A taxonomic revision of Finlaysonia Wall. and Streptocaulon Wight and Arn. (Apocynaceae; Periplocoideaea) in Asia is presented. This revision comprises an investigation of the nomenclature of the two genera and their species, macromorphology of all plant parts; micromorphology of leaf epidermal surfaces, seed coat surfaces and translators, pollen wall architecture, geographical distribution, habitat preferences and phylogenetic relationships. The investigation resulted in the identification of characteristics for effective delimitation of the two genera and their respective species, identification keys for both genera and the species within each genus, correction of nomenclature, determination of inter-and intra-phylogenetic relationships and determination of their distribution patterns. Available type material was investigated, type literature was confirmed for all species and synonyms were declared where applicable. Lectotypes, selected from isotypes or syntypes, were declared where holotypes were not cited by authors or were not found in their collections or were destroyed or could not be located at all. Finlaysonia and Streptocaulon are closely related genera and have many characters in common. This includes the presence of colleters on the interpetiolar ridges, in leaf axils, on the leaf petiole and main vein, in the axils of inflorescences and at the inner bases of sepals. The flowers in both genera are rather similar with bowl-shaped, inverted corolla tubes and reflexed lobes, presence of only the primary corona which is divided into a foot and lobe, presence of interstaminal nectaries, translators and pollinia, two semi-inferior, apocarpous many ovuled-ovaries, a compound style, a gynostegium that is the result of fusion between stylar head and anthers, paired follicles and seeds with comas at the micropylar end except in F. obovata where the coma is replaced by a winged, fimbriate margin. Finlaysonia is characterized by trichomes on the outer or inner surfaces of the corolla, presence of anther callosities except in F. pierrei. Streptocaulon, in contrast, is characterized by a glabrous corolla, absence of anther callosities. A number of characters, unique to a specific species and thus diagnostic were used in identifying of the species. Vegetative features provide the most effective means to distinguish and identify the species and combinations of leaf shape, leaf length:width ratios, texture, leaf indumentum and petiole length proved to be taxonomically the most valuable characters. Corolla lobe apex shape, corona lobe shape, anther connective indumentum, style indumentum, follicle and seed shape and size, seed margin appearance and coma length and presence/absence of coma are diagnostically useful. Micromorphological features of the leaf epidermis, such as primary sculpture, as well as stomata characteristics and distribution can also be useful. However, a single character is often insufficient to distinguish between the genera and a combination of characters should to be applied. Finlaysonia and Streptocaulon are widely distributed in Asia with the largest concentration of species in Thailand. Species like F. khasiana, F. obovata, F. pierrei, S. juventas and S. wallichii are common, while F. decidua, F. puberulum, F. venosa, F. insularum, S. cumingii, S, curtisii, S. lanuginosa and S. sylvestre have restricted distributions, at present only known from one or two localities. Most of the species are found on limestone and form part of scrub forest and mixed deciduous forest. Finlaysonia obovata typically are found in mangrove forests along coastal lagunes and tidal rivers, while S. sylvestre and S. juventas are found in riverine forest along fresh water rivers. The phylogenetic treatment was based on morphological characters of vegetative parts, flowers and fruits. The analyses yielded polytomies as strict concensus trees unless the Bootstrap support values were ignored. However, an exciting result from the strict concensus trees was the pairing of S. lanuginosa and S. curtisii in a clade, confirming the finding of Ionta and Judd (2007) and justifying the transfer of these two species from Finlaysonia to Streptocaulon.

