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Influence of soil moisture on the incidence and severity of leaf spot (Alternaria alternata) in Glycine max genotypes
By Guillermo Ascencio Luciano, Nicolás Maldonado Moreno, Reinaldo Méndez Aguilar, Moisés Felipe Victoriano*
*Corresponding Author.
Received: 21/August/2024 – Published:
06/March/2026
DOI:
https://doi.org/10.18781/R.MEX.FIT.2408-00
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Abstract Background/Objective. The soybean crop is affected by various diseases caused by fungi, which can severely reduce yields, in some cases up to 100%. The objective of this study was to identify the fungus associated with leaf spot in soybean and to evaluate the influence of soil moisture on the incidence and severity of the disease in plant and leaf in 30 soybean genotypes.
Materials and Methods. Three soybean leaves with leaf spot symptoms were collected per genotype for morphological identification of the fungus using taxonomic keys. Two moisture conditions (irrigated and rainfed) were evaluated. Plant incidence was estimated from 10 randomly selected plants; during the same period, foliar incidence and severity were evaluated. For foliar incidence, healthy and diseased leaves were counted from 10 plants per genotype. Subsequently, from 10 plants per genotype, one leaf in the fifth position from top to bottom was selected. The leaves were photographed, and the damaged area and total leaf area were calculated using the ImageJ software, thereby determining leaf severity.
Results. Alternaria alternata was identified as associated with leaf spot. In the rainfed environment, leaf incidence by A. alternata ranged from 4.4 to 50.55%; for severity, the values ranged between 0.3 and 17.4%. In the irrigated environment, the incidence varied from 7 to 50.9%; the severity ranged from 0 to 24.7%.
Conclusion. A. alternata was associated with leaf spot in soybean, which is little studied in Mexico, and currently its effects on this crop are unknown; therefore, it is of scientific interest to continue working on research projects with this species.
Keywords: Disease, Leaf blight, Leaf spot, Glycine max
Table 1. Incidence and severity on the leaf of leaf spot caused by Alternaria alternata, on soybean genotypes under irrigation and rainfed conditions in Altamira, Tamaulipas, 2022.
Figure 1. Alternaria alternata on soybean, A) Leaves with symptoms, B) Signs observed under the stereoscopic microscope at 4X, C) A. alternata conidia observed under the light microscope at 40X.
Figure 2. Incidence of leaf spot per plant caused by Alternaria alternata, in soybean genotypes under conditions of irrigation and rainfed in Altamira, Tamaulipas, 2022. HUAS = Huasteca.
Figure 3. Symptoms of leaf spot in soybean, induced by Alternaria alternata, leaves located in the fifth position from top to bottom in irrigated soybean genotypes, (genotypes with less damages) H10-3057 (1-2), H02-1706 (3-4), H85-1937 (5-6), H06-1014 (7-8); (genotypes with more damage) H80-0994 (9-10), H17-0331 (11-12), H02-2091 (13-14), H98-1068 (15-16); rainfed conditions, (genotypes with less damage) H02-1706 (17-18), HUAS-700 (19-20), H98-1076 (21-22), H85-1937 (23-24); (genotypes with more damage), H02-2331 (25-26), H02-2295 (27-28), H06-1014 (29-30), H17-0707 (31-32).
