Produce An Infectious Disease

Published Date: 02 Nov 2017

Isolates of B. cinerea collected from different hosts showed variations in respect to their morphological, cultural and biochemical characteristics. Variations in pathogenic behavior of all four isolates were also observed under in vitro conditions. In respect of cultural characteristics, the isolates of B. cinerea showed marked variations in colony color, shape, margin and texture. Colony color was cottony white, greenish and ashy white. Colony texture was fluffy and velvet in all isolate but some depicted effuse type of texture.

B. cinerea isolates also showed variations in conidia shape, conidia production and sclerotia formation. The conidia were one-celled, ellipsoid or ovoid in shape and colorless or pale brown. Differences in conidia production, shape and size have also been reported by Kwon et al., 2011; Karakaya and Bayraktar, 2009. The pathogen produced sclerotia on culture media and the sclerotia formation was very much peculiar. In all the four isolates sclerotia were observed in different patterns. Some were arranged in concentric rings, some were centrally placed and some arranged towards the periphery. Sclerotia formation in fungus is often correlated with chance of survival of pathogen under adverse conditions. A broad classification of B. cinerea isolates could be done by macroscopic viewing of sclerotia formation. Spore count was more profound in isolates grown on PDA as compared to MEA and PCA. This finding is also supported by Hosen et al., (2010) who observed marked variations in spore count in different isolates of B. cinerea.

Pathogenicity is the ability of a pathogen to produce an infectious disease in an organism. Pathogenicity assay was performed under in vitro conditions. Maximum pathogenicity was observed in BC 4 as compared to other isolates. Variation in virulence of B. cinerea populations against one host plant has been frequently reported (Derckel et al., 1999; Buck and Jeffers, 2004). (Valiuškaite et al., 2010) also studied variations in pathogenic characteristics among B. cinerea isolates. The present study suggests the existence of pathogenic variability among B. cinerea isolates.

It is important to identify determinants of B. cinerea for developing strategies to combat its spread among agronomically important crops. Oxalic acid has been described as pathogenicity factor in B. cinerea (Kubicek et al., 1988; Lyon et al., 2004). In S. sclerotiorum, a necrotrophic fungus closely related to B. cinerea, a key role has been postulated for oxalic acid in pathogenesis and plant maceration (Godoy et al., 1990, Guimaraes and Stotz, 2004) and its suppressor effect on the oxidative burst of the plant has also been shown (Cessna et al., 2000). The size of lesions induced by different strains of B. cinerea has been found to be correlated with the amount of OA secreted in vitro (Germeier et al., 1994). Secretion of OA as virulence factor results in lowering the pH of the surroundings. A shift from apoplastic pH to acidic pH due to higher secretion of OA helps in spread of B. cinerea (Manteau et al., 2003; Kunz et al., 2006). Acidic pH encourages degradation of plant cell wall by secretion of a set of enzymes such as PGs and PMEs (Wubben et al., 2000; Valette-Collet et al., 2003). The cell wall degrading enzymes (CWDEs) secreted by pathogenic fungi are the earliest factors released during infection that determine fungal penetration into plant tissues. During plant infection, the active CWDEs may differ depending on the host tissue. Pectinases have been studied because of their involvement in pathogenicity. Pectin degradation by enzymes such as polygalacturonase and pectin methyl esterase appears to play a role in pathogenicity in some fungi. Since B. cinerea causes maceration on a wide range of plants it is legitimate to hypothesize that PME and PG activity in B. cinerea can be an important determinant of its pathogenicity. Studies in B. cinerea also showed endo-PG gene expression in vitro (Wubben et al, 2000) and in vivo (ten Have et al, 2000). The data revealed significant differences among all the isolates in both PG and PME concentration. BC 4 isolate showed highest concentration of both the enzymes which also had a direct relation with the pathogenic index. In general, it could be postulated that reduced enzyme activities govern reduced fungal invasion and less disease severity by the B. cinerea isolates. The study proved the synthesis of virulence factors (oxalic acid, PG and PME) in all the isolates of B. cinerea.

B cinerea isolates showed high genetic variability which might be a major factor in the development of fungicide resistance (Leroux et al., 2002). Fungicide assay is based on measurement of inhibition of mycelial growth. Fungicide assay was performed at 20°C which was regarded as optimum temperature for mycelial development of B. cinerea (Bakr and Ahmed, 1992; Bakr et al., 1997; Leroux, 2004; Ahmed et al., 2007). In present investigation, isolates of B. cinerea were examined for their response to five Botrytis specific fungicides in order to determine variability among isolates being sampled to varied concentrations of fungicides. The aim of this study was to explore which fungicide was effective against grey mold. (Giraud et al., 1999) has shown that there is a significant genetic differentiation among isolates collected from different host plants in France and that the level of fungicide resistance differs significantly. B. cinerea is a high-risk fungal pathogen in the development of fungicide resistance because of its short life cycle and prolific reproduction (Brent and Hollomon, 1998). In present study it was observed that isolates developed resistance against thiram and no zone of inhibition was found even at 200 μg ml-1.

Thus, the present findings suggested that B. cinerea is a highly variable fungus which might also contribute to its pathogenic behavior. It supports the variable phenotypic nature of the fungus on different media. An analysis of the factors responsible for the virulence was also attempted.