Controle biológico da podridão basal (Thielaviopsis ethacetica) e nutrição mineral da palma de óleo.

Abstract

The oil palm (Elaeis guineense) is considered one of the most promising perennial crops for agribusiness in the global sphere, standing out as the most important oilseed in the world. However, its cultivation is limited by several fungal diseases. Basal sprout rot has become a threat to the crop because of its rapid spread and lack of effective control. Thus, it becomes increasingly important, disease studies. Therefore, this work aimed to study the etiology of basal rot, as well as to select Bacillus spp. and Trichoderma spp. in the biological control, to evaluate resistance inducers and foliar fertilization in the growth and mineral nutrition of the oil palm. For this, the isolate of Thielaviopsis sp. was obtained from plants presenting yellowish rot in the stipe and at the base of the arrow leaf and proceeded the morphological characterization and phylogenetic analysis. The pathogenicity test in oil palm confirmed the fungus Thielaviopsis sp. as the etiological agent of Basal Rot in both the intraspecific hybrid (HIE) Manicoré and the intraspecific hybrid Tenera. The fungus was classified as Thielaviopsis ethacetica based on morphological characteristics and phylogenetic analyzes based on the EF-1α and ITS regions. In vitro tests, biochemical characterization (protease and chitinase), in vivo tests and enzyme analysis related to the pathogenesis of oil palm seedlings (glucanase, chitinase, peroxidase guaiacol and polyphenoloxidase) were performed for the biocontrol study. The isolates of Trichoderma spp. showed up to 52% (T03) of inhibition of the growth of the pathogen while those of Bacillus spp. up to 100% (Bac 01, Bac 02 and Bac 03). The isolates of Bacillus spp. were positive for the protease, whereas for the isolates of Trichoderma spp. were negative. None of the isolates presented chitinase production. In the in vivo control, they provided a reduction in the symptoms of the disease. Plants treated with the isolates T06, T03, T07, Bac 61, T09, Bac 03, Bac 02, Bac 04, Bac 104 and Bac 01 reduced the percentage of the area of the injured tissue and showed less progress of the disease. There was a significant difference between treatments for glucanase, chitinase and polyphenoloxidase analyzed at the end of the 30 day period after treatment. Bac 03 isolated from other biocontrol agents because it presents a potential antagonist in the in vitro control of Thielaviopsis ethacetica, production of protease, besides reducing the severity of basal rot and inducing the activity of the enzymes glucanase, chitinase and polyphenoloxidase in the defense of the oil palm. In the subsequent stage of the research, resistance inducers and mineral nutrition were evaluated in oil palm seedlings. Seedlings were grown in greenhouse between October 2014 and October 2015. The treatments were commercial products: Bion®, Fulland®, Reforce®, Yantra®, Vitakelp® + Stayflex®, Dephensor®, calcium silicate , sodium silicate, four nutrient combinations (A, B, C and D) and three control treatments. Data were submitted to analysis of variance and means were compared by the Scott-Knott test at 5% probability. The treatments that provided the highest dry matter of oil palm were Fulland®, combination D (6% P2O5 and 15% K2O), calcium silicate and sodium silicate. Correction of soil acidity with a high magnesium content corrector improved the oil palm nutrition in calcium and magnesium. Resistance inducers, primarily nutrient sources, and mineral nutrition have the potential to enhance oil palm growth and mineral nutrition in key nutrients linked to plant resistance to disease.