**3. Results**

#### **3.1 Disease incidence (DI)**

In this study, a total of 56 PSPs comprising 32 of *Acacia*, 17 of *Eucalyptus pellita* and 14 of *F. mollucana* have been established and assessed with approximately 5600 trees of the three major species planted have been evaluated, data recorded and analysed. The study showed that DI was varied between tree species.

#### *3.1.1 Acacia*

Approximately 3200 *Acacia* stand aged between less than 1-year-old and 12-year-old were assessed in this study with three prominent diseases observed; Ceratocystis wilt disease, root rot disease and pink disease. Based on **Table 4**, Ceratocystis wilt disease was the most devasted and important disease observed. DI was recorded the highest with mortality recorded at 68% in the Bintulu region based on disease indicators rating as depicted in **Table 2**, and the DI rating is categorised at a serious level. The disease was observed in stands less than 1-year-old also in the Bintulu region with DI recorded at 1.9%. The DI is predicted to increase over time with rotation length. The disease was not observed in Miri and Sibu region; however, DI of 3% of the disease was documented in Kuching region in 12 -year-old *A. mangium.*

The disease incidence of root rot was recorded between 0 and 37% in trees aged less than 1 year old to 10 year old. 10 years of plantation of *Acacia mangium* in the Bintulu region recorded the highest incidence of the disease, and no incidences were recorded in the young stand. The disease rating based on the highest DI is light. Root rot disease seems to be the most encountered disease in most of the plots, with 17 out of 32 PSPs observed with the disease.

The pink disease was only observed in Sibu region and had affected 2-year-old taxa seed source trial plot established by Forest Department Sarawak. DI of pink disease was recorded at 5%.


#### *Current and Emerging Challenges in the Diseases of Trees*


*New and Emerging Disease Threats to Forest Plantations in Sarawak Borneo, Malaysia DOI: http://dx.doi.org/10.5772/intechopen.107027*

> **Table 4.**

*Details on DI (DI) of observed diseases recorded in* Acacia.


*\*Forestry Region (see Figure 1): BTU, Bintulu; SBW, Sibu; KCH, Kuching; MY, Miri; R&D. \*\*Types of stand: R&D, Research and Development; CS, Commercial Stands.*

#### **Table 5.**

*Details on disease incidence (DI) of observed diseases recorded in* E.pellita.

### *3.1.2* E. pellita

Approximately 1700 *E. pellita* stands aged between less than 1-year-old and 13-year-old were assessed in this study with the establishment of 17 PSPs as detailed in **Table 5**. Canker disease was found in 6 PSPs with the highest DI of 7% recorded in 2-year-old stand in Bintulu region. Out of the 6 PSPs, mostly canker incidences were found in Kuching with 11% DI accumulatively. Root rot was observed in the Bintulu region with accumulative DI of 12% in 2 PSPs located within the same area. Bacterial wilt disease with a DI of 3% was encountered in one PSP established within R&D tree breeding plot at Bintulu. No other PSPs recorded such disease.

### *3.1.3* F. molluccana

A total of 14 PSPs with comprises of approximately 1400 of *F. molluccana* stands of less than 1-year-old and 2- and 3-year-old were established and assessed for DI as


*New and Emerging Disease Threats to Forest Plantations in Sarawak Borneo, Malaysia DOI: http://dx.doi.org/10.5772/intechopen.107027*

*\*Forestry Region (see Figure 1): BTU, Bintulu; SBW, Sibu; KCH, Kuching; MY, Miri; R&D. Types of stand: R&D, Research and Development; CS, Commercial Stands.*

#### **Table 6.**

*Details on disease incidence (DI) of observed diseases recorded in* F. molluccana.

detailed in **Table 6**. Based on the survey, gall rust disease was the most important prominent disease observed with DI recorded at an alarming 69.7% in an R&D (taxa seed source trials) established at Bintulu. Miri region also recorded gall rust DI of 1.9% in stands less than 1-year-old. Another disease observed affecting *F. molluccana* was canker disease and attacked stands less than 1-year-old also in the Bintulu region with DI recorded at 1.9%. No diseases were observed in the Sibu region.

## **3.2 Symptoms and signs**

### *3.2.1 Diseases of* Acacia

#### *3.2.1.1 Ceratocystis wilt disease of Acacia*

Ceratocystis infections observed typically start on the lower stem and move up, causing dark staining of the woody xylem. However, we did observe some symptomatic trees with initial infection starting at the upper stem with dead foliage hanging throughout the tree or on some major branches. The infected blackish gummosis stem upon debarking showed dark brown to black discolouration in the woody xylem, radial pattern in pattern, which is a unique symptom of Ceratocystis wilt disease. Within every plot observed with Ceratocystis, all trees showed these wilt symptoms were noted for Ceratocystis wilt (**Figure 2a–d**). But it was further confirmed upon root excavation to differentiate root rot disease as the latter also exhibits symptoms such as wilting and severe defoliation.

