolerance of steers (Bos taurus) to sorghum ergot (Claviceps africana) during cooler months in south-east Queensland. Sorghum grain containing 2.8% ergot and 28 mg/kg ergot alkaloids (84% dihydroergosine, 10% dihydroelymoclavine, 6% festuclavine) was incorporated into feedlot rations. In a previous study in summer–autumn, ergot (1.1–4.4 mg alkaloids/kg ration) severely reduced performance in steers when the temperature–humidity index (THI; dry bulb temperature °C + 0.36 dew-point temperature °C + 41.2) was ~70, whereas a THI of ~79 was tolerated by steers fed ergot-free rations. Experiment 1 was conducted in winter–spring, with rations containing 0, 2.8, 5.6, 8.2 or 11.2 mg ergot alkaloids/kg ration. All ergot inclusions depressed feed intake (14% average reduction) and growth rate (34% average reduction), even when the weekly average daily THI was less than 65. Rectal temperatures were occasionally elevated in ergot-fed steers (P < 0.05), primarily when the THI exceeded ~65. All ergot inclusions depressed plasma prolactin concentrations in steers. Experiment 2 was predominantly carried out in winter, with weekly average daily THI <65 throughout the experiment. Rations containing 0, 0.28, 0.55 or 1.1 mg ergot alkaloids/kg were fed for 4 weeks but produced no significant effect on feed intakes and growth rates of steers. Alkaloid concentrations were then changed to 0, 2.1, 4.3 and 1.1 mg/kg, respectively. Subsequently, feed intakes declined by 17.5% (P < 0.05), and growth rates by 28% (P > 0.05) in the group receiving 4.3 mg/kg alkaloid, compared with Controls. Plasma prolactin concentrations were depressed, relative to the Controls, by dietary alkaloid inclusion greater than 1.1 mg/kg, with alkaloid intake of 4.3 mg/kg causing the greatest reduction (P < 0.05). Cattle performance in these studies shows steers can tolerate up to ~2 mg ergot alkaloid/kg (0.2% ergot) in feedlot rations under low THI conditions (< ~60–65), but previous findings indicate a much lower threshold will apply at higher THI (>65).

Teratosphaeria pseudoeucalypti, new cryptic species responsible for leaf blight of Eucalyptus in subtropical and tropical Australia

Sub-tropical and tropical plantations of Eucalyptus grandis hybrids in eastern Australia have been severely affected by anamorphs of Teratosphaeria (formerly Kirramyces) causing a serious leaf blight disease. Initially the causal organism in Queensland, Australia, was identified as Teratosphaeria eucalypti, a known leaf parasite of endemic Eucalyptus spp. However, some inconsistencies in symptoms, damage and host range suggested that the pathogen in Queensland may be a new species. Isolates of T. eucalypti from throughout its known endemic range, including Queensland and New Zealand, where it is an exotic pathogen, were compared using multiple gene phylogenies. Phylogenetic studies revealed that the species responsible for leaf blight in Queensland represents a new taxon, described here as Teratosphaeria pseudoeucalypti. While the DNA sequence of T. pseudoeucalypti was more similar to T. eucalypti, the symptoms and cultural characteristics resembled that of T. destructans. The impact of this disease in central Queensland has increased annually and is the major threat to the eucalypt plantation industry in the region.

Optimization of aeroponic technology for future integration in quality potato seed production systems in tropical environments

Virus and soil borne pathogens negatively impact on the production of potatoes in tropical highland and sub-tropical environments, limiting supply of an increasingly popular and important vegetable in these regions. It is common for latent disease infected seed tubers or field grown cuttings to be used as potato planting material. We utilised an International Potato Centre technique, using aeroponic technology, to produce low cost mini-tubers in tropical areas. The system has been optimised for increased effectiveness in tropical areas. High numbers of seed tubers of cultivar Sebago (630) and Nicola per m2 (>900) were obtained in the first generation, and the system is capable of producing five crops of standard cultivars in every two years. Initial results indicate that quality seed could be produced by nurseries and farmers, therefore contributing to the minimisation of soil borne diseases in an integrated management plan. This technology reduces seed production costs, benefiting seed and potato growers. © ISHS.

First record of Nematospora coryli in Australia and its association with dry rot of Citrus

Nematospora (Eremothecium) coryli was isolated from Citrus and identified for the first time in Australia. This insect-transmitted yeast was associated with dry rot in cultivated and native Citrus fruits. Although N. coryli is known as a serious seed pathogen of many tropical and sub-tropical plants, evidence is presented that it has been present and undetected in Queensland for at least ninety years.

