Spongy tissue development in Alphonso mango: association with Staphylococcus xylosus

Abstract

A Gram-positive and catalase positive Staphylococcus strain was found to be associated with spongy tissue defect of Alphonso mango. The organism was identified to species level by physiological, morphological and biochemical characterization and fatty acid profile. The strain was identified as Staphylococcus xylosus (IMTECH, India, Accession No. MTCC 7441). The optimal growth of the organism was observed in the pH range of 5.0-9.0 and temperature range of 10-45°C. It was mannitol and arabinose-positive and able to produce acid from various sugars. The organism was able to grow in a medium containing 2-10% NaCl. It was further identified to species level by genomic sequencing of 1,387 base pairs of DNA (Gene Bank accession No. EU019195). Based on nucleotide homology and phylogenetic analysis, the microbe was found to be S. xylosus. The survey of Alphonso mango trees with a known history of producing spongy fruits showed that some of the twigs, leaves and flowers were coated with a honeydew-like sticky substance and mango hopper insects were observed over the inflorescence. The source of contamination of spongy fruits by S. xylosus was in the sticky mass. Gram staining, the catalase test and morphological features of the culture isolated from the sticky mass exhibited characteristics identical to the Staphylococcus strain isolated from the spongy pulp. Pathogenicity tests on different varieties of mangoes, apples and guavas indicated that the disease was experimentally transmitted from infected to healthy fruits. This observation suggested that this organism develops spongy symptoms in the fruits post-harvest and lacks specificity. In inoculated fruits, catalase and peroxidase enzymes were expressed as in naturally infected fruits. This report shows that the infection by S. xylosus could be a major initiating factor for spongy tissue development in Alphonso mangoes. Keywords Internal physiological disorder . Mangifera indica . Spongy tissue . Staphylococcus . X-ray imaging Abbreviations BHI brain heart infusion BPA Baird Parker agar NA nutrient agar PCA plate count agar PDA potato dextrose agar PMSF phenylmethanesulfonyl fluoride POX peroxidase Eur J Plant Pathol (2008) 122:335-348

Profile of peroxidase isoforms influenced by spongy tissue disorder in Alphonso mango (Mangifera indica L.) fruits

“…The spongy tissue formation was found to be associated with natural staphylococcus xylosus infection (Janave and Sharma 2008). The pathogen was observed over the inflorescence of the Alphonso mango trees with a known history of producing spongy fruits.…”

“…The presence of the pathogen over the inflorescence indicated that, the microbe might enter the developing fruit through the micro wounds created by the insects, during the early stages of fruit development. After entry, it may remain dormant until the fruits mature, and multiply when the internal physiological conditions of the fruit, such as TSS, acidity, and pH, favors the bacterial growth (Janave and Sharma 2008) leading to spongy tissue development. The mode of entry of this organism could be, either the mango hoppers observed over the inflorescence serve as a potential vector, or the microbe could be air-borne (Janave and Sharma 2008).…”

“…After entry, it may remain dormant until the fruits mature, and multiply when the internal physiological conditions of the fruit, such as TSS, acidity, and pH, favors the bacterial growth (Janave and Sharma 2008) leading to spongy tissue development. The mode of entry of this organism could be, either the mango hoppers observed over the inflorescence serve as a potential vector, or the microbe could be air-borne (Janave and Sharma 2008). Increased levels of POX in spongy fruits due to Staphylococcus xylosus infection (Janave 2007;Janave and Sharma 2008) prompted further studies on the profile of POX isoenzymes.…”

“…Biochemical characterization and DNA sequencing indicated that, the isolated organism belonged to Staphylococcus xylosus (Janave and Sharma 2008). The Koch's postulate studies after inoculating the isolated strain reproduced the same disease in various fruits, indicating that, the development of spongy tissue could be due to Staphylococcus xylosus infection.…”

“…Alphonso, were procured within 2 days after harvest, from a commercial market. Internal flesh breakdown in the fruits was detected by passing the whole fruits through an X-ray imaging machine (ECIL Model XBS 9050S, Electronics Corporation of India Limited, Hyderabad, India), as detailed in the previous papers (Janave 2007;Janave and Sharma 2008). The fruits were separated in batches, as non-spongy and spongy, and allowed to ripen at 28-30°C.…”