Amelioration of the Structural and Biochemical Features of Kidney Bean against Root Rot and Rust Diseases

Abstract

The influential fabaceous crop; Phaseolus vulgaris L. is subjected to destructive infection by root rot and rust diseases, causing serious damage to productivity. The possible role of gibberellic acid (GA3), paclobutrazol (PBZ), and abscisic acid (ABA) in improving the structural and biochemical resistance against such kidney bean diseases were studied. Pathogenicity test indicated that all tested root rot pathogenic fungi caused symptoms of damping-off. Pythium ultimum was the most aggressive in pre-emergence damping-off while Fusarium oxysporum gave the highest values of post-emergence damping-off and seedlings mortality. PBZ and ABA showed fungicidal activity against mycelia growth of root rot fungi. The high concentration of PBZ (150 ppm) was the most effective. PBZ and ABA significantly reduced the root rot and rust diseases, but GA3 induced both diseases. Botanically, GA3 (150 ppm) maximized plant height, and (PBZ 100 ppm) maximized branches number. Biochemically, both PBZ and ABA increased chlorophyll content, carotenoids, total phenolics and total soluble carbohydrates except the high level of ABA (15 ppm), which gave opposite results. On the other hand, GA3 decreased chlorophyll content, phenols and total soluble carbohydrates. With regard to enzymes activity GA3, PBZ and ABA induced the activity of peroxidase enzyme while reduced polyphenol oxidase activity. Anatomically, infected roots characterized by complete distraction changes in the epidermis and separation of some cortex tissue area. On the other side, all tested treatments decreased the harmful effects of pathogen fungi on root structure. In this respect, PBZ gave the highly effect. PBZ and ABA increased the thickness of leaflet and mesophyll tissue. So also, observed increase on stem diameter, cortex thickness, number of cortex cell layers and phloem fibers thickness. The application of PBZ at 100 ppm maximized the number of plant pods. GA3 at 100 ppm gave the highest 100-seed weight. Therefore, treatments with either PBZ (100 ppm) or ABA (10 ppm) is recommended for alleviation the harmful effects of root rot and rust diseases in kidney bean.