The effect of using uncertified citrus seeds on huanglongbing disease incidence in Karo District

North Sumatra Province is one of the major citrus producers for Siam cultivars in Indonesia. Recently, it experienced a significant decline in citrus production. One of the causes is the presence of huanglongbing (HLB) disease which results in decreased production and plant mortality. The research aim to obtain information on the origin of citrus seeds and to map HLB incidence in eight subdistricts within Karo District. This research was carried out through direct questionnaires to farmers, visual symptoms scoring, and molecular detection with Polymerase Chain Reaction (PCR). At least two villages were taken from each sub-district and three orchards were taken from each village as samples in January 2019. The results showed that in general, citrus plants aged 3 to 15 years. Mostly, citrus planted in Karo originated from uncertified seedlings bought from local and outside seed breeders in the province of North Sumatra. The highest symptoms severity of HLB diseases based on leaf scores and canopy scores were recorded in Barus Jahe subdistrict with 82-83% intensity. The highest HLB incidence were recorded in three subdistricts namely Kabanjahe, Munte, and Brastagi, each with 100% HLB prevalence. This shows that asymptomatic plants are not always free from C Las pathogens. Certified citrus seeds which are free from systemic diseases, followed by improve farmer’s awareness to apply good agriculture practice the initial to sustain Indonesian citrus agroindustry.