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Búsquedas previas al 2023, Núm. 3. En la sección Volúmenes 30 - 41 (2012 - 2023).
Bipolaris oryzae associated agent at the leaf spot disease in Cocos nucifera hybrid “Brazilian Green Dwarf”
By Oscar Guillermo Rebolledo Prudencio, Wilberth Chan Cupul*, Guadalupe Moreno Zúñiga, Carlos Adrián Cruz Jiménez, Juan Carlos Sánchez Rangel
* Corresponding Author. Email: / Institution:
Received: 15/November/2024 – Published: 21/February/2025 – DOI: https://doi.org/10.18781/R.MEX.FIT.2024-09
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Abstract Background/objective. In Tecoman, Colima, Mexico, a leaf spot (LS) disease was detected with an incidence of 92.0% in Cocos nucifera hybrid Brazilian Green Dwarf (BGD). The objective was to characterize morphologically, molecularly and biochemically the fungus associated with LS in BGD coconut palm and evaluate its susceptibility to commercial biological fungicides.
Materials and methods. The isolate was characterized morphologically and molecularly. Their growth, sporulation and laccase production were evaluated using different culture media. The in vitro mycelial inhibition and mean lethal doses (LD50) of commercial biological fungicides based on antagonistic fungi (Trichoderma harzianum and T. viride), bacteria (Bacillus subtilis and B. amyloliquefaciens) and actinobacteria (Streptomyces lydicus and S. jofer) were determined.
Results. Bipolaris oryzae was the associated agent of LS, it produces 25.54 and 22.17 U mg of protein-1 of laccase activity in the Sivakumar and wheat bran (WB) media. The WB medium allowed the greatest sporulation. Trichoderma harzianum inhibited B. oryzae at 100% in the four evaluated doses. B. subtilis and B. amyloliquefaciens inhibited B. oryzae at 100% at the highest tested doses (20 mL L-1).
Conclusion. Bipolaris oryzae is the associated agent of LS, it produced the highest laccase activity in Sivakumar and WB culture media. The highest sporulation and daily growth rate were in WB. T. harzianum stood out over T. viride by inhibiting B. oryzae growth by 100%. B. subtilis, S. lydicus and B. amyloliquefaciens were more effective against B. oryzae in vitro compared to S. jofer.
Keywords: Antagonism, Bipolaris, actinobacteria, bacteria, coconut, Colima.
Table 1. Sequences used to generate the phylogenetic tree for Bipolaris oryzae, an agent associated to the coconut tree leaf spot.
Table 2. Laccase activity, daily growth rate (DGR) and sporulation of Bipolaris oryzae in semi-solid media.
Table 3. Inhibition of the mycelial growth (%MGI) of Bipolaris oryzae by different doses of commercial biological fungicides.
Table 4. Ninety lethal dose (LD90) of six commercial biological fungicides on Bipolaris oryzae.
Figure 1. Leaves with symptoms of leaf spot in hybrid coconut tree “Brazilian Green Dwarf”. A) Brown oval spots and yellow halo, B) palm leaves with multiple oval spots and C) view of the nursery with plants with leaf spot.
Figure 2. Cultural and morphological characteristics of Bipolaris oryzae. A and B) Conidiophores; C to F) conidiospores; G) cluster of conidiophores; H) septated hyphae; I) young mycelium, aged 5 days in medium; J) mature mycelium after 20-day growth in PDA medium.
Figure 3. Phylogenetic analysis based on the maximum likelihood method using the 2 parameter Kimura method (G+I). Tree created with the highest probability logarithm (-5759.36) of the sequence of rDNA 28S of the Bipolaris strains, similar to those of the agent associated to LS in the BGD coconut tree (Bipolaris oryzae ACMFCnhEVB_1) using MEGA11. This tree was rooted using Fusarium oxysporum and was used as an external group.
Figure 4. Growth of Bipolaris oryzae five days after inoculation in PDA modified with different doses of commercial biological fungicides.
Figure 5. Linear regression between the inhibition (%) in the growth of Bipolaris oryzae and the doses of each commercial biological fungicide used.
