Thesis (MSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: Much has been written about the effects of soil salinity on plant growth. Its devastating effects have already been reported 2000 years BC. In the 21· century an alarming 80 million hectares of cultivated land area are affected by salt (Munns, 2002a) and represent a growing threat to agriculture. Salt tolerance is a complex trait moderately expressed in only a few plant genotypes (Ruiz, 2001). An attempt to transfer salt tolerance genes from the wild grass, Thinopyrum distichum, to triticale and éommon wheat was initiated by Marais and Marais (2003). A study of Th. distichum x rye hybrids enabled the authors to identify chromosomes 2Jld , 3Jld , 4Jld and SJld as being involved in the determination of salt tolerance. Indirect (yet unconfirmed) evidence suggested that 7Jld might also have a role. A programme aiming to transfer regions of the critical chromosomes to homoeologous triticale chromosomes, which relies heavily on the use of molecular markers, was launched. While an RFLP marker is available for each of the Thinopyrum chromosomes, these are not suited for the screening of large numbers of segregates. This study therefore represents an attempt to convert the RFLP markers into less time consuming and cost-effective SCAR markers. The published DNA sequences of the RFLP probes in question were used as templates to design PCR primers. The PCR reactions were optimised using DNA of Th. distichum, rye and their FI hybrid. When Thinopyrum specific amplification products were obtained, the primers were also tested on a panel of genotypes with and without the target chromosomes. Seemingly polymorphic bands were confirmed by Southern blotting and hybridisation with the corresponding RFLP probes. The primers were also tested on a panel of genotypes that included 'Rex' triticale to ensure that they would also detect a difference in a triticale genetic background during transfer. Polymorphic bands were then isolated and sequenced to further refine the markers. In certain eases, sequences of the same fragment amplified in triticale ('Rex') and Thinopyrum were aligned in an attempt to design more specific markers. Using this approach, it was possible to develop chromosome specific SCARs for Thinopyrum chromosomes 3Jld and 7J2 d . Three and one set(s) of PCR markers, respectively, have been developed and can be used to unequivocally detect the Thinopyrum chromosomes involved in salt tolerance against a triticale background. A SCAR marker was also found for chromosome 6J. Thus, an attempt was made to convert thirteen RFLP probes to SCAR markers. Only three were successfully converted. The main reason for the low success rate is the syntenic relationships between the genomes of the different cereals that made it an arduous- task to find discriminating primer sets. Based on the results obtained, an adapted procedure is suggested for future attempts to develop chromosome specific markers utilizing published sequence information that was obtained for a different species. / AFRIKAANSE OPSOMMING: Baie is al geskryf oor die uitwerking van grond versouting op plantproduksie. Die vernietigende gevolge van versouting is alreeds 2000 jaar VC gerapporteer. In die 21* eeu is 'n geraamde 80 miljoen hektaar (Munns, 2002a) bewerkte land-area sout-geaffekteerd. Die ontstellende verwikkelinge verteenwoordig 'n groeiende bedreiging vir die landbou. Soutverdraagsaamheid is 'n komplekse kenmerk en slegs enkele plantgenotipes met matige verdraagsaamheid kon nog ontwikkel word (Ruiz, 2001). 'n Poging om soutverdraagsaamheidsgene vanaf die wilde gras, Thinopyrum distichum, na triticale en gewone koring oor te dra, is deur Marais en Marais (2003) geïnisieer. 'n Studie van Th. distichum x rog hibriede het die skrywers in staat gestelom chromosome (2Jld, 3Jld, 4Jld en SJld) wat bydra to soutverdraagsaamheid te identifiseer. Indirekte (maar onbevestigde) aanduidings is gevind dat 7J1dook' n rol mag speel. 