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RESEARCH: SUPER DWARF CULTIVAR STUDIES: RICE

BACK TO DWARF CROPS

‘Super Dwarf’ rice is a mutant selection from Oryza sativa cv. Shiokari.   Its short stature, high yield, high harvest index, and no extraordinary environmental requirements make 'Super Dwarf' rice an excellent model plant for yield studies in controlled environments. It does lack the enzyme 3ß- hydrozylase that catalyzes the conversion of GA₂₀ (inactive) to GA₁ (active) so germination is poor; however, 90% germination can be achieved by germinating the seed under water, without aeration, at 33°C.

GENERAL INFO / RECOMMENDED CULTURAL CONDITIONS:

          HEIGHT:
          LIFE CYCLE:
          TEMPERATURE:
          PPF:
          PHOTOPERIOD:
          PLANTING DENSITY:

20 cm tall
45 days to heading; 80 days to harvest
600 to 2000 µmol m^-2 s^-1
32/26 °C d/n pre-anthesis; 28/22 °C post-anthesis
12-h
500 to 1000 plants m^-2

CLICK ON TITLES TO VIEW ABSTRACTS:

• Characterizing the Environmental Response of a
  Gibberellic Acid Deficient Rice for Use as a Model Crop
  Jonathan Frantz, D. Pinnock,
  S. Klassen, and B. Bugbee - 2004
  Agronomy Journal 96:1172-1181

ABSTRACT  Rice (Oryza sativa L.) is a useful model crop plant. Rice was the first crop plant to have its complete genome sequenced. Unfortunately, even semidwarf rice cultivars are 60 to 90 cm tall, and large plant populations cannot be grown in the confined volumes of greenhouses and growth chambers. We recently identified an extremely short (20 cm tall) rice line, which is an ideal model for larger rice cultivars. We called this line ‘Super Dwarf’ rice. Here we report the response of Super Dwarf to temperature, photoperiod, photosynthetic photon flux (PPF), and factors that can affect time to head emergence. Vegetative biomass increased 6% per degree Celsius, with increasing temperature from 27 to 31°C. Seed yield decreased by 2% per degree Celsius rise in temperature, and as a result, harvest index decreased from 60 to 54%. The time to heading increased by 2 d for every hour above a 12-h photoperiod. Yield increased with increasing PPF up to the highest level tested at 1800 µmol m^–2 s^–1 (12-h photoperiod; 77.8 mol m^–2 d^–1). Yield efficiency (grams per mole of photons) increased to 900 µmol m^–2 s^–1 and then slightly decreased at 1800 µmol m^–2 s^–1. Heading was delayed by addition of gibberellic acid 3 (GA₃) to the root zone but was hastened under mild N stress. Overall, short stature, high yield, high harvest index, and no extraordinary environmental requirements make Super Dwarf rice an excellent model plant for yield studies in controlled environments.

• Mutation Breeding of 'Super Dwarf' Rice
  Jonathan Frantz, S. Klassen,
  T. Hudelson, and B. Bugbee - 2003

• HPS vs. MH Lamps & Phasic Photoperiod Rep 2
  Derek Pinnock and B. Bugbee - 2001

SUMMARY ‘Super Dwarf’ rice was grown at four plant densities (50, 100, 200, and 600 plants m^-2) in each of three growth chambers to replicate two previous trials involving lamp type (High Pressure Sodium; HPS and Metal Halide; MH)  and photoperiod (12-h continuous and 12-h until anthesis then 24-h until harvest).  Individual  plots (0.2 m²) were separated by polished aluminum to minimize guard row effects.

• Anaerobic Conditions Improve Germination
  of a Gibberellic Acid Deficient Rice
  Jonathan Frantz and B. Bugbee - 2001

ABSTRACT Dwarf plants are useful in research because multiple plants or plant communities can be grown in small growth chambers. We have studied a gibberellic acid (GA) mutant of rice (Oryza sativa japonica cv. 'Shiokari' line N-71) that is extremely dwarf (20-cm tall). Unfortunately, this GA mutation is associated with poor germination (70%) under aerobic conditions. Neither exogenous GA, nor a dormancy-breaking heat treatment improved germination. However, excellent germination (95%) was achieved by germinating the seeds anaerobically, either in a pure N₂ environment or submerged in unstirred tap water.

• Hydroponic vs. Soilless Media:
  Interaction with Plant Density
  Derek Pinnock and B. Bugbee - 2000

INTRODUCTION  Water stress can cause early heading in some plant species.  'Super Dwarf' Rice was grown in hydroponic culture and soilless media to determine if a slight water stress, caused by the soilless media, would cause earlier heading.

