Relationship between Dubas Bug (Ommatissus lybicus) Infestation and the Development of Fungal-Induced Leaf Spots in Date Palms (Phoenix dactylifera)

SIMPLE SUMMARY: Insect infestation can cause severe loss to the production of agricultural crops in two ways. The first is direct injury to the plant by the feeding insect, which eats the tissues of leaves, stems, fruits, or roots. The second type is indirect damage, in which the insect itself does little or no harm but transmits or influences the infection of bacteria, viruses, or fungi into a crop. We examined the development of fungal infection in date palm leaves following dubas bug infestation. The study provided evidence that dubas bug infestation in date palm leaves facilitated the infection of several fungal species, such as Alternaria destruens, Cladosporium pseudochalastosporoides, C. endophyticum, Fusarium fujikuroi species complex, F. humuli, F. microconidium, Quambalaria cyanescens, Phaeoacremonium krajdenii, and P. venezuelense. This was the first study to report this kind of association between dubas bugs and these fungi in date palms. Future studies should focus on the management of dubas bug infestations to limit the development of other diseases in the host plants. ABSTRACT: The dubas bug (Ommatissus lybicus) (Hemiptera: Tropiduchidae) is a serious pest in date palms in several date-producing countries, including Oman. Infestation results in a severe reduction in yield and a weakening of date palm growth. In addition, egg laying, which causes injuries to date palm leaves, results in the development of necrotic lesions on the leaves. This study aimed at investigating the role of fungi in the development of necrotic leaf spots following dubas bug infestation. Leaf samples developing leaf spot symptoms were collected from dubas-bug-infested leaves, as the leaf spot symptoms were not observed on the non-infested leaves. Isolation from date palm leaves collected from 52 different farms yielded 74 fungal isolates. Molecular identification of the isolates revealed that they belonged to 31 fungal species, 16 genera, and 10 families. Among the isolated fungi, there were five Alternaria species, four species each of Penicillium and Fusarium, three species each of Cladosporium and Phaeoacremonium, and two species each of Quambalaria and Trichoderma. Out of the thirty-one fungal species, nine were pathogenic on date palm leaves and induced varying levels of leaf spot symptoms. The pathogenic species were Alternaria destruens, Fusarium fujikuroi species complex, F. humuli, F. microconidium, Cladosporium pseudochalastosporoides, C. endophyticum, Quambalaria cyanescens, Phaeoacremonium krajdenii, and P. venezuelense, which were reported for the first time as leaf spot causal agents in date palms. The study provided novel information on the effect of dubas bug infestation in date palms on the development of fungal infection and associated leaf spot symptoms.