ABSTRACT
Tomato ranks among the most consumed fruit vegetables in Kenya and in the world. The Kenyan agro-ecosystem, however, faces persistent challenges of inadequate water resources and nitrogen deficient soils that limit productivity of the crop. There exists a wide range of abiotically adapted African tomato accessions that could be harnessed to develop better varieties adaptable to limited moisture conditions and improved nitrogen use efficiency. A study was conducted with objectives of: (i) evaluate the effect of water stress on growth and yield of 10 African tomato accessions [VI005895, VI007540, VI005987, VI006840, VI006825, VI006828, RVI01885, GBK050580, VI005871, VI005990] and five commercial varieties [Rio grande, Cal J, Stallion F1, Master F1, ATM F1] (ii); evaluate the effect of varying levels of nitrogen on growth and yield of selected African tomato accessions and commercial varieties. Trials were set up in 2018 and 2019 both in the greenhouse (for water stress evaluation) and in the field (for nitrogen nutrition evaluation) in randomized complete block design with three replications. The greenhouse experiment was conducted at the University of Nairobi’s Kabete field station while the field experiment was conducted at Kabete field station and at Kenya Agricultural and Livestock Research Organization (KARLO) –Mwea field station, Kenya. Greenhouse-grown tomato plants were subjected to three water levels throughout the season: 100%, 70% and 40% pot capacity (PC) i.e the moisture held by pot soil after draining for 24 hours determined using gravimetric moisture determination method. Open field-grown tomato plants were subjected to six levels of nitrogen (control of 0 kg N/Ha, 50 kg N/Ha, 100 kg N/Ha, 150 kg N/Ha, 200 kg N/Ha and 250 kg N/Ha) at vegetative growth stage. Data was collected on growth parameters (plant height, number of primary branches, stem girth, internode length, single leaf area, days to 50% flowering) and yield parameters (total yield, number of fruits per plant/plot, single fruit weight, fruit length and fruit width, total fruit weight per plant). Data collected were subjected to analysis of variance using Genstat V.15 and means were separated using the least significant difference test at (P≤0.05). Moisture stress of 70% PC and 40% PC caused significant reductions in plant height, internode length, stem girth and single leaf area of the tomato plants compared to unstressed moisture conditions (100% PC). Total number of fruits per plant, total fruit weight per plant, average single fruit weight, fruit length and fruit width were significantly reduced by reduction in moisture level from 100% PC to 70% PC and below. There was significant variability among genotypes in all the growth and yield traits evaluated. Indigenous tomato genotypes had higher variability than commercial genotypes in growth traits i.e plant height, internode length, and stem girth. Level of nitrogen applied significantly affected (P≤0.05) the growth parameters observed. Vegetative growth parameters: number of primary branches, plant stem height, stems girth and single leaf area increased with each level of nitrogen applied from control to the other five levels (50, 100, 150, 200 and 250 kg N/Ha) with 250 kg N/Ha recording the highest means for the traits evaluated. Number of fruits per plot and fruit yield per plant increased with increase in N level from 0 to 250 kg N/Ha. The growth and yield traits evaluated in the field varied significantly with genotype. Indigenous tomato genotypes (VI005871, VI005895 and VI005987) were higher performers than commercial genotypes Cal J and Rio Grande in terms of single fruit weight per plant, number of fruits per plant and fruit yield per plant. Variability was mostly evident on agro-morphological parameters such as plant stem height and fruit yield per plant. This genetic variability and better adaptability to drought can be exploited to develop new or improve tomato cultivars through integrating desirable yield traits such as high single fruit weight. These genotypes can also be selected as competitive, cheaper tomato opv seed source option for tomato farmers in Kenya and sub-Saharan Africa.
