Stomatal Penetration and Temporal Dynamics of Ingress of Two Fungal Isolates Associated with Leaf Spot Disease of JASMINE (Jasminum sambac L.)

Jasmine (Jasminum sambac L.) is an ornamental crop grown in South and Southeast Asia for its flowers for garlands, tea and essential oil production. However, certain fungal foliar and floral diseases significantly reduce its yield. In this study, Colletotrichum sp.-like (cylindrical conidia) and Fusarium sp.-like (lunate conidia) isolates causing leaf spot disease were characterized based on the ingression process and fungal germination in planta. Four-day single-spore cultures in PDA of isolating C1 (Colletotrichum sp.-like) and F2 (Fusarium sp.-like) were obtained. Suspensions of 108 conidia mL-1 were made and sprayed onto young leaves of jasmine. Specimen collection was done at 2, 6, 12, 24, 36, 48, 60 and 72 h after inoculation (hai). Formalin-acetic acid was used to clear the tissues and fungal structures are selectively stained using lactophenol-acid fuschin. Average ingression sites (IS) were counted for each time point under 50X magnification, then IS per leaf area (cm2) was calculated. Fungal isolates remain at the surface of the leaf until 36 h. IS of C1 and F2 almost doubled at 48 hai. However, ingression sites declined at 72 hai for both pathogens, which either imply a progression of sub surface colonization or unsuccessful penetration. Leaf yellowing and a few spots were observed at 48 hai for F2 and at 60 hai for C1. More severe necrotic leaf spots with yellow halo (severity rating of 5) were seen in plants inoculated with Fusarium sp.-like isolated than in those inoculated with Colletotrichum sp.-like isolated. Lastly, at 48 to 60 hai, it was evident that the pathogen started to seek for stomata, which seemed to be the preferred penetration site for both fungal pathogens.