#### **Figure 2.**

*Ceratocystis wilt disease implicates damages to* Acacia mangium *plantation in Sarawak (a–i); (a) blackish lower stem with foamy exudate at the upper stem and wilting and dying 2-year-old tree; (b) blackish streak-like inner bark due to Ceratocystis infection; (c) foamy exudates and slime typical of Ceratocystis infection on stem of the tree; (d) initial infection starting at the upper stem with dead foliage hanging throughout the tree; (e) dead tree with severe bark damage caused by squirrels with wood discolouration; (f) severe bark damage but tree observed free from Ceratocystis infection (g) traces of wood-boring insect holes on the stem;(h) Ambrosia beetle found under bark and the wood appeared with blackish lesion; (i) side view image of wood-boring insect identified as* Immanus desectus *(eggers) collected from the infested tree.*

*New and Emerging Disease Threats to Forest Plantations in Sarawak Borneo, Malaysia DOI: http://dx.doi.org/10.5772/intechopen.107027*

Some symptomatic and dead trees as young as 6-month-old that were adjacent to the conservation or buffer area were observed with wound damage on the stem of juvenile trees inflicted by squirrels grazing (**Figure 2e**). These wounds would act as the point of entry for Ceratocystis pathogen to infect the trees. However, we did observe that some trees inflicted with these wounds but did not show any Ceratocystis symptoms (**Figure 2f**).

Wood-boring insects were also found present in infected trees, with wood infested exhibited blackish lesions typical of *Ceratocystis* pathogen (**Figure 2g**–**i**). The woodboring insects collected from the tree were identified as those of ambrosia beetle species.

Culture characteristics and morphology of Ceratocystis isolates from *A. mangium* were observed and analysed based on morphological characteristics, such as colony form, mycelium colour and reverse media colour [3–5], were further identified as *C. fimbriata sensu stricto (s.s) complex*, having the characteristic of olive-green colonies with the underside of the cultures was light grey at the margin and became darker towards the centre and typical pineapple-fruit odour. The isolates of *C. fimbriata* showed superficial or submerged in the substrate perithecia, with colours ranging from brown to black both at the base and neck of the perithecium (**Figure 3c**). They had globose to sub-globose ascomata with long necks and typical divergent ostiolar hyphae at their tips (**Figure 2**). Teleomorph and anamorph structures were produced within 2 weeks on MEA cultures (**Figure 3d**).

#### *3.2.1.2 Root rot disease of Acacia*

The trees showed symptoms typical of red root rot including dying trees at the periphery of rot centres that had wilting leaves. Most of the affected trees were dead stands that exhibited chlorotic/yellowing foliage and loss of foliage.

The diseased trees were observed to be clustered in patches that were roughly circular. The trees with symptoms of root rots were adjacent to one another. Fruit bodies were only observed on the stem of some of the trees. Types of root disease were distinguished by the colour of infected roots, red root rot, brown root rot and white root rot.

Underground symptoms observed include the presence of red-coloured rhizomorphs with blackish exudates (**Figure 4c**) on the surface of the roots and white mycelium (denote as *My* in **Figure 4d**)**.** Yellow mottles of the foliage with patches in the majority of the infected *A. mangium* trees were easy to recognise as typical of red root rot and further identified as *G. philippii*. Trees discovered to be infected with brown root rot were observed with soft, fibrous and totally rotten roots and sandy particles adhering to the rhizomorph (**Figure 4e**). The causal pathogens identified were *G. philippii* and *Phellinus noxius.*

#### *3.2.1.3 Pink disease of Acacia*

Pink disease in *A. mangium* was observed both in the base of the main stem and branches and twigs. Trees observed with pink disease (**Figure 5**) initially exhibited silky-like whitish mycelium on the surface of the bark, known as the 'cobweb'stage, infecting the branch and stem. Pinkish to salmon cobweb-like structures were observed soon after known as the pustule stage, and subsidiaries symptoms of wilting of the branch's foliage and subsequently turned brown and branches that extending to all parts of the plant until dieback observed by death in the canopy. Infected branches and stems showed sign of bark crack and scaled bark. Where infection was observed centralised in certain areas of the stem or bark, cankers and wounds developed. In this

#### **Figure 3.**

*Microscopic structures of identified* Ceratocystis fimbriata *obtained from* Acacia mangium *plantations in Sarawak (a–d); (a) culture of* C. fimbriata *grown on MEA appeared cotton-like, sparse, initially white, later turning to olive grey with white to grey at the margin after 5–7 days with banana-like aroma and salmon-like shiny globose spores; (b) Salmon-like colour ascospores mass extruded at the tips of the long-necked black fruiting bodies (perithecia); (c) long, divergent ostiolar hyphae (arrow); (d) spores of* C. fimbriata*.,* Thelaviopsis *sp. elongated, cylindrical condia of* Thelaviopsis *sp. (imperfect state) and hat-shaped ascoscopres of* C. fimbriata *(teleomorph or perfect state).*

survey, we observed severe infection in one PSP in Sibu region and inflicted mortality of the tree stands. The symptoms described above showed similarity with the symptoms described [8] and thus, the pathogen of pink disease was identified as *Erythricium salmonicolor.*