'n Program is daarna geloods om segmente van chromosome na homoeoloë triticale chromosome oor te dra, 'n onderneming wat swaar steun op die gebruik van molekulêre merkers. Alhoewel daar'n RFLP merker beskikbaar is vir elk van die Thinopyrum chromosome, is hierdie merkers nie geskik vir die sifting van groot getalle segregate nie. Hierdie studie verteenwoordig 'n poging om die RFLP merkers om te skakel na 'n minder tydrowende en meer koste-effektiewe SCAR merkers. Die gepubliseerde DNS-volgordes van die betrokke RFLP peilers is as templaat gebruik om PKR inleiers te ontwerp. Die PKR reaksies is geoptimiseer deur gebruik te maak van DNS van Th. distichum. rog en hulle FI hibried. In gevalle waar Thinopyrum spesifieke amplifikasie produkte verkry is, is die inleiers ook getoets op 'n paneel van genotipes met en sonder die teikenchromosoom. Skynbare polimorfiese bande is bevestig deur 'n 'Southern' klad te maak en te hibridiseer met die tersaaklike RFLP peiler. Die inleiers is ook getoets op 'n paneel van genotipes waarby 'Rex' triticale ingesluit was om te verseker dat dit ook verskille in 'n triticale genetiese agtergrond opspoor (nodig tydens oordrag). Polimorfiese bande is verder verfyn. Dit is geïsoleer en die DNS-volgorde daarvan is bepaal. Tn sekere gevalle is ooreenstemmende fragmente geamplifiseer in triticale ('Rex') en Thinopyrum. Die volgordes is dan bepaal en met mekaar vergelyk in 'n poging om meer spesifieke merkers te ontwerp. Met die gebruik van hierdie benadering was dit moontlik om chromosoom-spesifieke SCAR-merkers vir die Thinopyrum chromosome 3Jld en 7J2d te ontwikkel. Drie en een stel(le) PKR merkers is onderskeidelik ontwikkel en kan gebruik word om ondubbelsinnig te bepaal of die betrokke Thinopyrum chromosoom segregeer in 'n triticale kruising. 'n SCAR merker is ook gevind vir chromosoom 6J. Dus, daar is probeer om dertien RFLP peilers na SCAR merkers om te skakel. Slegs drie van die pogings was suksesvol. Die hoofrede vir die lae sukseskoers is die hoë graad van sintenie tussen die genome van die verskillende grane wat dit 'n moeilike taak gemaak het om diskriminerende inleierstelle te ontwerp. Op grond van die resultate word 'n ietwat gewysigde prosedure vir die toekomstige pogings om chromosoom-spesifieke merkers te ontwerp met gebruik van gepubliseerde volgorde inligting vanaf' n ander spesie, voorgestel.

[Truncated abstract] Dryland salinity is a major environmental challenge facing agriculture in Australia. One option to manage dryland salinity is the use of perennial forages that increase water use of agricultural systems. However, the current array of perennial forages is limited. Forage species that satisfy the range of climatic and edaphic environments, and production systems, in southern Australia are needed (Chapter 1). In particular, low rainfall regions lack options other than lucerne (Medicago sativa L.) (Chapter 1). The Dorycnium genus (canary clovers) contains perennial species that might be useful forage plants for southern Australia. Dorycnium are sub-shrubs and their plant form differs from current perennial forages (Chapter 1). The aim of this project was to investigate some of the agronomic traits of several species of the genus Dorycnium to explore where they might be used in Australia and how they might be integrated into agricultural systems for management of dryland salinity. First, two desktop investigations assessed the potential adaptation and role of Dorycnium species in southern Australia: a review of the current literature on the agronomic characteristics of Dorycnium (Chapter 2) and an eco-geographical analysis to explore the ecology of Dorycnium species (Chapter 3). The agronomy of Dorycnium has been previously researched mainly in New Zealand, and although this provides some indications on where and how Dorycnium might be best used in Australia, this still requires testing in Australia. In particular, the aluminium tolerance of Dorycnium species indicates that they may be more suitable for acid soils than lucerne. Little ecological data was obtained for germplasm and herbarium collection sites of Dorycnium species. Climate comparisons between the native distribution of Dorycnium species in the Mediterranean basin and Australia, using spatial aridity data and CLIMEX climate match modelling, revealed that D. hirsutum and D. rectum might be suitably adapted to the temperate pasture regions of southern Australia. Suitable germplasm of D. pentaphyllum may also exist, but subsequent investigations in this project focussed on D. hirsutum and D. rectum.

