Distribution and pathogenesis of date palm fungi in Egypt.
Twenty-one fungal species belonging to fifteen genera were isolated from diseased date palm samples collected from different Egyptian localities. Thielaviopsis paradoxa [Ceratocystis paradoxa] was the most prevalent fungus followed by Graphiola phoenicis, D. phoenicum, Botryodiplodia theobromae and Fusarium oxysporum. Alternaria alternata, F. solani and F. moniliforme [Gibberella moniliformis] had moderate frequency percentages. Fusarium equiseti, Phomopsis sp., Phoma sp., Mycosphaerella sp., Chaetomium sp., Gliocladium sp., Omphalia sp., Chaetosphaeropsis sp., Mauginiella sp. and F. semitectum [F. pallidoroseum] had low frequency percentages. The lowest frequency was recorded for Paecilomyces sp. Some date palm pathogens were previously recorded in Egypt, such as G. phoenicis, Diplodia sp., T. paradoxa, Phomopsis sp., M. scaettae, Chaetosphaeropsis sp., Botryodiplodia sp. and Chaetomium sp., while the isolated species of Fusarium, Alternaria, Mycosphaerella, Omphalia and Phoma were recorded for the first time in Egypt as fungal pathogens of date palm trees. The fungal genera isolated from diseased date palms were attributed to the isolation sites on date palm tree, i.e. root, trunk, leaf or inflorescence. Diplodia, Fusarium and Thielaviopsis were isolated from all diseased roots, trunks and leaves of date palm. On the other hand, Phomopsis, Omphalia, Chaetomium and Paecilomyces were also isolated from the roots. Diplodia, Fusarium, Gliocladium and Thielaviopsis was isolated from diseased trunks of date palm. Diseased leaf samples of date palm exhibited 11 fungal genera, i.e. Alternaria, Botryodiplodia, Chaetosphaeropsis, Diplodia, Fusarium, Graphiola, Gliocladium, Mycosphaerella, Phoma, Phomopsis and Thielaviopsis. Rotted-root samples of date palm exhibited 8 fungal genera, i.e. Chaetomium, Diplodia, Fusarium, Gliocladium, Omphalia, Paecilomyces, Phomopsis and Thielaviopsis. However, rotted inflorescences yielded only Mauginiella scaettae. A study of the geographical distribution of date palm fungi in Egypt proved that the prevalence of each one was affected by environmental conditions. Thielaviopsis isolates were present in all examined localities, except the hot areas at New Valley. Botryodiplodia isolates were associated with Sharkia, Ismailia and Behaira. The causal agent of false smut disease and Gliocladium leaf spot were found at Damietta and North Sinai which had experienced rainy weather. Diplodia isolates were obtained only from samples from Behaira. The other leaf spot fungi, i.e. Alternaria, Mycosphaerella, Chaetosphaeropsis, Phoma and Phomopsis, were associated with the conditions of the Sahara climate. The tested fungi varied in their dependence on wounds for entry to host tissues. Phomopsis sp., Chaetosphaeropsis sp., Mycosphaerella sp., Gliocladium sp. and Phoma sp. formed some limited brown lesions on the midrib of date palm leaflets at puncture sites. It was suggested that these fungi were wound parasites. In the case of Alternaria sp., Thielaviopsis sp., Diplodia sp. and Botryodiplodia sp., wounds were not always necessarily a host entrance for these fungi. The second bioassay of detached roots was designed to measure peroxidase enzyme activity as an indicator of successful root infection. Date palm root tissues infected with Omphalia sp., Chaetomium sp. and Paecilomyces sp. exhibited high levels of peroxidase enzyme activity in punctured tissues only. This means that these fungal isolates are wound parasites. By contrast, roots infected with Fusarium spp. exhibited high levels of peroxidase activity in punctured and unpunctured tissues. This means that wounds are not necessary for Fusarium infection.