Studies on the effect of hexanal against major post harvest pathogens of mango
|Parthasarathy Seethapathy (email@example.com)|
|Plant Pathology, Tamil Nadu Agricultural University|
|Anthracnose and stem end rot are the major post harvest diseases of mango. Anthracnose is caused by Colletotrichum gloeosporioides (Penz.) (Penz. and Sacc) and stem end rot is caused by Lasiodiplodia theobromae (Pat.) (Griffon and Maubl). Virulent isolates of C. gloeosporioides and L. theobromae were obtained from Dept. of Plant Pathology, TNAU, Coimbatore. Further, pathogens were cultured on Potato dextrose medium (PDA) and proved the pathogenecity in vitro by pin prick plus spore suspension methods.
The efficacy of the hexanal on the mycelial growth and spore germination of
C. gloeosporioides and L. theobromae was studied. Among the different concentrations of hexanal tested, 0.06% showed maximum inhibition in mycelial growth of
C. gloeosporioides and L. theobromae (95.56 and 93.33 per cent respectively). In vitro efficacy of bacterial antagonists was tested against the pathogens. Pseudomonas fluorescens strain, Pf 1 was most effective and showed reduction in the mean mycelial growth of C. gloeosporioides and L. theobromae (36.16 and 54.16 mm respectively) accounting for 53.83 and 35.83 per cent inhibition over control. Bacillus subtilis strain EPCO 16, significantly reduced the mean mycelial growth of
C. gloeosporioides and L. theobromae (30.09 and 43.36 mm respectively) accounting for 59.02 and 46.63 per cent inhibition over control. Compatibility of potential antagonists
P. fluorescens (Pf 1) and B. subtilis (EPCO 16) with hexanal was tested in vitro by poisoned food technique and turbidometric method. The compatible formulation of antagonists and carbendazim was tested in the field and post-harvest conditions against the anthracnose and stem end rot diseases of mango. The results revealed that pre-harvest spraying of 2% hexanal + 0.5% P. fluorescens (Pf 1) at 30+15 (days before harvesting) followed by post-harvest dipping of fruits in 2% hexanal + 0.5% P. fluorescens (Pf 1) stored under cold condition showed maximum inhibition in anthracnose incidence next to 0.1% carbendazim. Toxic compounds produced by the pathogens viz., C. gloeosporioides and L. theobromae were extracted and their role in pathogenicity was tested by inoculation of crude culture filtrates and differentially diluted filtrates on mango leaves. Crude toxins extracted separately by solvent extraction method were tested with mango leaves and fruits at different dilutions to detect their role in pathogenecity. Non-host selective nature of the toxin was determined by seedling and seed germination bioassay using nine non-host plants and three cereal seeds. The toxic compounds were extracted from the yeast extract and potato dextrose broths inoculated with C. gloeosporioides and L. theobromae respectively, by solvent diffusion method and partially purified by Thin Layer Chromatography (TLC) using standardized diluents (Di-methyl sulfoxide) and mobile phase of Chloroform: glacial acetic acid: ethanol (3:1:1) for C. gloeosporioides and Butanol: water: glacial acetic acid (5:3:2) for L. theobromae. The toxic compounds partially purified by TLC were identified through Gas Chromatography /Mass Spectrometer (GC/MS). The profile of unique volatile compounds emanated by mango fruits treated with hexanal and artificially inoculated with C. gloeosporioides and L. theobromae separately were detected by GC/MS. Mango fruits were inoculated with C. gloeosporioides and L. theobromae separately, followed by treatment with hexanal, biocontrol agents and carbendazim. The changes induced in respect of starch, sugar, phenolics and total soluble proteins were observed. Among them, starch, phenolics and total soluble protein content were reduced in the inoculated and treated fruits while the sugar content increased. Moreover, expression of isoforms of defense related enzymes viz., peroxidase (PO), polyphenol oxidase (PPO) phenylalanine ammonia lyase (PAL) superoxide dismutase (SOD) and catalase (CAT) were enhanced in the inoculated and treated fruits. Antifungal activity of mango latex was detected by poisoned food technique and effect of hexanal on the treated mango fruits were detected by thin layer chromatography.