Biology subjects

Murray-Watson, R. E.

Publications and source records attributed to Murray-Watson, R. E..

4 recordsLinked to original sources

bioRxiv2022

Expanding growers' choice of disease management options can promote suboptimal social outcomes

1Previous models of growers decision-making during epidemics have unrealistically limited disease management choices to just two options. Here, we expand previous game-theoretic models of grower decision-making to include three control options: crop that is either tolerant, resistant, or susceptible to disease. Using Tomato Yellow Leaf Curl Virus (TYLCV) as a case study, we investigate how growers can be incentivised to use different control options to achieve socially-optimal outcomes. To do this, we consider the efforts of a "social planner" who moderates the price of crops. We find that subsidising tolerant crop costs the social planner more in subsidies, as its use encourages selfishness and widespread adoption. Subsidising resistant crop, however, provides widespread benefits by reducing the prevalence of disease across the community of growers, including those that do not control, reducing the number of subsidies required from the social planner. We then use Gini coefficients to measure equitability of each subsidisation scheme. This study highlights how grower behaviour can be altered using crop subsidies to promote socially-optimal outcomes during epidemics.

ecology↗

bioRxiv2022

Tolerant crops increase growers' yields but promote selfishness: how the epidemiology of disease resistant and tolerant varieties affect grower behaviour

1O_LIDisease management often involves genetically improved crops. Resistant varieties are less susceptible, and so less likely to act as reservoirs of inoculum. Tolerant varieties can be highly susceptible, but limit yield loss for those who grow them. Population-scale effects of deploying resistant or tolerant varieties have received little consideration from epidemiologists. C_LIO_LIWe examined how tolerant and resistant crop have opposing consequences upon the uptake of control using a behavioural model based on strategic-adaptive expectations. Growers compared last seasons profit with an estimate of what could be expected from the alternative crop type, thereby assessing whether to alter their strategy for the next season. C_LIO_LITolerant crop only benefited growers using it, decreasing yields for others. This incentivises widespread use via a negative feedback loop. Resistant crop was more widely beneficial, with reduced population-scale disease pressure leading to increased yields for all. However, this positive externality allows growers who do not deploy resistant crop to "free-ride" upon the management of others. C_LIO_LIThis work highlights how a community of growers responds to the contrasting incentives caused by tolerant and resistant crop varieties, and how this leads to very distinct effects on yields and population-scale deployment. C_LI

ecology↗

bioRxiv2021

It ain't what you do, it's what drives why you do it: how the basis of growers' decision making affects the effectiveness of disease control

While the spread of plant disease depends strongly on biological factors driving transmission, it also has a human dimension. Disease control depends on decisions made by individual growers, who are in turn influenced by a broad range of factors. Despite this, human behaviour has rarely been included in plant epidemic models. Considering Cassava Brown Streak Disease, we model how the perceived increase in profit due to disease management influences participation in clean seed systems (CSS). Our models are rooted in game theory, with growers making strategic decisions based on the expected profitability of different control strategies. We find that both the information used by growers to assess profitability and the perception of economic and epidemiological parameters influence long-term participation in the CSS. Over-estimation of infection risk leads to lower participation in the CSS, as growers perceive that paying for the CSS will be futile. Additionally, even though good disease management can be achieved through the implementation of CSS, and a scenario where all controllers use the CSS is achievable when growers base their decision on the average of their entire strategy, CBSD is rarely eliminated from the system. These results are robust to stochastic and spatial effects. Our work highlights the importance of including human behaviour in plant disease models, but also the significance of how that behaviour is included. 1 Author SummaryModels of plant disease epidemics rarely account for the behaviour of growers undertaking management decisions. However, such behaviour is likely to have a large impact on disease spread. Growers may choose to participate in a control scheme based on the perceived economic advantages, acting to maximise their own profit. Yet if many growers participate in a control scheme, their participation will lower the probability of others becoming infected and consequently disincentivise them from participating themselves. How these dynamics play out will alter the course of the epidemic. We incorporate these economic considerations into an epidemic model of Cassava Brown Streak Disease using two broad approaches, which vary in the amount of information provided to growers. We also consider the effect of grower misperception of economic and epidemiological parameters. Our work shows that both the inclusion of grower behaviour, and its means of inclusion, affect disease dynamics, and highlights the importance of including grower decision-making in plant epidemic models.

ecology↗

bioRxiv2019

Spatiotemporal dynamics and modelling support the case for area-wide management of citrus greasy spot in a Brazilian smallholder farming region

Citrus greasy spot (CGS), caused by Zasmidium citri, induces premature defoliation and yield loss in Citrus spp. CGS epidemiology is well understood in areas of high humidity such as Florida (USA), but remains unaddressed in Brazil, despite differing climatic conditions and disease management practices. We characterize the spatiotemporal dynamics of CGS in the Reconcavo of Bahia, Brazil, focusing on four hierarchical levels (quadrant, plant, grove and region). A survey conducted in 19 municipalities showed that disease is found throughout the entire region with a prevalence (i.e. proportion of affected sampling units) of 100% in groves and plants, and never lower than 70% on leaves. Index of dispersion (D) values suggest the spatial pattern of symptomatic units lies somewhere between random and regular. This was confirmed by the parameters of the binary power law for plants and their quadrants (log(A)<0 and b<1). Variability in disease severity at different plant heights (0.7 m, 1.3 m and 2.0 m) was tested, but no consistent differences were observed. We introduce a simple compartmental model synthesising the epidemiology of the disease, in order to motivate and guide further research. The data we have collected allow such a model to be parameterised, albeit with some ambiguity over the proportion of new infections that result from inoculum produced within the grove vs. external sources of infection. By extending our model to include two populations of growers - those who control and those who do not - coupled by the spread of airborne inoculum, we investigate likely performance of the type of cultural controls that would be accessible to citrus growers in Northeastern Brazil. Our model shows that control via removal of the key source of inoculum - i.e. fallen leaves - can be very effective. However, successful control is likely to require area-wide strategies, in which a large proportion of growers actively manage disease.

ecology↗