Genetic variation of and environmental effects on inducibility of resistance in tomatoes (Solanum lycopersicum L.) to Phytophthora infestans (Mont) de Bary

Many plant strengtheners are promoted for their supposed effects on nutrient uptake and/or resistance induction (IR). In addition, many organic fertilizers are supposed to enhance plant health and several studies have shown that tomatoes grown organically are more resistant to late blight, caused by Phytophthora infestans to tomatoes grown conventionally. Much is known about the mechanisms underlying IR. In contrast, there is no systematic knowledge about genetic variation for IR. Therefore, the following questions were addressed in the presented dissertation: (i) Is there genetic variation among tomato genotypes for inducibility of resistance to P. infestans? (ii) How do different PS compare with the chemical inducer BABA in their ability to IR? (iii) Does IR interact with the inducer used and different organic fertilizers? A varietal screening showed that contrary to the commonly held belief IR in tomatoes is genotype and isolate specific. These results indicate that it should be possible to select for inducibility of resistance in tomato breeding. However, isolate specificity also suggests that there could be pathogen adaptation. The three tested PS as well as two of the three tested organic fertilisers all induced resistance in the tomatoes. Depending on PS or BABA variety and isolate effects varied. In contrast, there were no variety and isolate specific effects of the fertilisers and no interactions with the PS and fertilisers. This suggests that the different PS should work independent of the soil substrate used. In contrast the results were markedly different when isolate mixtures were used for challenge inoculations. Plants were generally less susceptible to isolate mixtures than to single isolates. In addition, the effectiveness of the PS was greater and more similar to BABA when isolate mixtures were used. The fact that the different PS and BABA differed in their ability to induce resistance in different host genotype -pathogen isolate combinations puts the usefulness of IR as a breeding goal in question. This would result in varieties depending on specific inducers. The results with the isolate mixtures are highly relevant. On the one hand they increase the effectiveness of the resistance inducers. On the other hand, measures that increase the pathogen diversity such as the use of diversified host populations will also increase the overall resistance of the hosts. For organic tomato production the results indicate that it is possible to enhance the tomato growing system with respect to plant health management by using optimal fertilisers, plant strengtheners and any measures that increase system diversity.

Clay pot irrigation for tomato (Lycopersicon esculentum Mill) production in the north east semiarid region of Ethiopia

Water shortage is one of the major constraints for production of horticultural crops in arid and semiarid regions. A field experiment was conducted to determine irrigation water and fertilizer use efficiency, growth and yield of tomato under clay pot irrigation at the experimental site of Sekota Dryland Agricultural Research Center, Lalibela, Ethiopia in 2009/10. The experiment comprised of five treatments including furrow irrigated control and clay pot irrigation with different plant population and fertilization methods, which were arranged in Randomized Complete Block Design with three replications. The highest total and marketable fruit yields were obtained from clay pot irrigation combined with application of nitrogen fertilizer with irrigation water irrespective of difference in plant population. The clay pot irrigation had seasonal water use of up to 143.71 mm, which resulted in significantly higher water use efficiency (33.62 kg m^-3) as compared to the furrow irrigation, which had a seasonal water use of 485.50 mm, and a water use efficiency of 6.67 kg m^-3. Application of nitrogen fertilizer with irrigation water in clay pots improved fertilizer use efficiency of tomato by up to 52% than band application with furrow or clay pot irrigation. Thus, clay pot irrigation with 33,333 plants ha^-1 and nitrogen fertilizer application with irrigation water in clay pots was the best method for increasing the yield of tomato while economizing the use of water and nitrogen fertilizer in a semiarid environment.

