Pest status of citrus psyllids in relation to citrus greening disease (Huanglongbing) in major citrus growing areas of Tanzania
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Date
2024-05
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Sokoine University of Agriculture
Abstract
The citrus industry is a significant contributor to the global economy,
with East African countries like Tanzania playing a crucial role.
However, the emergence of Asian citrus greening disease, facilitated
by insect vectors such as Diaphorina citri and Trioza erytreae, poses
a substantial threat to this sector. This study aims to document the
impact of citrus greening and psyllid infestations on Tanzania‘s citrus
industry, which results in diminished fruit yield, compromised quality,
and economic losses.
Field surveys were conducted in major citrus-growing regions in
Tanzania, including Ruvuma, Arusha, Morogoro, and Tanga. Data
was collected using molecular detection techniques, and the
prevalence and severity of Huanglongbing, distribution and
abundance of Diaphorina citri and Trioza erytreae were recorded.
These factors were then correlated with altitude, temperature
variations, and citrus varieties. DNA samples were extracted and
analysed using polymerase chain reaction (PCR) to confirm the
presence of Huanglongbing in selected samples.
The study found regional variations in the distribution and
abundance of Diaphorina citri and Trioza erytreae. Altitude
significantly influenced psyllid species abundance, with Diaphorina
citri decreasing and Trioza erytreae increasing with altitude. The
temperature had a weak positive correlation with Diaphorina citri
abundance and a moderately negative correlation with Trioza
erytreae abundance. Different citrus varieties significantly affected
Diaphorina citri abundance, with the ―Late Valencia (Kitenesi)‖
variety having the highest average Diaphorina citri counts per tree.
The study also found a negative correlation between altitude and the
Disease Severity Index (DSI), suggesting that as altitude increases,
the DSI decreases. However, a weak positive correlation was
observed between the number of citrus trees in an orchard or backyard and the DSI. Significant variations in Huanglongbing
prevalence were observed at both the regional and ward levels.
The study concluded that the Mediterranean variety was particularly
susceptible to Huanglongbing, while the Valencia, Local variety,
Washington navel, and Bitijuma varieties exhibited more resistance.
The study also confirmed the presence of Ca. L. asiaticus in
symptomatic leaves and the absence of bacteria in asymptomatic
leaves using PCR Analysis for pathogen detection.
The findings of this study have significant implications for developing
region-specific management strategies to protect Tanzania‘s citrus
industry, which is vital for food security and rural livelihoods. It is
recommended to combine molecular and visual methods to enhance
our understanding of the dynamics of Tanzania‘s two crucial citrus
psyllid species, Diaphorina citri and Trioza erytreae, reflecting the
complex ecological interactions involved. This will aid in the
development of effective strategies to mitigate the impact of citrus
greening disease.
Description
MSc Dissertation
Keywords
Citrus greening disease, Citrus psyllids, Huanglongbing, Tanzania