Effect Of Cuticular Wax Of Pingguoli Pear From Developing And Storage On Alternaria Alternata Pre-penetration Process

Changes in physical structure of cuticular wax of surface and Alternaria alternata pre-penetration process on Pingguoli pear at different development and storage stages were observed or analysized by frozen scanning electron microscope(FSEM) and light microscope; effects of cuticular wax extracts on pre-penetration phase of A. alternata infection on the onion epidermis and glass slide were also evaluated; cutinase activity of A. alternata determined through in vivo and in vitro test. Meanwhile hydrophobicity(contact angle) of different surfaces and their correlation with infection structure of A. alternata pre-penetration were explored. The results showed as follows:1. Observed by frozen scanning electron microscope, cuticle layer of Pingguoli pear at 30 days after full bloom(DAFB) had formation but wax membrane was incomplete, and then became thick gradually and formed micro-cracks in the partial surface at 60DAFB; at the end of development period, the thickness of cuticle layer obviously increased, lenticel was covered by cuticular wax, and cuticle layer covered with large quantity flaky shape waxy crystals. During cold storage, the thickness of cuticle layer had no significant changes, at the early storage, the waxy crystals were sheet. But at late storage stage, smoothly bulk crystals covered the wax layer.2. The pre-penetration phase of A. alternata infection on the Pingguoli pear include: the conidia of A.alternata form germ tube, which elongates and differentiates into a hooked, apical appressorium, part of appressorium formed infection hyphae, finally it penetrated lenticel or pear surface. Intact pear surface could effcectively promote the formation of appressorium and infection hyphae of A.alternata compared with dewaxed pear surface by in vivo surface transparency test, pear surface of different development period had significant difference in promoting the formation of infect structure and process of infection. The conidia of A.alternata germinated after incubation 2 hours on pear surface at the 60 DAFB, then a large number of appressorium appeared after 9 hours incubtion, the rate of appressorium were up to 55%, which significant higher than that of other development period; In vitro test further confirmed that cuticular wax extracted from different developing Pingguoli pear could also promote infection process and structure formation of A. alternata, while the promotion level was different due to the difference of recrystallized wax at different coating surface. Cuticular wax extracted from pear fruit at the 120 DAFB signifficantly increased infection hyphae formation, the rates of infection hyphae were 22.3%, 11%, and 4% on wax coated onion epidermis, Formvar membrane and silanization glass slide respectively. The surface hydrophobicity in the different developing pear and wax coating membrane in vitro had difference, the hydrophobicity on coating wax extracted surface higer than that of intact pear surface. By correlation analysis, contact angle(hydrophobicity) was positively related to APP and infection hyphae formation. At the same contact angle surfaces coated with beewax and pear wax, the pear wax extract could more signifficantly promote the infection structures formation than beewax. In vivo and in vitro test showed that cuticular wax of pear fruit during developing period induced gene expression and activity of A. alternata cutinase. Meanwhile the results of chemical composition analysis showed that A. alternata could degrade on cuticular wax of Pingguoli pear after non-wounded incubation.3. Although intact pear surface had some inhibition on spore germination of A. alternata compared with dewaxed pear surface, but it stimulated the formation of infection structures and the length of germ tube, promoting role of pear surface at different storages had varied. In vitro test also confirmed that the cuticular wax extracts from storage pear fruit effectively promoted appressorium and infection hyphae formation of A. alternata. With storage time prolonged, stimulus effect of cuticular wax extracts on infection structure formation of A. alternata increased obviously. Hydrophobic tests showed that contact angle of pear fruit surface during storage were higher than that of fruit surface during development. Correlation analysis also confirmed that the surface hydrophobicity were positively correlated with appressorium and infection hyphae formation of A. alternata. Wax extracted from pear during storage could induce cutinase activity of A. alternata, but had little effect on gene expression of cutinase.In summary, chemical composition, hydrophobicity and structural of cuticlar wax and their changes during Pingguoli pear development and storage period might regulate pre-penetration process and infect structures formation of A. alternata.