Euphytica 95: 57–66, 1997. 57 c 1997 Kluwer Academic Publishers. Printed in the Netherlands. Assessment of tolerance to salt stress in Kenyan tomato germplasm Stephen Gaya Agong 12 *, Siegfried Schittenhelm 1 & Wolfgang Friedt 3 1 Institute of Crop Science, Federal Agricultural Research Centre, Braunschweig-V¨ olkenrode (FAL), Bundesalle 50, D-38116 Braunschweig, Germany; 2 present address: Department of Horticulture, Jomo Kenyatta University of Agriculture and Technology, P.O. Box 62000, Nairobi, Kenya; 3 Institute of Crop Science and Plant Breeding I, Justus-Liebig University Giessen, Ludwigstr. 23, D-35390 Giessen, Germany; (* author for correspondence) Received 9 January 1996; accepted 13 January 1997 Key words: Lycopersicon esculentum, tomato landraces, salt stress tolerance, osmotic adjustment, adaptation, breeding potential Summary Tomato is an important vegetable crop in Kenya and the development of salt tolerant cultivars would enhance its productivity in the vast marginal areas of the country. This study was aimed at determining the magnitude of genotypic variability for salt tolerance in the Kenyan tomato germplasm. Pot experiments with 22 landraces and 9 market cultivars were laid out as a two and four replicate split-plot design in glasshouse in Experiments 1 and 2, respectively. Salt treatments in Experiment 1 were 0 and 5 g NaCl kg 1 resulting into 0.5 and 9.1 dS m 1 of the soil saturation extracts, respectively. In Experiment 2 the treatments were 0, 4, and 8 g NaCl kg 1 soil corresponding to 0.5, 7.4, and 14.2 dS m 1 , respectively. Data were recorded on agronomic and biochemical parameters. The germplasm showed large variation for salt tolerance. Fruit and seed production at soil salinity of 14.2 dS m 1 demonstrated that these tomatoes are fairly tolerant of NaCl. Osmotic adjustment was achieved by higher fruit electrical conductivity, brix and total titratable acidity. Low and high contents of K , Ca 2 and Mg 2 within tomato tissues and soil, respectively, under salt treatment, confirmed competition and antagonism involving Na and these cations. Low Na and Cl contents in the fruit at 7.4 dS m 1 revealed their exclusion and ensured production of physiologically normal seeds and nutritionally healthy fruits. Two landraces ‘Chwerotonglo’ and ‘Nyanyandogo’ were identified as salt tolerant. Comparatively, the market cultivars showed superior fruit yields despite their susceptibility to salinity. Accordingly, tolerance of landraces in combination with superior yields of the market cultivars is suitable for tomato improvement for salt tolerance. Introduction The rapid human population growth rate in Kenya (3.9%) and the continued scarcity of arable land have forced quite a large proportion of the population to cultivate the more marginal areas of the country. How- ever, suitable crop varieties for this large proportion of the country (80%) with evapotranspiration always exceeding the precipitation rate (Biamah et al., 1994), are desperately lacking. Furthermore, technology for the exploitation of this vast marginal area is highly lim- ited given the restricted economic potential. In order to meet both increased production and self-sufficiency in food, there is an urgent need for breeding strategies and packages which would address the use of locally adapted plant germplasm. Breeding tolerant crop varieties for salt stress is considered to be an effective energy saving approach in bringing a greater portion of semiarid and arid land into productive agriculture. Furthermore, genetic advancement in salt tolerance is a fundamental strate- gy in increasing agricultural production and stabilising productivity (Jones, 1986). Several technical options are available for the management of saline soils, for example irrigation (Rush & Epstein, 1976). Howev- er, the question of the quality, cost and availability of irrigation water remains largely unresolved. Use of higher yielding and more salt tolerating crop species