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Characterizing the Environmental Response of a Gibberellic Acid–Deficient Rice for Use as a Model Crop

^a USDA-ARS, ATRU, Univ. of Toledo, Mail Stop 604, 2801 W. Bancroft, Toledo, OH 43606-0604
^b Crop Physiol. Lab., Dep. of Plants, Soils, and Biometeorol., Utah State Univ., Logan, UT 84322-4820
^c U.S. Fish and Wildlife Serv., Ecol. Serv. Office, 315 S. Allen St., State College, PA 16801

View larger version (70K): [in a new window]   Fig. 1. A comparison of rice cultivars 29-Lu-1 and Super Dwarf. 29-Lu-1, a semidwarf variety, is 80 cm tall; Super Dwarf is only 20 cm tall.

View larger version (24K): [in a new window]   Fig. 2. Effect of temperature on yield and harvest index. Grain yield was similar across temperatures, but vegetative biomass increased as temperature increased (P = 0.02). As a consequence, harvest index declined significantly (P = 0.0002). Days to heading were longest at 27°C but were about 45 d at 29 and 31°C. Error bars indicate standard error of means (n = 12 for each point). There are no error bars on days to heading because all replicates headed on the same day.

View larger version (24K): [in a new window]   Fig. 3. Effect of temperature on days to heading, number of heads per square meter, and harvest index, as measured using the units grams dry weight (gdw) of heads (seed plus rachis) and total biomass. The optimum temperature for time to heading and number of heads per square meter was about 29°C.

View larger version (24K): [in a new window]   Fig. 4. Effect of photoperiod on development and yield. Increasing the photoperiod increased days to heading by 1 d for each additional hour (P < 0.0001). No other harvest parameters were statistically significant at the P = 0.05 level. Data from 10 pots were pooled and then divided by 10, and yield was calculated on a per square meter of ground area basis.

View larger version (25K): [in a new window]   Fig. 5. The effect of photosynthetic photon flux (PPF) on yield. Both grain yield (open circles, r2 = 0.986) and vegetative biomass (including roots, closed circles, r2 = 0.990) increased with higher PPF, so harvest index remained relatively constant (r2 = 0.07) at slightly below 50%. Increase in yield was likely due to higher number of fertile heads at higher PPF (r2 = 0.969). No fertile heads were observed at PPF of 200 µmol m–2 s–1 or less. Error bars indicate standard error of means (n = 4 for each point).

View larger version (16K): [in a new window]   Fig. 6. The effect of (top graph) gibberellic acid 3 (GA3) added to the root zone on days to heading in Super Dwarf rice and (bottom graph) N concentration in hydroponic solution on days to heading. Without GA3, Super Dwarf headed in 47 d, but the rate of development decreased with additional GA3. Super Dwarf headed in 48 d under intermediate N stress but required longer time at both high and low N stress.