The incorporation of cereal straw/stubble often immobilises nitrogen (N). This can help conserve N in soil in organic forms, thus reducing loss through leaching over dormant winter periods. However, N-depressions that arise during decomposition can reduce crop yield. The inclusion of a legume green manure can supply fixed-N, thus alleviating the low N availability to crops. In this study, the effect of lupin (Lupinus angustifolius L.) green manure incorporation on barley (Hordeum vulgare L.) straw/stubble decomposition, and N availability was investigated. A field experiment was used to determine the effects of the green manure on decomposition. Decomposition of straw/stubble was monitored using the litterbag technique. Following green manure incorporation, soil cores were incubated in a glasshouse to determine mineral-N availability. Though not significant, the inclusion of lupin green manure seemed to increase the decomposition of straw/stubble during the growth period, then slowing it after its incorporation at 110 d. This was described by a logarithmic pattern of loss of - 4.97 g AFDW residue day⁻¹, with 60% remaining after 140 d. Treatments without lupin had a linear decomposition of - 0.12 g AFDW residue day⁻¹, with 49% remaining after 140 d. The loss of cellulose confirmed the differences in decomposition with the inclusion of lupin resulting in 2.79% less cellulose remaining in straw/stubble after 140 d compared to its exclusion. Lupin significantly increased pot oat N uptake and DM yield by 55 % and 46 %, respectively, compared to its exclusion. However, this effect was not observed in field sown wheat yields and the soil mineral-N measurements made. This study showed that the potential of lupin to increase straw/stubble decomposition by improving the retention and availability of N, leading to long-term yield benefits, needed further investigation.

Plant immune system is entirely based on the immunities of the individual cells in which systemic signals originate from the infection sites. Powdery mildew disease is one of the agents causing these infection sites, resulting in significant yield losses, if disease develops. Understanding the molecular basis of plant-pathogen interactions is the new trend for fighting against plant pathogens, since classical methods used in selection of resistant plants are becoming less and less efficient nowadays. Thus, finding out the genes which are responsible in plant&rsquo / s resistance is becoming very important. In this thesis, effect of &lsquo / General Control Nondepressible-2&rsquo / (GCN2) homolog protein in barley defense mechanism was aimed to be studied. The GCN2 of yeast was v previously identified in our laboratory as an interacting protein when the yeast cDNA library was screened with a putative yellow rust R gene (Yr10) fragment. There are reports available in the literature for the function of GCN2 protein, which makes it a good candidate for a role in disease resistance. Thus, the barley homologue of GCN2 might have a role in the R protein mediated early disease response of which may be proceeding via Programmed Cell Death (PCD). In order to observe such function of HvGCN2 in barley, silencing of its expression via Virus Induced Gene Silencing (VIGS) was investigated. Therefore, the GCN2 homologue was found to function as dampening the severity of the disease. The silencing with triple technical replicates was observed in 5 of the 6 samples, at an average of 43.2% by qRT-PCR analysis. The pathogen growth levels at different time points were analyzed under light microscope on the silenced and the control samples by measuring the primary and secondary hyphae lengths. The total of 24 seedlings and 292 individual spores were analyzed, and then the level of disease formation was quantitated with 603 primary hyphae and 106 secondary hyphae measurements. Up to 25% hyphae growth rate differences between the control and silenced groups were observed with a probability value less than 0.05 on t-test.

