This thesis focused on the possibilities to improve greenhouse tomato (Lycopersicon esculentum cv. Moneymaker) in terms of yield. The domestic tomato has a very narrow genetic base which makes breeding for better performance a difficult task. The wild, crossable relatives of tomato present the possibility to introduce more variation in the gene pool of the cultivated tomato. An example of such an accession is Lycopersicon pennellii LA716. We used a classical approach for crop improvement while exploiting modern technological tools. The approach consists of introducing genetic variation by making crosses using L. pennellii LA716 as a male parent followed by recurrent backcrossing to greenhouse tomato and selecting for interesting traits in the hybrid progenies. The genetic variation emerging in the progenies of the interspecific cross was immortalized through the creation of a backcross inbred line library (BIL-population). A BIL-library is a group of genotypes with single introgressions which gives together a total coverage of the L. pennellii LA716 genome.The focus was not only on economic yield which by definition is the biomass allocated to the harvestable organs (fruits). But yield was also examined in a broader biological sense as total above ground biomass produced though out the period of growth. Further, we seek an understanding of growth, development and physiological processes which underlie yield. Relative growth rate (RGR) and its major physiological components; net assimilation rate (NAR) and leaf area ratio (LAR) were analyzed. The results of a growth, development, and physiological analysis conducted on old cultivars representing genetic variation in domesticated tomato cultivars fromEuropeshowed that genetic differences and the pattern of change in RGR during plant development are genotype specific. Correlation studies showed that genetic differences in RGR are directly affected by variations in NAR which is a measure for the efficiency of assimilation of photosynthates to biomass.Growth analyses enabled the identification of three BILs giving better growth in greenhouse tomato. BIL1.2, BIL2.3 and BIL8.2 showed an increase in RGR in the range of 5-3%, 15-4%, and 10-3% respectively. The faster RGR's observed in BIL1.2, BIL2.3 and BIL8.2 effected end point biomass production with respective increases of 16%, 22% and 3%. Additionally the results of BIL1.2 and BIL8.2 showed that the pattern of change (delta RGR) during plant development plays also a strong role in crop performance.Yield analysis showed that BIL1.2 and BIL2.3 produced 17-20% respectively 3% more fresh fruits. BILs 1.2, 2.3 and 8.2 produced about 16%, 22% and 3% more biomass (dry matter). Also, interesting trends in biomass allocation were observed, such as BIL1.2 which produced 20% more fresh fruits but only 16% more biomass. This was clearly different in BIL2.3 which produced 3% more fresh fruits but an amazing 22% more biomass. Finally BIL8.2 with 0.5% more fresh fruits produced 3% more biomass than Moneymaker. This shows that different BILs have different biomass allocation patterns and prompted us to execute a thorough analysis of biomass allocations to the above plant organs such as fruits, stem and leaves. It was seen that the biomass partitioning patterns were genotype specific and were controlled by either the presence of homozygous introgressions of L. pennellii LA716 or the absence of the replaced Moneymaker segment. The results suggested that BIL5.3 and BIL12.2 have a more efficient biomass allocation to the fruits. A tempting calculation shows that BIL2.3 in combination with the introgression of BIL5.3 or BIL 12.2 can give a potential 20-41% yield advantage.