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Effects of Irradiance and Penetration Resistance on Root and Shoot Growth of Rice

A.H.M.Z. ALI
Department of Soil, Water & Environment, University of Dhaka, Dhaka‐1000, Bangladesh

Abstract/ Executive Summary:

Plants of BR?29 rice were grown at low (0.05 MPa) and high (0.9 MPa) penetration resistances under low (187 μmol/sec/m²) and high (375 μmol/sec/m²) irradiances for three and nine days. There was no significant effect of irradiance (p > 0.05) on seminal root axis lengths of rice at three days after transplanting. At nine days after transplanting, seminal root axis lengths were significantly greater in high than low irradiances (p < 0.05), but only in low penetration resistance. Significant effect (p < 0.05) was also found on number of laterals in both low and high penetration resistances. In case of shoot lengths no significant differences (P > 0.05) were found at three or nine days after transplanting between low and high irradiances. But increase in leaf length with time was higher at low irradiance (up to 120 hours) than at high irradiance (up to 96 hours). However, in the phytotron, plants were getting irradiance at a constant rate for the total day length (12 hours) with little mutual leaf shading. It was assumed that these conditions would be likely to give a rate of photosynthesis close to the maximum. Therefore, it may be concluded from this experiment that irradiance can have more prominent effect on root than shoot at different penetration resistances in soil.

Keywords: Irradiance, Penetration resistance, Growth, Rice

Location: Plant & Soil Science Department, University of Aberdeen, Aberdeen

Start Date: 00-00-2011

End Date: 00-00-2011

Program Area: Variety and Species

Commodity: Rice

Objectives:

1. To see the effects of irradiance on the root and shoot growth of rice (BR?29) in both low (unimpeded) and high penetration (impeded) resistances in soil.

Methodology:

Perspex cylinders were packed with soil uniformly mixed with nutrient solution following the packing styles developed for an unimpeded treatment with a penetration resistance (PR) of 0.05 MPa and an impeded treatment with a PR of 0.9 MPa. Variation in mean penetration resistances within a cylinder in unimpeded (PR = 0.05 MPa) and impeded (PR = 0.9 MPa) treatments are shown. Seeds of BR?29 variety of rice were germinated on wet filter paper. Preliminary germination trials were carried out to determine germination rates under these conditions. Thus, the times when the seeds were placed on wet filter paper were chosen to ensure that each seed was at the same stage of germination when transferred to the packed growth cylinders. Packed cylinders were placed in high light phytotron. Irradiance inside the phytotron varied from (320 ? 430 μmol/m²/s). The phytotron was separated into two parts by placing shade cloth over half of the phytotron. Average irradiance inside the phytotron without shade cloth was 375 μmol/sec/m2 and under shade cloth was 187 μmol/sec/m². Average temperature inside the phytotron was about 27°C. At the time of harvesting, the growth cylinders were collected from the high light phytotron and submerged in a container full of water for one hour after removing the base of cylinders. When the soil became loose it fell freely down the cylinder as it was removed from the cylinder. The plants were then collected from the container placed in a Petri dish, and washed thoroughly with distilled water to remove soil or sand attached to the roots. The plants were temporarily kept in these Petri dishes full of water during mearuement of root and shoot parameters. The length of the seminal root axis was measured using digital vernier callipers (± 0.01 mm). The number of first order laterals were counted under a large?field illuminated bench magnifier keeping the root system in a Petri dish. Shoot length (longest leaf) was measured to ± 0.01 mm using digital vernier callipers. Increase in leaf lengths were also measured at 24 hour intervals in both unimpeded and impeded treatments. Statistical analysis was made using Minitab Statistical Software, release 10 Xtra.

Source of Information: Dhaka Univ. J. Biol. Sci. 20(1): 65‐70, 2011 (January)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

In the phytotron, plants were getting irradiance at a constant rate for the total day length (12 hours) with little mutual leaf shading. It was assumed that these conditions would be likely to give a rate of photosynthesis close to the maximum. Consequently, it was felt that these conditions were as close to tropical field conditions which could be reasonably achieved in the laboratory under constant irradiance. Therefore, it may be concluded from this experiment that effects of irradiance is more pronounced on root than shoot growth at different penetration resistances in soil.

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