Evaluation of fixed sample-size plans for Plutella xylostella (Lepidoptera: Plutellidae) on broccoli crops in Australia

Fixed sample-size plans for monitoring Plutella xylostella (L.) (Lepidoptera: Plutellidae) on broccoli and other Brassica vegetable crops are popular in Australia for their simplicity and ease of application. But the sample sizes used are often small, ≈10–25 plants per crop, and it may be that they fail to provide sufficient information upon which to base pest control decisions. We tested the performance of seven fixed sample-size plans (10, 15, 20, 30, 35, 40, and 45 plants) by resampling a large data set on P. xylostella in commercial broccoli crops. For each sample size, enumerative and presence-absence plans were assessed. The precision of the plans was assessed in terms of the ratio of the standard error to the mean; and at least 45 and 35 samples were necessary for the enumerative and presence-absence plans, respectively, to attain the generally accepted benchmark of ≤0.3. Sample sizes of 10–20 were highly imprecise. We also assessed the consequences of classifications based on action thresholds (ATs) of 0.2 and 0.8 larvae per plant for the enumerative case, and 0.15 and 0.45 proportion of plants of infested for the presence-absence case. Operating characteristic curves and investigations of the frequency of correct decisions suggest improvements in the performance of plans with increased sample size. In both the enumerative and presence-absence cases, the proportion of incorrect decisions was much higher for the lower of the two ATs assessed, and type II errors (i.e., failure to suggest pest control upon the AT is exceeded) generally accounted for the majority of this error. Type II errors are the most significant from a producer’s standpoint. Further consideration is necessary to determine what is an acceptable type II error rate.

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.

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.

Quantitative microbial risk assessment models for consumption of raw vegetables irrigated with reclaimed water

Quantitative microbial risk assessment models for estimating the annual risk of enteric virus infection associated with consuming raw vegetables that have been overhead irrigated with nondisinfected secondary treated reclaimed water were constructed. We ran models for several different scenarios of crop type, viral concentration in effluent, and time since last irrigation event. The mean annual risk of infection was always less for cucumber than for broccoli, cabbage, or lettuce. Across the various crops, effluent qualities, and viral decay rates considered, the annual risk of infection ranged from 10–3 to 10–1 when reclaimed-water irrigation ceased 1 day before harvest and from 10–9 to 10–3 when it ceased 2 weeks before harvest. Two previously published decay coefficients were used to describe the die-off of viruses in the environment. For all combinations of crop type and effluent quality, application of the more aggressive decay coefficient led to annual risks of infection that satisfied the commonly propounded benchmark of ≤10–4, i.e., one infection or less per 10,000 people per year, providing that 14 days had elapsed since irrigation with reclaimed water. Conversely, this benchmark was not attained for any combination of crop and water quality when this withholding period was 1 day. The lower decay rate conferred markedly less protection, with broccoli and cucumber being the only crops satisfying the 10–4 standard for all water qualities after a 14-day withholding period. Sensitivity analyses on the models revealed that in nearly all cases, variation in the amount of produce consumed had the most significant effect on the total uncertainty surrounding the estimate of annual infection risk. The models presented cover what would generally be considered to be worst-case scenarios: overhead irrigation and consumption of vegetables raw. Practices such as subsurface, furrow, or drip irrigation and postharvest washing/disinfection and food preparation could substantially lower risks and need to be considered in future models, particularly for developed nations where these extra risk reduction measures are more common.

Deterministic versus stochastic quantitative microbial Risk Assessment models for wastewater irrigation of food crops

Reuse of wastewater to irrigate food crops is being practiced in many parts of the world and is becoming more commonplace as the competition for, and stresses on, freshwater resources intensify. But there are risks associated with wastewater irrigation, including the possibility of transmission of pathogens causing infectious disease, to both workers in the field and to consumers buying and eating produce irrigated with wastewater. To manage these risks appropriately we need objective and quantitative estimates of them. This is typically achieved through one of two modelling approaches: deterministic or stochastic. Each parameter in a deterministic model is represented by a single value, whereas in stochastic models probability functions are used. Stochastic models are theoretically superior because they account for variability and uncertainty, but they are computationally demanding and not readily accessible to water resource and public health managers. We constructed models to estimate risk of enteric virus infection arising from the consumption of wastewater-irrigated horticultural crops (broccoli, cucumber and lettuce), and compared the resultant levels of risk between the deterministic and stochastic approaches. Several scenarios were tested for each crop, accounting for different concentrations of enteric viruses and different lengths of environmental exposure (i.e. the time between the last irrigation event and harvest, when the viruses are liable to decay or inactivation). In most situations modelled the two approaches yielded similar estimates of risk (within 1 order-of-magnitude). The two methods diverged most markedly, up to around 2 orders-of-magnitude, when there was large uncertainty associated with the estimate of virus concentration and the exposure period was short (1 day). Therefore, in some circumstances deterministic modelling may offer water resource managers a pragmatic alternative to stochastic modelling, but its usefulness as a surrogate will depend upon the level of uncertainty in the model parameters.

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.

Reducing the energy density of an entrée decreases children’s energy intake at lunch

Background: Strategies need to be developed to reduce preschool children’s energy intake.

Objective: To test the effect of reducing the energy density of an entrée on children’s ad libitum energy intake.