Effects of shoot pruning and inflorescence thinning on plant growth, yield and fruit quality of greenhouse tomatoes in a tropical climate

The combined effects of shoot pruning (one or two stems) and inflorescence thinning (five or ten flowers per inflorescence) on greenhouse tomato yield and fruit quality were studied during the dry season (DS) and rainy season (RS) in Central Thailand. Poor fruit set, development of undersized (mostly parthenocarpic) fruits, as well as the physiological disorders blossom-end rot (BER) and fruit cracking (FC) turned out to be the prevailing causes deteriorating fruit yield and quality. The proportion of marketable fruits was less than 10% in the RS and around 65% in the DS. In both seasons, total yield was significantly increased when plants were cultivated with two stems, resulting in higher marketable yields only in the DS. While the fraction of undersized fruits was increased in both seasons when plants were grown with a secondary stem, the proportions of BER and FC were significantly reduced. Restricting the number of flowers per inflorescence invariably resulted in reduced total yield. However, in neither season did fruit load considerably affect quantity or proportion of the marketable yield fraction. Inflorescence thinning tended to promote BER and FC, an effect which was only significant for BER in the RS. In conclusion, for greenhouse tomato production under climate conditions as they are prevalent in Central Thailand, the cultivation with two stems appears to be highly recommendable whereas the measures to control fruit load tested in this study did not proof to be advisable.

Changes of traditional farming systems and their effects on land degradation and socio-economic conditions in the Inle Lake region, Myanmar

At many locations in Myanmar, ongoing changes in land use have negative environmental impacts and threaten natural ecosystems at local, regional and national scales. In particular, the watershed area of Inle Lake in eastern Myanmar is strongly affected by the environmental effects of deforestation and soil erosion caused by agricultural intensification and expansion of agricultural land, which are exacerbated by the increasing population pressure and the growing number of tourists. This thesis, therefore, focuses on land use changes in traditional farming systems and their effects on socio-economic and biophysical factors to improve our understanding of sustainable natural resource management of this wetland ecosystem. The main objectives of this research were to: (1) assess the noticeable land transformations in space and time, (2) identify the typical farming systems as well as the divergent livelihood strategies, and finally, (3) estimate soil erosion risk in the different agro-ecological zones surrounding the Inle Lake watershed area. GIS and remote sensing techniques allowed to identify the dynamic land use and land cover changes (LUCC) during the past 40 years based on historical Corona images (1968) and Landsat images (1989, 2000 and 2009). In this study, 12 land cover classes were identified and a supervised classification was used for the Landsat datasets, whereas a visual interpretation approach was conducted for the Corona images. Within the past 40 years, the main landscape transformation processes were deforestation (- 49%), urbanization (+ 203%), agricultural expansion (+ 34%) with a notably increase of floating gardens (+ 390%), land abandonment (+ 167%), and marshlands losses in wetland area (- 83%) and water bodies (- 16%). The main driving forces of LUCC appeared to be high population growth, urbanization and settlements, a lack of sustainable land use and environmental management policies, wide-spread rural poverty, an open market economy and changes in market prices and access. To identify the diverse livelihood strategies in the Inle Lake watershed area and the diversity of income generating activities, household surveys were conducted (total: 301 households) using a stratified random sampling design in three different agro-ecological zones: floating gardens (FG), lowland cultivation (LL) and upland cultivation (UP). A cluster and discriminant analysis revealed that livelihood strategies and socio-economic situations of local communities differed significantly in the different zones. For all three zones, different livelihood strategies were identified which differed mainly in the amount of on-farm and off-farm income, and the level of income diversification. The gross margin for each household from agricultural production in the floating garden, lowland and upland cultivation was US$ 2108, 892 and 619 ha-1 respectively. Among the typical farming systems in these zones, tomato (Lycopersicon esculentum L.) plantation in the floating gardens yielded the highest net benefits, but caused negative environmental impacts given the overuse of inorganic fertilizers and pesticides. The Revised Universal Soil Loss Equation (RUSLE) and spatial analysis within GIS were applied to estimate soil erosion risk in the different agricultural zones and for the main cropping systems of the study region. The results revealed that the average soil losses in year 1989, 2000 and 2009 amounted to 20, 10 and 26 t ha-1, respectively and barren land along the steep slopes had the highest soil erosion risk with 85% of the total soil losses in the study area. Yearly fluctuations were mainly caused by changes in the amount of annual precipitation and the dynamics of LUCC such as deforestation and agriculture extension with inappropriate land use and unsustainable cropping systems. Among the typical cropping systems, upland rainfed rice (Oryza sativa L.) cultivation had the highest rate of soil erosion (20 t ha-1yr-1) followed by sebesten (Cordia dichotoma) and turmeric (Curcuma longa) plantation in the UP zone. This study indicated that the hotspot region of soil erosion risk were upland mountain areas, especially in the western part of the Inle lake. Soil conservation practices are thus urgently needed to control soil erosion and lake sedimentation and to conserve the wetland ecosystem. Most farmers have not yet implemented soil conservation measures to reduce soil erosion impacts such as land degradation, sedimentation and water pollution in Inle Lake, which is partly due to the low economic development and poverty in the region. Key challenges of agriculture in the hilly landscapes can be summarized as follows: fostering the sustainable land use of farming systems for the maintenance of ecosystem services and functions while improving the social and economic well-being of the population, integrated natural resources management policies and increasing the diversification of income opportunities to reduce pressure on forest and natural resources.