Cryptolepis R.Br. (Apocynaceae, Periplocoideae) was taxonomically revised. Detailed descriptions of macro and micro-morphology, palynology, geographic distribution and ecological characteristics were presented. An identification key to the species was compiled and the nomenclature of all species was revised while all available type material was studied and lectotypes and neotypes were designated where necessary. Molecular phylogenetic analyses, based on the gene regions ITS, trnDâT and trnTâF, of representative species of 28 periplocoid genera and 22 Cryptolepis species were presented and the monophyly of Cryptolepis was evaluated. Historically a total of 81 species names and four subspecies names were published for Cryptolepis. However, a large number of species names were later placed in synonymy or transferred to other genera, while several new combinations were published. This resulted in a total of 29 accepted Cryptolepis species at the commencement of this study. Three new species, C. ibayana, C. thulinii and C. villosa, resulted from this study and the latter two were described in this thesis. One species, C. producta, was synonymised with C. oblongifolia. Cryptolepis, therefore, comprises a total of 31 species at present. In terms of species diversity, distribution and potential pharmaceutical and economic value, Cryptolepis is one of the most significant genera in the Periplocoideae. Cryptolepis grows throughout sub-Saharan Africa, the southern parts of Yemen, the island archipelago of Socotra, and southern Asia ranging from India to southern China, Taiwan, the Philippines and Indonesia. Most of the species grow in tropical forests or savannah, but 13 species are also adapted to arid environments. The majority of Cryptolepis species are concentrated in four centres of diversity along the east coast of Africa and on Socotra. These hotspots are associated with both arid and forest refugia in areas which have been regarded as local centres of endemism for a number of other plant taxa. The phylogenetic analysis of Cryptolepis indicates that most of these hotspots were colonized repeatedly by different Cryptolepis groups. In addition to the influence of climate shifts, edaphic conditions and also fire had a significant influence on species diversity and distribution in Cryptolepis. Macro and micro-morphological investigations indicated that numerous characters, including growth form, leaf shape and size, leaf epidermal characters, venation, inflorescence structure, floral structure and seed coat surface characters, are of diagnostic value at species level in Cryptolepis. However, the species can only be accurately identified by using a combination of these characters. The molecular phylogenetic analyses revealed that Cryptolepis is paraphyletic and, in order to establish a monophyletic genus, it was proposed that the circumscription of the genus be broadened to include Parquetina as a synonym of Cryptolepis. Several vegetative and reproductive characters showed a high degree of homoplasy, suggesting a high degree of morphological plasticity. This plasticity was also found at species level in C. oblongifolia, which showed significant variation in vegetative and reproductive features. This, together with a high tolerance for disturbance, has resulted in C. oblongifolia becoming the most widely distributed of all Cryptolepis species.

Bacterial brown spot (BBS), caused by Pseudomonas syringae pv. syringae (Pss), Van Hall, is one of the important bacterial diseases of common bean (Phaseolus vulgaris L.) globally including South Africa. The disease is seed-borne and is widely prevalent in dry bean producing areas of South Africa. It mainly infects foliage and to a lesser extent pods. Use of resistant dry bean cultivars is considered the most durable means of managing the disease. This study aimed at updating the incidences of BBS and severities, characterisation of BBS isolates, determining reaction of South African dry bean cultivars and germplasm, and investigating heritability to project possibilities of improving resistance in the local cultivars. Thirty one locations in five provinces were surveyed for BBS incidences. BBS was observed in 87% of locations. BBS incidence ranged between 40-100% during the 2008/09 season and between 0-100% during the 2010/11 season in all the farming systems surveyed. BBS was more severe in the strip and National Cultivar Trials (NCTs) during the 2008/09 season and in the commercial and NCT during the 2010/11 season. Findings of this study signal the importance of developing BBS resistant dry bean cultivars for South Africa. The biochemical and genetic variability of 140 Pss isolates collected from dry bean producing areas in South Africa was assessed. Pure isolates were subjected to LOPAT tests and SyrB gene assessment. Biolog GN Microplates were used to assess carbon substrate utilisation. The SyrB gene was present in 42% of isolates. The Biolog GN Microplates showed biochemical variation among isolates. Variable genomic patterns were observed in 48.5% by the BOX A1R primer and in 37.1% of isolates by the ERIC 2 primer. Thus, variability exists in Pss populations of dry beans. Thirty six dry bean cultivars were assessed at three locations and replicated for three seasons to determine reaction to BBS. Teebus, Teebus-RR1 and Kranskop-HR1 had high BBS mean ratings of 4.7, 4.5 and 4.2, respectively. A similar trend was evident in AUDPC with values of 103.83 (Teebus) and 97.67 (Teebus-RR1) and 96.85 (RS 6). Improvement of BBS resistance in South African cultivars is necessary. Twenty-eight common bean accessions were assessed over three seasons and locations for resistance to BBS. Hystyle and VAX 4 had lowest disease ratings of 2 and 1.7 and AUDPC values of 29.2 and 39.0, respectively, and are therefore, potential resistance sources. Crosses between BBS resistant selected sources (Hystyle and BBSR 17) and susceptible local cultivars (Kranskop-HR1, Sederberg and Teebus-RCR2) were made. The parental lines, as well as the F1, F2, BC1F1 and BC1F2 progenies were planted in a commercial greenhouse and the F3 in the field. The Teebus/BBSR 28 population (F5:6) and the Kranskop/VAX 4 population (F6:8) and (F6:9) were received from the Agricultural Research Council â Grain Crops Institute and planted in the field. All F1 plants were resistant to BBS, the F2 populations showed 3:1 (resistant:susceptible) segregation ratio while the F3 families showed a 1:2:1 segregation ratio. Resistance in both Hystyle and BBSR 17 is conditioned by a single dominant gene. This suggests that resistance may be easily overcome and it is essential that more BBS resistance genes be identified if efficient and long lasting resistance is to be ensured. Furthermore, the BBS resistance gene and yield traits in Hystyle and BBSR 17 are moderately to highly heritable. These findings highlight the increasing threat of BBS in farming systems and experimental trials, thereby increasing risk of food security and lower profits. The current BBS epidemics, incidences and severities signify the importance and urgency for development of BBS resistant dry bean cultivars.

