Virulence of Rigidoporus microporus Isolates Causing White Root Rot Disease on Rubber Trees (Hevea brasiliensis) in Malaysia

Latex production from Hevea brasiliensis rubber tree is the second most important commodity in Malaysia, but this industry is threatened by the white root rot disease (WRD) caused by Rigidoporus microporus that leads to considerable latex yield loss and tree death. This study aimed to characterize and compare the virulence of five R. microporus isolates obtained from infected rubber trees located at different states in Malaysia. These isolates were subjected to morphological and molecular characterization for species confirmation and pathogenicity test for the determination of virulence level. BLAST search showed that the ITS sequences of all the pathogen isolates were 99% identical to R. microporus isolate SEG (accession number: MG199553) from Malaysia. The pathogenicity test of R. microporus isolates conducted in a nursery with 24 seedlings per isolate showed that isolate RL21 from Sarawak has developed the most severe above- and below-ground symptoms of WRD on the rubber clone RRIM600 as host. Six months after being infected with R. microporus, RL21 was evaluated with the highest average of disease severity index of 80.52% for above- and below-ground symptoms, followed by RL22 (68.65%), RL20 (66.04%), RL26 (54.38%), and RL25 (43.13%). The in vitro growth condition tests showed that isolate RL21 of R. microporus has optimum growth at 25–30 °C, with the preference of weakly acidic to neutral environments (pH 6–7). This study revealed that different virulence levels are possessed among different R. microporus isolates even though they were isolated from the same host species under the same climate region. Taken together, field evaluation through visual observation and laboratory assays have led to screening of the most virulent isolate. Determination of the most virulent isolate in the present study is vital and shall be taken into consideration for the selection of suitable pathogen isolate in the development of more effective control measures in combating tenacious R. microporus.

Current Status and Future Prospects of White Root Rot Management in Pear Orchards: A Review

The current social demand for organic, sustainable, and eco-friendly approaches for farming, while ensuring the health and productivity of crops is increasing rapidly. Biocontrol agents are applied to crops to ensure biological control of plant pathogens. Research on the biological control of white root rot disease caused by a soil-borne pathogen, Rosellinia necatrix, is limited in pears compared to that in apple and avocado. This pathogenic fungus has an extensive host range, and symptoms of this disease include rotting of roots, yellowing and falling of leaves, wilting, and finally tree death. The severity of the disease caused by R. necatrix , makes it the most harmful fungal pathogen infecting the economical fruit tree species, such as pears, and is one of the main limiting factors in pear farming, with devastating effects on plant health and yield. In addition to agronomic and cultural practices, growers use chemical treatments to control the disease. However, rising public concern about environmental pollution and harmful effects of chemicals in humans and animals has facilitated the search for novel and environmentally friendly disease control methods. This review will briefly summarize the current status of biocontrol agents, ecofriendly methods, and possible approaches to control disease in pear orchards.

In vitro Evaluation of the Fungicidal Potential of Aqueous and Methanolic Extracts of Thevetia peruviana on the Development of Rigidoporus lignosus, Causal Agent of White Root rot of Hevea brasiliensis

Aims: The objective of this work is to evaluate the effect of (aqueous (EAq) and methanolic (ME)) extracts of Thevetia peruviana on the in vitro development of Rigidoporus lignosus. Study Design: A synthetic fungicide (Onazol 100), two extracts at differents concentrations: C1 = 3.5 mg / ml; C2 = 7 mg / ml; C3 = 15 mg / ml; C4 = 30 mg / ml; C5 = 50 mg / ml and C6 = 100 mg / ml for EAq; C1 = 3.5 ml/ml; C2 = 7 ml/ml; C3 = 15 ml/ml; C4 = 30 ml/ml; C5 = 50 ml/ml for ME and a negative control (T = 0 mg / ml) were used. Place and Duration of Study: The study was conducted in pathology laboratory at University of Yaounde I and IRAD of Nkolbisson in 2018. Methodology: Daily measurements of the pathogen's development was used to evaluate the average growth (D) of the mycelium. The inhibition percentages of the different doses of EAq, ME and ONAZOL 100 were calculated after 4 to 5 days of growth of the fungus. Results: The major result obtained compared to the rate of rot showed that the treatments EAq, ME (C6) and ONAZOL 100 were closed. The disease rates at different concentrations of C1 to C6 were 13.91 to 100% for ME, 9.34 to 100% for EAq, and 100% for ONAZOL 100. Conclusion: The two extracts are promising, and on small and medium scale, could be an effective and cheap formulation for the control of Rigidoporus lignosus.

Rubber Agroforestry Experiments in Jambi at the end of a 25-Year Cycle

The rubber agroforestry experiments in Jambi started with the theory of change that productive clonal rubber could be economically used in low-labour intensity rubber agroforests, allowing selective retention of forest species or planted fruit trees in interrows. At the end of what was expected to be a 25-year production cycle we revisited the farmers (or their next generation), recorded what had happened to the plot and registered farmer plans for a way forward. Qualitatively, the results showed a wide range of directions of actual change. The envisaged plots, with full-grown tapped rubber in a secondary forest setting did occur – but as exception rather than rule. Some plots had early on been converted to oil palm when white root rot disease killed many of the rubber trees. Others were in a gradual transition to oil palm, already interplanted, or depended on natural regeneration of rubber within the plot for the trees currently being tapped. Some plots had been completely destroyed as the land was sold to a local coal-mine developer. Overall tapping frequency was low, as farmgate rubber prices have in recent years been low and farmers had other options (including participating in small-scale gold mining). Farmer experience with the various clones tested led to mixed opinions on which (if any) of the clones introduced were superior to what farmers used in the past (and what still regenerates in the landscape). GT1, a robust clone, was seen as hardly more productive as local germplasm, the PB260 and BPM1 clone were productive, but especially PB260 clone sensitive to white root rot disease. The quality of rubber wood was a concern for some farmers. The most successful intervention, from farmers’ as well as environmental perspective, has probably been the interplanting of meranti (Shorea leprosula) or tembesu (Fagraea fragrans) trees in young rubber stands, with good prospects for generating substantial income.