The Risk Of Pythium Aphanidermatum In Hydroponic Baby-Leaf Spinach Production

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Pythium aphanidermatum has been identified as the main obstacle/risk in the production of hydroponically grown babyleaf spinach. This organism is so prevalent that even crops grown in fresh nutrient solution will often show signs of Pythium damage at harvest time. Previous studies have identified nutrient solution temperature as a key factor in determining the growth and development of Pythium. The goal of this study was to estimate the risk of Pythium outbreaks under different hydroponic production strategies. To provide these estimates, a greenhouse simulation model was coupled with a spinach growth and Pythium disease model. Through Monte-Carlo simulation, estimates of the time between and the seasonality of outbreaks were determined. The strategies modeled included using nutrient solution temperatures of 18, 20, 22, 24C and unregulated temperature. Within these temperature regimes different harvesting schedules were examined. Assuming supplemental lighting control to a daily light integral of 17 mol m-2, crop durations of 12, 14 and 16 days in pond were examined. To quantify the importance of supplemental lighting, crop durations were replaced with target harvest biomasses. The target harvest biomasses were then achieved without supplemental lighting. A further strategy examined within the fixed duration conditions was the use of a two pond system where crop cohorts older than half the total crop duration were moved to a separate pond. A nutrient solution temperature of 18C with a 12 day crop duration resulted in an expected frequency of Pythium outbreak of 0.032 per year, compared to 1.47 outbreaks per year for a 16 day crop grown without nutrient solution temperature control. The same conditions without supplemental lighting resulted in outbreaks frequencies of 7.9 per year and 16 per year respectively. Under a two pond system the expected frequency of outbreak was approximately halved at 18C and increased with increasing temperature until there was no difference between the one and two pond systems for the uncontrolled temperature conditions.

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