Table of Contents
DECLARATION ii
DECLARATION OF ORIGINALITY iii
DEDICATION iv
ACKNOWLEDGEMENTS v
LIST OF TABLES ix
LIST OF FIGURES xii
ABBREVIATIONS AND ACRONYMS xiii
ABSTRACT 1
CHAPTER ONE: INTRODUCTION
1.1 Background Information 3
1.2 Problem statement 4
1.3 Justification 6
1.4 Objectives 7
1.5 Hypotheses 7
CHAPTER TWO: LITERATURE REVIEW
2.1 Tomato taxonomy, origin and botany 8
2.2 Tomato uses and nutritional benefits 9
2.3 Ecological requirements and production of tomato 11
2.4 Factors limiting tomato production in Kenya 13
2.5 Effect of Water stress on tomato growth and yield 14
2.6 Effect of nitrogen nutrition on tomato growth and yield 16
CHAPTER THREE: EFFECT OF WATER STRESS ON GROWTH AND YIELD OF SELECTED AFRICAN WILD TOMATO ACCESSIONS AND COMMERCIAL TOMATO VARIETIES
3.1 Abstract 18
3.2 Introduction 19
3.3 Materials and methods 20
3.3.1 Site description 20
3.3.2 Planting materials 21
3.3.3 Planting media preparation 22
3.3.4 Treatments and experimental design 22
3.3.5 Crop husbandry 23
3.3.6 Data collection 23
3.3.7 Data analysis 24
3.4 Results 25
3.4.1 Effect of water stress on growth attributes of selected African tomato accessions and commercial varieties. 25
3.4.2 Effect of water stress on yield attributes of selected African tomato accessions and commercial varieties 30
3.4.3 Correlation analysis for growth and yield traits 35
3.5 Discussion 36
3.6 Conclusion 39
CHAPTER FOUR: EFFECT OF NITROGEN NUTRITION STRESS ON GROWTH AND YIELD OF SELECTED AFRICAN TOMATO ACCESSIONS AND COMMERCIAL TOMATO VARIETIES
4.1 Abstract 41
4.2 Introduction 42
4.3 Materials and methods 43
4.3.1 Sites Description 43
4.3.2 Planting materials 44
4.3.3 Soil analyses 45
4.3.4 Treatments and experimental design. 46
4.3.5 Crop husbandry 46
4.3.6 Data collection 47
4.3.7 Data analysis 49
4.4 Results 49
4.4.1 Effect of nitrogen fertilizer rate on growth attributes of selected African tomato accessions and commercial varieties 49
4.4.2 Effect of nitrogen nutrition on yield components of selected African tomato accessions and commercial varieties 58
4.4.3 Correlation analysis for tomato growth traits and yield traits 67
4.4.4 Nitrogen agronomic efficiency 67
4.4.5 Response of tomato yield components to N fertilizer application rates 70
4.5 Discussion 72
4.6 Conclusion 78
CHAPTER 5: GENERAL DISCUSSION, CONCLUSION AND RECOMMEDATIONS
5.1 Discussion 79
5.2 Conclusion 80
5.3 Recommendations 81
REFERENCES 82
LIST OF TABLES
Table 2.1: Nutritional Composition for Tomatoes (red, ripe, raw, year round average)…pg 10 Table 2.2: Tomato production in selected counties in Kenya 2013-2014 pg 12
Table 3.1: African tomato genotypes and Kenyan commercial varieties used in the trial pg 21
Table 3.2: Mean values for plant height of tomato genotypes under different moisture levels 25
Table 3.3: Mean values for stem girth of tomato genotypes under different moisture levels…26 Table 3.4: Mean values for internode length of tomato genotypes under different moisture levels pg 27
Table 3.5: Mean values for single leaf area of tomato genotypes under different moisture levels pg 28
Table 3.6: Mean values for days to floral initiation of tomato genotypes under different moisture levels pg 30
Table 3.7: Mean values for total harvested fruits of tomato genotypes under different moisture levels pg 31
Table 3.8: Mean values for total fruit weight per plant of tomato genotypes under different moisture levels pg 32
Table3.9: Mean values of single fruit weight of tomato genotypes under different moisture levels pg 33
Table 3.10: Mean values of average fruit length of tomato genotypes under different moisture levels pg 34
Table 3.11: Mean values of fruit width of tomato genotypes under different moisture levels 35
Table 3.12: Correlation table for growth and yield traits of greenhouse grown tomato genotypes… page 36
Table 4.1: Weather conditions at Kabete station between September 2018 and February 2019 cropping season pg 44
Table 4.2: Weather conditions at Mwea station between September 2018 and February 2019 cropping season pg 44
Table 4.3: African tomato genotypes and Kenyan commercial varieties used in the trial pg 45
Table 4.4: Chemical characteristics of sampled soil, Kabete field station pg 45
Table 4.5: Chemical characteristics of sampled soil, Mwea field station… pg 46
Table 4.6: Mean values of number of primary branches of tomato genotypes grown under different N levels at Kabete and Mwea field stations pg 51