Maize is among the most commonly bred crops in the world and maize breeding programmes are increasingly using molecular tools to enhance the efficiency and speed of developing productive cultivars. Breeding efforts of CIMMYT have focused on incorporating drought tolerance into elite germplasm. The incorporation of the Fbr1 gene into its elite germplasm was one such effort as the improvement of drought tolerance relies on manipulation of adaptive traits that limit yield under the target stress. The aim of this study was to find the genetic basis and effect of the Fbr1 tassel mutation on maize grain yield under stress and non-stress environments. A number of elite CIMMYT lines have been successfully converted to the Fbr1 mutation, and were homozygous for the 1074 SNP loci used, thus could be used in breeding programmes involving these new tassel mutants. The UPGMA cluster analysis revealed two discrete clusters of the inbred lines according to predefined CIMMYT heterotic groups. In the principal component analysis, the SNP loci were effective in characterising the maize inbred lines since they separated maize lines according to tassel size. Positive relationships between grain yield and pollen yield and its components were found, under drought conditions. However, the Fbr1 tassel trait did not have a positive effect on yield under stress and Fbr1 x Fbr1 hybrids had lower grain and pollen yield, and were less adapted to abiotic stress conditions. This raised questions on the value of incorporating such trait in breeding programmes targeting stress tolerance. Therefore, incorporation of the Fbr1 tassel trait should accompany selection for other traits associated with stress tolerance under low N and drought conditions, such as the âstay greenâ trait, factors associated with premature senescence, synchrony between male and female flowering and decreased barrenness if yield gain is to be realized. Estimates of genetic components of variance revealed importance of both additive and dominance components in the determination of grain yield, pollen yield and their components. Additive gene action was predominant in determining tassel size and pollen yield, thus progress can be made by selecting within segregating progenies when improving maize populations for the Fbr1 trait. The investigation of GxE interaction showed significant variation in stability of Fbr1 lines and hybrids as measured by mean yield and ASV. The AMMI and the GGE biplots ranked the best and poorest genotypes similarly in terms of yield performance and stability. The two classification models could be used simultaneously to make selection of genotypes more precise. Genetic distances were positively correlated with hybrid performance, SCA, and heterosis indicating that genetic distance could accurately predict hybrid performance in this set of germplasm. This study showed that yield is a complex trait and its improvement under stress should involve simultaneous selection of other traits associated with stress tolerance. The SNP markers are the marker of choice in genetic characterisation and determination of marker-based genetic distances because of their wide coverage of the maize genome. A number of lines homozygous for the Fbr1 tassel trait, has been identified in this study. These lines could be used in future research such as the developing of mapping populations aimed at tagging the Fbr1 trait, since the position of the Fbr1 gene in the maize genome is still unknown.

