A set of 135 rice landraces from different geo-climatic regions of Sri Lanka were tested for their rooting characteristics with high throughput physiological screening methods. In the preliminary screening, nearly half of the variation in toxicity symptoms observed in all 135 landraces due to herbicide layer (TRIK, 100 mg / plant) buried at 30cm depth was explained by landrace. Deep rooted and shallow rooted landraces were distinguished by herbicide score. Selected 36 landraces with diverse herbicide scores were tested in hydroponics for 5 weeks for root traits. Root length and root thickness had significant genotypic differences explaining 60% and 30% of the variation. From 36, 12 landraces were then grown in rhizotrons for 6 weeks and their root characteristics were confirmed. Genotypic differences accounted for 62, 74 and 54% of variation in root length, root angle and root thickness. Root screening concluded that Podi wee-1, Sinnavellai, Niyan Wee-1 and 2 are the most deep rooting, drought resistant landraces among the set of 135 Sri Lankan landraces. These landraces showed better relative growth than shallow rooted landraces under drought environment. Cluster analysis of SNP data from 378 markers indicated that there are 6 different subpopulations among landraces. The most deep rooted, upland landrace Podi Wee-1was identified as a tropical japonica variety .Other deep rooted landraces, Sinnavellai, Niyan Wee-1 and Niyan Wee-2, were grouped as indica 2, a significantly different group from all other indicas due to their high mean herbicide score and high drought resistant properties. None of the OryzaSNP indica landraces grouped with the indica 2, suggesting that the indica 2 group identified here represents a local subpopulation of indica adapted to drought prone environments. It was proven that differences in rooting depth were associated with genetic variation both at the whole genome level.

Rice (Oryza sativa L.) is one of the main staple foods of the world. With the increase of population and the deficit of irrigated water, the increase in rice production that is predicted will be dependent on areas prone to drought. Root depth is important for plant growth and survival during drought because of its role in facilitating water uptake from deep soil layers. By advances in genomics, the plant root systems can be linked to quantitative trait locus (QTL) information to achieve a most beneficial design of root system architecture. There is a demand to develop and validate techniques that permit estimation of the root system. Therefore, two techniques (root penetration ability to non-woven fabric and a buried herbicide method at depth 30 cm) were used in this study to assess root traits in a total of 36 rice cultivars. The results from these screens were assessed with root traits measured on the same cultivars in the rhizotrons and hydroponic experiment. Correlations between these methods showed that herbicide score at day 35 was most strongly related to traits of the rhizotron experiment, especially number of roots passed 50 cm at 35 days, root angle at day 21, root thickness, water use and % root mass. Using all of these traits obtained in the rhizotron in a best subset regression suggests that up to 71% of the variation in herbicide score can be explained. These data strongly imply that symptoms are related to root development and transpiration demand and are therefore ideal for assessing water extraction by roots at depth. The herbicide method has been applied to screen root depth in 138 recombinant inbred lines derived from crossing between two subspecies Indica Bala and Japonica Azucena. Analysis of mapping population revealed two putative QTLs on chromosome 6 near marker RZ682 and one on chromosome 7 near marker RG351 and two significant QTLs near marker G1010b and G1073 for root depth on chromosome 8. The same method has been used to evaluate root depth in 325 rice diversity panel allowing high resolution genetic mapping. Using efficient mixed model (statistical analyses for genome wide association), four associations were detected, two on chromosome 1 and one on each of chromosome 4 and 6. In addition, the same rice diversity panel has been evaluated for drought avoidance by assessing leaf rolling (as one plant mechanism against drought stress) and drought recovery. A total of three significant associations, on chromosomes 4, 6 and 7 were identified for leaf rolling while only one significant association on chromosome 2 for drought recovery was found. Positional candidate genes underneath QTLs were examined bioinformatically and through the literature revealing several interesting genes which may offer potential for developing drought resistant rice cultivars. Therefore, developing a cost effective high-throughput system that can measure traits related to drought avoidance and drought recovery on a large number of plants would aid genetic studies in breeding and gene identification.

The presence of wild rice (Zizania palustris var. palustris L.) in the Timmins District has been documented by local residents since 1930; efforts to extract this crop for commercial purposes have only been implemented since 1977. In the past, local residents have valued this crop as a waterfowl attractant rather than an economically viable food crop. Consequently, waterbodies allocated by the Ministry of Natural Resources for the commercial harvest of rice, have been dispensed to outsiders rather than local residents. Annual harvest figures range from 23.0 - 7990.0 kg; thus the Timmins District accounts for 33-100% of wild rice production in the northern administrative region. Harvested rice is shipped to northwestern Ontario and Manitoba for processing after which it is transported to the U.S. for packaging. Today, local residents value this crop as a waterfowl attractant; few, if any, efforts were made to increase the crop yield for commercial purposes even though suitable areas for its development exist. Since the beginning of harvest operations in the Timmins District, harvest activities have been frequently curtailed because of land-use conflicts between the harvester and local residents: cottagers claim harvesters are noisy and decrease the aesthetic appearance of the cottage sites, waterfowl hunters claim the harvesters are responsible for decreasing the waterfowl population during the hunting season. This report proposes that wild rice operations in the Timmins district can be expanded as an economically feasible venture. However, increased public awareness of wild rice harvest operations as well as increased local acceptance and participation is mandatory for such an operation to be a success. A sound management plan is imperative to the development and implementation of a wild rice program.

No description available.

Graduation date: 1950

Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1990. / Includes bibliographical references (leaves 193-201). / Microfiche. / xiii, 201 leaves, bound ill. 29 cm

Thesis (Ph.D.) -- University of Western Sydney, Hawkesbury, 1997. / Thesis submitted for the degree of Doctor of Philosophy. Includes bibliographical references (leaves 299-319).

Thesis (M.S.)--University of Wisconsin--Madison, 1983. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 134-142).

Thesis (M. Phil.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 94-101).

Thesis (M.Phil.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 94-101) Also available in print.