The relationship between brown and corky root rot caused by Pyrenochaeta lycopersici and yield loss in tomatoes established by the use of artificially infested soils

In an experiment conducted in a commercial glasshouse, tomato plants were grown in pots containing soils infested with a range of levels of Pyrenochaeta lycopersici in a randomized block design. There was found to be a negative correlation ( r = -0.93) between total yield in kg per plant (y) and % disease severity ( x ) recorded 8 weeks after planting when the disease data were exponentiated; the best fit was obtained by the equation v = 45.7–42.3 x ^0.006 Fruit number was reduced by 0.2% for each 1% increase in the disease, but a stronger correlation was obtained by the equation y (fruit number) = 417–368 x 0.006
In a separate trial, the relationship between disease severity 8 weeks after planting and yield loss was shown to be affected by soil type. Early-season loss of potential yield was found to be lower in sandy soil than in peat and clay. By the end of the season, loss in total potential yield was greater in peat soil than in clay. The effect that soil conditions can have in modifying the relationship between disease severity and yield loss is discussed.