Subjects: Subjects were 2- to 5-year-old children (37 boys and 40 girls) in a university day-care facility.

Intervention: In this within-subjects crossover study, children were served a test lunch once per week for 6 weeks. Two versions of a macaroni and cheese entrée were formulated to differ in energy density while maintaining similar palatability. Each version was served to children three times. The higher-energy-density entrée had 2.0 kcal/g and the other entrée was 30% lower in energy density. Lunch, consumed ad libitum, also included broccoli, applesauce, and milk.

Main outcome measures: Food intake and energy intake were measured.

Statistical analyses: A mixed linear model tested effect of energy density of the entrée on food intake and energy intake. Results are reported as mean±standard error.

Results: Decreasing the energy density of the entrée by 30% significantly (P<0.0001) reduced children’s energy intake from the entrée by 25% (72.3±8.3 kcal) and total lunch energy intake by 18% (71.8±7.9 kcal). Children consumed significantly more of the lower-energy-density entrée (10.1±4.2 g; P<0.05). Children’s sex-specific body mass index–for-age percentiles did not affect the relationship between energy density of the entrée and children’s intakes.

Conclusions: Decreasing the energy density of a lunch entrée resulted in a reduction in children’s energy intake from the entrée and from the total meal. Reducing the energy density of foods may be an effective strategy to moderate children’s energy intake.

Salicylic acid and its role in defence against plasmodiophora brassicae

Salicylic acid is a crucial plant hormone involved defence responses against biotrophic pathogens. This thesis aimed to induce a defence response against the soil-borne biotroph, Plasmodiophora brassicae, by application of salicylic acid. Using broccoli and Arabidopsis thaliana pathway mutants I have shown that salicylic acid is essential in this interaction.

The associations of vegetable consumption with food mavenism, personal values, food knowledge and demographic factors

Background: Poor dietary choices, in particular low consumption of fruits and vegetables are associated with the prevalence of diet related diseases. Ways to increase consumption are urgently required. This paper examines the associations of demographic, psychographic and food knowledge variables with reported vegetable consumption. Methods: An online questionnaire was administered in late 2012 to a national sample 2146 Australians who were selected to represent the Australian population in terms of age, sex, education and location of residence. It was divided into sections which assessed food knowledge, food involvement, food mavenism, personal values and personality factors, demographic characteristics and reported consumption of 13 vegetables and the total number of servings of vegetables per day. Principal components analyses of the individual vegetable consumption ratings derived three forms of vegetable consumption scores. These and total serving per day were used as dependent variables in a structural equation model to identify pathways between them and their likely antecedents. Major findings: Three types of vegetable consumption were formed:. Salad vegetables (onion, tomato and lettuce);. Dinner vegetables (carrot, peas and beans); and 'Green' vegetables (cabbage, spinach broccoli and cauliflower). Food mavenism, food knowledge, food involvement and equality-universalist values mediated the relationships between demographics and conscientiousness and the vegetable consumption variables. Conclusions: The three types of vegetable consumption and total servings per day were associated with different antecedent pathways. The mediating roles of food mavenism, food knowledge, food involvement and equality-universalist values may present opportunities for health promotion and the horticultural industry to increase population vegetable intake. Further research is required to test these associations via experimental and longitudinal studies and qualitative investigation of the meaning and place of the three forms of vegetable consumption in people's daily lives is recommended.

The perceptual properties of the virgin olive oil phenolic oleocanthal are not associated with PROP taster status or dietary intake

Oleocanthal, has been identified as the sole oropharyngeal irritant in virgin olive oil with large individual variation in the perceived intensity of irritation. In this study participants were screened for sensitivity to the oropharyngeal irritation of oleocanthal and bitterness of 6-n-propylthiouracil (PROP), and categorized as hypersensitive (extremely sensitive) or hyposensitive (extremely insensitive). In addition, we determined if a relationship existed between sensitivity to oleocanthal and PROP and dietary intake. Participants (n = 168) took part in the initial screening for irritation to oleocanthal (gLMS range 1.70-70.31). From this sample 87 participants also completed a 4-day diet diary and rated the intensity of oropharyngeal irritation of olive oil and the bitterness of PROP using a gLMS scale. There was large variability in the perceived intensity of irritation from olive oil (gLMS range 4.26-57.15) and the perceived bitterness of PROP (gLMS range 0.0-62.52) with no association between PROP sensitivity and oleocanthal irritation (r = -0.04, p = 0.71). We report no relationship between oleocanthal sensitivity and total energy intake (r = 0.13, p = 0.29), carbohydrate intake (r = 0.12, p = 0.92), protein intake (r = -0.11, p = 0.37), or fat intake (r = 0.14, p = 0.22). There was no association between PROP sensitivity and total energy intake (r = -0.08, p = 0.46), carbohydrate intake (r = 0.12, p = 0.31), protein intake (r = 0.12, p = 0.32), or fat intake (r = -0.08, p = 0.53). We did find a significant negative correlation between PROP sensitivity status and the intake of broccoli (r = -0.24, p< 0.05). In the present study individual variation in sensitivity to the irritation of virgin olive oil or bitterness of PROP was not related to diet with the exception of PROP sensitivity and broccoli intake.