Odour Emissions from Tunnel Ventilated Poultry Housing

In Australia, factors such as local planning processes, urban encroachment into rural areas and intensification of the poultry industry have increased the potential for odour and dust nuisance. At present, accurate estimates of odour emissions from mechanically ventilated poultry housing systems do not exist for Australian conditions. This has made the poultry industry vulnerable to unsubstantiated criticism. Recently, the Australian poultry industry have made a significant investment in research to obtain accurate estimates of odour, dust and volatile chemical emission rates from typical poultry housing systems. This paper describes the measurement of odour emissions from tunnel ventilated poultry housing systems in different climatic zones in Queensland and Victoria, Australia (humid sub-tropical and Mediterranean respectively) during two seasons (summer and winter). Samples were collected at defined intervals over typical batch production cycles to define the odour emission profiles. These samples were analysed using dynamic olfactometry according to the Australian Standard 4323.3 to derive the odour concentration values. Ventilation rates were measured concurrently, allowing the calculation of odour emission rates. Odour concentration and emission rates were assessed in terms of ventilation rate, ambient and shed air temperature and relative humidity and litter moisture status. Odour emission rates varied with bird age. Seasonal differences in odour emission rate were also observed.

Ultraviolet radiation effects on fruit surface respiration and chlorophyll fluorescence

High-value fruit crops are exposed to a range of environmental conditions that can reduce fruit quality. Solar injury (SI) or sunburn is a common disorder in tropical, sub-tropical, and temperate climates and is related to: 1) high fruit surface temperature; 2) high visible light intensity; and, 3) ultraviolet radiation (UV). Positional changes in fruit that are caused by increased weight or abrupt changes that result from summer pruning, limb breakage, or other damage to the canopy can expose fruit to high solar radiation levels, increased fruit surface temperatures, and increased UV exposure that are higher than the conditions to which they are adapted. In our studies, we examined the effects of high fruit surface temperature, saturating photosynthetically-active radiation (PAR), and short-term UV exposure on chlorophyll fluorescence, respiration, and photosynthesis of fruit peel tissues from tropical and temperate fruit in a simulation of these acute environmental changes. All tropical fruits (citrus, macadamia, avocado, pineapple, and custard apple) and the apple cultivars 'Gala', 'Gold Rush', and 'Granny Smith' increased dark respiration (A0) when exposed to UV, suggesting that UV repair mechanisms were induced. The maximum quantum efficiency of photosystem II (Fv/Fm) and the quantum efficiency of photosystem II (ΦII) were unaffected, indicating no adverse effects on photosystem II (PSII). In contrast, 'Braeburn' apple had a reduced Fv/Fm with no increase in A0 on all sampling dates. There was a consistent pattern in all studies. When Fv/Fm was unaffected by UV treatment, A0 increased significantly. Conversely, when Fv/Fm was reduced by UV treatment, then A0 was unaffected. The pattern suggests that when UV repair mechanisms are effective, PSII is adequately protected, and that this protection occurs at the cost of higher respiration. However, when the UV repair mechanisms are ineffective, not only is PSII damaged, but there is additional short-term damage to the repair mechanisms, indicated by a lack of respiration to provide energy.

Development of key soil health indicators for the Australian banana industry

To improve the sustainability and environmental accountability of the banana industry there is a need to develop a set of soil health indicators that integrate physical, chemical and biological soil properties. These indicators would allow banana growers, extension and research workers to improve soil health management practices. To determine changes in soil properties due to the cultivation of bananas, a paired site survey was conducted comparing soil properties under conventional banana systems to less intensively managed vegetation systems, such as pastures and forest. Measurements were made on physical, chemical and biological soil properties at seven locations in tropical and sub-tropical banana producing areas. Soil nematode community composition was used as a bioindicator of the biological properties of the soil. Soils under conventional banana production tended to have a greater soil bulk density, with less soil organic carbon (C) (both total C and labile C), greater exchangeable cations, higher extractable P, greater numbers of plant-parasitic nematodes and less nematode diversity, relative to less intensively managed plant systems. The organic banana production systems at two locations had greater labile C, relative to conventional banana systems, but there was no significant change in nematode community composition. There were significant interactions between physical, chemical and nematode community measurements in the soil, particularly with soil C measurements, confirming the need for a holistic set of indicators to aid soil management. There was no single indicator of soil health for the Australian banana industry, but a set of soil health indicators, which would allow the measurement of soil improvements should include: bulk density, soil C, pH, EC, total N, extractable P, ECEC and soil nematode community structure.

