Chilling tolerance and field performance of an F1 cooking tomato cultivar, Nitaki-Koma, relative to its parents

Chilling is one of the major environmental stresses for plants including tomato. A newly established F-1 hybrid cooking tomato cultivar, Lycopersicon esculentum Mill cv. Nitaki-Koma, has been recognized as a promising hybrid to satisfy consumers' demands in Japan. However, there are few reports on agronomical and physiological characteristics, which are necessary to increase its cultivation. Thus, we evaluated the responses of Nitaki-Koma to chilling temperatures as well as its agronomical characteristics in the field and compared the results with those of its parents. The maternal parent cultivar, Coudoulete (referred to as 'P1'), had some good agronomical characteristics, germinated faster, and was more tolerant to chilling temperatures than the paternal parent cultivar, Piline (referred to as 'P2'). P2 had, however, some desirable agronomical characteristics but germinated slowly under chilling conditions and was sensitive to chilling. The F-1 hybrid, Nitaki-Koma, showed the better-parent heterosis in some favorable characteristics, such as the number of clusters/plant, the total number of fruits/plant and the total fruit production/plant. It also showed the mid-parent heterosis in other characteristics, such as average fruit weight, plant height and chilling tolerance. Furthermore, seeds of F-1 germinated faster under chilling conditions than the paternal parent (P2). Therefore, F-1 was considered as a chilling tolerant tomato cultivar good for fruit production. These results further suggest the usefulness of tomato breeding for chilling tolerance by producing the F-1 hybrids by crossing chilling-tolerant cultivars.