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major cotton production area in southeast Turkiye (USDA 2021). In the summers of 2021 and
2022, the mid-to-late season desiccation of leaves, stems, and bolls as well as severe
defoliation was observed in different cotton fields and cultivars in a 30-ha area centered
around 36°51′15.7″N, 39°07′12.2″E. Approximately 45% of the plants were severely affected or
completely desiccated. Initially, symptoms were circular, pinhead, necrotic lesions surrounded
by a purple halo, scattered all around the infected leaves. As the disease progressed, it spread
to bracts, petioles, stems, and bolls. The necrotic lesions continued to expand, formed
irregular shapes by coalescing, and occupied the whole tissue. Finally, severe infection
resulted in premature defoliation. A secondary host (Prosopis farcta) of the inoculum of
Alternaria alternata was found in the field where the symptoms of pathogen were seen. The
disease symptoms were similar to those described in cotton by Macauley (1982). Infected leaf
samples with mycelia were collected (n = 35) from 25 diseased plants. The samples derived
from lesions on infected leaves were cut into 4- to 5-mm pieces, treated in 2% sodium
hypochlorite, dipped in water, plated on potato dextrose agar (PDA) amended with 30 mg/liter
of streptomycin sulfate, and kept at 27°C in the dark. All the isolated fungal samples formed
dark olive-green colonies. For morphological characterization, the colonies were examined with
light microscopy at 400× magnification. Conidia formed both cross or longitudinal septa, were
obclavate to elliptical, and measured 16.2 to 30.5 μm long and 7.5 to 10.6 μm wide (n = 14).
The morphological characters were consistent with the genus Alternaria using a taxonomic key
(Barnett and Hunter 1972). For the pathogenicity test, healthy cotton plants were grown at 15
to 29°C in a greenhouse. A conidial suspension (106/ml) was sprayed on 30-day-old plants (n
= 16), whereas the control plants were sprayed with water. Then, the plants were covered with
plastic bags (28 × 45 cm) at nights and opened in the morning. The disease symptoms were
seen 20 days after artificial inoculation. However, the control group showed no symptoms. The
pathogen was reisolated from infected leaves. To confirm the result, the pathogenicity test was
conducted twice. Then, DNA was extracted from conidia and mycelia using the CTAB method
with slight modification (Doyle and Doyle 1990). The nuclear rDNA internal transcribed spacer
(ITS) and plasma membrane ATPase regions were (Lawrence et al. 2014; White et al. 1990)
amplified, using the primers ITS4/ITS5 and ATPDF1/ATPDR1, respectively. The PCR products
were Sanger-sequenced and were uploaded to GenBank (accession nos.: ITS, OP615138.1;
ATPase, OP612816.1). The sequenced parts of the genes were 554 and 1,025 bp and showed
100% (ITS) and 97.99% (ATPase) nucleotide identity with the corresponding sequences
(MT446176.1 and ON442363.1) of the reference strains of A. alternata. To the best of our
knowledge, this is the first report of A. alternata causing leaf blight of cotton in Turkiye. In
several cotton-growing regions, A. alternata leaf spot epidemics have caused yield loss from
25% (Israel) to 37% (India) (Padaganur et al. 1989; Rotem et al. 1988). Although yield loss
caused by the pathogen depends on environmental conditions, observations in Turkiye cotton
fields suggest A. alternata has the potential to cause yield loss up to 30% under severe
infection.
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2022, the mid-to-late season desiccation of leaves, stems, and bolls as well as severe
defoliation was observed in different cotton fields and cultivars in a 30-ha area centered
around 36°51′15.7″N, 39°07′12.2″E. Approximately 45% of the plants were severely affected or
completely desiccated. Initially, symptoms were circular, pinhead, necrotic lesions surrounded
by a purple halo, scattered all around the infected leaves. As the disease progressed, it spread
to bracts, petioles, stems, and bolls. The necrotic lesions continued to expand, formed
irregular shapes by coalescing, and occupied the whole tissue. Finally, severe infection
resulted in premature defoliation. A secondary host (Prosopis farcta) of the inoculum of
Alternaria alternata was found in the field where the symptoms of pathogen were seen. The
disease symptoms were similar to those described in cotton by Macauley (1982). Infected leaf
samples with mycelia were collected (n = 35) from 25 diseased plants. The samples derived
from lesions on infected leaves were cut into 4- to 5-mm pieces, treated in 2% sodium
hypochlorite, dipped in water, plated on potato dextrose agar (PDA) amended with 30 mg/liter
of streptomycin sulfate, and kept at 27°C in the dark. All the isolated fungal samples formed
dark olive-green colonies. For morphological characterization, the colonies were examined with
light microscopy at 400× magnification. Conidia formed both cross or longitudinal septa, were
obclavate to elliptical, and measured 16.2 to 30.5 μm long and 7.5 to 10.6 μm wide (n = 14).
The morphological characters were consistent with the genus Alternaria using a taxonomic key
(Barnett and Hunter 1972). For the pathogenicity test, healthy cotton plants were grown at 15
to 29°C in a greenhouse. A conidial suspension (106/ml) was sprayed on 30-day-old plants (n
= 16), whereas the control plants were sprayed with water. Then, the plants were covered with
plastic bags (28 × 45 cm) at nights and opened in the morning. The disease symptoms were
seen 20 days after artificial inoculation. However, the control group showed no symptoms. The
pathogen was reisolated from infected leaves. To confirm the result, the pathogenicity test was
conducted twice. Then, DNA was extracted from conidia and mycelia using the CTAB method
with slight modification (Doyle and Doyle 1990). The nuclear rDNA internal transcribed spacer
(ITS) and plasma membrane ATPase regions were (Lawrence et al. 2014; White et al. 1990)
amplified, using the primers ITS4/ITS5 and ATPDF1/ATPDR1, respectively. The PCR products
were Sanger-sequenced and were uploaded to GenBank (accession nos.: ITS, OP615138.1;
ATPase, OP612816.1). The sequenced parts of the genes were 554 and 1,025 bp and showed
100% (ITS) and 97.99% (ATPase) nucleotide identity with the corresponding sequences
(MT446176.1 and ON442363.1) of the reference strains of A. alternata. To the best of our
knowledge, this is the first report of A. alternata causing leaf blight of cotton in Turkiye. In
several cotton-growing regions, A. alternata leaf spot epidemics have caused yield loss from
25% (Israel) to 37% (India) (Padaganur et al. 1989; Rotem et al. 1988). Although yield loss
caused by the pathogen depends on environmental conditions, observations in Turkiye cotton
fields suggest A. alternata has the potential to cause yield loss up to 30% under severe
infection.
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