Construction of microsatellite linkage maps for Corymbia

The genus Corymbia is closely related to the genus Eucalyptus, and like Eucalyptus contains tree species that are important for sub-tropical forestry. Corymbia's close relationship with Eucalyptus suggests genetic studies in Corymbia should benefit from transfer of genetic information from its more intensively studied relatives. Here we report a genetic map for Corymbia spp. based on microsatellite markers identified de novo in Corymbia sp or transferred from Eucalyptus. A framework consensus map was generated from an outbred F 2 population (n = 90) created by crossing two unrelated Corymbia torelliana x C. citriodora subsp. variegata F1 trees. The map had a total length of 367 cM (Kosambi) and was composed of 46 microsatellite markers distributed across 13 linkage groups (LOD 3). A high proportion of Eucalyptus microsatellites (90%) transferred to Corymbia. Comparative analysis between the Corymbia map and a published Eucalyptus map identified eight homeologous linkage groups in Corymbia with 13 markers mapping on one or both maps. Further comparative analysis was limited by low power to detect linkage due to low genome coverage in Corymbia, however, there was no convincing evidence for chromosomal structural differences because instances of non-synteny were associated with large distances on the Eucalyptus map. Segregation distortion was primarily restricted to a single linkage group and due to a deficit of hybrid genotypes, suggesting that hybrid inviability was one factor shaping the genetic composition of the F2 population in this inter-subgeneric hybrid. The conservation of microsatellite loci and synteny between Corymbia and Eucalyptus suggests there will be substantial value in exchanging information between the two groups.

Habitat dynamics in the bed sediments of an intermittent upland stream

The effects of the hydrological regime on temporal changes to physical characteristics of substratum habitat, sediment texture of surface sediments (<10 cm), were investigated in a sub-tropical headwater stream over four years. Surface discharge was measured together with vertical hydraulic gradient and groundwater depth in order to explore features of sediment habitat that extend beyond the streambed surface. Whilst the typical discharge pattern was one of intermittent base flows and infrequent flow events associated with monsoonal rain patterns, the study period also encompassed a drought and a one-in-a-hundred-year flood. Rainfall and discharge did not necessarily reflect the actual conditions in the stream. Although surface waters were persistent long after discharge ceased, the streambed was completely dry on several occasions. Shallow groundwater was present at variable depths throughout the study period, being absent only at the height of the drought. The streambed sediments were mainly gravels, sand and clay. Finer sediment fractions showed a marked change in grain size over time, although bedload movement was limited to a single high discharge event. In response to a low discharge regimen (drought), sediments characteristically showed non-normal distributions and were dominated by finer materials. A high-energy discharge event produced a coarsening of sands and a diminished clay fraction in the streambed. Particulate organic matter from sediments showed trends of build-up and decline with the high and low discharge regimes, respectively. Within the surface sediment intersticies three potential categories of invertebrate habitat were recognised, each with dynamic spatial and temporal boundaries.

Parthenium hysterophorus L. (Asteraceae)

Parthenium is a serious problem in several tropical and sub-tropical areas around the world and particularly an emerging problem in southern Africa. It is a Weed of National Significance in Australia. The chapter summarises current knowledge about the taxonomy, biology, distribution, ecology, impacts and biological control of the weed worldwide. Queensland has led attempts to achieve biological control of parthenium since it first began foreign exploration in 1977. Since then nine insects and two rusts have been released in Queensland. Some of these have since been, or will be, used by other countries. The program has brought significant benefits to Queensland through an increase in grass biomass in some areas. Instances of non-target attack by one agent, particularly in India, are discussed with the conclusion that the effects were ultimately negligible and possibly due to parthenium pollen lodging on the leaves of non-target plants. The insects introduced for parthenium have also given a measure of control for the very closely related weeds, ragweed and Noogoora burr. The paper draws a conclusion that local climatic conditions are very important when considering whether a successful agent in one country will be useful in a second country.

Chromolaena odorata (L.) King and Robinson (Asteraceae)

Chromolaena, or Siam weed, is a serious problem in several tropical and sub-tropical areas around the world. In our own region, it is a serious weed in New Guinea, East Timor and Indonesia and is also under an eradication regime in North Queensland. The chapter summarises current knowledge about the taxonomy, biology, distribution, ecology, impacts and control of the weed. Biological control has been a major multinational initiative against this weed in recent years and these efforts are described in some detail. Interestingly agents have not been universally effective because of weed biotype differences and climate. Considerable success has been achieved in New Guinea, principally with the tephritid fly Cecidocares connex and by the efforts of Michael Day, Rachel McFadyen and Graham Donnelly from Alan Fletcher Research Station.

Lantana camara Linn. (Verbenaceae)

Lantana is a serious problem in several tropical and sub-tropical areas around the world. It is a Weed of National Significance in Australia where it costs the grazing industry alone over $104 million per annum. The chapter summarises current knowledge about the taxonomy, biology, distribution, ecology, impacts and biological control of the weed worldwide. Attempts to achieve biological control of lantana date back to 1902 making this weed one of our oldest targets. Although control has been achieved in some areas of the world, in many other areas control is still sub-optimum. Factors thought to contribute to the difficulty of achieving biocontrol include the plant's biology, the wide genetic variation associated with hundreds of varieties or biotypes and the wide range of climatic habitats associated with the weed. This chapter provides a good summary of the present day position.