Interaction of Fluorescent Pseudomonads with Pythium ultimum and Rhizoctonia solani in Cucumber Roots

Abstract

The effects of the fluorescent pseudomonad isolate CW2 on hyphae of Pythium ultimum (Trow) and Rhizoctonia solani (Kühn) and root colonization were studied in gnotobiotic systems under scanning electron microscopy (SEM). Results of SEM revealed that the frequency of bacterial colonization was higher in cucumber roots infested with the fungi than in healthy roots. Isolate CW2 caused irregular and abnormal fungal growth. Swellings and shrinkages of P. ultimum and R. Solani hyphae were obvious when cucumber roots were drenched with CW2. SEM studies were also conducted to evaluate the effect of CW2 on hyphae of both fungi on PDA medium. The hyphae of P. ultimum and R. solani showed distinct morphological alterations and degradation compared to untreated healthy control hyphae of Pythium or Rhizoctonia which were slender and uniform in shape. The results provide direct evidence of bacterial attachment and colonization to fungal hyphae of both tested spp. and show that fungal growth to be significantly reduced in the presence of isolate CW2.

Biocontrol of Sclerotium rolfsii Using Antagonistic Activities of Pseudomonads

“…Fluorescent Pseudomonas spp. are important for biological control [32] as they can suppress diseases caused by phytopathogenic fungi [11,4,33] and are candidates as hosts for the delivery of genes. Pseudomonas spp.…”

“…are emerged as the largest and most promising group of biocontrol agents owing to their potential of rapid and aggressive colonization, rhizosphere abundance, catabolic versatility, and their capacity to produce a diverse array of antifungal compounds [7,8,9,10]. Pseudomonads provide different mechanisms for suppressing plant pathogens [11,12,13]. They include competition for nutrients and space [14,15], antibiosis by producing antibiotics viz., pyrrolnitrin, pyocyanine, pyoluteorin, phenazines and 2, 4diacetyl phoroglucinol [16] and production of siderophores (fluorescent yellow-green pigment), viz., pseudobactin which confines the accessibility of iron required for the growth of pathogens [17,18].…”

Isolation and selection of fluorescent pseudomonads based on multiple plant growth promotion traits and siderotyping

“…Seeds treated with PC1 showed RL of 14.94 ± 0.96 cm, 100% germination, and VI 1197.4, whereas seeds treated with and PC2 showed RL 17.2 ± 0.94 cm, 100% germination, VI 1051.4) against distilled water control (RL 9.73 ± 2.41 cm, 84% germination, VI of 529.2) shows that fluorescent isolates have positive impact on test plant. Impact of fluorescent pseudomonads on growth promotion and yield and their role as biocontrol agent has been reported (Salman et al, 2013). Use of PGPR to nurture soil fertility and improve growth and yield of agronomically important crops is a consequential alternative to chemical fertilizers in sustainable agriculture (Stajkovic et al, 2011).…”

“…Fluorescent siderophores are unique to fluorescent pseudomonads -an inherent trait that has implicated them as PGPR (Upadhyay and Srivastava, 2010) and many of the siderophore producing bacteria have been used as biocontrol agents to combat phytopathogens (Salman et al, 2013). An absorption peak between 365 and 410 nm indicates the presence of pyoverdin nature of siderophores, as per Bhattacharya (2010).…”