Abstract
Rhizoctonia solani was found to be associated with root rot symptoms of guar plants collected from different fields in New Valley governorate, Egypt. All the obtained isolates were able to attack guar plants (cv. Local) causing damping-off and root rot diseases. R. solani isolates No. 8 (RG8) was the more virulent ones in the pathogenicity tests. Salicylic acid (SA) and Pseudomonas fluorescens (PF) individually or in combination were examined for their potential in suppression damping-off and root rot and growth promotion of guar plants in vitro and in vivo. Both SA and P. fluorescens either individually or in combination inhibited the growth of the tested pathogenic fungi.SA combined with P. fluorescens recorded the highest inhibited growth followed by P. fluorescens alone. Under greenhouse and field conditions, all treatments significantly reduced damping-off and root rot severity. The combination of SA and P. fluorescens was more effective than using them individually. Under field conditions, all these treatments significantly increased growth parameters (plant height and No. of branches plant-1) and yield components (No. of pods plant-1, weight of 100 seeds and total yield fed.-1 and Guaran content (gm plant-1) in both locations (El-Kharga and Mallawy Agric. Res. Stations) during growing season 2014.The combination of SA and P. fluorescens were recorded the highest growth parameters and yield components. Generally, the combination of SA and P. fluorescens recorded the best results for controlling damping-off and root rot diseases in greenhouse and field with addition improved plant growth and increased yield components in the field. In physiological studies, activity of defense-related enzymes, including peroxidase (PO), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), pathogenesis related (PR) protein (chitinase and β 1,3 gluconase), were increased in inoculated and non-inoculated plants treated with the SA and P. fluorescens either individually or in combination, during the experimental period. The combination of SA and P. fluorescens recorded the highest increase in activity of all enzymes. In general, the activity of these enzymes begins to accumulate after two days of treatment and reached maximum levels at 6 to 10 days, then the activities of these enzymes were decreased progressively. On the other hand, total phenols and lignin increased in guar plants inoculated with R. solani and treated with SA and P. fluorescens individually or in combination. The highest accumulation of phenols was recorded 8th days from application, while lignin recorded the highest level at 10th days from application. In the end, these results suggested that SA and P. fluorescens either individually or in combination may play an important role in controlling the guar damping-off and root rot diseases, though they have induction of systemic resistance in guar plants.
Highlights
% Inhibition = (A-B)/A ×100 Where: A = Colony diameter of pathogen in control B = Colony diameter in treated plates In vivo studies Greenhouse Experiments: The effects of salicylic acid (SA) and Pseudomonas fluorescens (PF) as plant growth promoting rhizobacteria individually or in combination against guar damping-off and root rot diseases incited by R. solani were evaluated under greenhouse conditions
Biochemical changes associated with Salicylic acid (SA) and P. fluorescens treatment: To detect the accumulation of peroxidase (PO), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL) and pathogenesis related protein (Chitinase and β-1,3-glucanase) and content each of phenolic compounds and lignin, 15 days old seedlings were injected with SA (1 mM), P. fluorescens (2.5 × 108 CFU/mL), SA+ P. fluorescens and sterilized distilled water (SDW), 50 μl plant−1
Effect of salicylic acid and P. fluorescens against damping-off and root rot diseases caused by R. solani in pots under greenhouse conditions: Data shown in Figure 3 clearly indicate that both treatments (SA and P. fluorescens) either applied individually or in combination have significantly reduced damping-off and root rot diseases caused by R. solani isolate RG2 compared with the untreated control plants under greenhouse conditions
Summary
THE ROLE OF SALICYLIC ACID AND PSEUDOMONAS FLUORESCENS IN SYSTEMIC RESISTANCE AGAINST RHIZOCTONIA SOLANI KÜHN IN GUAR (CYAMOPSIS TETRAGONOLOBA (L.) TAUB.). Abdel-Monaim* Plant Pathology Research Institute, Agriculture Research Center, Giza, Egypt
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