Date of Graduation


Document Type


Degree Type



Davis College of Agriculture, Natural Resources and Design


Applied and Environmental Biology

Committee Chair

James B. Kotcon.


The objective of this research was to determine if disease on susceptible tomato cultivars is reduced by intercropping with resistant cultivars. A second objective was to investigate the mechanism of the disease reduction observed. Early blight (caused by Alternaria solani) rate of disease increase and lesion expansion were lower on susceptible tomato cv. 'Brandywine' when intercropped with resistant cv. 'Juliet' than with 'Brandywine' monoculture in both the field and greenhouse. Yield from 'Brandywine' plants was 17.3% greater when intercropped with 'Juliet' than when grown in monoculture. Reduction in lesion expansion on 'Brandywine' when intercropped with 'Juliet' suggests an interaction initiating a defense response in 'Brandywine'. Increase in foliar salicylic acid (SA) concentration was greater in 'Juliet' than in 'Brandywine' following inoculation with A. solani, indicating that SA accumulation may contribute to increased resistance in 'Juliet'. In greenhouse experiments, there was a trend toward increased production of salicylic acid content in the leaves of 'Brandywine' when planted with resistant cultivars compared to those next to 'Brandywine', however this was not statistically significant. In addition, SA production 72 hours after inoculation with A. solani in the greenhouse was correlated with resistance in the field on 16 cultivars of tomato. A reduction in the spread of the parasitic nematode Meloidogyne incognita to 'Brandywine' when interplanted with root knot disease resistant cultivar 'Celebrity' was observed in the greenhouse. Results suggest that intercropping with resistant cultivars is effective in reducing diseases on susceptible cultivars caused by diverse pathogens. The main mechanism of disease reduction is attributed to reduced susceptible leaf material in the plot, however the potential for induced resistance in 'Brandywine' is discussed.