Selection of Rice (<i>Oryza sativa</i>L.) Cultivars Tolerant to Drought Stress at the Vegetative Stage under Field Conditions

Water status is one of the critical factors affecting rice production. Rice cultivars tolerant to drought stress at the vegetative stage under field conditions were selected. Seven rice cultivars, namely, KDML 105, IR58821, CT9993, IR62266, IR57514, IR52561 and BT, were included in this study. The plant height, number of tillers per plant, leaf rolling, leaf death, leaf water potential, relative leaf water content and proline content in plants subjected to drought stress for 0, 20 and 60 days were recorded. Based upon the levels of water stress tolerance, three groups of rice cultivars were recognized, as follows: highly drought-tolerant, moderately drought-tolerant and drought-sensitive cultivars. The CT9993 rice cultivar was considered to be a highly drought-tolerant cultivar. The moderately drought-tolerant cultivars included KDML 105, IR58821, IR57514, IR52561 and BT. The IR62266 cultivar was considered sensitive to drought.

Development of species-specific SCAR markers for identification of three medicinal species of Phyllanthus

Phyllanthus amarus Schum. & Thonn. has been widely used in traditional medicine in Thailand as an antipyretic, a diuretic, to treat liver diseases and viral infections. Two closely related species, P. debilis L. and P. urinaria Klein ex Willd., with different and less effective medicinal properties, are less commonly used. These three species are similar in morphology and often occur in overlapping populations in nature. The latter two species can easily be mistaken for P. amarus and collected for medicinal uses, which can lead to undesirable results. DNA fingerprints of these species were obtained using RAPD-PCR techniques. RAPD markers specific for each species were identified. Primers for highly specific sequence-characterized-amplified-regions (SCAR) were then designed from nucleotide sequences of specific RAPD markers. These primers efficiently amplified SCAR markers of 408, 501 and 319 bp unique to P. amarus, P. debilis and P. urinaria respectively. This method of plant identification was rapid and highly specific when tested against DNA of several closely related species and was able to amplify specific markers from mixed DNA samples.

Genetic Transformation of <i>Citrus sinensis</i>L. with an <i>antisense ACC oxidase</i>Gene

This work was carried out to optimize the conditions for highly effective embryogenic callus induction from mature seeds, plantlet regeneration and genetic transformation of Citrus sinensis L. by Agrobacterium tumefaciens strain EHA105 (pCAMBIA 1305.1). Embryogenic calli could be successfully induced from mature seeds employing the MT medium supplemented with 500 mg/l malt extract. The percentage of embryogenic callus induction was 85. With the same medium, the high proliferation rate of embryogenic callus was achieved. The liquid MT medium containing 500 mg/l malt extract in combination with 50 mg/l lactose could be used as the embryoid development medium. Somatic embryos, however, could be regenerated with normal shoots and roots in the MS medium, with the regeneration percentage of 60. The delivery of an antisense ACC oxidase gene into the species C. sinensis mediated by Agrobacterium tumefaciens strain EHA 105 was successful by co-cultivating explants with the strain EHA 105 for 10 min, following that by eliminating the bacterium with 200 mg/l cefotaxime, and subsequently selecting transformed embryoid with 20 mg/l hygromycin. Verified histochemically by GUS assay, putative transformants showed the percentage of gus gene expression of 100. Molecular analysis using PCR confirmed the integration of the antisense ACC oxidase gene into plant genome.