The influence of cultivars, nitrogen supply, location and water stress on performance and oil quality of linseed (Linum usitatissimum L.) in Kenya

Abstract

Flaxseed, also known as linseed, belongs to the Linaceae family. It is emerging as a major ingredient in health promoting foods (functional foods or nutraceuticals), as well as in animal feeds due to high omega-3 fatty acid and lignans content. Its current production in Kenya is minimal and the extent of genetic variability within the Kenyan germplasm in unknown. This study therefore addressed four related objectives as a contribution towards increased cultivation of linseed in Kenya namely to assess 1) genetic variation among linseed cultivars in Kenya using SSR markers; 2) effect of nitrogen fertilizer application on growth and seed yield; 3) effect of location and nitrogen fertilizer application on oil quantity and quality; and 4) effect of water deficit on growth of linseed cultivars. Thirteen linseed cultivars (Jawhar, CI-1652, Norlea, S19/31, S19/12, Summit, CI-1525, Raja, S19/21, S/10/03, Concurrent, S25/61 and 7331) were characterized using 28 SSR markers. DNA extraction followed a modified CTAB protocol. Twenty six of the 28 SSRs showed amplifications with at least one of the genotypes with sizes of the amplification products varying between 50 and 200bp. A total of 46 alleles were detected at 26 loci, with an average of 1.769 alleles per locus. The average polymorphic information content was 0.2033. The tested linseed cultivars fell into three main clusters. Growth and yield performance of five linseed cultivars (Summit, S19/21, Raja, Jawhar and S19/12) were evaluated in two agro-ecologically different locations, Njoro and Juja, for two seasons, February-June and July-December 2012 under 0, 75 and 150kgN/ha fertilizer rates. There were no interactions between nitrogen and cultivars in the two sites and seasons. There were significant differences in the number of tillers, dry weight, number of heads and seed yield (p<0.05) but not number of leaves and plant height among the cultivars in both sites. While vegetative growth was not significantly affected by addition of nitrogen fertilizer (P>0.05) at both sites in both seasons, capsules and seed yield increased with application of nitrogen. Raja yielded more seed than the other cultivars at both locations and seasons and would therefore be recommended as a choice cultivar. The oil content and fatty acid profiles of resultant seeds from above field experiment were determined to give an indication of the influence of location on oil content and fatty acid profiles on linseed germplasm. Oil was extracted using soxhlet apparatus and fatty acid profiles determined using gas chromatography. There were inter-cultivar differences in oil content and fatty acid profiles depending on season and location. Therefore with the right cultivar, good quality linseed could be produced in both Juja and Njoro without supplemental nitrogen fertilizer application. Incidences of drought are becoming increasingly common in Kenya. A study to evaluate the effect of water deficit stress on growth of three linseed cultivars (S19/12, Summit and Raja) was conducted in a greenhouse in JKUAT in February-May and August-November 2014. Stressed pots had watering completely withheld from the 4th week after sowing while the well watered control was maintained at 90% field capacity throughout the experiment. The cultivars did not significantly differ in growth in both seasons. Water stress caused 20-40% reduction in growth and begun when 30-80% of available soil water had been used up. Relative water content declined after 25-67% of available soil water had been used up. The study therefore concludes that Raja could grow well and produce good quality oil in regions similar to Juja and Njoro without addition of nitrogen fertilizer provided soil water levels don’t fall below 0.2-0.7 fraction of available soil water.