Heat stress effects on grain sorghum productivity-biology and modelling

Heat stress can cause sterility in sorghum and the anticipated increased frequency of high temperature events implies increasing risk to sorghum productivity in Australia. Here we summarise our research on specific varietal attributes associated with heat stress tolerance in sorghum and evaluate how they might affect yield outcomes in production environments by a crop simulation analysis. We have recently conducted a range of controlled environment and field experiments to study the physiology and genetics of high temperature effects on growth and development of sorghum. Sorghum seed set was reduced by high temperature effects (>36-38oC) on pollen germination around flowering, but genotypes differed in their tolerance to high temperature stress. Effects were quantified in a manner that enabled their incorporation into the APSIM sorghum crop model. Simulation analysis indicated that risk of high temperature damage and yield loss depended on sowing date, and variety. While climate trends will exacerbate high temperature effects, avoidance by crop management and genetic tolerance seems possible.

SorGSD: a sorghum genome SNP database

Sorghum (Sorghum bicolor) is one of the most important cereal crops globally and a potential energy plant for biofuel production. In order to explore genetic gain for a range of important quantitative traits, such as drought and heat tolerance, grain yield, stem sugar accumulation, and biomass production, via the use of molecular breeding and genomic selection strategies, knowledge of the available genetic variation and the underlying sequence polymorphisms, is required.

Fine Mapping of qDor7, a Major QTL Affecting Seed Dormancy in Sorghum (Sorghum bicolor (L.) Moench)

Seed dormancy is a key domestication trait for major crops, which is acquired in long-term systems development processes and enables the survival of plants in adverse natural conditions. It is a complex trait under polygenic control and is affected by endogenous and environmental factors. In the present study, a major seed dormancy QTL in sorghum (Sorghum bicolor (L.) Moench), qDor7, detected previously, was fine mapped using a large, multi-generational population. The qDor7 locus was delimited to a 96-kb region which contains 16 predicted gene models. These results lay a solid foundation for cloning qDor7. In addition, the functional markers tightly linked to the seed dormancy QTL may be used in marker-assisted selection for seed dormancy in sorghum.

Cryopreservation of avocado (Persea Americana Mill.) using somatic embryos

Avocado genetic resources are currently maintained in the form of field repositories at great cost and risk of natural disasters, pest and diseases. Cryopreservation offers a necessary, complimentary method that is safe, cost-effective and long-term. However, long-term maintenance and regeneration of plantlets from avocado somatic embryos has been a major barrier in the development of new avocado cultivars. In this study, two protocols for vitrification-based cryopreservation of avocado somatic embryos were investigated. Globular somatic embryos of two avocado cultivars were tested, revealing cultivar-dependent differences in desiccation tolerance and subsequent freezing resistance, possibly attributed to their size and culture age. A two-step regeneration system, involving an intermediate liquid phase step between subcultures in solid medium, significantly enhanced shoot development from somatic embryo tissue. This work will add considerable value towards cryopreservation of avocado somatic embryos for germplasm conservation and the generation of new and improved avocado cultivars.

Domestication and the storage starch biosynthesis pathway: Signatures of selection from a whole sorghum genome sequencing strategy

Next-generation sequencing of complete genomes has given researchers unprecedented levels of information to study the multifaceted evolutionary changes that have shaped elite plant germplasm. In conjunction with population genetic analytical techniques and detailed online databases, we can more accurately capture the effects of domestication on entire biological pathways of agronomic importance. In this study, we explore the genetic diversity and signatures of selection in all predicted gene models of the storage starch synthesis pathway of Sorghum bicolor, utilizing a diversity panel containing lines categorized as either ‘Landraces’ or ‘Wild and Weedy’ genotypes. Amongst a total of 114 genes involved in starch synthesis, 71 had at least a single signal of purifying selection and 62 a signal of balancing selection and others a mix of both. This included key genes such as STARCH PHOSPHORYLASE 2 (SbPHO2, under balancing selection), PULLULANASE (SbPUL, under balancing selection) and ADP-glucose pyrophosphorylases (SHRUNKEN2, SbSH2 under purifying selection). Effectively, many genes within the primary starch synthesis pathway had a clear reduction in nucleotide diversity between the Landraces and wild and weedy lines indicating that the ancestral effects of domestication are still clearly identifiable. There was evidence of the positional rate variation within the well-characterized primary starch synthesis pathway of sorghum, particularly in the Landraces, whereby low evolutionary rates upstream and high rates downstream in the metabolic pathway were expected. This observation did not extend to the wild and weedy lines or the minor starch synthesis pathways.

