Rhizopus spp Promoting and Inducing Late Blight (Phytophthora infestans) Resistance in Solanum lycopersicum L.

Abstract

Tomato (Solanum lycopersicum L) which is highly consumed by humans, suffer severe attacks of various pathogens. Among these pathogens, Phytophthora infestans is the most prominent causing a devastating tomato disease called late blight. This study was aimed at evaluating the protective effects of Rhizopus spp on tomato plant growth upon infection with P. infestans. The work was partition into two phases: phase 1 delt with the effect of Rhizopus spp on tomato growth parameters while phase 2 was on the protective effects of Rhizopus spp against late blight in tomato and its attributes on biochemical parameters. In phase 1 seedlings were raised and divided into five groups of six plants each. Group I was the control while Groups II to V were treated with Rhizopus spp (2.5; 5.0; 7.5 and 10.0 mg/ml respectively) for 25 days. After every 5 days’ plants were treated and on each day of treatment, growth parameters (number of leaves and height) and chlorophyll contents measured. On day 25, samples were collected for biochemical analysis (flavonoids, phenolic content, total protein, vitamin C, catalase (CAT), reduced glutathione (GSH)). In phase 2, Rhizopus at 5 mg/ml obtained as best results in phase one was used. Raised seedlings were divided into four groups: Group 1 was healthy (H), Group 2 of plants infected with P. infestans (50 mg/ml) (I), Group 3 of plants stimulated with Rhizopus spp (5.0 mg/ml) (St), and Group 4 of plants inoculated with P. infestans after stimulation with Rhizopus spp (St + I) for 7days. Every two days, diseases incidence and severity were recorded and after 10th days samples were collected for biochemical (total protein, CAT and GSH) analysis. As results, Rhizopus spp inoculation induced an increase in the number of leaves, plant height and chlorophyll contents compared to the control group with plants of group II (Rhizopus spp 5.0 mg/ml) having the best result. A significant increase (p< 0.05) in flavonoid, phenolic content, reduced glutathione level and catalase activity were recorded. Another significant increase (p< 0.05) in disease incidence and severity in plants treated with the pathogen when compared to the control. Co-inoculation of plants with Rhizopus spp and P. infestans significantly decreased disease incidence and severity. Also a significant decrease in GSH level and CAT activity were noticed. Co-inoculation of plants with Rhizopus spp and P. infestans significantly increased (p< 0.05) GSH level and CAT activity when compared to the control group. In conclusion Rhizopus spp instigate plant growth and induce disease resistance in tomato upon infection with P. infestans causing late blight.