Silicon soil amendments for enhancing disease resistance while improving overall crop health for cucurbits in organic farming systems

Silicon soil amendments for enhancing disease resistance while improving overall crop health for cucurbits in organic farming systems

Summary

The purpose of this project is to address diseases in organic farming systems by targeting soil health as the fundamental principle towards achieving a healthy cucumber crop. The role of silicon, a naturally occurring but often not available and therefore deficient soil element, will be studied for enhancing the ability of cucumbers to resist or tolerate plant diseases. The element silicon has been demonstrated to reduce many soil-borne and foliar plant diseases in a number of crops, including rice, sugarcane, some vegetables and flowering ornamentals. Research also has shown that host resistance of susceptible and partially resistant cultivars can be augmented with silicon to the same general level as those containing complete genetic disease resistance. In this study, the effect of amending soils naturally low in plant available silicon will be investigated on the cucumber’s ability to tolerate or resist plant diseases, assess the role of plant generated phytolexins (low molecular weight antifungal compounds produced by the plant) as the potential mechanism for the cucumber’s response, determine if specific cover crops can be utilized to sequester silicon during the summer and winter fallow periods, and determine the economic costs and benefits of this soil amendment in the organic cropping system.

Experiments were started in the Fall 2007:

Objective 1. Survey natural organic farm ecosystem for diseases infecting cucumber amended without and with silicon.

The effect of silicon on naturally occurring cucumber diseases were tested at one organic farm, Hammock Hollow Herb Farm, and at the University of Florida’s organic research plots in Citra. These sites were chosen because they were found to be very low (< 4 ppm) in silicon. Previous research has demonstrated that soils less than 19 ppm are considered to be extremely low in this element. The cucumber cultivar ‘Straight Eight’ was selected for all experiments because it is very susceptible to a number of plant diseases. The experimental design was three silicon rates x two years with a two level cover crop factor as a split plot treatment. This cover crop factor will occur during the non-cash crop period when the plots will be split so that one half is seeded with either rye grass (winter non-cash crop period) or sorghum (summer non-cash crop period and the other half is left fallow. All treatments were arranged in a randomized complete block design with four replications. Silicon amendments were applied at three rates: 0, 200, 400 and 600 kilograms of elemental silicon/ha. Wollastonite (calcium silicate, CaSiO3), a naturally occurring mined mineral ore was the silicon source used. Cucumbers were grown following the NOPS. Approximately one week after transplanting ‘Straight Eight’ an outbreak of downy mildew (Pseudopernospora cubensis) occurred. Plants were monitored biweekly and assessed for the incidence and severity of downy mildew development. Plant tissue was collected for silicon analysis at transplanting, first flowering, first fruit set and two weeks before the last harvest. At first fruit set, fruit was harvested every other day for about 5 weeks. Currently, all data are being either processed or analyzed, and the results of this information will be forthcoming.

Collaborators: