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Somaclonal variation in rice and tolerance to low soil zinc

Juma-Soragha, Mwatima (1989) Somaclonal variation in rice and tolerance to low soil zinc. Masters by Research thesis, Murdoch University.

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The objective of this study is to examine the possibility of using somaclonal variation to improve the tolerance to 1ou soil Zn in rice. This necessitated developing methods for regeneration of plantlets from rice cultivars of interest and for screening regenerated plants for tolerance to low soil Zn.

Conditions were identified for the establishment of callus and plant regeneration for four rice cultivars IR20, IR26, IR36 and Calrose. The genotype of the cultivar was a key factor in regeneration, but the type of explant and hormone contribution was also important. A scutellum explant was best for plantlet regeneration in Calrose and IR20, while a shoot explant was best for plantlet regeneration in IR26 and IR36. Imbibition of seeds in medium with 2,4-D was found to be necessary for callusing of scutellum explants, as no callus was formed if the scutellum was isolated more than two days after seed germination in hormone-free medium.

Preliminary experiments to develop a test system for screening regenerated plants and to characterise the parent showed that 800 lines ug Zn applied to 3 kg of Lancelin sand eliminated Zn deficiency symptoms and gave maximum yield of shoots in IRS. A level of 200 ug applied Zn was chosen to be used for screening regenerated plants as at this level plants showed deficiency symptoms and their growth was depressed, but without being severely stunted, within four weeks of sowing.

Varietal differences in tolerance to 1ou soil Zn among Calrose, IR20, IR26 and IR36 were confirmed on the basis of Zn deficiency symptoms, shoot dry matter and, to some extent, Zn content of shoots. These characters, together with plant length and Zn concentration, were used as criteria for screening of tolerance to low soil Zn among regenerated plants.

The initial early experiments were done in waterlogged soils in winter. In later experiments during summer, plants grown under the same conditions at Zn200 recovered from Zn deficiency. The recovery was shown to be due to a greater uptake of Zn by plants apparently from an effect of the anaerobic conditions in releasing Zn from the saturated soil. Plants grown in soil watered to field capacity responded to a range of Zn levels in a similar manner to the early experiments but showed no sign of recovery even when grown in summer. The screening of regenerated plants was therefore done in Lancelin sand given 200 ug Zn/3 kg and watered to field capacity.

Statistical analysis indicated evidence for genetically controlled variability for tolerance to 1ou soil Zn among regenerated plants when the best individuals in R2 families were compared to the best individuals in the parent line. Variability was evident in Zn deficiency symptoms, shoot dry matter, plant length and to some extent Zn content

Item Type: Thesis (Masters by Research)
Murdoch Affiliation(s): School of Biological and Environmental Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): McComb, Jen and Loneragan, Jack
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