• HPS vs. MH Lamps: Interaction with Plant Density
  Derek Pinnock and B. Bugbee - 2000

INTRODUCTION Super Dwarf' rice was grown at four plant densities in each of two growth chambers, one with HPS lamps, one with MH lamps. Individual plots (0.2 m2) were separated by polished aluminum to minimize guard row effects.

• 'Super Dwarf' Rice Temperature Studies
  Steve Klassen and B. Bugbee - 1999

Detailed temperature studies are a prerequisite to the optimization of crop productivity because field studies at ambient CO₂ provide only a general guide to optimal temperatures. Meristem temperature has a profound effect on crop development rate, and the optimum temperature usually decreases as the crop matures. Previous studies with semi-dwarf rice (Ai-nan-tsao & 29-Lu-1) indicated that temperatures above about 33 şC reduce seed set if they occur during anthesis. In rice, high temperatures are especially detrimental if there is rapid dark-to-light temperature increase. Conversely, average day/night temperatures in the mid 20's delay heading and cause an undesirable increase in vegetative biomass. We examined 3 temperatures prior to anthesis (30/24; 32/26; & 34/28). Temperature of all treatments was decreased to 30/24 at 3-d prior to anthesis and further decreased to 28/22 during grain fill to prolong the duration of grain fill and increase harvest index. Vegetative biomass was increased by 10% per ^oC with increasing temperature, but seed yield was not significantly increased at the warmer temperatures so harvest index decreased. Super dwarf rice continues forming tillers throughout vegetative growth, presumably because of the lack of apical dominance caused by a lack of active gibberellic acid. At the relatively low plant density used in this study (100 plants per m²), many late tillers were formed and 25 to 30% of the heads were sterile. We are now conducting density studies and adding low levels of GA to the nutrient solution to decrease late tillers and improve harvest index.

• 'Super Dwarf' Rice PPF studies
  Steve Klassen and B. Bugbee - 1999

Increasing photosynthetic photon flux (PPF) increases yield but decreases energy efficiency so the optimum PPF depends on the relative importance of energy, mass, and volume. We examined PPF levels of 600, 900, and 1800 µmol m^-2 s^-1 in a 12-h photoperiod (20 to 80 mol m^-2 d^-1). We assumed a PPF compensation point of 200 µmol m^-2 s^-1. Yield and yield efficiency were similar to PPF response data for wheat (Bugbee & Salisbury 1988 P Physiol. 88:869-878, Exploring the Limits of Crop Productivity) except that wheat can utilize continuous light so the PPF input and yield are doubled. Crops with vertical leaves (wheat &rice) can utilize PPF levels well above 1000 µmol m^-2 s^-1. Crops with horizontal leaves (potatoes, soybeans & other dicots) light saturate much sooner than grasses.

• Characterizing ‘Super Dwarf’ Rice
  for Use in Advanced Life Support
  Jonathan Frantz, D. Pinnock, S. Klassen, and B. Bugbee
  Life Support and Biosphere Science - 1999

Rice and wheat are the two most significant grain crops in human nutrition. Genotypes and procedures from growing wheat in advanced life-support (ALS) systems are well characterized, but dwarf rice cultivars such as Ai-Nan-Tsao and 29-Lu-1 are too tall (70 cm). The excessive height of these rice cultivars has meant that rice has not been well studied in controlled environments. We recently identified an extremely short rice variety (20-cm tall) with a high harvest index (60%), which we named Super Dwarf rice. We have begun to characterize this cultivar by determining: 1) techniques for optimum stand establishment, 2) root-zone oxygen sensitivity, 3) optimum planting density 4) optimum day/night temperatures, 5) photoperiod sensitivity, and 6) PPF response curves. Stand establishment can be significantly improved by breaking seed dormancy, either by a heat treatment or germination under anaerobic conditions. Super Dwarf grows equally well in an anaerobic root-zone as in an aerobic root-zone. Vegetative biomass was increased by 10% per C with increasing temperature, but seed yield was not significantly increased at the warmer temperatures so harvest index decreased. Super Dwarf tillers profusely, so the optimum planting density is only 200 to 500 plants m^-2. Higher planting densities reduced harvest index. The time to heading is increased by 2 days for every hour above a 12-h photoperiod and appears to be hastened by a well-timed stress during vegetative development. Low concentrations of GA3 in the nutrient solution did not reduce the number of days to heading. Yield and yield efficiency were similar to PPF response data for wheat except that wheat can utilize continuous light. Overall, the short height, relatively high yields, and high harvest index, makes Super Dwarf rice an ideal cultivar for ALS.

