Host selection and utilisation of Sonchus oleraceus (Asteraceae) by Helicoverpa armigera (Lepidoptera : Noctuidae): A genetic analysis

The cotton bollworm (Helicoverpa armigera) prefers the common sowthistle (Sonchus oleraceus L.) to cotton (Gossypium hirsutum L.), sorghum (Sorghum bicolor L.) and maize (Zea mays L.) for oviposition in the field in Australia. Using the common sowthistle and cotton as host plants, we carried out this study to evaluate genetic variation in both oviposition preference and larval growth and genetic correlation between maternal preference and larval performance. There was a significant genetic component of phenotypic variation in both characters, and the heritability of oviposition preference was estimated as 0.602. Helicoverpa armigera larvae survived slightly better and grew significantly faster on common sowthistle than on cotton, but genetic correlation between maternal preference and larval growth performance was not detectable. Instead, larval growth performance on the two hosts changed with families, which renders the interaction between family and host plant significant. As a result, the genetic correlation between mean values of larval growth across the two host species was not different from zero. These results are discussed in the context of the relationship between H. armigera and the common sowthistle and the polyphagous behaviour of this insect in general.

Differentiation of peanut seedborne potyviruses and curcumoviruses by RT-PCR

Seedborne peanut viruses pose important constraints to peanut production and safe movement of germ plasm. They also pose a risk of accidental introduction into previously disease-free regions. We have developed reverse transcription-polymerase chain reaction (RT-PCR) assays based on identical cycling parameters which identified peanut stripe, Peanut mottle, Peanut stunt, and Cucumber mosaic viruses through production of specific DNA fragments of 234 bp, 327 bp, 390 bp, and 133 bp, respectively. Assay sensitivity in the picogram range was achieved. The two potyviruses and two cucumoviruses could be differentiated using duplex RT-PCR assays. These assays should be useful for testing peanut leaves or seeds for virus identification in epidemiological studies, seed testing or in post-entry quarantine.

Promoters for pregenomic RNA of banana streak badnavirus are active for transgene expression in monocot and dicot plants

Two putative promoters from Australian banana streak badnavirus (BSV) isolates were analysed for activity in different plant species. In transient expression systems the My (2105 bp) and Cv (1322 bp) fragments were both shown to have promoter activity in a wide range of plant species including monocots (maize, barley, banana, millet, wheat, sorghum), dicots (tobacco, canola, sunflower, Nicotiana benthamiana, tipu tree), gymnosperm (Pinus radiata) and fern (Nephrolepis cordifolia). Evaluation of the My and Cv promoters in transgenic sugarcane, banana and tobacco plants demonstrated that these promoters could drive high-level expression of either the green fluorescent protein (GFP) or the beta -glucuronidase (GUS) reporter gene (uidA) in vegetative plant cells. In transgenic sugarcane plants harbouring the Cv promoter, GFP expression levels were comparable or higher (up to 1.06% of total soluble leaf protein as GFP) than those of plants containing the maize ubiquitin promoter (up to 0.34% of total soluble leaf protein). GUS activities in transgenic in vitro-grown banana plants containing the My promoter were up to seven-fold stronger in leaf tissue and up to four-fold stronger in root and corm tissue than in plants harbouring the maize ubiquitin promoter. The Cv promoter showed activities that were similar to the maize ubiquitin promoter in in vitro-grown banana plants, but was significantly reduced in larger glasshouse-grown plants. In transgenic in vitro-grown tobacco plants, the My promoter reached activities close to those of the 35S promoter of cauliflower mosaic virus (CaMV), while the Cv promoter was about half as active as the CaMV 35S promoter. The BSV promoters for pregenomic RNA represent useful tools for the high-level expression of foreign genes in transgenic monocots.