Soil salinity and the arid climate in Libya are major constraints in agriculture and predominantly in foodstuff production which are limiting wheat production and yield. The effect of pre-sowing seed treatments with 50 mM of KCl, NaCl, CaCl2, and distilled water as hydropriming on germination and early seedling growth in two wheat (Triticum aestivum L.) cultivars S-24 (tolerant) and Slambo (untested before) under 0, 100, 200 and 300 mM NaCl concentrations was examined. CaCl2 was the only priming treatment that significantly improved the germination percentage, germination rate, and mean germination time in both cultivars under almost all NaCl concentrations. Thus, priming with CaCl2 was selected for further experiments. In the greenhouse, seeds primed with 50 mM of CaCl2 also improved the emergence percentage, emergence rate, shoot and root length, and fresh and dry weight of shoots and roots of both cultivars under all NaCl concentration except at 300 mM where the emergence was completely inhibited. The response of wheat cultivars to three compost treatments including cow manure compost (CC), greenwaste compost (GC) and 50:50 mixture (mix) between them and sand at percentage inclusions of 10 and 30 % by weight under 0, 100, 200, and 300 mM of NaCl was also investigated. Among all compost treatments, 30% GC and 30% mix were the best treatment and improved almost all growth parameters under salt stress, and 30% GC was also the only treatment that had any emergence at 300 mM NaCl. 30% GC and 30% mix were selected for further experiments. The effect of the combination of the selected priming agent (CaCl2) and the best two compost treatments (30% GC and 30% mix) on the emergence and early seedling growth of both cultivars was tested. The results showed that all the treatments enhanced plant growth parameters including seedling ion uptake in both cultivars, with preference to primed seeds sown in 30% GC. The treatments had the following order of the performance of both cultivars under salt stress. Primed seeds sown in 30% GC > unprimed seeds sown in 30% GC > primed seeds sown in 30% mix > unprimed seeds sown in 30% mix. This enhancement is possibly due to the provision of Ca2+ and / or the improvement in the availability of water as both of them were improved by the application of priming and compost.

Two problems hampering efforts to produce salt-tolerant plants through constitutive expression of transgenes include: 1. Spatial control. Particular cell-types must respond specifically to salt stress to minimise the amount of Na⁺ delivered to the shoot; and, 2. Temporal control. Transgenes are typically expressed in plants at similar levels through time, irrespective of the stress encountered by the plant, which may exacerbate pleiotropic effects and means that, particularly in low-stress conditions, costly and/or detrimental metabolic processes may be active, thus reducing yield. To address these issues, Gateway® destination vector constructs were developed combining the GAL4 UAS (upstream activating sequence) with the ethanol-inducible gene expression system to drive inducible cell-specific expression of Na⁺ transporter transgenes (or to silence salt transporter transgenes inducibly and cell-specifically). Rice (Oryza sativa L. cv. Nipponbare) GAL4-GFP enhancer trap lines (Johnson et al., 2005: Plant J. 41, 779-789) that express GAL4 and GFP specifically in either the root epidermis or xylem parenchyma (and therefore ‘trap’ cell-type specific enhancer elements) were transformed with this GAL4 UAS – ethanol switch construct, thereby allowing both spatial and temporal control of transgenes. In preliminary experiments, the expression system successfully limited the expression of RFP to specific cell-types after induction with ethanol. Other genes expressed using this system include PpENA1, a Na⁺-extruding ATPase from the moss, Physcomitrella patens, and AtHKT1;1, a Na ⁺ transporter from Arabidopsis thaliana. The two enhancer trap rice lines were also transformed with the GAL4 UAS driving stable expression of AtHKT1;1 and PpENA1 specifically in root epidermal or xylem parenchyma cells. Expression of AtHKT1;1 in root epidermal cells reduced Na⁺ accumulation in the shoots, while expression in the root xylem parenchyma appeared to have little effect on shoot Na⁺ accumulation. Using cryo-scanning electron microscopy (SEM) X-ray microanalysis, the outer cells of the roots of the line expressing AtHKT1;1 in the epidermal cells were found to accumulate higher levels of Na⁺ than the parental enhancer trap line. Additionally, this line had decreased unidirectional ²²Na⁺ influx. Similar results were observed for plants expressing AtHKT1;1 driven by the CaMV 35S / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1325289 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2008