Plants emit a vast array of volatile organic compounds to which surrounding plants can respond. Recent research suggested volatile signalling between leaf rust (Puccinia triticina Erikss.) infected and uninfected wheat (Triticum aestivum L.). The current project was undertaken to further investigate these putative events. Uninfected wheat was exposed to volatiles emitted by leaf rust infected wheat in a continual air flow system. Different combinations of resistant (Thatcher+Lr9) and susceptible (Thatcher) wheat lines were used for the volatile exposure experiments. When susceptible seedlings were exposed to volatiles from either resistant or susceptible plants there was a significant decrease in percentage leaf area infected and pustule size after a subsequent infection with leaf rust. The volatile exposure was also linked with an induced defence response as confirmed with increased enzyme activity and gene expression. Generally, an induction of β-1,3-glucanase activity was observed at 8 hours post exposure in exposed resistant and susceptible seedlings regardless of the infected line that released the volatiles. Pathogen-related protein 2 gene expression was also induced at 8 hours post exposure in both lines exposed to volatiles released by infected resistant seedlings but not in those exposed to infected susceptible seedling volatiles. This induction of the defence response could only be attributed to volatiles emitted by infected wheat seedlings. Emitted volatiles were captured by solid phase micro-extraction and classified by gas chromatography mass spectrometry. Infected resistant seedlings released a number of unique volatiles including ocimene that was not observed in both the mock infected resistant or infected and mock infected susceptible seedlings. Fewer unique volatiles were observed in the infected susceptible seedlings compared to the mock infected susceptible seedlings with green leaf volatiles being common in both treatments. Some of the identified volatiles were previously linked to the defence response in plants.

Grain crops are often afflicted with a disease commonly referred to as root rot or foot rot. Because root rot diseases are very variable in their symptom expression, they are frequently overlooked as the abnormal condition is often attributed to drought, wind, frost or other causes. For these reasons it is difficult to estimate the damage caused exclusively by root rots. It is generally agreed that the fungus Helminthosporium sativum P.K. & B. is of prime importance in the root rot complex affecting barley and wheat. By plating tests of seed samples of barley and wheat grown in representative areas of Canada, Greaney (1944) showed that the most important pathogen present was H. sativum. Oswald (1950) in California found the four primary pathogenic fungi attacking barley and wheat, in their order of apparent economic importance, to be Helminthosporium sativum, Fusarium roseum f. cerealis, Ophiobolus graminis and Fusarium nivale. Simard and Ludwig (1946) found that, in the years 1942 and 1943, 65 per cent of the Quebec grown barley seed samples examined by them carried H. sativum. The significance or Helminthosporium sativum in the barley and wheat growing areas is indicated by estimates of the damage caused by this fungus. Maohaeek (1943) concluded from the results of a three year survey in Manitoba that barley and wheat yields are reduced by as much as 12 per cent because of root rot.[...]

<p> Auxin is a crucial plant hormone that shapes and directs plant growth. Indole-3-acetic acid (IAA) is the predominant auxin in nature. Auxin regulates cell expansion and cell division in a dose dependent way. Therefore, plants evolved an extremely complex yet highly coordinated network to maintain auxin homeostasis, including IAA biosynthesis, transport, conjugation and oxidation. Among these, the least known process is IAA oxidation. Discovering how IAA is terminated is very important in completing the whole picture of IAA homeostatic regulation. By partial purification of IAA oxidases from <i>Arabidopsis </i>, we detected IAA oxidation activity from both microsomal fractions and soluble fractions. We first investigated the protein in microsomal fraction and identified one oxidase named as ACC oxidase 2 (ACO2), an ethylene synthetase that belongs to 2-oxoglutarate and iron (II) [2OG(Fe)] dependent dioxygenase family. <i>In vitro</i> enzyme assays with IAA showed that ACO2 could catabolize IAA and that the product had the same retention time as indole-3-carbinal (ICA), an decarboxylative IAA oxidation product. The same enzyme assay with the ACO2 homologues ACO3 was conducted, and ACO3 showed similar activity. An <i>ACO2</i> loss-of-function allele showed ethylene related phenotypes, including longer hypocotyls and reduced apical hook angle in etiolated seedlings, and delayed bolting. Further, null aco2 mutants also showed reduced phototropic bending, a typical auxin related phenotype. These results indicate that ACO2 might be involved in both ethylene and auxin signaling.</p><p> We also investigated the soluble IAA oxidases, <i>AtDAO1 (DAO1) </i> and <i>AtDAO2 (DAO2)</i>. <i>In vitro</i> enzyme assays showed that both recombinant DAO1 and DAO2 have IAA oxidation activity and the product is the non-decarboxylated 2-oxindole-3-acetic acid (oxIAA), the major IAA metabolite observed under normal growth conditions. Analysis of the loss-of-function null allele <i>dao1-1</i> showed that DAO1 is the predominant IAA oxidase and is responsible for 95% of oxIAA production in <i>Arabidopsis</i> seedlings. Dysregulation of IAA oxidation altered the IAA metabolism profile and causes accumulation of other IAA conjugates and a series of morphological alteration, including elongation of organs, increased lateral roots and delayed sepal opening. Investigation of expression patterns shows that DAO1 is a cytosolic protein that widely expressed throughout the plant, especially in the root tip, the pericycle of root, the cotyledon, and the sepal, highly correlating to the phenotypes of <i>dao1-1</i>. These results suggest that IAA oxidation plays an important role in IAA homeostasis during the whole life of <i>Arabidopsis</i>.</p>

