Salicylic acid suppression of clubroot in broccoli (Brassicae oleracea var. italica) caused by the obligate biotroph Plasmodiophora brassicae

The obligate soil-borne biotroph Plasmodiophora brassicae has a significant economic impact on Brassicaceae crops. The pathogen severely disrupts the roots by inducing the production of galls which leads to malformation and reduced growth of the roots and a reduced ability to take up water and nutrients. Control of P. brassicae is difficult because it has a number of survival and dissemination strategies that involve both motile and resting stages that need to be targeted by any control agent. We investigated, under controlled conditions and in glasshouse and field experiments, the potential of salicylic acid (SA), a key phytohormone, that is required for defence against certain biotic and abiotic stresses, to reduce infection by P. brassicae in broccoli (Brassicae oleracea var. italica). Under controlled conditions in a growth cabinet exogenous application of SA to roots resulted in its transport systemically to the leaves where it promoted the up-regulation of the pathogenesis related genes PR-1 and PR-2 in an SAR-like response as early as 24 h post-treatment. Concentrations of SA >20 mM reduced significantly both shoot and root weights when applied exogenously but lower concentrations had little measureable effect on plant growth. When SA was applied to plants above 5 mM there was a significant reduction (25-65 %) in gall formation 6 weeks post-inoculation with P. brassicae, indicating that the pathogen was being controlled by the addition of SA. A combination of SA and JA was also shown to reduce severity (25-35 %) of disease associated with P. brassicae. These findings indicate that there may be SA inducible mechanisms in B. oleracea that if fine-tuned could provide enhanced resistance to clubroot disease.

Studies on physiologic specialisation of albugo candida causing white blister on broccoli in Victoria

White blister caused by oomycete Albugo candida (Pers. Ex. Lev.) Kuntze, (AC), is an important disease affecting many cruciferous hosts, including vegetable brassicas. The outbreaks of white blister in broccoli and cauliflower crops (Brassica oleracea var. italica and var. botrytis) in Southern Australia in the last three years led to restrictions on movement of fresh produce and seedlings from the disease-affected areas. Current classification of AC races is based on physiologic specialisation of this pathogen. Race 9 has been identified to cause white blister on B. oleracea in the USA. We report on specialisation of AC causing disease in Victorian broccoli crops and the use of molecular tools for the separation of AC races. In a glasshouse, 12 Brassicaceae species/varieties replicated 6 times, were inoculated twice at the fully developed cotyledon stage with a distilled water suspension of zoosporangia (1x104 per ml) collected from a single broccoli leaf. Two weeks after inoculation the incidence of white blister on cotyledons and seedling leaves of cauliflower, broccoli, black mustard and Indian mustard was 79.7, 78.4, 73.7 and 6.9% respectively. Cabbage plants were symptomless indicating that further specialisation of the pathogen may have occurred in Australia. High disease incidence among black mustard plants shows that the Australian isolate differs from overseas AC race 9. The interaction of a number of B. oleracea varieties to a range of AC isolates from various hosts will be investigated. Degenerate primers are now being used to amplify actin and β-tubulin genes to identify race specific polymorphisms in AC isolates from three different hosts (wild radish, Chinese cabbage, and broccoli). Differing PCR amplification efficiencies from broccoli and wild radish isolates using degenerate actin primers indicates sequence differences in the two isolates. The fragments are now being cloned and sequenced for race comparison.

Races of Albugo candida causing white blister rust on brassica vegetables in Australia