Table 4.7: Mean values of plant height (cm) at 50% flowering of tomato genotypes grown under different N levels at Kabete and Mwea field stations pg 52
Table 4.8: Mean values of internode length (cm) of tomato genotypes grown under different N levels at Kabete and Mwea field stations pg 53
Table 4.9: Mean values of stem girth (cm) of tomato genotypes grown under different N levels at Kabete and Mwea field stations pg 54
Table 4.10: Mean values of single leaf area (cm2) of tomato genotypes grown under different N levels at Kabete and Mwea field stations pg 56
Table 4.11: Mean values of days to 50 % flowering of tomato genotypes grown under different N levels at Kabete and Mwea field stations pg 57
Table 4.12: Mean values of fruit length of tomato genotypes grown under different N levels at Kabete and Mwea field stations pg 59
Table 4.13: Mean values of fruit width of tomato genotypes grown under different N levels at Kabete and Mwea field stations pg 60
Table 4.14: Mean values of single fruit weight of tomato genotypes grown under different N levels at Kabete and Mwea field stations pg 62
Table 4.15: Mean values of number of fruits per plant of tomato genotypes grown under different N levels at Kabete and Mwea field stations pg 63
Table 4.16: Mean values of total fruit weight per plant of tomato genotypes grown under different N levels at Kabete and Mwea field stations pg 65
Table 4:17: Mean values of fruit yield per hectare of tomato genotypes grown under different N levels at Kabete and Mwea field stations pg 66
Table 4.18: Correlation table for growth and yield traits for tomato genotypes grown under different N levels at Kabete and Mwea field stations pg 68
LIST OF FIGURES
Fig 2.1: Pictorial tomato morphological growth cycle pg 08
Fig 2.2: Production share of tomatoes in different regions of the world, average 2010-2016… 11
Fig 4.1: Tomato crop growing at the field during vegetative and fruit development stages. pg 47
Fig. 4.2: Nitrogen agronomic efficiency graphs of tomato genotypes grown at Kabete field station for rate of 250 kg N/ha pg 69
Fig. 4.3: Nitrogen agronomic efficiency graphs of tomato genotypes grown at Mwea field station for rate of 250 kg N/ha pg 69
Fig 4.4 Linear regression relationship between number of fruits per plant and nitrogen fertilizer levels in Kabete field station and Mwea field station pg 70
Fig 4.5 Linear regression relationship between total fruit weight per plant and nitrogen fertilizer levels in Kabete field station and Mwea field station pg 71
Fig 4.6 Linear regression relationship between yield per hectare and nitrogen fertilizer levels in Kabete field station and Mwea field station pg 71
ABBREVIATIONS AND ACRONYMS
AFA Agriculture and Food Authority
ASALs Arid and Semi-Arid Lands
AVRDC Asian Vegetable Research Development Centre
CAN Calcium Ammonium Nitrate
FAO Food and Agriculture Organization of the United Nations
GoK Government of Kenya
Ha Hectare
HCD Horticulture Crops Directorate
IITA International Institute for Tropical Agriculture
KALRO Kenya Agricultural and Livestock Research Organization
KEPHIS Kenya Plant Health Inspectorate Services
MoALF Ministry of Agriculture, Livestock and Fisheries
NAAIAP National Accelerated Agricultural Inputs Access Programme
NFNSP National Food and Nutritional Policy of Kenya
PC Pot Capacity
RCBD Randomized Complete Block Design
WHO World Health Organization
CHAPTER ONE
INTRODUCTION
1.1 Background Information
Tomato (Solanum lycopersicum) is one of the most frequently used vegetable in the world and ranks among the top nutritional culinary vegetables consumed in most meals. It is also one of the most affordable crop produce options in improving nutritional security and ameliorating micronutrient deficiencies, especially in Kenya, where malnutrition is prevalent (NFNSP, 2011). Being a tropical crop that can grow even in semi arid areas tomato is a suitable alternative to curb malnutrition in such areas. Tomato fruit is an excellent source of Vitamin C (13.7 mg/100g serving) that is essential for the enhancement of the body immune system and Vitamin K (7.9g/100g serving) important for bone protein formation and in aiding blood clotting. It is also a leading source of potassium (237mg/100 g serving) which is important in lowering blood pressure (USDA National Nutrient Database for Standard Reference, 2018).
