THE INVESTIGATION OF POST HARVEST INFECTION STRATIGY OF PENICILLIUM MOULD ON CITRUS FRUITS

Abstract

Fungal disease of post harvest which infect fruits from acceutuated and dangerous pathogenic micro- organism which cause large economical losses reach to 50% , developed and spreads during transport and storage. The citrus fruits are one of the major important agricultural product especially in western region of Libya . In this study we founed on post harvest citrus green mould disease which caused by Penicillium digitatium after running Kock pastulate . In this research we traying to investigate and trace the mode and mechanism of infection of Penicillium digitatium on local and imported four citrus varities ( Orange , Mandarine , Lemon and Grapefruits ) . The optained results of pathogenicity test indicate that Penicillium digitatum and is the main causal agent . The ability of this fungus to infect four citrus varities with same virulence after application three methods of artificial inoculation . Through cooling experiment we founed the optimum growth temperature ranged betwwen 25-27°C . Study the effect of depth and wound location on the previous citrus varities does not show any effect role on infection in varities sampled . After study natural micro-flora associated with studied fruits surface three species of bacteria are identified : Staphylococcus hominis , Staphylococcus haemolyticus and Staphylococcus warneri . After artificial inoculation with Penicillium digitatum with inoculum density ( 10 ) the washed fruits speed infected compared with non – washed fruits with dispersal time about 12 hours . In test of three types of juice ( Peel Juice – Sac Juice – Whole fruit ) , all tested juice from citrus varities studied showed Penicillium digitatum growth with more rapidly on peel juice compared with other two types of juice extracts , which make ensure that the tested fungus was this obligate aerobic . Through intervene modulation to change acidic medium of studied fruits by inject two concentrations of apple vineiger and solution of sodium bicarbonate , solution of sodium chloride , sterile distill water as control showed that there is no role in prevent infection by Penicillium digitatum but just delaying infection time about five days by used solution of sodium bicarbonate NaHCO3. In study aerodynamic spore mechanism and epidemology of Penicillium digitatum the results showed the spores of Penicillium digitatum have low weight to became longtime before fall down , indicating that Penicillium digitatum have dry spores . The sedimentation of these spores on fruit surfaces was more vertically faster than horizontally , conferming the way of storage fruits above long distance from ground surface does not prevent the infection incidence . From studying of lignification effect on peels of studied citrus varities after injuires and kept for 12 hours then injection showed the lignin formation do not prevent the infection but just lated about 6 days . From study specific different isolates showed all species have specific to infect the host fruit without the other . Through study the maturity of lemon fruits on enhance or lated infection with Penicillium digitatum show the mature lemon fruits infected earlier through 4 days compared with immature lemon fruits infected after 6 days . The result obtained from Interaction experiment of different isolates in vitro on Sabroid Agar showed the all isolates followed to same genus of Penicillium . Finally the results optained from programs to this disease on injected and non-injected fruits by selective two physical methods ( Hot water – Sea water ) , two natural oils (Eucalyptus oil – Olive oil) and one mineral oil ( Johnson's baby oil ) and wax , showed all of these method can not prevent the invection but just delated the infection period , wax test delay five days and the other two treatments were delay about three days only .