Nitrogen use efficiency in summer sorghum grown on clay soils

Nitrogen fertilizer inputs dominate the fertilizer budget of grain sorghum growers in northern Australia, so optimizing use efficiency and minimizing losses are a primary agronomic objective. We report results from three experiments in southern Queensland sown on contrasting soil types and with contrasting rotation histories in the 2012-2013 summer season. Experiments were designed to quantify the response of grain sorghum to rates of N fertilizer applied as urea. Labelled 15N fertilizer was applied in microplots to determine the fate of applied N, while nitrous oxide (N2O) emissions were continuously monitored at Kingaroy (grass or legume ley histories) and Kingsthorpe (continuous grain cropping). Nitrous oxide is a useful indicator of gaseous N losses. Crops at all sites responded strongly to fertilizer N applications, with yields of unfertilized treatments ranging from 17% to 52% of N-unlimited potential. Maximum yields ranged from 4500 (Kupunn) to 5450 (Kingaroy) and 8010 (Kingsthorpe) kg/ha. Agronomic efficiency (kg additional grain produced/kg fertilizer N applied) at the optimum N rate on the Vertosol sites was 23 (80 N, Kupunn) to 25 (160N, Kingsthorpe), but 40-42 on the Ferrosols at Kingaroy (70-100N). Cumulative N2O emissions ranged from 0.44% (Kingaroy legume) to 0.93% (Kingsthorpe) and 1.15% (Kingaroy grass) of the optimum fertilizer N rate at each site, with greatest emissions from the Vertosol at Kingsthorpe. The similarity in N2O emissions factors between Kingaroy and Kingsthorpe contrasted markedly with the recovery of applied fertilizer N in plant and soil. Apparent losses of fertilizer N ranged from 0-5% (Ferrosols at Kingaroy) to 40-48% (Vertosols at Kupunn and Kingsthorpe). The greater losses on the Vertosols were attributed to denitrification losses and illustrate the greater risks of N losses in these soils in wet seasonal conditions.

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.

Domestication and the storage starch biosynthesis pathway: signatures of selection from a whole sorghum genome sequencing strategy

Next-generation sequencing of complete genomes has given researchers unprecedented levels of information to study the multifaceted evolutionary changes that have shaped elite plant germplasm. In conjunction with population genetic analytical techniques and detailed online databases, we can more accurately capture the effects of domestication on entire biological pathways of agronomic importance. In this study, we explore the genetic diversity and signatures of selection in all predicted gene models of the storage starch synthesis pathway of Sorghum bicolor, utilizing a diversity panel containing lines categorized as either ‘Landraces’ or ‘Wild and Weedy’ genotypes. Amongst a total of 114 genes involved in starch synthesis, 71 had at least a single signal of purifying selection and 62 a signal of balancing selection and others a mix of both. This included key genes such as STARCH PHOSPHORYLASE 2 (SbPHO2, under balancing selection), PULLULANASE (SbPUL, under balancing selection) and ADP-glucose pyrophosphorylases (SHRUNKEN2, SbSH2 under purifying selection). Effectively, many genes within the primary starch synthesis pathway had a clear reduction in nucleotide diversity between the Landraces and wild and weedy lines indicating that the ancestral effects of domestication are still clearly identifiable. There was evidence of the positional rate variation within the well-characterized primary starch synthesis pathway of sorghum, particularly in the Landraces, whereby low evolutionary rates upstream and high rates downstream in the metabolic pathway were expected. This observation did not extend to the wild and weedy lines or the minor starch synthesis pathways.

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).

Preparation and In Vitro Release of Drug-Loaded Microparticles for Oral Delivery Using Wholegrain Sorghum Kafirin Protein

Kafirin microparticles have been proposed as an oral nutraceutical and drug delivery system. This study investigates microparticles formed with kafirin extracted from white and raw versus cooked red sorghum grains as an oral delivery system. Targeted delivery to the colon would be beneficial for medication such as prednisolone, which is used in the management of inflammatory bowel disease. Therefore, prednisolone was loaded into microparticles of kafirin from the different sources using phase separation. Differences were observed in the protein content, in vitro protein digestibility, and protein electrophoretic profile of the various sources of sorghum grains, kafirin extracts, and kafirin microparticles. For all of the formulations, the majority of the loaded prednisolone was not released in in vitro conditions simulating the upper gastrointestinal tract, indicating that most of the encapsulated drug could reach the target area of the lower gastrointestinal tract. This suggests that these kafirin microparticles may have potential as a colon-targeted nutraceutical and drug delivery system.