Albugo Candida races of Australian isolates from B. oleracea var. italica (broccoli), B. rapa var. pekinensis (pak choi) and var. chinensis (Chinese cabbage), and Capsella bursa-pastoris (shepherd's purse) were identified on a set of Brassicaceae hosts. Isolates from broccoli were identified as A. candida race 9 (Ac 9), from pak choi and Chinese cabbage as the sub-race V of Ac 7 or as a mixed population of sub-races A and V of the same race. Isolates from Shepherd's purse were identified as Ac 4. Australian Ac 9 isolates caused white blister disease on broccoli, broccolini, cauliflower, Brussels sprout and other related Brassicaceae hosts including B. nigra (black mustard), B. napus (oilseed rape), and on B. rapa (turnip rape) 'Torch' (a differential host of Ac 7). All cultivars of cabbage (B. oleracea var. capitata) and one new broccoli 'Booster' inoculated with isolates from broccoli were immune to the isolate tested. This result indicates that the Australian A. candida varies from the European one that causes disease on cabbage as well as on other B. oleracea varieties and additionally on shepherd's purse and an American one that causes disease on cabbage. The genotype of B. nigra tested was susceptible to both Ac 9 and Ac 7. This result indicates that B. nigra can serve as a host for both races. This study provides the first record of white blister disease on B. napus ('Hobson' and 'Regent') in Australia.

Investigation of plasmodiophora brassicae (clubroot disease) in vegetable brassica using arabidopsis thaliana as a model system

Clubroot, caused by Plasmodiophora brassicae, is the most devastating soil-borne disease of vegetable brassicas. It occurs all over the world and is responsible for crop losses of up to 10% every year. In Australia, the disease is being managed effectively with chemicals and cultural practices, but ideally control can be improved in the long term by the introduction of resistant cultivars. The life cycle ofP. brassicae and mode of action of plant resistance has not been fully elucidated because of the technical difficulties of working with an obligate, soil-borne plant pathogen. However, Arabidopsis thaliana, which is a host ofP. brassicae, has great potential as a model system for studying the life cycle, the infection process and development of resistance. We have developed a sand-liquid-culture system for growing Arabidopsis that allows easy observation of all life stages and, most importantly, the primary plasmodial stages within the root hair. The method was first optimised for observations of the lifecycle of the pathogen in a susceptible Arabidopsis ecotype (Col-3) where all stages of the lifecycle have now been observed and characterised. Further screening of Arabidopsis ecotypes for disease resistance has utilised one of the most virulent Australian pathotypes of brassica (ECD number 16/19/31). To date, Arabidopsis ecotype Ta-0 has shown a level of tolerance to the disease even though the roots get infected. It has been reported earlier that resistance toP. brassicae in Arabidopsis is due to one or a small number of genes. To examine changes in gene expression during the early, critical stages of infection, RNA was extracted from the susceptible and resistant ecotypes at two time points, 4 days and 17 days after inoculation. Microarray analysis will be used to investigate genome wide changes in gene expression during infection but also to identify candidate genes that may confer resistance to Australian isolates of the pathogen.

Optimal lag-length choice in stable and unstable VAR models under situations of homoscedasticity and ARCH

The performance of different information criteria - namely Akaike, corrected Akaike (AICC), Schwarz-Bayesian (SBC), and Hannan-Quinn - is investigated so as to choose the optimal lag length in stable and unstable vector autoregressive (VAR) models both when autoregressive conditional heteroscedasticity (ARCH) is present and when it is not. The investigation covers both large and small sample sizes. The Monte Carlo simulation results show that SBC has relatively better performance in lag-choice accuracy in many situations. It is also generally the least sensitive to ARCH regardless of stability or instability of the VAR model, especially in large sample sizes. These appealing properties of SBC make it the optimal criterion for choosing lag length in many situations, especially in the case of financial data, which are usually characterized by occasional periods of high volatility. SBC also has the best forecasting abilities in the majority of situations in which we vary sample size, stability, variance structure (ARCH or not), and forecast horizon (one period or five). frequently, AICC also has good lag-choosing and forecasting properties. However, when ARCH is present, the five-period forecast performance of all criteria in all situations worsens.

A structural VAR analysis of electricity consumption and real GDP : evidence from the G7 countries

In this paper, we depart from the literature on electricity consumption–real GDP in that for the first time we examine the reaction of real GDP to shocks in electricity consumption. To achieve this goal, we use the structural vector autoregressive (SVAR) model and examine the impact of electricity consumption shocks on real GDP for the G7 countries. We find that except for the USA, electricity consumption has a statistically significant positive impact on real GDP over short horizons. This finding implies that except for the USA, electricity conservation policies will hurt real GDP in the G7 countries.

