Selected Physiological And Growth Response Of Four Soy Beanvarieties To Aluminium Chloride Stress

ABSTRACT

Soy bean

v arieties commonly gro wn in Kenya`s acidic soils that contain aluminium are SB 97,

SB 19, SB 20 and SB 123. Soy bean grains have high protein content, vitamins and used to

manufacture industrial products. Aluminium toxicity affect growth and physiology of plant

growth . The effects of aluminium chloride solution on plant growth, uptake of mineral nutrients

and di stribution in vegetative parts of soy beans are still not fully understood. The objective of

this study was to investigate the effects of aluminium chloride stress on four varieties of soy

bean grown in Kenya with a view of identifying the tolerant varieties among them to be

recommended for growing in a reas prone to aluminium stress. The experiment was done under

greenhouse conditions. Seeds were planted in 20 litre PVC pot s filled with soil. R andomized

C omplete B lock D esign in a factorial way , with three replicates an d five levels of 0 (control),

25 mg/l, 50 mg/l, 75 mg/l and 10 0 mg /l aluminium chloride concen tration s in tap water was

used. G rowth and physiological paramete rs ; including mineral concentration in leaves,

c hlorophyll fluorescence and photosynthetic pigment contents were measured . The data was

subjected to factorial A nalysis of Variancy and Tukey`s HSD tests at 5% was used to separate

treatment Variety means Growth parameters measured mostly show ed clearly the tolerance

difference levels of the varieties . Aluminium reduced water absorption hence decreasing

productivity. Variety SB 20 concentrated more aluminium in leaves . Some varietal difference

which were no t significant were observe d in mineral accumulation. This indicate that varieties

could be behaving differently in absorption and accumulation of nutrients. Maximum quantum

yield and effective quantum yield had the highest mean value in SB 20. Non photochemical

quenching was high est in SB 123. These implies that varieties behaved diffe re ntly in PSII

impairment activity. Major decrease in t otal chlorophyll with increased aluminium chloride

concentrations was observed in SB 19, SB 97 , and SB 123 s uggest ing selective chlorophyll

photobleaching showing that smaller amounts of energy was delivered for electron transport.

There was a marked decrease in chlorophyll a/b ratio under aluminium chloride solution

treatment. SB 123 had a large r mean value of carotenoids in comparison to SB 20 , SB 19 and

SB 97 . Carotenoids concentration was more at 100 mg /l aluminium chloride concen tration. It

was to assist in transfer of energy and oxygen in accessory pigments. Tukey`s HSD tests

showed no significant difference (p≥0.05) within varieties for physiological parameters

measured. Variety SB 20 and SB 19 were identified to be more tolerant to aluminium stress and

hence recommended for growing in aluminium prone soils . Mineral nutrients accumulation,

photochemical parameters of PSII and photosynthetic pigments parameters measured were

found to be sensitive to a luminium chloride treatment s the later two parameters showed that

AlCl 3 affects the overall rate of photosynthe sis