In the fast growing horticulture industry in Kenya, tomato is ranked second to potato in production among the leading vegetables with approximately 20,111 ha production area, producing 341,026 Metric tonnes valued at Kenyan shillings 13.68 billion in the year 2016 (AFA-HCD, 2015-2016). Despite the importance of tomato in Kenya, various constraints have hindered consistency in production of this crop leading to unfavorable fluctuations in supply hence prices (Sigei et al, 2014). These include highly expensive hybrid seeds, high pest and diseases management costs, drought exacerbated by climate change, poor agronomic practices, low soil fertility and high post harvest losses. Unreliable rainfall and frequent droughts in Kenya interrupt open field tomato production often leading to tomato crop failure in many parts of the country (Sigei et al, 2014). Tomato crop is sensitive to drought stress, requiring 400-600 mm of water supply daily after transplanting depending on climate (FAO, 2018).
Most Kenyan arable land soils have shown deficiency in nitrogen nutrient due to high mining rate through continuous cropping without adequate external nutrient replenishment among other factors (NAAIAP, 2014). To ensure high productivity of tomato, especially on continuously cultivated arable land, farmers have had to adopt different ways to replenish the soil in order to supply sufficient plant nutrients such as using compost manure, farm yard manure and synthetic fertilizers. Incorrect fertilizer use continues to be a major challenge to many farmers even as the government implements fertilizer subsidy programmes to facilitate access by the Kenyan resource challenged farmer to promote agricultural productivity (NAAIAP, 2014). However, there exists a knowledge gap among farmers in the area of the level of fertilizers to apply for optimum yield without making economic losses (Mangale et al., 2015). Therefore most farmers just apply the fertilizers incorrectly with generalized consideration of crop’s optimum requirements which may lead to reduced quantity and quality of the yield, soil acidity and poor returns on agro-investment
1.2 Problem statement
Production of tomato in Kenya is largely dependent on irrigation (AFFA-HCD, 2014) which, in most cases, is insufficient particularly with the current shortage of annual rainfall associated with climate change. Research indicates that water requirement for greenhouse grown tomato crops especially in the tropics range from 0.9 litres to 2.3 litres per plant per day (Hermanto, 2005). Tomato being herbaceous is very sensitive to shortage in soil moisture during growth. Severe water stress causes a reduction in vegetative growth rate which results in reduced stem diameter, stem height and chlorophyll content (Sibomana, 2013). If intense water stress occurs at flowering or fruit formation stage, flower abscission occurs and small sized fruits result thus lower yield (Nurrudin, 2001). Kenya has overtime experienced intra- and inter-seasonal fluctuations in rainfall necessitating adaptation strategies to manage the available water resources for horticultural production which cannot do without sufficient water availability. Effects of such rainfall fluctuations have adversely affected the horticultural subsector in Kenya which includes tomato production. HCDA (2010) indicated a decline in vegetable exports from 82,000 to 72,000 tonnes in year 2008-2009 and attributed this majorly to drought in the same period. FAOSTAT (2016) reported a decline in tomato production in Kenya between year 2008 to 2009 of 30.6 t/ha to 20.9 t/ha and this could be attributed to drought conditions experienced in the country during that period (Republic of Kenya, 2012). A survey carried out in one of the leading tomato producing counties in Kenya, Kiambu, indicated that the major constraint in optimum tomato production is insufficient moisture (Karuku et al., 2017). This suggests the need to evaluate climate resilient crop strategies such as using drought tolerant indigenous tomato or developing new cultivars that are better adapted to low soil moisture availability in order to mitigate against climatic variability effects.
