Me. Mcgiffen et al., PATH-ANALYSIS OF TOMATO YIELD COMPONENTS IN RELATION TO COMPETITION WITH BLACK AND EASTERN BLACK NIGHTSHADE, Journal of the American Society for Horticultural Science, 119(1), 1994, pp. 6-11
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.