s. k. sabbagh

 One of the most important diseases of cucumber is cucumber stem and root rot by agent Fusarium oxysporum f.sp. radicis-cucumerinum. The use of resistance inducers, which on the one hand activate the plant's defense mechanisms before confronting the pathogen and on the other hand do not pose environmental risks, has been considered by researchers in recent years. Recently, the use of sodium silicate as a potential activator of acquired resistance is being developed. Sodium silicate plays an important role not only in systemic acquired resistance but also in the expression of genetic resistance and stimulates the production of pathogen-related proteins (markers of systemic acquired resistance). The use of sodium silicate increases the tolerance of plants to environmental stresses and increases the quality and quantity of agricultural products. Hence it modulates the time and amount of plant defense responses and acts as a secondary messenger in induced systemic resistance.The effect of sodium silicate was investigated in order to induce defense reactions in cucumber cultivars and control the disease.

First, different concentrations of sodium silicate were applied on the growth of the pathogen in the laboratory. The effect of different concentrations of sodium silicate on pathogen growth was tested by mixing with culture medium. Different concentrations of sodium silicate (1, 2, 4 mM) are each combined in 100 ml of PDA culture medium and poured into 9 cm culture dishes. The percentage of sodium silicate inhibition on fungi is calculated according to the following formula: N = A-B / A. The effects of different concentrations of sodium silicate were applied in the soil on cucumber in the greenhouse. At time intervals of 0, 48, 72 and 96 hours after inoculation with pathogen, sampling of treated seedlings was performed to measure secondary metabolites and enzymatic activity. Disease severity, growth factors, production of secondary metabolites and activity of defense enzymes in cucumber plant and thus disease control were evaluated. Disease severity and growth factors were studied in a completely randomized design and Biochemical factors in a completely randomized design with factorial arrangement in which the main factors are the applied treatments and the sub-factors are the sampling times with three replications.

Sodium silicate showed a direct antifungal effect on fungal growth after 5 days and by increasing its concentration up to 4 mM caused a significant increase in antifungal effects. A significant decrease in colony diameter compared to the control was observed only at concentrations of 2 and 4 mM . This effect was observed as termination the growth of fungi at 72 hours after cultivation of fungi in culture medium containing sodium silicate. This effect remained stable with increasing incubation time. Fusarium fungi are root pathogens and reduce the absorption of water and minerals and clog the vessels, thus directly affecting the growth parameters in the roots and green parts of the plant. Infected control compared to healthy control showed a significant decrease in all growth parameters measured. Disease severity and growth factors were significantly affected by the effects of sodium silicate at a probability level of 1%. Application of sodium silicate in all concentrations had favorable results in significantly reducing the symptoms of the disease. Application of sodium silicate in diseased plants improved growth parameters. The mean value of growth parameters in different treatments and their treatment grouping based on LSD test is done at 5% probability level. Based on the results of this study, a decrease in chlorophyll and carotenoids and an increase in phenolic compounds and antioxidant enzymes and proline were observed in infected control plants compared to healthy controls. In this study, in the presence of sodium silicate in diseased plants, the amounts of pigments, phenol, flavonoids, anthocyanins, proline, protein and the activity of oxidative enzymes were significantly increased compared to the infected control.

According to the results, sodium silicate had direct antifungal effects in culture medium. In addition, a reduction in disease severity was observed in plants treated with sodium silicate in the greenhouse. Sodium silicate can be used as a chemical stimulant of plant defense and plant growth enhancer, for effective protection of cucumber plant against disease. Therefore, induction of resistance has found its place as a new technology for controlling plant diseases and its effect has been proven in laboratories and some farms.

Chickpea is an important grain legume in Asia, and makes a significant contribution to the food and nutrition security of the people. Fusarium wilt is an important disease of chickpea, causing significant yield loss. This malady is the most important and destructive soil-borne disease of chickpea in Iran. Excessive use of chemical fungicides to control this soil-born pathogen can have adverse effects on human health and environment, and can lead to fungal resistance to fungicides. Increasing induced resistance using resistance inducers as bio-fertilizers can be considered as an alternative method to plant disease control. The use of nitroxine a bio-fertilizer containing Azosprillium and Azotobacter species as well as mycorrhizal fungi to induce systemic resistance mechanisms has been demonstrated in different plants under biotic stress. The aim of this study was to investigate the effect of bio-fertilizers to induce acquired resistance in chickpea plant under pathogen stress as compared to non-infected plants.