Use of farmer-prioritized vertisol management options for enhanced green gram and tomato production in central Kenya

Green grams (Phaseolus aures L.) and tomato (Solanum lycopersicum L) are widely grown in the vertisols of the Mwea Irrigation Scheme alongside the rice fields. Green grams can fix nitrogen (biological nitrogen fixation) and are grown for its highly nutritious and curative seeds while tomatoes are grown for its fruit rich in fibres, minerals and vitamins. The two can be prepared separately or together in a variety of ways including raw salads and/or cooked/fried. They together form significant delicacies consumed with rice which is the major cash crop grown in the black cotton soils. The crops can grow well in warm conditions but tomato is fairly adaptable except under excessive humidity and temperatures that reduce yields. Socio-economic prioritization by the farming community and on-farm demonstrations of soil management options were instituted to demonstrate enhanced green gram and tomato production in vertisol soils of lower parts of Kirinyaga County (Mwea East and Mwea West districts). Drainage management was recognized by the farming community as the best option although a reduced number of farmers used drainage and furrows/ridges, manure, fertilizer and shifting options with reducing order of importance. Unavailability of labour and/or financial cost for instituting these management options were indicated as major hindrances to adopt the yield enhancing options. Labour force was contributed to mainly by the family alongside hiring (64.2%) although 28% and 5.2% respectively used hired or family labour alone. The female role in farming activities dominated while the male role was minimal especially at weeding. The youth role remained excessively insignificant and altogether absent at marketing. Despite the need for labour at earlier activities (especially when management options needed to be instituted) it was at the marketing stage that this force was directed. Soils were considered infertile by 60% but 40% indicated that their farms had adequate fertility. Analysis showed that ridging and application of farm yard manure and fertilizer improved fertility, crop growth and income considerably. Phosphate and zinc enhancement reduced alkalinity and sodicity. Green gram and tomato yields increased under ridges and farm yard manure application by 17-25% which significantly enhanced household income.

Alternate furrow irrigation of four fresh-market tomato cultivars under semi-arid condition of Ethiopia – Part I: Effect on fruit yield and quality

Scarcity of freshwater due to recurrent drought threatens the sustainable crop production in semi-arid regions of Ethiopia. Deficit irrigation is thought to be one of the promising strategies to increase water use efficiency (WUE) under scarce water resources. A study was carried out to investigate the effect of alternate furrow irrigation (AFI), deficit irrigation (DI) and full irrigation (FI) on marketable fruit yield, WUE and physio-chemical quality of four fresh-market tomato cultivars (Fetan, Chali, Cochoro and ARP Tomato d2) in 2013 and 2014. The results showed that marketable yield, numbers of fruits per plant and fruit size were not significantly affected by AFI and DI irrigations. WUE under AFI and DI increased by 36.7% and 26.1%, respectively with close to 30% irrigation water savings achieved. A different response of cultivars to irrigation treatments was found for marketable yield, number of fruits and fruit size, WUE, total soluble solids (TSS) of the fruit juice, titratable acids (TA) and skin thickness. Cochoro and Fetan performed well under both deficit irrigation treatments exhibited by bigger fruit size which led to higher WUE. ARP Tomato d2 showed good yields under well-watered conditions. Chali had consistently lower marketable fruit yield and WUE. TSS and TA tended to increase under deficit irrigation; however, the overall variations were more explained by irrigation treatments than by cultivars. It was shown that AFI is a suitable deficit irrigation practice to increase fresh yield, WUE and quality of tomato in areas with low water availability. However, AFI requires suitable cultivars in order to exploit its water saving potential.