Major diseases of citrus in Pakistan: A review

Among the citrus diseases in Pakistan citrus greening, citrus slow decline,citrus canker and citrus whither tip are most damaging and are gainingimportance. Leaf mottling is the best foliar symptom for the diagnosis of greening.Fruits on severely affected trees are small, lopsided and poorly coloured,remaining dull green, hence the name greening given to the disease. Causalorganisms of this disease has been remained the subject of debate. The highestincidence and severity of this disease has been reported in Peshawar followed bySargodha. The first evident symptom of citrus slow decline (CSD) is drying oftwigs and reduction in terminal growth. These trees are not killed but maintainlife on a limited scale and produce a reduced crop of inferior fruit. Tylenchulussemipenetrans Cobb. and other nematode species are associated with therhizosphere of diseased plants. Citrus canker is a bacterial disease incited byXanthomonas campestris (Pammel) Dopws. Pv. citri (Hasse) Dye. Symptoms of thedisease can appear on fruit, leaves and twigs of infected plants, and typicallyconsist of small, round blister-like formations called lesions. These lesions areusually raised, crate-like and are tan to brown in colour and surrounded by anoily, water soaked margin. Citrus wither tip caused by Colletotrichumgloeosporioides Penz. is one of the serious diseases throughout the country.Symptoms appear initially from top and transmit downward to bottom of infectedtree. Diseased twigs start drying at tips and all affected parts become silverygray and develop black dots. Defoliation and death of the entire plant also occurunder severe conditions. Some other fungal diseases in Pakistan are Septoria spot(Septoria sp.), stem end rot (Phomopsis sp. and Diploidia sp.), Trunk gummosis(Phomopsis sp. and Diploidia sp), foot rot (Phytophthora sp.), root rot (waterlogging + fungi), damping off (Pythium sp., Rhizoctonia solani, Phytophthora sp.),and citrus quick decline [Fusarium solani (Mart.) Sacc.].