Two problems hampering efforts to produce salt-tolerant plants through constitutive expression of transgenes include: 1. Spatial control. Particular cell-types must respond specifically to salt stress to minimise the amount of Na⁺ delivered to the shoot; and, 2. Temporal control. Transgenes are typically expressed in plants at similar levels through time, irrespective of the stress encountered by the plant, which may exacerbate pleiotropic effects and means that, particularly in low-stress conditions, costly and/or detrimental metabolic processes may be active, thus reducing yield. To address these issues, Gateway® destination vector constructs were developed combining the GAL4 UAS (upstream activating sequence) with the ethanol-inducible gene expression system to drive inducible cell-specific expression of Na⁺ transporter transgenes (or to silence salt transporter transgenes inducibly and cell-specifically). Rice (Oryza sativa L. cv. Nipponbare) GAL4-GFP enhancer trap lines (Johnson et al., 2005: Plant J. 41, 779-789) that express GAL4 and GFP specifically in either the root epidermis or xylem parenchyma (and therefore ‘trap’ cell-type specific enhancer elements) were transformed with this GAL4 UAS – ethanol switch construct, thereby allowing both spatial and temporal control of transgenes. In preliminary experiments, the expression system successfully limited the expression of RFP to specific cell-types after induction with ethanol. Other genes expressed using this system include PpENA1, a Na⁺-extruding ATPase from the moss, Physcomitrella patens, and AtHKT1;1, a Na ⁺ transporter from Arabidopsis thaliana. The two enhancer trap rice lines were also transformed with the GAL4 UAS driving stable expression of AtHKT1;1 and PpENA1 specifically in root epidermal or xylem parenchyma cells. Expression of AtHKT1;1 in root epidermal cells reduced Na⁺ accumulation in the shoots, while expression in the root xylem parenchyma appeared to have little effect on shoot Na⁺ accumulation. Using cryo-scanning electron microscopy (SEM) X-ray microanalysis, the outer cells of the roots of the line expressing AtHKT1;1 in the epidermal cells were found to accumulate higher levels of Na⁺ than the parental enhancer trap line. Additionally, this line had decreased unidirectional ²²Na⁺ influx. Similar results were observed for plants expressing AtHKT1;1 driven by the CaMV 35S / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1325289 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2008

Two problems hampering efforts to produce salt-tolerant plants through constitutive expression of transgenes include: 1. Spatial control. Particular cell-types must respond specifically to salt stress to minimise the amount of Na⁺ delivered to the shoot; and, 2. Temporal control. Transgenes are typically expressed in plants at similar levels through time, irrespective of the stress encountered by the plant, which may exacerbate pleiotropic effects and means that, particularly in low-stress conditions, costly and/or detrimental metabolic processes may be active, thus reducing yield. To address these issues, Gateway® destination vector constructs were developed combining the GAL4 UAS (upstream activating sequence) with the ethanol-inducible gene expression system to drive inducible cell-specific expression of Na⁺ transporter transgenes (or to silence salt transporter transgenes inducibly and cell-specifically). Rice (Oryza sativa L. cv. Nipponbare) GAL4-GFP enhancer trap lines (Johnson et al., 2005: Plant J. 41, 779-789) that express GAL4 and GFP specifically in either the root epidermis or xylem parenchyma (and therefore ‘trap’ cell-type specific enhancer elements) were transformed with this GAL4 UAS – ethanol switch construct, thereby allowing both spatial and temporal control of transgenes. In preliminary experiments, the expression system successfully limited the expression of RFP to specific cell-types after induction with ethanol. Other genes expressed using this system include PpENA1, a Na⁺-extruding ATPase from the moss, Physcomitrella patens, and AtHKT1;1, a Na ⁺ transporter from Arabidopsis thaliana. The two enhancer trap rice lines were also transformed with the GAL4 UAS driving stable expression of AtHKT1;1 and PpENA1 specifically in root epidermal or xylem parenchyma cells. Expression of AtHKT1;1 in root epidermal cells reduced Na⁺ accumulation in the shoots, while expression in the root xylem parenchyma appeared to have little effect on shoot Na⁺ accumulation. Using cryo-scanning electron microscopy (SEM) X-ray microanalysis, the outer cells of the roots of the line expressing AtHKT1;1 in the epidermal cells were found to accumulate higher levels of Na⁺ than the parental enhancer trap line. Additionally, this line had decreased unidirectional ²²Na⁺ influx. Similar results were observed for plants expressing AtHKT1;1 driven by the CaMV 35S / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1325289 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2008

