PATHOLOGICAL STUDIES ON IMPORTANT LEAF SPOT DISEASES OF SOME ORNAMENTAL FOLIAGE PLANTS.

Abstract

Foliage ornamental plants are important tool for modem indoor decoration, but their values and appearance are usually affected by several diseases including leaf spot which are more prevalence, particularly in warm and moist conditions where the disease can lead to heavy defoliation. Corynespora leaf spot caused by the cosmopolitan fungus C. cassiicola (Berk.& Curt.)Wei, was consistently associated with a serious disease on five foliage ornamental plants for the first time in Egypt during 1999 &2000 season . Pathogenic capability and cross- inoculation tests confirmed that each of four C. cassiicola isolates was pathogenic to Dracaena, Dieffenbachia , Pothos and Nephtbytis recording the highest disease indexes on its plant source. Host range test revealed tbat Dracaena isolate fuiled to infect any of tbe I 0 foliage plant species tested. Results of the in vitro physiological studies revealed that maximum mycelial growth was produced on Nephthytis Leaf Agar medium, the highest yield of spores were produced on Czapek's Dox Agar, the maximum mycelial fresh and dry weights were produced on PO, Maximum mycelial growth and the highest number of conidia were obtained at 25 °C, tbe optimum temperature for conidium germination was 30 °C, maximum mycelial growth and sporulation was obtained at IOO%relative humidity , optimum pH for growth was pH 5.1, the best carbon sources for growth was maltose followed by sucrose,while sucrose followed by maltose were the best carbon sources for sporulation, sodium nitrate was tbe best source of nitrogen sources for growth and sporulation followed by glycen, tbere was a negative correlation between the period of exposure to light and the radial growtb but there was a positive correlation witb abundance of spore formation , the yellow and green wave length as well as neutral light were the most favourable to conidia formation. Results of biochemical changes due to infection by C. cassiicola tested isolates revealed that a gradual reduction in total, reducing and non- reducing sugars of infected leaves compared with healthy ones, infection by each isolate resulted in an increase in total, free and conjugated phenols . Determination of enzyme activity for the isolates revealed that isolate of Dracaena produced the highest amount of (PG), (CX) and (PME). Regarding genetic variation, The four tested isolates of C. cassiicola showed high similarity levels ( 94.33%) while, isolate 4 which was isolated from Dieffenbachia in a single cluster included two sub- clusters. Healthy plants, infected plants and fungal materials had some similar protein patterns beside that some disappeared after inoculation or new bands were formed. DNA patterns, the RAPD analysis, using the primer No.I, showed differences between the isolates tested. Disease management revealed that Trichoderma harizianum and T virde were the most effective bioagents , Eucalyptus globulus was the most effective extracts, Amconil followed by Topsin-M showed the highest effective fungicides. The superiority was to T harzianum and Amconil, whic.h completely prevented disease incidence when •.'.'.. sprayed 24 h before inoculation by each fungal isolate.