PATH-ANALYSIS OF TOMATO YIELD COMPONENTS IN RELATION TO COMPETITION WITH BLACK AND EASTERN BLACK NIGHTSHADE

Path analysis is a statistical method for determining the magnitude an d direction of multiple effects on a complex process. We used path ana lysis to assess 1) the impact of black nightshade (Solanum nigrum L.) or eastern black nightshade (Solanum ptycanthum Dun.) competition on t he yield components of 'Heinz 6004' processing tomato (Lycopersicon es culentum Mill.) and 2) the relationship between tomato yield component s and total and marketable yield. Either black or eastern black nights hade was interplanted with tomatoes at population densities from 0 to 4.8/m2. Path analysis revealed that increasing weed population density led directly to fewer green and total fruit per plant, two components of marketable yield. However, the percentage of culls per plant and f ruit weight were not affected by nightshade population density. Using correlation coefficients alone would have lead to the erroneous conclu sion that the percentage of culls did not affect marketable yield; our path analysis demonstrated that decreasing the percentage of culls th rough breeding or cultural practices will strongly affect marketable y ield. The total number of fruit was the most important yield component in determining total and marketable yields per plant. Breeding and ma nagement practices that maximize fruit set, increase maturity at harve st, and decrease the percentage of culls would be expected to increase marketable yield.