Gilbert, J. C.
In the older breeding lines under selection for root knot resistance and fruit size at the Hawaii station, a persistent problem in the homozygous root knot resistant lines was an enlarged stem scar on the fruits of tomatoes grown at our Poamoho farm. This also occurred at other places in Hawaii, but not everywhere, and the condition was clearly associated with some environmental factor. Related Hawaiian tomato lines which did not carry the gene for root knot resistance did not show the enlarged stem scars. The sizes of the stem scars varied from one fruit to another of similar size on the same plant, and of course the larger fruits showed larger stem scars. A convenient method of obtaining data for comparing stem scar sizes of tomato lines involved 30 fruit samples in which the ratio of fruit weight (grams) per centimeter of stem scar diameter was obtained for each fruit. The mean ratio for the 30 fruit sample was used to represent the stem scar per fruit weight ratio of each line. The approximate mean diameter of the stem scars could be obtained to the nearest millimeter with a transparent ruler. This ratio was found to vary somewhat with the size of the fruit samples as the increase in fruit weight was not quite matched by increases in stem scar diameters. By limiting the 30 fruit samples to tomatoes within a size range of 20 grams, highly significant differences between the mean stem scar diameter of different lines could be demonstrated. When a line with large stem scars was crossed with another having small stem scars on the fruit, the fruits of the F1 resembled the latter in this respect, and so these enlarged stem scars appeared to be conditioned by one or more recessive genes. Recently, true breeding root-knot resistant lines free of the enlarged stem sears were obtained in the breeding program by using some parental material with distinctly small stem scars.