Minimizing the harmful effects of cadmium on vegetative growth, leaf anatomy, yield and physiological characteristics of soybean plant [Glycine max (L.) Merrill] by foliar spray with active yeast extract or with garlic cloves extract.

Pot experiments were carried out during the two successive summer seasons of 2010 and 2011 in the greenhouse of Crops Physiology Research Department, Field Crops Research Institute, Agricultural Research Center, Giza, Egypt to investigate the effect of pollution with cadmium at concentrations of 50, 100 and 200 ppm on vegetative growth, leaf anatomy, yield and certain physiological aspects of soybean 'Giza 35'. In addition, the use of natural extracts from active yeast (60ml/L.) and garlic cloves (30 ml/L.) for minimizing the harmful effects of environmental pollution caused by cadmium on vegetative and reproductive growth as well as on leaf anatomy and physiological behaviour of soybean was also investigated. The obtained results revealed that all assigned concentrations of cadmium induced significant decrease in all investigated morphological characters of vegetative growth (plant height, number of branches and leaves/plant, total leaf area /plant and shoot dry weight/plant) and in all studied yield characters (number of pods and seeds/plant, specific seed weight and seed yield/plant) of soybean 'Giza 35'. Moreover, the significant decrease in morphological and yield characters got higher as the concentration of cadmium increased in irrigation water. Worthy to note that, soybean plants grown under stress of pollution with different levels of cadmium and sprayed with either yeast or garlic extract had better growth behavior and yield than those of unsprayed with natural extracts. Likewise, the concentrations of photosynthetic pigments (Chl. a, Chl. b and carotenoids), total sugars and phytohormones from IAA and GA3 in leaves of cadmium polluted soybean plants were decidedly lower than those of control plants. In this respect, increasing cadmium concentration in irrigation water decreased gradually photosynthetic pigments, total sugars, IAA and GA3 . It was found that yeast as well as garlic extracts were able to minimize the harmful effect of cadmium and improve the concentrations of photosynthetic pigments, total sugars, IAA and GA3 in leaves of cadmium polluted soybean plants. Also, the percentage of crude protein and total lipids in seeds of cadmium polluted soybean plants were decidedly lower than those in seeds of control plants and increasing cadmium concentration in irrigation water decreased gradually the percentage of crude protein and of total lipids. It is clear that foliar application with yeast or garlic extract was sufficient for reducing the harmful effect of cadmium and improve the percentage of crude protein and of total lipids in seeds of cadmium polluted soybean plants. At the same time, the concentration of phytohormone ABA in leaves and of cadmium in leaves and seeds of soybean plants was increased due to cadmium treatments, and the application of yeast or garlic extract on soybean plants grown under stress of pollution with cadmium minimized the harmful effect of such heavy metal on concentration of ABA in leaves and on cadmium accumulation in leaves and seeds of cadmium polluted soybean plants. Concerning the anatomical structure of leaflet blades, treatment with 100 ppm cadmium decreased the thickness of both midvein and lamina due to the decrease induced in thickness of both palisade and spongy tissues as well as in the dimensions and components of main midvein bundle. The mean values of number of xylem rows and vessels/midvein bundle as well as of vessel diameter in leaflets of stressed soybean plants were decidedly lower than those of control. The application of yeast or garlic extract caused enhancement in leaflets structure of polluted plants and the best results were obtained from treatment with 60 ml. active yeast extract/L. which caused recovery of the reduction occurred in most of the histological characters where their mean values reached or surpassed those of control.