Waiti Martin Maina

Tomato production in Kenya agronomically faces challenges of insufficient water for growth and nitrogen depleted soils. Selection and breeding for adaptable varieties from wild accessions could be key in alleviating these challenges. 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 th 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. 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.This genetic variability in morphology and adaptability to drought can be exploited to develop new or improve tomato cultivars through integrating desirable traits.