Temporal causality between human capital and real income in cointegrated VAR processes : empirical evidence from China, 1960-1999

This article examines the causal relationship between human capital and real income using data for China from 1960 to 1999. In the long run there is unidirectional Granger causality running from human capital to real income, while in the short run there is unidirectional Granger causality running from real income to human capital

A factor-augmented VAR approach : the effect of a rise in the US personal income tax rate on the US and Canada

In this paper a factor-augmented vector autoregressive (FAVAR) model is estimated to characterize the dynamic effects of shocks in the personal income tax rate in the United States on United States and Canadian economies. The representation and the estimate of the FAVAR model is based on Stock and Watson (2005) and the shocks are recovered applying the identification scheme proposed by Bernanke et al. (2005); this method allows impulse response functions to be generated for all the variables in the dataset and provides a description of the domestic and international transmission mechanisms of United States movements in the personal income tax rate. A distinguishing feature of our model is the disaggregation of traded goods sector where imports and exports are disaggregated into 12 and 13 industries, respectively. This provides extra information on the domestic and international transmission mechanism across the two countries. The results show that the FAVAR approach generates a reasonable characterisation of the effects of United States movements in the US personal income tax rate on the United States economy and its transmission to the Canadian economy.

Optimisation of Bacillus thuringiensis var. israelensis (Vectobac) applications for the blackfly control programme on the Orange River, South Africa

The Orange River, South Africa’s largest river, is a critical water resource for the country. In spite of the clear economic benefits of regulating river flows through a series of impoundments, one of the significant undesirable ecological consequences of this regulation has been the regular outbreaks of the pest blackfly species Simulium chutteri and S. damnosum s.l. (Diptera: Simuliidae). The current control programme, carried out by the South African National Department of Agriculture, uses regular applications, by helicopter, of the target-specific bacterial larvicide Bacillus thuringiensis var. israelensis. While cost-benefit analyses show significant benefits to the control programme, benefits could potentially be further increased through applying smaller volumes of larvicide in an optimised manner, which incorporates upstream residual amounts of pesticide through downstream carry. Using an optimisation technique applied in the West African Onchocerciasis Control Programme, to a 136 km stretch of the Orange River which includes 31 blackfly breeding sites, we demonstrate that 28.5% less larvicide could be used to potentially achieve the same control of blackfly. This translates into potential annual savings of between R540 000 and R1 800 000. A comparison of larvicide volumes estimated using traditional vs. optimised approaches at different discharges, illustrates that the savings on optimisation decline linearly with increasing flow volumes. Larvicide applications at the lowest discharge considered (40 m³·s^-1) showed the greatest benefits from optimisations, with benefits remaining but decreasing to a theoretical 30% up to median flows of 100 m3·s-1. Given that almost 70% of flows in July are less than 100 m³·s^-1, we suggest that an optimised approach is appropriate for the Orange River Blackfly Control Programme, particularly for flow volumes of less than 100 m³·s^-1. We recommend that trials be undertaken over two reaches of the Orange River, one using the traditional approach, and another using the optimised approach, to test the efficacy of using optimised volumes of B.t.i.

Sperm cells of the pollen tubes of Brassica : ultrastructure and isolation

Sperm cells of pollen tubes grown both in vivo and in vitro form a male germ unit. Extensions from both sperm cells of each pollen tube are closely associated with the tube nucleus. A high yield (2.7 × 104. 20 mg−1 pollen grains germinated) of intact sperm cells was obtained following release by osmotic shock from pollen tubes grown in vitro. Structural integrity of isolated sperm was maintained by isolation at low temperature in an osmotically balanced medium. At 4° C many isolated sperm pairs were still enclosed within the pollentube inner plasma membrane. Sperm cells not enclosed within this membrane no longer remained connected as a pair. During isolation vesicles formed on the sperm cell surface from disruption of the fibrillar components bridging the periplasmic space. Both in the pollen tube and after isolation the sperm nucleus is in close association with at least one region of the sperm plasma membrane. Sperm isolated at room temperature showed the presence of nucleopores, and nuclei were euchromatic, instead of heterochromatic as in intact sperm in the pollen tube.