Masters Dissertetion
Pine Pitch Canker (PPC) is a disease of pine trees caused by Fusarium circinatum. The
disease is reported to damage pine plantations and woodlots in Tanzania. Disease attack
result in a reduction of productivity which causes significant loss of national income. The
disease occurrence and distribution is influenced by various factors such as climate,
topography, and management practices. Currently in Tanzania there is an increasing rate of
PPC disease incidences on pine plantations and woodlots mostly affecting tree aged 5 – 6
years. The risk of disease spread in Tanzania is high due to the wide distribution of host
range, as pine covers about 78% of planted trees in mono-culture plantations.
Numerous studies have been conducted to predict the suitable areas of PPC disease
distribution to various parts of the world. The global prediction of climatic suitability to
pitch canker disease by the CLIMEX model showed Tanzania as one of the areas suitable
for disease establishment. However, the model was biased showing a larger portion of PPC
establishment on water bodies in Tanzania, possibly due to limited occurrence records for
Tanzania during model calibration.
Furthermore, there is no records of PPC disease
incidence and severity; and the pattern of suitable areas for disease establishment in
Tanzania.
Therefore, the study aimed (i) to determine incidence and severity of PPC disease in pine
plantations for different management regimes, (ii) to determine the influence of
management practice and stand characteristics on PPC disease incidence and severity, and
(iii) to predict the suitable areas for PPC disease distribution in Tanzania.
The study employed different sampling and data collection methods. To determine the
incidence and severity of PPC disease in pine plantations, purposive sampling was usediii
where three management regimes comprising of government managed plantation, large-
scale private managed plantation, and small-scale private pine woodlots were selected. A
total of 14 square plots of 20 x 20 meters were established, at an interval of at least 100 m
apart in each selected plantation. Assessment of disease infestation was done to 25
individual trees near the plot center totaling 1050 trees for the whole study area. A Pine
Pitch Canker severity ranking system was used to determine disease severity index (DSI),
and a total number of symptomatic trees were used to determine disease incidence (DI). The
management practices were obtained from compartment register and by interviewing key
informant. Stand parameters including tree diameter at breast height (DBH) and height were
measured.
Analysis of Variance (ANOVA) was used to compare means of disease incidence and
severity index between management regimes. Then, Tukey’s Honest Significant Difference
(HSD) test was employed to separate the means within different management regimes.
Pearson correlation coefficient was used to establish the association between disease
incidences, severity index and stand parameters. The effect of management practices on
PPC disease incidence and severity index was determined by using multiple linear
regression model. The management practices comprise; land preparations techniques, seed
source, weeding, spacing, pruning, and thinning.
Maximum Entropy (MaxEnt) was used to predict the suitable areas of PPC establishment.
Pine Pitch Canker disease occurrence and environmental variables (climate and
topographic) were used in prediction. The GPS coordinates for affected areas were obtained
from the field survey, plantation managers, woodlots owners and various published and
unpublished reports. A total of 70 affected points were used in prediction of the potential
distribution of PPC disease in Tanzania.iv
The disease incidence was significantly higher in large-scale private plantations and
woodlots (p< 0.05) than government-owned plantations. The results were similar to disease
severity index which was significantly higher at large-scale private plantations than
government managed plantations (p< 0.05). It was found that, the disease incidence and
severity was significant negatively correlated with stand age, DBH and height regardless of
the management regime. Among the practice that may cause a wound to tree stems, only
pruning had a positive significant influence on disease incidence and severity.
Maximum Entropy model accurate predicted the suitable area for PPC disease establishment
in Tanzania with area under the curve (AUC) value greater than 0.9. Bioclimatic variables
related to temperature have a high percentage contribution to the model. The mean
temperature of the coldest quarter (Bio11) and temperature seasonality (Bio4) contributed
higher to the prediction with 68% and 32% respectively. The PPC disease establishment is
much favored under scenario of low emission of Green House Gases (RCP 2.6). Since under
RCP 2.6, the predicted suitable area for PPC disease occurrence will be stable in 2050 with
a minor smaller decrease in 2070. But under scenario of high greenhouse gases emission
(RCP 8.5) the model predicts a continuous decrease of suitable areas for PPC disease
occurrence from the current climate condition to future (2070) climatic condition. The
model predicts areas suitable for PPC disease will cover much on southern, southern
highland, and northern zones of Tanzania.
The study conclude that PPC disease exist in all management regimes with a high
occurrences on the private managed plantation in Tanzania. The disease incidence and
severity correlated negatively with height, DBH and age. The management practices that are
likely to cause a wound on tree stems especially pruning
increase chance of PPC
occurrence and severity. Bioclimatic variables related to temperature (mean temperature ofv
the coldest quarter (Bio11) and temperature seasonality (Bio4)) influence and limit the
distribution of PPC disease. Southern highland, southern and northern zones of Tanzania
were predicted to be high susceptible to PPC disease infestations. The PPC disease
establishment is much favored with a low concentration of greenhouse gas that provides an
intermediate warmer environment and high humidity level. Under current conditions, the
area suitable for PPC disease establishment is much larger than that of future climate
scenarios.
The study recommends development of holistic management approach to include all tree
growers to reduce the spread of PPC disease to pine plantations. Pruning should be done
during the dry season with minimum damage level, to reduce the chances of infections
through wounds.
Also effective screening of imported seeds should be done before
planting. Furthermore, the study recommends the development of strict quarantine and
monitoring system of the disease so as to prevent introductions of the pathogen to the
predicted regions where PPC disease is not reported.