Cryopreservation of somatic embryos for avocado germplasm conservation

Presently avocado germplasm is conserved ex situ in the form of field repositories across the globe including Australia. The maintenance of germplasm in the field is costly, labour and land intensive, exposed to natural disasters and always at the risk of abiotic and biotic stresses. The aim of this study was to overcome these problems using cryopreservation to store avocado (Persea americana Mill.) somatic embryos (SE). Two vitrification-based methods of cryopreservation were optimised (cryovial and droplet-vitrification) using four avocado cultivars (‘A10′, ‘Reed’, ‘Velvick’ and ‘Duke-7′). SE of the four cultivars were stored for short-term (one hour) in liquid nitrogen using the cryovial-vitrification method and showed a viability of 91%, 73%, 86% and 80% respectively. While when using the droplet vitrification method viabilities of 100%, 85% and 93% were recorded for ‘A10′, ‘Reed’ and ‘Velvick’. For long-term storage, SE of cultivars ‘A10′, ‘Reed’ and ‘Velvick’ were successfully recovered with viability of 65–100% after 3 months of LN storage. For cultivar ‘Reed’ and ‘Velvick’ SE were recovered after 12 months of LN storage with viability of 67% and 59%, respectively. The outcome of this work contributes towards the establishment of a cryopreservation protocol that is applicable across multiple avocado cultivars.

Heterosis in locally adapted sorghum genotypes and potential of hybrids for increased productivity in contrasting environments in Ethiopia

Increased productivity in sorghum has been achieved in the developed world using hybrids. Despite their yield advantage, introduced hybrids have not been adopted in Ethiopia due to the lack of adaptive traits, their short plant stature and small grain size. This study was conducted to investigate hybrid performance and the magnitude of heterosis of locally adapted genotypes in addition to introduced hybrids in three contrasting environments in Ethiopia. In total, 139 hybrids, derived from introduced seed parents crossed with locally adapted genotypes and introduced R lines, were evaluated. Overall, the hybrids matured earlier than the adapted parents, but had higher grain yield, plant height, grain number and grain weight in all environments. The lowland adapted hybrids displayed a mean better parent heterosis (BPH) of 19%, equating to 1160 kg ha− 1 and a 29% mean increase in grain yield, in addition to increased plant height and grain weight, in comparison to the hybrids derived from the introduced R lines. The mean BPH for grain yield for the highland adapted hybrids was 16% in the highland and 52% in the intermediate environment equating to 698 kg ha− 1 and 2031 kg ha− 1, respectively, in addition to increased grain weight. The magnitude of heterosis observed for each hybrid group was related to the genetic distance between the parental lines. The majority of hybrids also showed superiority over the standard check varieties. In general, hybrids from locally adapted genotypes were superior in grain yield, plant height and grain weight compared to the high parents and introduced hybrids indicating the potential for hybrids to increase productivity while addressing farmers' required traits.

Sorghum Crop Modeling and Its Utility in Agronomy and Breeding

Crop models are simplified mathematical representations of the interacting biological and environmental components of the dynamic soil–plant–environment system. Sorghum crop modeling has evolved in parallel with crop modeling capability in general, since its origins in the 1960s and 1970s. Here we briefly review the trajectory in sorghum crop modeling leading to the development of advanced models. We then (i) overview the structure and function of the sorghum model in the Agricultural Production System sIMulator (APSIM) to exemplify advanced modeling concepts that suit both agronomic and breeding applications, (ii) review an example of use of sorghum modeling in supporting agronomic management decisions, (iii) review an example of the use of sorghum modeling in plant breeding, and (iv) consider implications for future roles of sorghum crop modeling. Modeling and simulation provide an avenue to explore consequences of crop management decision options in situations confronted with risks associated with seasonal climate uncertainties. Here we consider the possibility of manipulating planting configuration and density in sorghum as a means to manipulate the productivity–risk trade-off. A simulation analysis of decision options is presented and avenues for its use with decision-makers discussed. Modeling and simulation also provide opportunities to improve breeding efficiency by either dissecting complex traits to more amenable targets for genetics and breeding, or by trait evaluation via phenotypic prediction in target production regions to help prioritize effort and assess breeding strategies. Here we consider studies on the stay-green trait in sorghum, which confers yield advantage in water-limited situations, to exemplify both aspects. The possible future roles of sorghum modeling in agronomy and breeding are discussed as are opportunities related to their synergistic interaction. The potential to add significant value to the revolution in plant breeding associated with genomic technologies is identified as the new modeling frontier.