Date of Award

Winter 1979

Project Type


Program or Major

Plant Science

Degree Name

Doctor of Philosophy


The objectives of this study were to determine if a relationship exists between selected morpho-physiological traits and general combining ability for yield in determinate and indeterminate tomato inbred lines, to determine if a relationship exists between these traits and the average probability that an inbred can produce transgressive segregates, and to determine if the levels of some physiological traits that contribute to yield differ between growth habits.

Among determinate inbreds, general combining ability for yield is significantly correlated with yield and fruit number but not with harvest index, photosynthesis, specific leaf weight, or average fruit size. Among indeterminates, general combining ability for yield is significantly correlated only with yield.

Regression analysis indicates that inbred yield is the best predictor of general combining ability for yield among determinate inbreds. Inbred yield is also a good predictor of general combining ability for yield among indeterminate inbreds. However, the addition of harvest index, fruit number, and average fruit size as independent variables to the regression model increases the accuracy of this prediction.

The predictive model for determinate inbreds accurately estimates general combining ability for yield when tested using four additional determinate inbreds. No test was made of the predictive model for indeterminate inbreds.

The average probability that a determinate inbred can produce transgressive segregates when crossed with other lines is significantly correlated with harvest index and fruit number. Although the correlation between this probability and inbred yield is high, it is not significant.

It can be concluded from these results that none of the morpho-physiological traits studied can be used to screen large amounts of parental material for possible use in breeding programs. Breeders should continue to select parental inbreds on the basis of their yields when trying to improve yield. It is possible that harvest index may provide an additional criterion for evaluating parental material provided a method is found for reliably measuring this trait.

A comparison between determinate and indeterminate inbred lines indicates that the determinate inbreds have, on average, higher photosynthetic rates, higher specific leaf weights, and higher harvest indices than the indeterminate inbreds. Since the determinate and indeterminate inbreds produce the same total yield, these results indicate that the relative efficiencies of some of the physiological processes that contribute to these yields differ between growth habits.