Additionally, Kenyan soils have shown significant nitrogen deficiency due to high mining rate through continuous cropping without adequate external nutrient replenishment (NAAIAP, 2014). This necessitates use of synthetic fertilizers to supply the various nutrients. Karuku et al., (2017) reported that low soil fertility in tomato fields is the second major constraint to high tomato yield attainment by farmers in Kenya. Even though in tomato the level of nitrogen fertilizer to be applied will depend on target yield, variety and absence of other abiotic stresses such as water, various field trials by fertilizer and seed companies have indicated that for optimal yields from tomato of 75- 100 t/ha, one should supply the crop with 200-250 kg N/ha. This is because 2.2 to 2.4 kg of nitrogen is removed from the soil per each tonne of tomato fruits produced (Yara, 2010). The presence of high level of diversity in tomato accessions (Tembe, 2016) presents an opportunity to evaluate their nitrogen use efficiency as compared with the commercial varieties which, in most cases, have higher demand for nitrogen and other macro nutrients to enable high performance than local accessions.
1.3 Justification
While drought stress and low soil fertility are some of the major constraints to optimization of tomato production, there exist a wide range of water stress tolerant tomato accessions in Africa that could be harnessed to improve the current available commercial varieties for adaptability to limited moisture conditions. Accessions and wild tomato genotypes are potentially the best source of drought tolerance genes for tomato improvement. African tomato accessions have been evaluated for diversity in agro-morphological traits and shown to exhibit widely varied genetic diversity (Tembe et al, 2017). Evaluation of various African accessions with respect to tolerance to water stress demonstrated significant variations in response to different levels of water stress (Tembe et al, 2017).
Agong et al. (2001) reported that there exists a wide range of variation among the genotypes and within genotype groups that contribute to diversity in morphological expression of tomato traits such as varying fresh fruit weight in the study plants. Etissa et al., (2013) reported that NPK application 200 kg N/Ha application in tomato Money Maker increased the biomass yield of such as increased leaf area for photosynthesis. Therefore certain indigenous tomato accessions with superior traits can be used to breed for drought tolerant and nitrogen use efficient tomato hybrids for the Kenyan farmers. The accessions can also be used as competitive alternatives to the expensive, one season hybrid tomato varieties, saving costs for the resource poor farmers who wish to have higher tomato yield production but are constrained by insufficient inputs like fertilizers and irrigation water that are often necessary for hybrid tomato production.
Tomato productivity is imperative to the horticulture subsector, considering that it ranks 2nd after potato in this economic subsector, contributing greatly to the Kenyan economy. In addition, tomatoes contain vitamins such as vitamin C which is useful for strong immune systems, vitamin K needed by the body for stronger bones and vitamin A which is a pre-cursor of beta-carotene and important for vision (Serio et al, .2005). Tomato is also a major source of important carotenoids such as lycopene and beta-carotene which are natural dietary antioxidants that destroy free radicals thus reducing risks of cancers in individuals (Bhowmik et al, 2012). Cancer is a leading cause of death ranking 3rd in Kenya accounting for 7% of deaths in the country (KNCCS, 2011-2016). This strategy (KNCCS) outlined low vegetable and fruit intake as one of the risk factors leading to cancer cases and sought to increase intake of fruits and vegetables such as tomato by 5% by 2016. This underscores the nutritional importance of tomato in Kenya.
1.4 Objectives
The general objective of the study was to contribute to enhancement of productivity of tomato in Kenya through drought tolerant and nitrogen-use efficient varieties.
The specific objectives of the study were:
(i) To evaluate the effects of water stress on growth and yield components of selected African tomato accessions and commercial varieties
(ii) To evaluate the effects of varying levels of nitrogen nutrient supply on growth and yield components of selected African tomato accessions and commercial varieties
1.5 Hypotheses
(i) The selected African tomato genotypes are more tolerant to soil moisture stress conditions than commercial tomato varieties.
(ii) The selected African tomato genotypes are more responsive to nitrogen fertilizer application than the commercial tomato varieties.
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