Effects of arbuscular mycorrhizal fungi and Trichoderma harzianum on growth and basal stem rot disease suppression in oil palm

The Malaysian oil palm industry is a major sector that plays an important role in supporting Malaysia’s economy. This industry faced huge challenges to increase oil palm yields due to the limited land area for oil palm cultivation and the basal stem rot (BSR) disease that attacks oil palm. Chemical fertilizers and chemical fungicides have been used to overcome these problems, but the results have not been satisfactory. Thus, biological approaches using beneficial microorganism such as arbuscular mycorrhiza and Trichoderma harzianum, could be another alternative to complement the role of conventional fertilizers and fungicides. Arbuscular mycorrhiza (AM) and T. harzianum have been well known as plant growth enhancer and protector against diseases in various plant species. Therefore, both of these fungi were used in the present study to determine their effects on oil palm. The objectives of this study were: i) to compare the effects of AM and T. harzianum (isolate FA 1132) as single and mixed inoculums on oil palm growth in nursery trial, ii) to compare the effects of AM and T. harzianum (isolate FA 1132) as single and mixed inoculums on growth of oil palms in the field, and iii) to compare the effects of AM and T. harzianum (isolate FA 1132) as single and mixed inoculums to suppress basal stem rot (BSR) disease in oil palm seedlings. Three different studies were conducted to fulfill these objectives. Experiment 1 was conducted in a nursery trial with seven treatments, which were single AM species (SAM), multiple AM species (MAM), Trichoderma harzianum (isolate FA 1132) infused-compost (TC), mixture of SAM with TC (SAM+TC), mixture of MAM with TC (MAM+TC), chemical fertilizers (F)and the control (C). Oil palm vegetative parameters were observed six times over 24 weeks. Leaf and soil samples were analyzed for chemical nutrients. Experiment 2 was conducted under field conditions at Mungka plantation, Segamat, Johore. There were five treatments, which were MAM, TC, MAM+TC, F and C. Vegetative growth parameters were observed every six weeks until week 30. Leaf and soil samples were also analyzed for chemical nutrients. Experiment 3, the disease resistance study, was conducted in a glasshouse with oil palms artificially infected with Ganoderma boninense. Seven treatments as in Experiment 1 were given after the artificial infection. Trichoderma harzianum (isolate FA 1132) infused-compost (TC) oil palms showed the best overall growth performance in Experiment 1. Oil palms receiving TC had the highest mean shoot dry weight (15.74 g), leaf area (1181.65 cm2) and potassium (K) content (2.68 %). Oil palms receiving TC, SAM+TC and MAM+TC also had higher stem girth and frond numbers compared to other treatments. Higher chlorophyll a (2.51 mg g-1), chlorophyll b (0.84 mg g-1) and total chlorophyll (3.35 mg g-1) were also recorded in TC treated oil palms. Application of TC also increased the mean pinnae number (15.30) better than in F and control oil palms. Oil palms treated with TC had higher nitrogen, N (3.79 %) and phosphorus, P (0.14 %) contents. Overall, the performance of the treatments in decreasing order of growth performance in the nursery trial was TC > SAM+TC > MAM+TC > MAM > SAM > F > C. The results of the field trial (Experiment 2) were similar to Experiment 1, and TC treatments gave the best overall growth performance. Oil palms receiving the TC treatment had the best stem girth (80.2 cm), frond length (193.50 cm), pinnae number (112.3) and fruit bunch number (1.90). Higher frond numbers (20.3), chlorophyll a (3.70 mg g-1), chlorophyll b (1.72 mg g-1) and total chlorophyll (5.42 mg g-1) contents were recorded in TC treated oil palms. The contents of N (3.12 %), P (0.26 %), K (2.39 %) and calcium, Ca (0.65 %) recorded were also higher in TC treated oil palms. Overall, the performance of the treatments in decreasing order of growth performance in the field trial was TC > MAM+TC > MAM > F > C. Results of Experiment 3 showed that BSR disease was reduced by 100.00 % in TC treated oil palms, while the reduction was 91.17 % in SAM+TC and MAM+TC oil palms. However, oil palms treated with MAM (50.00%) and SAM (43.75 %) had higher percentage of disease severity compared to the oil palms treated with chemical fertilizers (33.30 %). Application of TC and the mixture of AM and TC showed satisfactory results in suppressing BSR disease in oil palms compared to AM inoculum alone. In conclusion, oil palms treated with Trichoderma harzianum (isolate FA 1132) showed the best growth performance both in the nursery and field trials. Trichoderma harzianum (isolate FA 1132) was also an effective antagonist against Ganoderma boninense that causes BSR disease in oil palm seedlings