Abscisic acid (ABA) is a plant hormone that regulates various developmental processes and environmental stress responses. ABA modulates growth of both primary roots and lateral roots, helping to shape root architecture. The lateral root organ defective (latd) mutants, disrupted in the MtLATD/NIP gene, encoding a nitrate transporter, have severe root growth defects that can be rescued by applying ABA. However, the way in which ABA stimulates latd root growth is unclear, and the downstream components of MtLATD/NIP and ABA signaling are completely unknown. To answer these questions, this dissertation focuses on two major potential downstream regulators: Reactive Oxygen Species (ROS) and transcription factors (TFs). ROS are important signaling molecules required in ABA-induced stomatal closure under drought or osmotic stresses, but their role in ABA regulation of root development is unclear. I found that latd mutant roots have increased ROS levels, and the expression level of several MtRboh genes, which encode major ROS-producing enzymes, the NADPH oxidases, is also increased. ABA decreases the amount of ROS in latd roots and also reduces expression of MtRbohC, in particular. In addition, I observed that latd mutant roots have cell elongation defects, which can also be rescued by exogenous ABA. I demonstrated that pharmaceutically decreasing ROS levels using an NADPH oxidase inhibitor, or reducing the expression of MtRbohC using RNA interference can increase cell elongation and stimulate lateral root elongation in latd roots. These findings have revealed a mechanism by which ABA restores root growth in latd mutant roots via regulating ROS levels, and identified MtRbohC as an important downstream target of ABA signaling mediated by MtLATD/NIP. TFs act as regulatory nodes controlling the transcription of gene clusters and playing a crucial role in plant growth and development. Using a high-throughput TF profiling approach, I have identified 20 TFs that exhibit altered expression levels in latd mutant roots as compared to wild type, 60% of which can be restored to normal levels by ABA. My analysis also revealed that ABA regulates the expression of a different set of TFs in latd roots, suggesting that MtLATD/NIP is crucial for ABA regulation of TF expression. Moreover, ABA changes the TFs regulated by MtLATD/NIP almost completely, indicating a tight control of ABA on TFs regulated by MtLATD/NIP. Surprisingly, I found that the expression of NODULATION SIGNALING PATHWAY 2 (MtNSP2), a GRAS family TF required for nodulation, is regulated by MtLATD/NIP, ABA and nitrate in non-symbiotic roots. In symbiotic roots, MtLATD/NIP is required for the transcriptional signaling pathway downstream of MtNSP2 in the epidermis as well as induction of MtNSP2 expression by cytokinin and subsequent activation of its downstream targets in the cortex. These findings indicate that MtLATD/NIP functions in nodulation signal transduction upstream of MtNSP2, and mediates crosstalk with cytokinin. Together, these two approaches have begun to characterize a signaling pathway downstream of ABA and MtLATD/NIP that involves ROS, MtNSP2, and a core group of TFs in the regulation of root development and nodulation in M. truncatula.

No description available.

Thesis (M.B.A.)--Boston University