[Truncated abstract] Lophopyrum elongatum, a wild relative of wheat, can be used as a source of novel genes for improving the salt tolerance of bread wheat. Na+ `exclusion? is a major physiological mechanism for salt tolerance in the wheat L. elongatum amphiploid, and a large proportion (~50%) of the improved Na+ `exclusion? is contributed by a gene(s) on chromosome 3E. This study integrated physiological analysis with comparative genomics to identify gene orthologues that may regulate Na+ transport, and designed and implemented molecular markers for developing wheat L. elongatum recombinant lines with reduced portions of L. elongatum chromatin retaining the Na+ `exclusion? trait. Physiological analysis of leaf Na+ accumulation in wheat L. elongatum substitution lines confirmed that the 3E chromosome contributes a major effect on reduced leaf Na+ accumulation in wheat when grown at 200 mM NaCl. Candidate genes from the model plant, Arabidopsis thaliana, controlling Na+ transport into and from cells (SOS1, HKT1) or compartmentalisation within vacuoles (NHX1, NHX5, AVP1, AVP2) were targeted for comparative analysis in wheat. Wheat gene orthologues were identified by BLAST searching to identify either FL-cDNAs or ESTs, which were subsequently used to amplify genomic DNA, and orthologues confirmed by similar intron-exon structure between Arabidopsis and rice. Intron-exon comparisons showed the majority of exons were conserved between Arabidopsis, rice and wheat, but also indicated exon shuffling events since divergence from a common ancestor. Gene orthologues were assigned to homoeologous chromosomes and non-syntenic regions between wheat and L. elongatum, with the SOS1 orthologue located on group 3 chromosomes in wheat and L. elongatum. ... The recombinant line 524-568 contains a small introgression on the distal end of the long arm of wheat chromosome 3A and represents the most desirable line presently available for further germplasm development. The main outcomes of this thesis have been an increased understanding of the physiology and evolution of orthologues for Na+ transport in wheat and L. elongatum, improved methodologies for designing alien-specific PCR markers, and the development of overlapping recombinant lines that provide a source of novel genes for pyramiding into wheat and improving its tolerance to salt stress.

The embryogenic calli were grown on MS medium containing NaCl with concentrations from 50 to 300 mM. After 2 weeks of culture, salinity tolerance threshold was identified at 150 mM NaCl. Higher concentrations of NaCl stimulated a significant reduction in the calli survival rate and the highest rate was 78.67% at 50 mM. After subculturing callus to the embryo culture medium containing NaCl, the growth and embryogenesis were not affected at the concentrations of 50 – 100 mM. Especially, at 50 mM NaCl the embryogenesis rate reached 83.33%. In contrast, 150 mM NaCl inhibited the somatic embryogenesis. After 4 weeks, culturing somatic embryos on medium MS with addition of 0.07 mg/l spermidin at 50 – 100 mM NaCl, the embryogenesis was considered good and embryos developed through several stages: globular, heart, torpedo and cotyledonary. However, at 150 mM NaCl the globular stage appeared in the culture process. The process of morphohistology and using dye carmine – iod and acridine orange observed the structure of generative callus and embryos at several stages. / Mô sẹo có khả năng phát sinh phôi được nuôi cấy trong môi trường có chứa muối NaCl với nồng độ thay đổi từ 50 – 300 mM. Sau 2 tuần nuôi cấy, chúng tôi xác định được ngưỡng chịu mặn của mô sẹo có khả năng sinh phôi cây Cọc rào là 150 mM. Nồng độ muối NaCl càng cao thì tỷ lệ sống của mô sẹo giảm dần và đạt giá trị cao nhất là 78,67% tại nồng độ 50 mM NaCl. Khi chuyển mô sẹo sang môi trường phát sinh phôi có chứa muối NaCl với nồng độ thay đổi, chúng tôi thấy ở nồng độ muối NaCl 50 – 100 mM không ảnh hưởng đến khả năng sinh trưởng và phát sinh phôi, đặc biệt là tại nồng độ 50 mM NaCl giúp kích thích sự hình thành phôi từ mô sẹo với tỷ lệ hình thành phôi đạt 83,33%. Ngược lại, nồng độ từ 150 mM NaCl gây ức chế quá trình hình thành phôi soma từ mô sẹo. Tiếp tục khảo sát ảnh hưởng của muối đến khả năng phát triển và nảy mầm của phôi soma. Ghi nhận kết quả sau 4 tuần nuôi cấy phôi soma trong môi trường MS có bổ sung 0.07 mg/l spermidin, tại nồng độ 50 – 100 mM NaCl khả năng hình thành phôi tốt và phôi phát triển qua các giai đoạn phôi hình cầu, hình tim, hình thủy lôi và hình lá mầm. Đặc biệt ở nồng độ 50 mM số lượng phôi lá mầm đạt giá trị cao với 13,33 phôi. Nồng độ muối NaCl 150 mM chỉ xuất hiện phôi hình cầu trong suốt thời gian nuôi cấy. Quá trình giải phẫu hình thái phôi và sử dụng thuốc nhuộm 2 màu carmin – iod và acridine orange đã cho thấy rõ hơn về cấu trúc mô sẹo có khả năng sinh phôi và phôi hình thái.