Advances in application of climate prediction in agriculture

Agricultural ecosystems and their associated business and government systems are diverse and varied. They range from farms, to input supply businesses, to marketing and government policy systems, among others. These systems are dynamic and responsive to fluctuations in climate. Skill in climate prediction offers considerable opportunities to managers via its potential to realise system improvements (i.e. increased food production and profit and/or reduced risks). Realising these opportunities, however, is not straightforward as the forecasting skill is imperfect and approaches to applying the existing skill to management issues have not been developed and tested extensively. While there has been much written about impacts of climate variability, there has been relatively little done in relation to applying knowledge of climate predictions to modify actions ahead of likely impacts. However, a considerable body of effort in various parts of the world is now being focused on this issue of applying climate predictions to improve agricultural systems. In this paper, we outline the basis for climate prediction, with emphasis on the El Nino-Southern Oscillation phenomenon, and catalogue experiences at field, national and global scales in applying climate predictions to agriculture. These diverse experiences are synthesised to derive general lessons about approaches to applying climate prediction in agriculture. The case studies have been selected to represent a diversity of agricultural systems and scales of operation. They also represent the on-going activities of some of the key research and development groups in this field around the world. The case studies include applications at field/farm scale to dryland cropping systems in Australia, Zimbabwe, and Argentina. This spectrum covers resource-rich and resource-poor farming with motivations ranging from profit to food security. At national and global scale we consider possible applications of climate prediction in commodity forecasting (wheat in Australia) and examine implications on global wheat trade and price associated with global consequences of climate prediction. In cataloguing these experiences we note some general lessons. Foremost is the value of an interdisciplinary systems approach in connecting disciplinary Knowledge in a manner most suited to decision-makers. This approach often includes scenario analysis based oil simulation with credible models as a key aspect of the learning process. Interaction among researchers, analysts and decision-makers is vital in the development of effective applications all of the players learn. Issues associated with balance between information demand and supply as well as appreciation of awareness limitations of decision-makers, analysts, and scientists are highlighted. It is argued that understanding and communicating decision risks is one of the keys to successful applications of climate prediction. We consider that advances of the future will be made by better connecting agricultural scientists and practitioners with the science of climate prediction. Professions involved in decision making must take a proactive role in the development of climate forecasts if the design and use of climate predictions are to reach their full potential. (C) 2001 Elsevier Science Ltd. All rights reserved.

Increasing profits and reducing risks in crop production using participatory systems simulation approaches

The development of cropping systems simulation capabilities world-wide combined with easy access to powerful computing has resulted in a plethora of agricultural models and consequently, model applications. Nonetheless, the scientific credibility of such applications and their relevance to farming practice is still being questioned. Our objective in this paper is to highlight some of the model applications from which benefits for farmers were or could be obtained via changed agricultural practice or policy. Changed on-farm practice due to the direct contribution of modelling, while keenly sought after, may in some cases be less achievable than a contribution via agricultural policies. This paper is intended to give some guidance for future model applications. It is not a comprehensive review of model applications, nor is it intended to discuss modelling in the context of social science or extension policy. Rather, we take snapshots around the globe to 'take stock' and to demonstrate that well-defined financial and environmental benefits can be obtained on-farm from the use of models. We highlight the importance of 'relevance' and hence the importance of true partnerships between all stakeholders (farmer, scientists, advisers) for the successful development and adoption of simulation approaches. Specifically, we address some key points that are essential for successful model applications such as: (1) issues to be addressed must be neither trivial nor obvious; (2) a modelling approach must reduce complexity rather than proliferate choices in order to aid the decision-making process (3) the cropping systems must be sufficiently flexible to allow management interventions based on insights gained from models. The pro and cons of normative approaches (e.g. decision support software that can reach a wide audience quickly but are often poorly contextualized for any individual client) versus model applications within the context of an individual client's situation will also be discussed. We suggest that a tandem approach is necessary whereby the latter is used in the early stages of model application for confidence building amongst client groups. This paper focuses on five specific regions that differ fundamentally in terms of environment and socio-economic structure and hence in their requirements for successful model applications. Specifically, we will give examples from Australia and South America (high climatic variability, large areas, low input, technologically advanced); Africa (high climatic variability, small areas, low input, subsistence agriculture); India (high climatic variability, small areas, medium level inputs, technologically progressing; and Europe (relatively low climatic variability, small areas, high input, technologically advanced). The contrast between Australia and Europe will further demonstrate how successful model applications are strongly influenced by the policy framework within which producers operate. We suggest that this might eventually lead to better adoption of fully integrated systems approaches and result in the development of resilient farming systems that are in tune with current climatic conditions and are adaptable to biophysical and socioeconomic variability and change. (C) 2001 Elsevier Science Ltd. All rights reserved.