Proportional loss models commonly used in disease surveys are based on the assumption that per cent yield loss is the same in all crops, regardless of their yield potential. Estimates of regional crop loss may be inaccurate if the relationship between disease and yield loss is affected by crop yield potential. The importance of crop yield potential in disease: yield loss modelling was investigated and models for more accurate regional crop loss estimates were developed, taking crop yield potential into account. Two spring sown barley (cv. Triumph) experiments were conducted in 1987/88 and 1988/89 in Canterbury, New Zealand, to study the effect of crop yield potential on the relationship between disease and yield loss. Crop yield potentials of 323 to 806gDM/m² were generated in seven crops by varying nitrogen and water inputs, sowing date (mid-spring and early-summer) and season. Leaf rust (Puccinia hordei Otth) epidemics of different severity were generated by applying fungicides at different times, frequencies and rates to control the natural epidemics. Disease was measured as per cent disease severity (%DS), green leaf area, radiation interception and near-infrared radiation (NIR) reflectance from crop canopies. Yield was measured as total and grain dry weight. Epidemics were severe in the fully diseased plots from GS 34 and 46 to maturity in the late and early sown crops respectively. Disease reduced grain yield by 50 to 63% in 1987/88 and 24 to 38% in 1988/89 in the fully diseased plots. Disease: yield loss models were derived by regression analysis for each crop in 1987/88. Single point, multiple point and area under curve models were derived from %DS and GLAI variables, and proportional (%) and actual (gDM/m²) grain yield. The effect of yield potential was determined by comparing regression equation coefficients for each crop with crop yield potential. An area under green leaf area index curve (AUGLAIC): actual yield model was best suited to determining the effect of yield potential on yield loss. This model was selected because AUGLAIC summarised the effect of disease on plant growth over the season and actual yield represented the crop yield potential in the absence of disease and the response of actual yield to disease. Crop yield potential did not affect actual yield loss caused by leaf rust. Disease measured as AUGLAIC explained most of the variation in yield (R²adj=0.93) for all crops in both years. Assessment of GLAI is not suitable for estimation of regional crop loss because of the requirement for a rapid and low cost method. Reflectance of NIR from the crop canopy was investigated as an alternative to GLAI measurements. Reflectance was correlated significantly (P<0.001) with GLAI (r=0.66 to 0.89) and green area index (r=0.76 to 0.92). Reflectance measured at grain-filling (GS 85-87) explained most (R²adj=0.94) of the variation in yield for all crops in both years. The relationship between AUGLAIC and yield was validated with data from independent diseased and healthy barley crops. The AUGLAIC: yield model described the effects of disease on yield accurately but overestimated yield by 49 to 108% in the healthy crops. Models based on accumulated PAR (photosynthetically active radiation) intercepted by green leaves explained the observed deviations in yield of these crops from the AUGLAIC: yield model. Accumulated PAR models accounted for differences in incident radiation, canopy structure, radiation interception by green leaves, radiation use efficiency and harvest index which are important in determining dry matter production and grain yield. Accumulated PAR models described the effects of disease on crop growth which were not represented by GLAI alone. Variation in crop yield potential at the regional scale is important in disease: yield loss modelling and can be accounted for by using either separate equations for each yield potential crop or crop category, robust models, inclusion of a form function for yield potential or choice of disease and yield variables which integrate yield potential.

The response of yarrow (Achillea millefolium L.) seedlings to reduced light, interference from barley (Hordeum vulgare) and some aspects of regeneration from rhizomes were the subject of investigations from 1976 until 1980. Seedlings grown under four intensities of photosynthetically active radiation (100, 46.8, 23.7 and 6.4% of full summer daylight) were harvested on six occasions and the changes with time in the logarithms of leaf area, leaf, stem, root and total dry weights per plant were described by polynomial regression equations. Relative growth (RGR), net assimilation rate (NAR), leaf area ratio (LAR), specific leaf area (SLA) and leaf weight ratio (LWR) were derived directly from the growth curves. SLA and LWR increased with increased shading causing LAR to rise, while NAR declined. Response curves of RGR on light intensity, derived from linear regressions of LAR and NAR on the logarithm of relative light intensity predicted maximum RGR to occur at light intensities which decreased with time. This was a consequence of ontogenetic changes in LAR, and changes in NAR apparently related to self shading. Linear regressions of LAR and NAR at a constant total plant dry weight of 1.62 g showed that the increase in LAR almost completely compensated for the reduction in NAR down to approximately 40% full daylight, and maximum RGR was predicted to occur at 59% full daylight. The light compensation point was estimated to be 3.6% full daylight. Yarrow populations established from 25 and 50 10 cm rhizome fragments m⁻² were grown alone and with barley at 194 or 359 plants m⁻². The barley populations were also grown alone. Growth analysis employing the regression technique showed the RGR of yarrow was reduced by barley from before jointing (Feekes Scale, Stage 6) as a consequence of reduced NAR. The NAR of yarrow was significantly reduced