Isolation trials from cotton seeds of cvs. Giza-86 and Giza-89 as well as damped-off seedlings resulted in several fungi belonging to 5 genera and 11 species. The isolated fungi were purified and identified as Alternaria alternata (Fr.) Keissler, Aspergillus niger van Tieghem, Fusarium dimerum (Penz.) v. Arx, Fusarium moniliforme, J. Sheld, Fusarium nivale (Fr.) Samuels & Hallett, Fusarium roseum Link emend., Snyder & Hansen, Fusarium semitectum Berk & Rav, Fusarium tricinectum (Corda) Sacc.,Fusarium solani (Mart.) Sacc. emend. Snyder & Hansen, Penicillium spp and Rhizoctonia solani Kuhn. R. solani isolates were the dominant fungi isolated from cotton seeds of cvs. Giza-86 and Giza-89 before and after delinting as well as from the inner surface of testa and rotten roots while, Fusarium roseum showed the highest frequency in the cotoyledons of both cvs. In general, the total number of isolated fungi from the cotoyledons was greatly low comparing with those isolated from seed testa for both cotton cvs. Among 4 tested pathogens, R. solani was more aggressive as it caused the highest rates of pre- and post- emergence damping-off on both cotton cvs.. Also, increasing the inoculum levels from 1 to 3% of soil weight increased gradually the percentage of infection. Also, means of survived cotton plants indicate that R. solani followed by F. semitectum were the highly pathogenic fungi at most tested inoculum levels whereas F. roseum was the least one. All the tested fungi were not able to produce aflatoxins (B1&B2), zearalenone, fumonisins and trichothesense in vitro on YES medium., Meanwhile, when cotton seed samples of both cvs. were infested with the same tested root rot pathogens, clear amounts of mycotoxins were detected in some cases. Moreover, infestation of cotton seeds with any of the tested root rot pathogens i.e., R. solani, F. moniliforme, F. semitectum, and F. roseum affected negatively oil content of the seeds. Increasing the incubation period from 5 to 15 days decreased gradually oil contents for all treatments compared with the un-infested seeds. The highest decrease in oil content was recorded in the case of seed infestation with R. solani and F. moniliforme at any tested incubation period for the seeds of both cotton cvs. |