The change of some antioxidant enzymes and gene expression analysis was examined to evaluate the effect of biofertilizers on increasing resistance in chickpea plants infected with Fusarium oxysporum fsp. ciceri. A factorial experiment based on complete randomized block design with three replications was conducted under greenhouse conditions in 2014. The eight treatments included: 1) Plant control without infection (sh), 2) Fusarium oxysporum (Foc), 3) Mycorrhiza (Gi), 4) Nitroxin (N), 5) Mycorrhiza+Nitroxin+Infection (GI+N+F), 6) Mycorrhiza+Nitroxin (GI+N), 6) Mycorrhiza + Fusarium oxysporum (Gi+F) and 8) Nitroxin+Fusarium (N+F). Mycorrhiza, Fusarium oxysporum and Nitroxin+Fusarium (M+F+N) were used in this study. Catalase, Proxidase, and Polyphenoloxidase activity was assessed by spectrophotometer with corresponding wavelengths. Total RNA was isolated using an extraction kit, according to the manufacturer’s protocol. Real-time RT-PCR was performed in a thermocycler using the following program: 5 min at 94 °C, followed by 35 cycles of 30sec at 95°C, 30 min at 59°C and 30 min at 72 °C, with final extension for 10min at 72°C. All acquired data were analyzed using SAS software version 9 and mean values were compared using Duncan's multiple range test. The changes of transcript level were measured via a comparative technique. Actin genes were used as internal reference.

Data analysis revealed that the highest rate of total phenol and protein (50/292 mg/mL) in treated plants was related to nitroxin and mycorrhiza treatments, respectively. The greatest change in all three enzymes was observed in mycorrhiza treatment 72h after plant infection. Mean comparison of gene expression data at different time intervals showed a high expression level 72h after plant infection in mycorrhizal application. Our results indicated that the maximum effect of bio-fertilizer application occurred 72h following plant infection with the pathogen. Application of both biofertilizers without Fusarium infection did not show any significant change in the expression level of the two tested gene.

Biofertilizer agents can improve plant growth through several different mechanisms such as protecting the plant under stressful conditions and defense against plant pathogen which can lead to reduced disease and death. The increase of total phenol and protein as the precursor of plant defense mechanism through apply biofertilizers in infected plants indicated the efficiency of these compounds to reduce disease. Antioxidant enzymes as a biomarker were used to evaluate the effect of exogenic compounds on increasing plant resistance against biotic stress. As with a similar work, we found a correlation between biofertilizer application and enzyme activity. Other parameters such as phenotypic characters and yield components can be used as a marker to investigate the effect of biofertilizers in these domains. Analysis of variance of the data related to gene expression confirmed the efficiency of biofertilizers on inducing resistance. Based on our results, we recommended use of biofertilizers in a single or mixture form to improve growth conditions in stressed plants especially under biotic stress. To make the bio-fertilizer more efficient in the field, a coordinated work by different science domains as bacteriology, chemistry, genetics, and agronomy as well as farmers as bio-fertilizer consumers seems necessary. This coordination could facilitate the adaptation of fungi and bacterium-based bio-fertilizers to different agriculture systems.

Cucumber root and crown rots are one of the main factors limiting cucumber production. Due to the soil borne nature of causal agents, their chemical control is not only ineffective, but also destroys the environment. Biological control strategies are one of the ways to combat these diseases. This research was conducted to study the biological control of cucumber soilborn diseases. The biocontrol influences of Trichoderma harzianum, T. virens, Pseudomonas fluorescens and Bacillus subtilis against cucumber root and crown rots caused by Fusarium oxysporum f.sp. radicis-cucumerinum, Pythium aphanidermatum and Phytophthora melonis were investigated in the laboratory. T. harzianum, which had the highest rate of the inhibitory growth in the laboratory, was used for the greenhouse studies. The disease severity and yield components of greenhouse cucumber Negin variety were evaluated in different treatments in a completely randomized design with four replicates using the SAS software. Highest percentage of inhibition in dual culture with 45.8% was observed by B. subtilis versus P. aphanidermatum. The results revealed that T. harzianum had the highest and lowest disease controls (32.8 and 18.8 percent) on F. oxysporum f.sp. radicis-cucumerinum and P. melonis, respectively. The treatment related to Trichoderma-inspired healthy plants had the greatest effect on the increase of the yield components in cucumber, while the infected plants with F. oxysporum f.sp. radicis-cucumerinum had the lowest yield. The disease severity index and root fresh weight showed a high correlation in different treatments. Therefore, fungal and bacterial antagonists were successful in controlling the cucumber root diseases.