The embryogenic calli were grown on MS medium containing NaCl with concentrations from 50 to 300 mM. After 2 weeks of culture, salinity tolerance threshold was identified at 150 mM NaCl. Higher concentrations of NaCl stimulated a significant reduction in the calli survival rate and the highest rate was 78.67% at 50 mM. After subculturing callus to the embryo culture medium containing NaCl, the growth and embryogenesis were not affected at the concentrations of 50 – 100 mM. Especially, at 50 mM NaCl the embryogenesis rate reached 83.33%. In contrast, 150 mM NaCl inhibited the somatic embryogenesis. After 4 weeks, culturing somatic embryos on medium MS with addition of 0.07 mg/l spermidin at 50 – 100 mM NaCl, the embryogenesis was considered good and embryos developed through several stages: globular, heart, torpedo and cotyledonary. However, at 150 mM NaCl the globular stage appeared in the culture process. The process of morphohistology and using dye carmine – iod and acridine orange observed the structure of generative callus and embryos at several stages. / Mô sẹo có khả năng phát sinh phôi được nuôi cấy trong môi trường có chứa muối NaCl với nồng độ thay đổi từ 50 – 300 mM. Sau 2 tuần nuôi cấy, chúng tôi xác định được ngưỡng chịu mặn của mô sẹo có khả năng sinh phôi cây Cọc rào là 150 mM. Nồng độ muối NaCl càng cao thì tỷ lệ sống của mô sẹo giảm dần và đạt giá trị cao nhất là 78,67% tại nồng độ 50 mM NaCl. Khi chuyển mô sẹo sang môi trường phát sinh phôi có chứa muối NaCl với nồng độ thay đổi, chúng tôi thấy ở nồng độ muối NaCl 50 – 100 mM không ảnh hưởng đến khả năng sinh trưởng và phát sinh phôi, đặc biệt là tại nồng độ 50 mM NaCl giúp kích thích sự hình thành phôi từ mô sẹo với tỷ lệ hình thành phôi đạt 83,33%. Ngược lại, nồng độ từ 150 mM NaCl gây ức chế quá trình hình thành phôi soma từ mô sẹo. Tiếp tục khảo sát ảnh hưởng của muối đến khả năng phát triển và nảy mầm của phôi soma. Ghi nhận kết quả sau 4 tuần nuôi cấy phôi soma trong môi trường MS có bổ sung 0.07 mg/l spermidin, tại nồng độ 50 – 100 mM NaCl khả năng hình thành phôi tốt và phôi phát triển qua các giai đoạn phôi hình cầu, hình tim, hình thủy lôi và hình lá mầm. Đặc biệt ở nồng độ 50 mM số lượng phôi lá mầm đạt giá trị cao với 13,33 phôi. Nồng độ muối NaCl 150 mM chỉ xuất hiện phôi hình cầu trong suốt thời gian nuôi cấy. Quá trình giải phẫu hình thái phôi và sử dụng thuốc nhuộm 2 màu carmin – iod và acridine orange đã cho thấy rõ hơn về cấu trúc mô sẹo có khả năng sinh phôi và phôi hình thái.

