Abstract:
Background:
In a prior study, Lasiodiplodia theobromae (Pat.) Griffiths and Maubl. and Bipolaris bicolor (Mitra) Shoemaker., were found to suppress the growth of Eleusine indica (L.) Gaertn, but limited information exists on their response to environmental factors and herbicides for integrated E. indica control.
Objective:
This study aimed to determine the tolerance levels of L. theobromae and B. bicolor to pH, temperature, photoperiod, relative humidity, and herbicides.
Methods:
The mycelia and conidia of L. theobromae and B. bicolor were exposed to a range of environmental conditions and herbicides in a controlled setting, including different levels of temperature (25, 30, 35 ⁰C), pH (4, 6, 8, 10), photoperiod (24 hours of darkness; alternating 12 hours of blue light followed by 12 hours of darkness; and alternating cycles of 6 hours of blue light and 6 hours of darkness), and relative humidity (75, 85, 95%). Herbicides such as topramezone, diuron, oxyfluorfen, and imazethapyr were applied at their recommended rates. Conidial germination was assessed by counting after an 18-hour incubation using a haemocytometer, while the diameter of mycelium growth was measured after 3 days of incubation, except for the herbicide effects evaluation, which were extended over 7 days.
Results:
Laboratory assays demonstrated that L. theobromae exhibited higher conidial germination of 85-95% and superior mycelial growth under varied pH, temperature, and photoperiod conditions compared to B. bicolor. Lasiodioplodia theobromae's mycelia remained unaffected by herbicides at full labelled rates, but they inhibited the conidial germination of the fungus. For B. bicolor, the conidia were not affected by imazethapyr and topramezone, but its mycelial growth was reduced by imazethapyr, oxyfluorfen, and diuron.
Conclusions:
These results indicate that the mycelia of L. theobromae presents a more favorable option for tank mixing with test herbicides, offering potential for the formulation of an integrated control strategy against E. indica.
Keywords:
Lasiodiplodia theobromae
;
Bipolaris bicolor
; Environmental Factors; Herbicides
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) and 
) under different environmental factors. Each datum is the average ± SD of six replicates. At least 500 conidia were counted for each value. A. Conidial germination rate at temperatures of 25, 30 and 35 ⁰C for 18 hours under darkness. B. Conidial germination rate at pH 4, 6, 8 and 10 at 27 ⁰C for 18 hours under darkness. C. Conidial germination rate at 27 ⁰C for 24 hours under darkness (
), alternating 6-h blue light (
) and alternating12-h blue light (
). Means followed by a different lowercase letter have a significant difference at the 5% significance level
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), and 
) under different environmental factors. Each datum is the average ± SD of five replicates. A. Mycelial growth at temperatures of 25, 30 and 35 ⁰C for 24 hours under darkness. B. Mycelial growth at pH 4, 6, 8 and 10 for 24 hours at 27 ⁰C under darkness. C. Mycelial growth at 27 ⁰C for 24 hours under darkness (
), alternating 6-h blue light (
) and alternating12-h blue light (
). D. Main effect of relative humidity on mycelial growth at 27 ⁰C for 24 hours averaged across fungus type under darkness. Means followed by a different lowercase letter have a significant difference at the 5% significance level
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), topramezone (
) and diuron (
) at respective commercial recommended rates. A. Conidial germination rate at 27 ⁰C for 48 hours under darkness after herbicide treatment. Each datum is the average ± SD of six replicates. At least 500 conidia were counted for each value. B. Mycelium growth at 27 ⁰C for seven days under darkness after herbicide treatment. Each datum is the average ± SD of five replicates. Means followed by a different lowercase letter have a significant difference at the 5% significance level
