Chlorophyll fluorescence parameters and photosynthetic pigments of four Glycine max varieties under Aluminium chloride stress

Abstract

Soil acidity limits agricultural production globally. Different kinds of stresses, mainly Al stress, generated from acid soils affect plant growth and result in food shortage and production. General effects of Al toxicity in plants include plant growth alterations, reduction of photochemical efficiency of photosystem II (PS II), reduced photosynthesis and inhibition of synthesis of photosynthetic pigments. There is need to improve food security in Kenya by encouraging the growing of soybean crop, however there is lack of information on physiological response of soybean varieties grown in Kenya to aluminium chloride toxicity. There is need to investigate the effects of aluminium toxicity to soy bean Varieties (Glycine max (L.) commonly grown in Kenya with a view of identifying the tolerant varieties among them to be recommended for growing in areas prone to aluminium toxicity. Such varieties include SB 97, SB 19, SB 20 and SB123. The experiment was conducted at Maseno University under greenhouse conditions. Randomized complete block design factorial was used with three replicates and five levels of 0(control), 25mg/l, 50 mg/l, 75mg/l and 100 mg/l aluminium concentration in tap water. Parameters determined included dry weight, chlorophyll fluorescence and photosynthetic pigment contents. SAS software was used to analyse the data by subjecting it to ANOVA. Tukey`s HSD tests at 5% was used to separate treatment and Variety means. Plant dry weights decreased with increased aluminium chloride concentration. Variety SB 123 had the highest dry weight compared to the other three soy bean varieties. Generally maximum quantum yield (Fv/Fm ratio) and Effective quantum yield (ɸPSII) reduced with increasing aluminium chloride concentration in all the varieties. Maximum quantum yield and effective quantum yield, and chlorophyll a and b contents were highest in variety SB 20 but measured low NPQ values. Variety SB 123 had higher carotenoids contents at 100 mg/l aluminium chloride solution in comparison to other three soybean varieties. Photochemical parameters of PSII and photosynthetic pigments parameters measured were found to be quite sensitive to AlCl3 solution stress. Soybean varieties SB 20 and SB 19 were found to be more tolerant to aluminium chloride solution stress under the current study.