Molecular detection of Collectrichum species infecting the mango plant
Raj | 13 Mar 2007
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Colletotrichum species causes anthracnose diseases on various temperate, subtropical and tropical fruits worldwide and are a particularly severe problem in tropical areas.
Although many cultivated fruit crops are infected by Colletotrichum species, the most significant losses occur when fruits are affected after harvest. Typically, conidia germinate on the fruit surface and produce appressoria and quiescent infections, which develop only after the fruit begins to ripen. The typical disease symptom known as anthracnose is characterized by sunken necrotic tissue where orange conidial masses are produced. It is difficult to predict however whether disease is likely to occur in a particular crop and how severe it will become. Early detection and diagnosis of plant pathogen can provide more accurate forecast of disease and improve the precaution of disease management practices.
Objectives of the study:
The main aim is to study the infection of mango by Colletotrichum sps.
a) Molecular characterization of Colletotrichum sps infecting mango.
b) Detection of fungi by PCR analysis: Because of its specificity and sensitivity, PCR is an attractive method for the detection of fungi. PCR can be used to detect groups of strains, pathotypes, species or higher taxa.
c) Preventive measures against infection of mango plant Colletotrichum sps.
Colletotrichum sps. must be detected in early infections because this fungi causes severe damage and results in the disease anthracnose. Morphological is difficult and hence molecular methods are employed for rapid identification of the causative agent of the disease.
The previously used method to detect and identify a pathogen is the enzyme-liked immunosorbent assay (ELISA) used since the 1970s. PCR is the latest method for the detention of plant pathogens.
The advantages of PCR over ELISA are:
1) PCR can detect lower pathogen amounts.
2) PCR assay development is faster and cheaper than ELISA because no antibodies need to be produced.
3) Because there are no antibodies used, antibody cross-reaction is not a problem. Very small amounts of sample are needed for PCR, and the sample tissues can be fresh dried or frozen.
4) PCR-based assays are more advanced for the detection of important plant pathogens.
Disease Cycle and Epidemiology:
Anthracnose disease spreads within mango trees by water by water-borne conidia of Colletotrichum gloeosporioides var. minor conidia which are produced in lesions on leaves, defoliated branch terminals, mummified inflorescences and flower bracts. Conidia can be trapped from these in the orchard during periods when anthracnose disease in developing both in flush growth and in flowers. Conidia are to be produced in the laboratory from acervuli in leaf lesions over a wide temperature range (10-30degree C) both in wet and humid (95-97% relative humidity) conditions. Conidia would then be present for dispersal within the tree throughout the entire season. Large numbers of conidia can be trapped during prolonged periods of rain.
The future of disease diagnosis and its application to disease management in crops is exciting. New technologies are being developed with increased sensitivities, the precision of traditional techniques are being enhanced or combined with novel nucleic acid based techniques for significant gains in sensitivity and innovative modifications are making complex procedures simpler and amenable to testing.