CELL COUNT AND SIZE IN RELATION TO FRUIT SIZE AMONG STRAWBERRY CULTIVARS

Fruit size, number of receptacle cells, and mean cell size were determined' throughout development of secondary fruit of three day-neutral strawberry (Fragaria xananassa Duch.) cultivars grown in a greenhouse. Cells were counted after enzymatic separation of receptacle tissue, and mean cell volume was estimated from cell count and receptacle tissue volume. Size of mature fruit was small (3.8 g) in 'Tillikum', medium (11.5 g) in 'Tristar, and large (15.6 g) in 'Selva'. Fruit size was correlated with the number of achenes per berry. Mature fruit of 'Tillikum' had a lower fruit fresh weight per achene and lower achene population density (achenes per square centimeter) than the larger-fruited cultivars. The average number of cells per mature fruit was 0.72 x 10(6), 1.96 x 10(6), and 2.94 X 10(6) for 'Tillikum', 'Tristar', and 'Selva', respectively. The relative difference among cultivars in the number of receptacle cells was established by the time of anthesis. In all cultivars, cell division was exponential for 10 days following anthesis and ceased by the 15th day. Mean cell volume increased slowly during active cell division, but rose rapidly and linearly for 10 days after cell division halted. Mean cell volume of all cultivars increased >12-fold after anthesis and was almost-equal-to 6 x 10(6) mum3 in mature fruit. The genotypic variation in the size of mature fruit was not the result of large differences in either duration of cell division after anthesis or mean cell volume, but rather was primarily due to differences in the number of receptacle cells established by anthesis.