Rice (Oryza sativa L.) is the principal crop of North Eastern Tanzania but production is threatened by salt affected soils, drought and the use of un-adapted cultivars, among other constraints. Little research and hardly any breeding have been done on the aspects of salt tolerance of the crop in sub Saharan Africa, leading to low yields and low production in rice irrigation schemes under arid and semi arid conditions. A project was therefore implemented in North Eastern Tanzania during 2007-2010 seasons to investigate the possible breeding contributions to enhance productivity and production of the crop in salt affected areas. The objective of this study was to: a) determine farmers’ perceptions on both salt problems and their effects on rice crop productivity as well as establishing farmers’ needs and preferences for rice varieties in the targeted irrigated environment; b) determine the extent of salt problem in both soil and irrigation water in the available rice irrigation schemes in the North-eastern Tanzania; c) identify the major physiological mechanisms associated with salt tolerance in farmer-preferred native varieties and landraces; and d) determine the mode of inheritance of salt tolerance in rice. Participatory rural appraisal was conducted in Mkomazi and Mombo villages in Tanga region with the aim of understanding characteristics of rice–based farm economy, farmers’ perception of agriculture constraints and variety preferences in salt affected areas of North-eastern Tanzania. This was followed by a preliminary study to understand soil characteristics in relation to salt problems and its extent in selected nine rice irrigation schemes. Studies was established under controlled conditions to assess the salt tolerance of some rice farmers preferred rice cultivar and evaluate the putative traits in the rice materials that contribute to the performance of a genotype under saline and saline-sodic condition. Thereafter, genetic mechanism governing various morpho-physiological parameters in selected Tanzania local farmers’ preferred varieties and salt tolerant donors under saline and sodic soil conditions of North Eastern Tanzania were determined. A participatory rural appraisal (PRA) established that rice was a major staple food and cash crop and rice farming was a major economic activity in the area. However, soil degradation through increased salt affected soils was identified as the major factor responsible for irrigated rice yield decline. Major varieties grown are salt sensitive, and salt tolerant varieties were not available. The study also revealed that most farmers’ preferred traits of rice cultivars were high yield potential, aroma, early maturing, medium plant stature, tolerance to salt and drought. Improvement of these characters in new salt tolerant varieties would increase food production in fields with low or zero productivity and the well-being of the poor farmers. A soil characterisation study indicated the magnitude of the problem, whereby, seven out of nine studied irrigation schemes were affected and sodic and saline-sodic conditions were the dominant types of soils. Poor irrigation canals and management of irrigation water were the driving factors that contributed to salts accumulation causing a decline in productivity. Experiments were established under controlled environments to evaluate the tolerance of 10 and 11 rice genotypes under saline and saline-sodic stresses, respectively. Significant variation between genotype and significant interactions between genotype and salt treatment (P<0.001) were observed for all characters studied. Genotype Pokkalli, IR 67076-2B-21-2 and IR 56 showed superior performance under saline, whereas CSR 27, Nerica 2 and IR 56 had superior performance under saline-sodic. The study therefore established that, all the local farmer preferred cultivars except IR 56 performed poorly under both salt stress environments. High seedling vigour, less leaf injury, less Na+ and high K+ accumulation in leaves, low Na+/K+ ratio of ion uptake, high spikelet fertility, increased grains per panicle and 1000 grain weight were considered as the desirable characteristics therefore can be used in developing lines for salt tolerance for production under saline and saline - sodic conditions. Gene action and combining ability studies for nine morpho-physiological traits were studied under normal, saline and sodic soil environments. The rice populations were generated through 7 x 7 full diallel crosses and advanced to F2. The parents comprised two donors for saline tolerance, one donor for sodic tolerance and four salt sensitive farmers preferred varieties. Both additive and non-additive gene effects were important in the inheritance of the characters studied in all soil environments. However, additive effects were more important for the number of tillers, shoot Na+, Na+/K+ ratio and plant height. Both additive and non-additive gene effects were important for spikelet fertility, days to 50% flowering, number of grains per panicle, 1000 grain weight, and grain yield; however the magnitude of additive gene effect was higher than non additive effects. Amongst the parental lines, the best general combiners for yield along with other traits were TXD 306 and IR 67076-2B-21-2 under normal non-saline/sodic condition; IR 56, Pokalli and TXD 306 under saline condition and CSR 27 and TXD 306 under sodic conditions. The overall results from this study indicated the possibility of improving both yield and salt tolerance from this set of germplasm; therefore contributing to increasing rice yields in the marginal salt affected environments. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.