A risk assessment framework for seed degeneration: Informing an integrated seed health strategy for vegetatively-propagated crops

Thomas-Sharma, Sara; Andrade-Piedra, Jorge; Yepes, Mónica Carvajal; Nopsa, John Fredy Hernández; Jeger, Michael; Jones, R. A. C.; Kromann, Peter; Legg, J.P.; Yuen, Jonathan; Forbes, Gregory A.; Garrett, Karen A.

doi:10.1101/105361

Cited by 11 publications

(21 citation statements)

References 52 publications

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“…Varieties Kabode and Polista were compared, with and without net tunnels, in an analysis with simplifying assumptions about the relationship between disease incidence and yield. Yield in the scenario analysis is sensitive to changes in management such as roguing rates and positive selection (Thomas-Sharma et al, 2017). Actionable economic thresholds can also be difficult to formulate without good models of yield loss and good information about farmer willingness to pay.…”

Section: Discussionmentioning

confidence: 99%

“…To model the likely influence of the management components evaluated in this study on seed degeneration over the course of 10 seasons, virus incidence data were used to estimate parameters in the model from Thomas-Sharma et al (2017). Four treatment combinations were compared using data from Mwasonge, the 'high virus' location.…”

Section: Modelling Of Seed Degenerationmentioning

confidence: 99%

“…Kabode were grown in the net tunnel, with seed continuously replaced from the net tunnel for each season, were compared with treatments where seed for these two cultivars was continuously grown and obtained from the open field. Virus incidence data collected for the last three generations (generations 6, 7 and 8) for each of these four treatment combinations were used to parameterize the proportional change in infection due to the combined effect of environment, host and management (Thomas-Sharma et al, 2017). Simulation experiments were carried out in the R programming environment (R Core Team, 2018) using the custom package seedHealth (https://www.garrettlab.com/softwa re/).…”

Section: Modelling Of Seed Degenerationmentioning

confidence: 99%

“…In an integrated seed health strategy, choice of seed and on-farm management should be considered together to optimize management of seed degeneration in vegetatively propagated crops (Thomas-Sharma et al, 2016). This study used the observed rates of seed degeneration in the model by Thomas-Sharma et al (2017) to evaluate the likely long-term patterns of degeneration and when purchase of quality-declared seed would be motivated, as a function of management decisions. Once estimates of the rate of infection for particular system combinationsvariety, location and managementare available, these can be used in scenario modelling to understand economic thresholds for purchase of quality-declared seed (Thomas-Sharma et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

“…This study used the observed rates of seed degeneration in the model by Thomas-Sharma et al (2017) to evaluate the likely long-term patterns of degeneration and when purchase of quality-declared seed would be motivated, as a function of management decisions. Once estimates of the rate of infection for particular system combinationsvariety, location and managementare available, these can be used in scenario modelling to understand economic thresholds for purchase of quality-declared seed (Thomas-Sharma et al, 2017). The models include the level of host resistance, environmental conduciveness, vector management, roguing, the amount of previously infected seed material, and rates of reversion to healthy status.…”

Section: Introductionmentioning

confidence: 99%

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Efficiency of insect‐proof net tunnels in reducing virus‐related seed degeneration in sweet potato

et al. 2019

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Virus‐related degeneration constrains production of quality sweet potato seed, especially under open field conditions. Once in the open, virus‐indexed seed is prone to virus infection leading to decline in performance. Insect‐proof net tunnels have been proven to reduce virus infection under researcher management. However, their effectiveness under farmer‐multiplier management is not known. This study investigated the ability of net tunnels to reduce degeneration in sweet potato under farmer‐multiplier management. Infection and degeneration were assessed for two cultivars, Kabode and Polista, grown in net tunnels and open fields at two sites with varying virus pressures. There was zero virus incidence at both sites during the first five generations. Sweet potato feathery mottle virus and sweet potato chlorotic stunt virus were present in the last three generations, occurring singly or in combination to form sweet potato virus disease. Virus infection increased successively, with higher incidences recorded at the high virus pressure site. Seed degeneration modelling illustrated that for both varieties, degeneration was reduced by the maintenance of vines under net tunnel conditions. The time series of likely degeneration based on a generic model of yield loss suggested that, under the conditions experienced during the experimental period, infection and losses within the net tunnels would be limited. By comparison, in the open field most of the yield could be lost after a small number of generations without the input of seed with lower disease incidence. Adopting the technology at the farmer‐multiplier level can increase availability of clean seed, particularly in high virus pressure areas.

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Section: Discussionmentioning

confidence: 99%

Section: Modelling Of Seed Degenerationmentioning

confidence: 99%

Section: Modelling Of Seed Degenerationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Efficiency of insect‐proof net tunnels in reducing virus‐related seed degeneration in sweet potato

et al. 2019

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Potato Seed Systems

Forbes¹,

Charkowski

Andrade-Piedra

et al. 2020

The Potato Crop

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Good quality seed is almost universally considered a requirement for high productivity in all potato production systems. Much of the yield gap currently constraining productivity in low-income countries is attributed to the poor quality of seed. Potato seed sector development is thus a major concern of governments, researchers, development agencies, and civil society organizations. Potato seed systems are often characterized as formal or informal, although the informal seed system is complex and particularly in low income countries there are many linkages between the two systems. Informal seed potato systems in the Andes have existed for centuries, and for a number of reasons often produce seed of relatively high quality. In other low-income countries, informal systems produce seed of variable and frequently poor quality, contributing to very large yield gaps, characteristic of those areas. In regions of high potato productivity (e.g., the USA and Europe), formal systems, with seed of certified high quality, are dominant, although some productions subsectors (e.g., organic producers) often use seed that is not certified. Efforts to implement formal seed systems in low-income countries have been largely unsuccessful; consequently the vast majority of low-resource potato farmers source their seed via the informal system. Sectors of the development community

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Optimal Control of Plant Disease Epidemics with Clean Seed Usage

et al. 2021

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The distribution and use of pathogen-free planting material ("clean seeds") is a promising method to control plant diseases in developing countries. We address the question of minimizing disease prevalence in plants through the optimal usage of clean seeds. We consider the simplest possible S-I model together with a simple economic criterion to be maximized. The static optimization problem shows a diversity of possible outcomes depending on economical and epidemiological parameters. We derive a simple condition showing to what extent subsidizing clean seeds relative to the epidemiological features of the disease may help eradicate or control the disease. Then we consider dynamic optimal control and Pontryagin's maximum principle to study the optimal usage of clean seeds to control the disease. The dynamical results are comparable to the static ones and are even simpler in some sense. In particular, the condition on the critical subsidy rate that makes clean seed usage economically viable is unchanged from the static optimization case. We discuss how these results may apply to the control of maize lethal necrosis (MLN) in East-Africa.

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A risk assessment framework for seed degeneration: Informing an integrated seed health strategy for vegetatively-propagated crops

Abstract: 24Pathogen build-up in vegetative planting material, termed seed degeneration, is a major problem 25 in many low-income countries. When smallholder farmers use seed produced on-farm or 26 acquired outside certified programs, it is often infected. We introduce a risk assessment

Cited by 11 publications

References 52 publications

Efficiency of insect‐proof net tunnels in reducing virus‐related seed degeneration in sweet potato

Efficiency of insect‐proof net tunnels in reducing virus‐related seed degeneration in sweet potato

Potato Seed Systems

Optimal Control of Plant Disease Epidemics with Clean Seed Usage

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