Towards improving the agronomic performance, chlorophyll fluorescence parameters and pigments in fenugreek using zeolite and vermicompost under deficit water stress

A comprehensive study has not been carried out so far to determine the outcome and impact of chlorophyll (Chl) fluorescence parameters and photosynthetic pigments in relation to qualitative and quantitative properties in fenugreek, especially in regions with limited water availability. Fenugreek (Trigonella foenum-graecum) is one of the most important medicinal plants in the world. To determine the effects of water deficit stress, nitrogen fertilization and zeolite on Chl fluorescence, pigments, trigonelline concentration and seed yield of fenugreek, a split factorial experiment was laid out in a randomized complete block design with three replications in a semiarid region of Iran in 2014 and 2015. Five irrigation regimes (unstress control, irrigation at 60% available soil water (ASW); mild stress, irrigation at 40% ASW during the vegetative and reproductive stages; severe stress, irrigation at 20% ASW during the vegetative and reproductive stages) were randomized to the main plots. Subplots consisted of a factorial combination of three nitrogen treatments (untreated plots, vermicompost @ 2.7 t ha(-1) and urea @ 11 kg ha(-1)) and two zeolite treatments (@ 0 and 9 t ha(-1)). The results demonstrated that water deficit stress decreased maximum CM fluorescence (F-m), variable Chl fluorescence (F-v), the photochemical efficiency of PSII (F-v/F-m), Chl (a, b and a + b), leaf area index (LAI), biological yield and seed yield but minimum fluorescence (F-0), carotenoids, Anthocyanin and trigonelline concentration increased under water deficit stress. There were negative and significant correlations between F-o and LAI, biological and seed yield and on the other side, positive and significant correlations between total Chl. and the above mentioned traits. Water deficit stress led to the photo inhibition of photosynthesis. In most treatments, both vermicompost and zeolite application increased LAI, biological yield, seed yield and trigonelline concentration in fenugreek. Greater concentration of trigonelline in fenugreek under mild water deficit stress conditions may not necessarily supply give economic benefits, as higher concentration is often compensated by lower seed yield.