Stay-green: A consequence of the balance between supply and demand for nitrogen during grain filling?

Retention of green leaf area in grain sorghum under post-anthesis drought, known as stay-green, is associated with greater biomass production, lodging resistance and yield. The stay-green phenomenon can be examined at a cell, leaf, or whole plant level. At a cell level, the retention of chloroplast proteins such as LHCP2, OEC33 and Rubisco until late in senescence has been reported in sorghum containing the KS19 source of stay-green, indicating that photosynthesis may be maintained for longer during senescence in these genotypes. At a leaf level, longevity of photosynthetic apparatus is intimately related to nitrogen (N) status. At a whole plant level, stay-green can be viewed as a consequence of the balance between N demand by the grain and N supply during grain filling. To examine some of these concepts, nine hybrids varying in the B35 and KS19 sources of stay-green were grown under a postanthesis water deficit. Genotypic variation in delayed onset and reduced rate of leaf senescence were explained by differences in specific leaf nitrogen (SLN) and N uptake during grain filling. Matching N supply from age-related senescence and N uptake during grain tilling with grain N demand found that the shortfall in N supply for grain filling was greater in the senescent than stay-green hybrids, resulting in more accelerated leaf senescence in the former. We hypothesise that increased N uptake by stay-green hybrids is a result of greater biomass accumulation during grain filling in response to increased sink demand (higher grain numbers) which, in turn, is the result of increased radiation use efficiency and transpiration efficiency due to higher SLN. Delayed leaf senescence resulting from higher SLN should, in turn, allow snore carbon and nitrogen to be allocated to the roots of stay-green hybrids during grain filling, thereby maintaining a greater capacity to extract N from the soil compared with senescent hybrids.

Development of a mungbean (Vigna radiata) RFLP linkage map and its comparison with lablab (Lablab purpureus) revelas a high level of colinearity between the two genomes

A genetic linkage map of mungbean (Vigna radiata, 2n = 2x = 22) consisting of 255 RFLP loci was developed using a recombinant inbred population of 80 individuals. The population was derived from an intersubspecific cross between the cultivated mungbean variety 'Berken' and a wild mungbean genotype 'ACC 41' (V radiata subsp. sublobata). The total length of the map, which comprised 13 linkage groups, spanned 737.9 cM with an average distance between markers of 3.0 cM and a maximum distance between linked markers of 15.4 cM. The mungbean map was compared to a previously published map of lablab (Lablab purpureus, 2n = 2x = 24) using a common set of 65 RFLP probes. In contrast to some other comparative mapping studies among members of the Fabaceae, where a high level of chromosomal rearrangement has been observed, marker order between mungbean and lablab was found to be highly conserved. However, the two genomes have apparently accumulated a large number of duplications/deletions after they diverged.

Dietary supplementation with vitamin E modulates avian intestinal immunity

The effect of dietary vitamin E on immunoglobulin A (IgA) antibody production, which acts as the first line of defence at the intestinal mucosa, has not been evaluated in chickens. In the present study the impact of the inclusion of supplementary levels of vitamin E to the diet, on total and antigen-specific IgA antibody titres, T-cell subsets and Ia+ cells, was assessed. From hatching, chickens received a maize-based diet which was supplemented with either 25, 250, 2500 or 5000 mg dl-alpha-tocopherol acetate/kg. Primary immunisation with tetanus toxoid (T. toxoid) emulsified in a vegetable oil-in-water adjuvant was administered by the intraperitoneal route at 21 d of age. At 35 d of age all birds received an oral booster vaccination of T. toxoid. Significantly higher total IgA antibody titres were present in the day 42 intestinal scrapings of birds receiving the 5000 mg/kg vitamin E-supplemented diet (VESD) (P=0.05) and a notable increase was observed in birds receiving the 250 mg/kg VESD (P=0.06). At days 21 and 42 total serum IgA antibody titres of birds receiving the 250 mg/kg VESD was significantly higher (P

