Survey for Diseases and Evaluation of Cotton Germplasm Against Alternaria Leaf Spot

Venkatesh, I.; Bhattiprolu, S. L.; Prasadji, J. Krishna; Rao, G. R.

doi:10.5958/0976-4615.2016.00010.7

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“…In this study, the fungus A. alternata also infected cotton plants and caused leaf spot/ blight diseases which were detected in almost all the cotton growing schemes in Sudan. The disease has been reported in all cotton growing countries of the world (Venkatesh 2014). The symptoms of Alternaria blight on Bt cotton leaves observed under natural conditions appeared late in the season as brown lesions with dark concentric rings surrounded by a yellow halo or leaf spots that were brown with gray centers.…”

Section: Discussionmentioning

confidence: 99%

Journal of Plant Protection Research

Mohamed,

Beshir,

Ahmed

2019

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Genetically modified Bt cotton (Gossypium hirsutum) leaves with typical symptoms of Alternaria early blight disease resembling that of tomato and potato were observed in the main cotton growing schemes in Sudan. Symptoms on leaves appeared as either brown 2leaf spot with gray centers or leaf blight with concentric rings. Pathogenicity tests using isolates with both symptoms showed that the isolated fungi were highly pathogenic to both G. hirsutum and G. barbadense cotton varieties. Alternaria alternata isolated from infected tomato and potato leaves with early blight symptoms was included for comparison. Microscopic examination showed that the mean length of conidia from cotton, tomato and potato isolates ranged from 26.25 to 45.45 µm, while the width ranged from 9.56 to 13.64 µm. The mean number of transverse septa among all isolates was 3.4 to 5.7 and the peak length ranged from 3.75 to 7.8 µm. Based on morphological characteristics the two isolates from cotton were identified as A. alternata. Genomic DNA was extracted directly from fungal cultures grown on potato dextrose agar (PDA) plates using a Zymo Research Quick DNA kit. A species-specific primer using the internal transcribed spacer ribosomal DNA (ITS rDNA) PCR scoring indicated the presence of A. alternata using primer pair ITS4/ITS5. Amplifications of the internal transcribed spacer region of 600 bp revealed 100% identity of the isolated fungus from cotton with A. alternata from tomato and potato. These data oblige us to reconsider the presence of A. alternata in the four main cotton growing schemes in Sudan while these symptoms have always been described for tomato and potato early blight disease.

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Section: Discussionmentioning

confidence: 99%