in the continued presence of barely, which by the time of the final barely harvest resulted in 91 and 94% reduction in the accumulated yarrow dry matter at 194 and 359 barely plants m⁻² respectively. The proportion of total dry matter allocated to seed and rhizome was also reduced by barley but the barley was unaffected by the yarrow. During the autumn and early winter, after removal of the barley, the suppressed yarrow had a higher RGR than the unsuppressed population, owing to higher LAR and NAR. Rhizome growth was vigorous during both autumn and winter in all yarrow populations, but the RGR of rhizome dry matter was higher in the suppressed yarrow during the autumn. This resulted in a progressive reduction in the difference in rhizome dry matter between suppressed and unsuppressed populations. Several aspects of the development and regenerative potential of rhizomes were investigated. In the first experiment, plants were established from seed and rhizome fragments and harvested on several occasions. Plants from both propagules formed rhizomes on which approximately 97% of auxiliary buds remained dormant, as long as the plants were undisturbed. Buds on rhizomes attached to the parent plant formed rhizome branches when the apex was damaged, had emerged from the soil, or in situations where internodes were congested. In the second experiment, rhizome fragments of 4, 8 and 16 cm in length were planted in soil at depths of 0, 2.5, 5.0, 10.0, 20.0 and 30.0 cm. All fragments on the soil surface died without forming shoots owing to desiccation whilst 100% mortality at 20 and 30 cm was probably the result of flooding. Within the 2.5 to 10.0 cm range, an increasing percentage of fragments survived (produced an aerial shoot(s)) as burial depth was reduced and fragment length increased. Within this depth range, the percentage of buds which had become active on undecayed fragments declined with increased length and burial depth. In the third experiment, single-node rhizome pieces were excised from rhizomes retrieved from field populations over a one year period, and incubated at 25°C for 10 days in darkness. More than 90% of buds formed vertical shoots throughout the year, indicating there was no period of innate dormancy in isolated buds. The effect of time of planting on the pattern of early regenerative development was assessed in the fourth experiment, in which 10 cm rhizome fragments were planted at 5 cm depth in soil on two occasions (in November and April). The developmental pattern was the same regardless of month of planting and new rhizomes were initiated at nodes on the vertical subterranean shoots when 5 to 6 aerial leaves had developed. The planted rhizome fragments declined in dry weight and a minimum weight occurred at about the time when rhizome initiation began.

ABSTRACT The xyloglucan endo-transglycosylase/hydrolase (XTH) genes are found in all vascular and some nonvascular plants. The XTH genes encode proteins which comprise a subfamily of glycoside hydrolase (GH) family 16 in the Carbohydrate-Active enZYmes (CAZY) classification. The XTH gene products are believed to play intrinsic role in cell wall modification during growth and development throughout the lifetime of the plant. In the present investigation, biochemical and reverse genetic approaches were used to better understand the functions of individual members of the XTH gene family of two important plants: the model organism Arabidopsis thaliana and the grain crop barley (Hordeum vulgare). A phylogenetic tree of the xyloglucan-active enzymes of GH16 has previously been constructed, where enzymes with similar activities have been shown to cluster together. Several members of phylogenetic Group I/II and III-B, predicted to exhibit xyloglucan endo-transglycosylase activity (EC 2.4.1.207) and members of Group III-A, predicted to exhibit xyloglucan endo-hydrolase activity (EC 3.2.1.151), were included to analyze the functional diversity of XTH gene products. A heterologous expression system using the yeast Pichia pastoris was found to be effective for recombinant protein production with a success rate of ca. 50%. XTH gene products were obtained in soluble and active forms for subsequent biochemical characterization. In order to be able to screen larger numbers of protein producing clones, a fast and easy method is required to identify clones expressing active protein in high enough amounts. Thus, a miniaturized XET/XEH assay for high-throughput analysis was developed, which was able to identify activities with good precision and with a reduced time and materials consumption and a reduced work load. Enzyme kinetic analysis indicated that the XET or XEH activity of all XTH gene products characterized in the present study corresponded to predictions based on the previously revised phylogenetic clustering. To gain insight into the biological function of the predominant XEHs AtXTH31 and AtXTH32, which are highly expressed in rapidly developing tissues, a reverse genetic approach was employed using T-DNA insertion lines of the A. thaliana Columbia ecotype. Genotypic and phenotypic characterization, together with in situ assays of XET and XEH activities, in single- and double-knock-out mutants indicated that these Group III-A enzymes are active in expanding tissues of the A. thaliana roots and hypocotyl.  Although suppression of in muro XEH activity was clearly observed in the double-knock-out, no significant growth phenotype was observed, with the exception that radicle emergence appeared to be faster than in the wild type plants. Keywords: Arabidopis thaliana, Hordeum vulgare, plant cell wall, xyloglucan, glycoside hydrolase family 16, xyloglucan endo-transglycosylase/hydrolase gene family, xyloglucan endo-transglycosylase, xyloglucan endo-hydrolase, heterologous protein expression, Pichia pastoris, T-DNA insertion, in situ XET/XEH assay, high-throughput screening / QC 20110114