Parthenocarpy modulation in field-grown tomato

Polish climatic conditions are not favorable for tomato production in the field. Low temperatures do not allow planting of tomatoes in the field before the third week of May. In June, variable temperatures and intermittent cold (even below 10 degrees C) adversely affects pollination and fruit setting. In early September, the growing period often comes to an end due to frost. In this situation, earliness and parthenocarpy are the two important factors of tomato breeding. In the breeding of tomato field varieties it is necessary to combine the proper genetic background with parthenocarpy genes (better fruit setting in cold) and avoid its negative consequences (fruit deformation and lower seed yield). Therefore, gene pat-2 derived from the Santiam variety was introduced into breeding material of different backgrounds. As a result, 11 lines were obtained and evaluated in 2000. These lines produced regularly shaped large fruits (78-115 g) with multiple locules, meeting the Polish market requirements. However, not all of them qualified as commercial varieties because of insufficient seed set (lower than 1.5 g per plant). Out of 11 lines developed, 5 were selected for further testing (2001-2003). During the three years of testing, the field growing conditions were variable and three of the five lines proved to be stable and fulfilled the requirements set for commercial varieties at a satisfactory level. The best lines were crossed with other male-sterile or non-parthenocarpic lines to produce hybrids. The hybrids were found to be just slightly better in fruit yield but the fruit weight was lower. Thus, it is possible to conclude that parthenocarpic lines can be competitive as parents for hybrids and reliable under difficult climatic conditions.