Diurnal Leaf Elongation of Contrasting Tall Fescue Genotypes1

Abstract

Leaf elongation rate (LER) of tall rescue (Festuca arundinacea Schreb.) leaves is associated with tillering rate and forage yield. We performed two experiments. Objectives of Exp. I were to determine if differences in LER among genotypes were due to differential growth during the photoperiod and dark period, and of Exp. II to determine the relationship between leaf water potential and LER. Plants were grown in a controlled environment chamber with a 14‐hour photoperiod and a constant temperature of 21 or 23 C measured at the leaf intercalary meristem. Potentiometers were used to measure leaf elongation of genotypes selected for high yield per tiller (HYT, rapid LER) and low yield per tiller (LYT, slow LER). In Exp. II, stomatal diffusive resistance, leaf water potential, and LER of these genotypes were measured.Mean LER for the HYT genotype (0.9 mm hour‐1) throughout two 48‐hour periods was greater than that for the LYT genotype (0.6 mm hour‐1). Mean LER of both genotypes was significantly higher during the dark periods than during the photoperiods, averaging respectively 1.1 and 0.7 mm hour‐1 for the HYT genotype, and 0.7 and 0.5 mm hour‐1 for the LYT genotype. The 67% increase in LER during the dark period over that during the photoperiod for the HYT genotype was significantly greater than the 33% increase for the LYT genotype. Brief, but substantial increases and decreases in LER coincided with the time the lights went off and on. This response was associated closely with times of increases and decreases in stomatal diffusive resistance, and subsequent changes in leaf water potential. Leaf water potential was higher for the HYT than for the LYT genotype and was associated with LER of both genotypes. In Exp. I, LER averaged 1.3 and 0.8 mm hour‐1 for the HYT and LYT genotypes, respectively, during a 41‐hour dark period. These rates were similar to those maintained during the normal 10‐hour dark periods, and we concluded that daily photosynthate production was not needed to maintain high LER in the dark. Thus, the difference in LER between genotypes was due, in part, to a genotype by leaf water potential interaction which allowed the HYT genotype to more effectively utilize the dark period.