Physiological and breeding studies using tomato varieties and their derivatives : a thesis ... for the degree of Master of Horticultural Science in Plant Science

Tomato plants, because of their economic importance and their wide adaptability, are grown under diverse climatic conditions in both Temperate and Tropical regions. Being highly inbred, tomato plants exhibit extensive variation in, among other characteristics, growth parameters (Table 1.7); growth habits (see Barby 1963) and other characters as reviewed by Rick (1956). The objectives of the three major experiments reported in this thesis were, respectively: (1) to compare the vegetative growth of two tomato lines, namely Potentate and Yellow seedling, and their F 1 hybrid grown under three nitrogen levels. Quantitative growth analysis using the orthogonal polynomial technique was employed to examine the following growth parameters: dry weight of entire plant and plant parts; shoot/root ratio; specific leaf weight and leaf area; relative growth rate, net assimilation rate and leaf area ratio; relative growth rate and "net assimilation rate" of plant parts. In addition, the chlorophyll concentration, nitrogen percentage, nitrogen yield and rate of nitrogen utilization were also determined to gain a better understanding of the differences in growth between the parents and their F 1 offsprings; (2) to examine the contribution made by a number of physiological and leaf characteristics to the observed differences in growth of the three tomato lines grown under two nitrogen regimes over various periods of time. These measurements included the photosynthetic rate of leaflets, the respiration rates of roots and leaflets, and various leaf characteristics such as specific leaf weight, leaf thickness index, stomatal length and density, mesophyll cell number and chlorophyll concentration. Furthermore, the rates of cumulative stem elongation and leaf production, and other reproductive characteristics were also determined; and (3) to examine the effect of the "yellow seedling" phenotypic condition on the genetic variation in relative growth rate of segregating F 3 families grown under two contrasting nitrogen concentrations