• Unique Procedures for Germinating 'Super Dwarf' Rice
  Jonathan Frantz and B. Bugbee - 1999

INTRODUCTION  Rice (Oryza sativa L.) is an important crop for advanced life support, but the height of even full-dwarf cultivars (80-cm tall) has made them difficult to use in controlled environments.  We identified a rice mutant that lacks 3ß-hydroxylase, the enzyme responsible for conversion of gibberellic acid 20 (GA₂₀) to GA₁ (Murai et al., 1990; Honda et al., 1996). GA₁ is the active form of GA in most plants, so this rice variety is extremely short (20-cm tall).  ‘Super Dwarf’ rice has a higher harvest index (50%) and similar yield to the commonly used rice cultivars ‘Ai-Nan-Tsao’ and ‘29-Lu-1' and its parent line ‘Shiokari’ (Kinoshita and Shinbashi, 1982).  Uniform stand establishment is critical with small research plots. It is therefore important to determine procedures for optimum germination.

• Improving Germination of 'Super Dwarf' Rice
  Jonathan Frantz and B. Bugbee - 1999
  American Society of Agronomy
  Oct. 1999; Salt Lake City, UT

ABSTRACT  We studied a rice (Oryza sativa L.) cultivar (‘Super Dwarf’) that lacks 3ß-hydroxylase, the enzyme responsible for conversion of gibberellic acid 20 (GA₂₀, inactive) to GA₁ (active). Under aerobic conditions, GA₁ activates alpha-amylase, a necessary step in rice germination, so ‘Super Dwarf’ has poor germination. Applying GA₃ only marginally improved germination, and caused a reversion to the tall phenotype. In rice, activation of alpha-amylase can occur by a different pathway under anoxic conditions (Perata et al., 1992, Planta, v.188). We examined germination under anoxic and hypoxic conditions by passing humidified N₂ or N₂/air mixtures through germination boxes. Surprisingly, germination was improved from 70% to 95% by anoxic conditions. Germination was also improved by 2.3% per °C from 20 to 33 °C. While rice has long been known to be able to germinate under anoxic conditions, ‘Super Dwarf’ requires anoxia for full germination.

• Advantages of 'Super Dwarf' Rice for Studies in
  Microgravity and for Advanced Life Support
  Bruce Bugbee, S. Klassen, T. Dougher,
  J. Frantz, and D. Pinnock - 1999
  American Society for Gravitational and Space Biology
  Nov. 1999; Seattle, WA

ABSTRACT  Rice (Oryza sativa L.) readily form aerenchyma in response to a hypoxic root-zone environment. Providing a root-zone that has a balance of air filled porosity and adequate water has been an enormous challenge in microgravity. Studies conducted with rice would eliminate the need for oxygen in the root-zone, but even semi-dwarf rice cultivars are more than 70 cm tall, which makes them unsuitable for the confined volumes of spaceflight. We recently screened the world germplasm collection of rice and identified a rice cultivar that is only 20 cm tall at maturity. Like other rice cultivars, it grows equally well with and without O₂ in the root-zone. It prefers warm temperatures (28 to 34 °C), which can significantly reduce the size of the heat removal system for the growth chamber. Super Dwarf rice heads about 40 days after emergence, matures in 70 days and has high yields. We are currently evaluating its sensitivity to ethylene.

• Improving Germination Using 'Super Dwarf' Rice
  Jonathan Frantz and B. Bugbee - 1999
  American Society for Gravitational and Space Biology
  Nov. 1999; Seattle, WA

ABSTRACT  ‘Super Dwarf’ rice (Oryza sativa L.) is a short (20-cm-tall) rice cultivar that lacks 3ß-hydroxylase, the enzyme responsible for conversion of gibberellic acid 20 (GA₂₀, inactive) to GA₁ (active). Under aerobic conditions, GA₁ activates alpha-amylase, a necessary step in rice germination. Consequently, ‘Super Dwarf’ has poor germination. Seeds germinated in microgravity is difficult because adhesion of water to seeds and porous media can cause hypoxic conditions. These low O₂ conditions prevent germination in almost all species, which is probably due to alpha-amylase not being activated in starchy seeds. In rice, activation of alpha-amylase still occurs under anoxic conditions, thereby allowing rice to germinate. The ability to germinate suggests either GA is active in rice under anoxia, or there is an alternative pathway for alpha-amylase activation under anoxia. We examined germination under anoxic and hypoxic conditions by passing humidified N₂ or N₂/air mixtures through germination boxes. Surprisingly, germination was improved from 70% to 95% by anoxic conditions. Germination was also improved by 2.3% per °C from 20 to 33 °C. While rice has long been known to tolerate anoxic conditions, ‘Super Dwarf’ requires anoxia for full germination. This surprising finding not only makes ‘Super Dwarf’ rice an excellent crop for studies in microgravity, but suggests an alternative mechanism for GA-mediated alpha-amylase activation.