Practical and economic advantages of choice feeding systems for laying poultry

Poultry can be managed under different feeding systems, depending on the husbandry skills and the feed available. These systems include the following: (1) a complete dry feed offered as a mash ad libitum; (2) the same feed offered as pellets or crumbles ad libitum; (3) a complete feed with added whole grain; (4) a complete wet feed given once or twice a day; (5) a complete feed offered on a restricted basis; (6) choice feeding. Of all these, an interesting alternative to offering complete diets is choice feeding which can be applied on both a small or large commercial scale. Under choice feeding or free-choice feeding birds are usually offered a choice between three types of feedstuffs: (a) an energy source (e.g. maize, rice bran, sorghum or wheat); (b) a protein source (e.g. soyabean meal, meat meal, fish meal or coconut meal) plus vitamins and minerals and (c), in the case of laying hens, calcium in granular form (i.e. oyster-shell grit). This system differs from the modern commercial practice of offering a complete diet comprising energy and protein sources, ground and mixed together. Under the complete diet system, birds are mainly only able to exercise their appetite for energy. When the environmental temperature varies, the birds either over- or under-consume protein and calcium. The basic principle behind practising choice feeding with laying hens is that individual hens are able to select from the various feed ingredients on offer and compose their own diet, according to their actual needs and production capacity. A choice-feeding system is of particular importance to small poultry producers in developing countries, such as Indonesia, because it can substantially reduce the cost of feed. The system is flexible and can be constructed in such a way that the various needs of a flock of different breeds, including village chickens, under different climates can be met. The system also offers a more effective way to use home-produced grain, such as maize, and by-products, such as rice bran, in developing countries. Because oyster-shell grit is readily available in developing countries at lower cost than limestone, the use of cheaper oyster-shell grit can further benefit small-holders in these countries. These benefits apart, simpler equipment suffices when designing and building a feed mixer on the farm, and transport costs are lower. If whole (unground) grain is used, the intake of which is accompanied by increased efficiency of feed utilisation, the costs of grinding, mixing and many of the handling procedures associated with mash and pellet preparation are eliminated. The choice feedstuffs can all be offered in the current feed distribution systems, either by mixing the ingredients first or by using a bulk bin divided into three compartments.

A synthetic xylanase as a novel reporter in plants

Transient gene expression assays are often used to screen promoters before stable transformation. Current transient quantification methods have several problems, including a lack of reporter gene stability and expense. Here we report a synthetic, codon-optimised xylanase gene (sXynA) as a reporter gene for quantitative transient analyses in plants. Azurine-crosslinked xylan (AZCL-xylan) was used as a substrate for assaying xylanase activity. The enzymatic nature of the protein allows for sensitive assays at the low levels of transgene protein found in transiently transformed tissue extracts. The xylanase (XYN) protein is stable, activity slopes are linear over long time periods and assays are cost-effective. Coupled with the GUSPlus reporter gene, the XYN reporter allows sensitive and accurate quantification of gene control sequences in transient expression systems.

Relationship between oviposition preference and offspring performance in Australian Helicoverpa armigera (Hubner) (Lepidoptera : Noctuidae)

We investigated the oviposition preference and larval performance of Helicoverpa armigera under laboratory conditions to determine if the oviposition preference of individual females on maize, cowpea and cotton correlates with offspring performance on the leaves of the same host plants. The host-plant preference hierarchy of females did not correlate with their offspring performance. Female moths chose host plants that contributed less to their offspring fitness. Plant effects accounted for the largest amount of variation in offspring performance, while the effects of female (family) was low. The offspring of most females (80%, n = 10) were broadly similar, but 20% (two out of 10), showed marked difference in their offspring performance across the host-plant species. Similarly, there was no relation between larval feeding preference and performance. However, like most laboratory experiments, our experi-mental design does not allow the evaluation of ecological factors (for example, natural enemies, host abundance, etc.) that can play an important role in larval performance in the field. Overall, the results highlight the importance of carrying out preference performance analysis on the individual or family level, rather than pooling individuals to obtain average population data.

Influence of planting date, method of handling and seed size on supersweet sweet corn seed quality

A supersweet sweet corn hybrid, Pacific H5, was planted at weekly intervals (P-1 to P-5) in spring in South-Eastern Queensland. All plantings were harvested at the same time resulting in immature seed for the last planting (P-5). The seed was handled by three methods: manual harvest and processing (M-1), manual harvest and mechanical processing (M-2) and mechanical harvest and processing (M-3), and later graded into three sizes (small, medium and large). After eight months storage at 12-14degreesC, seed was maintained at 30degreesC with bimonthly monitoring of germination for fourteen months and seed damage at the end of this period. Seed quality was greatest for M-1 and was reduced by mechanical processing but not by mechanical harvesting. Large and medium seed had higher germination due to greater storage reserves but also more seed damage during mechanical processing. Immature seed from premature harvest (P-5) had poor quality especially when processed mechanically and reinforced the need for harvested seed to be physiologically mature.

Linking physiological and architectural models of cotton

Despite the strong influence of plant architecture on crop yield, most crop models either ignore it or deal with it in a very rudimentary way. This paper demonstrates the feasibility of linking a model that simulates the morphogenesis and resultant architecture of individual cotton plants with a crop model that simulates the effects of environmental factors on critical physiological processes and resulting yield in cotton. First the varietal parameters of the models were made concordant. Then routines were developed to allocate the flower buds produced each day by the crop model amongst the potential positions generated by the architectural model. This allocation is done according to a set of heuristic rules. The final weight of individual bolls and the shedding of buds and fruit caused by water, N, and C stresses are processed in a similar manner. Observations of the positions of harvestable fruits, both within and between plants, made under a variety of agronomic conditions that had resulted in a broad range of plant architectures were compared to those predicted by the model with the same environmental inputs. As illustrated by comparisons of plant maps, the linked models performed reasonably well, though performance of the fruiting point allocation and shedding algorithms could probably be improved by further analysis of the spatial relationships of retained fruit. (C) 2002 Elsevier Science Ltd. All rights reserved.

Model studies on the role of citrate, malate and pectin esterification on the enzymatic degradation of Al- and Ca-pectate gels: possible implications for Al-tolerance

Aluminium (At) tolerance in plants may be conferred by reduced binding of Al in the cell wall through low root cation exchange capacity (CEC) or by organic acid exudation. Root CEC is related to the degree of esterification (DE) of pectin in the cell wall, and pectin hydrolysis plays a role in cell expansion. Therefore, it was hypothesised that Al-tolerant plants with a low root CEC maintain pectin hydrolysis in the presence of Al, allowing cell expansion to continue. Irrespective of the DE, binding of Al to pectin reduced the enzymatic hydrolysis of Al-pectin gels by polygalacturonase (E.C. 3.2.1.15). Pectin gels with calcium (Ca) were slightly hydrolysed by polygalacturonase. It was concluded, therefore, that Al tolerance conferred by low root CEC is not mediated by the ability to maintain pectin hydrolysis. Citrate and malate, but not acetate, effectively dissolved Al-pectate gel and led to hydrolysis of the dissolved pectin by polygalacturonase. The organic acids did not dissolve Ca-pectate, nor did they increase pectin hydrolysis by polygalacturonase. It was concluded that exudation of some organic acids can remove Al bound to pectin and this could alleviate toxicity, constituting a tolerance mechanism. (C) 2003 Editions scientitiques et medicales Elsevier SAS. All rights reserved.

Simulation supplements field studies to determine no-till dryland corn population recommendations for semiarid western Nebraska

In a 2-yr multiple-site field study conducted in western Nebraska during 1999 and 2000, optimum dryland corn (Zea mays L.) population varied from less than 1.7 to more than 5.6 plants m(-2), depending largely on available water resources. The objective of this study was to use a modeling approach to investigate corn population recommendations for a wide range of seasonal variation. A corn growth simulation model (APSIM-maize) was coupled to long-term sequences of historical climatic data from western Nebraska to provide probabilistic estimates of dryland yield for a range of corn populations. Simulated populations ranged from 2 to 5 plants m(-2). Simulations began with one of three levels of available soil water at planting, either 80, 160, or 240 mm in the surface 1.5 m of a loam soil. Gross margins were maximized at 3 plants m(-2) when starting available water was 160 or 240 mm, and the expected probability of a financial loss at this population was reduced from about 10% at 160 mm to 0% at 240 mm. When starting available water was 80 mm, average gross margins were less than $15 ha(-1), and risk of financial loss exceeded 40%. Median yields were greatest when starting available soil water was 240 mm. However, perhaps the greater benefit of additional soil water at planting was reduction in the risk of making a financial loss. Dryland corn growers in western Nebraska are advised to use a population of 3 plants m(-2) as a base recommendation.