المكافحة المتكاملة لمرض تعفن الجذور ولفحة السنابل في الحنطة وتقدير متبقيات بعض المبيدات المستخدمة في مكافحتها

Integrated Management of Root Rot and Spike Blight in Wheat, and Estimation of Residues of Certain Pesticides Used in Their Control

Abstract
A series of laboratory and field experiments were conducted at the College of Agriculture – University of Karbala, Karbala Governorate, during the agricultural season 2024-2025, with the aim of isolating and morphologically and molecularly identifying the causative agent of root and crown rot and head blight in wheat (Triticum aestivum L.), testing its pathogenicity, the response of a number of wheat varieties to infection with the disease, testing the antagonistic ability of a number of biological and chemical pesticides (Goldazim 50 SC, Score 25 EC), and estimating their residual effect on grains after harvest, in addition to evaluating the efficiency of the organic pesticide Blue Guard in controlling the most pathogenic pathogens that cause root rot and head blight in the laboratory and under field conditions.
The results showed that 39 fungal isolates were obtained 20 of fungal isolates belonging to the genus Fusarium spp., 6 isolates of Rhizoctonia sp., 4 isolates of Macrophmina sp., 4 isolates of Stemephilium sp., and 5 isolates of Alternaria sp. were identified morphologically. Fuarium spp. outperformed the molecularly identified fungi in the percentage of appearance and frequency, as the percentage of appearance reached 85.71%, and the frequency of the fungus reached 51.28%. The results of the laboratory pathogenicity showed that the isolates Fe1, Fo2, Fp1, Fc3, Fp4, and Fp2 were significantly (P>0.05) superior in reducing the percentage of wheat seed germination on the W.A culture medium, as the average germination percentage in them reached 0.0%. The isolates Fe1, Fe2, Fp2, Fp3, and Fo4 were superior in their pathogenicity in plastic pots under field conditions, as the germination percentage in them reached 0.00% and the infection percentage was 100%.
The results of molecular diagnosis of the most pathogenic isolates by analyzing the sequences of nitrogenous bases of the double-stranded DNA products by polymerase chain reaction (PCR-amylized products) for the selected genetic markers and using the BLAST program showed that these isolates belong to the fungi Alternaria infectoria (Al4), Fusarium equiseti (Fe1 and Fe2), Fusarium oxysporum (Fo4), Fusarium culmorum (Fc3), Fusarium pseudograminearum (Fp2 and Fp3). The results also demonstrated the presence of a percentage of variation between the molecularly diagnosed isolates in this study and the previously diagnosed isolates confirmed in the National Center for Technology Information (NCBI). Therefore, these isolates were registered in the aforementioned center under the accession number PV769992.1, PV769993.1, PV769996.1, and PV769994.1, PV769995.1, PV770002.1, PV774561.1 respectively.
The complete genomic characterization and identification of the most pathogenic fungi of crown rot and head blight of wheat were carried out using Next Generation Sequences (NGS) technology. These fungi are F. pseudograminearum and F. culmorum, using some genetic markers represented by the internal transcribed spacer gene, beta-tubulin gene, calmodulin gene, RNA polymerase II second gene, and translation elongation factor 1-alpha gene. The sequences of these genes were documented in GenBank under special accession numbers and were named Fusarium pseudograminearum isolate Karbala-1 and were as follows: PV478111, PV505453, PV505454, PV505455, and PV505456, respectively. In this study, we were able, for the first time in Iraq, to document the first complete genome sequence of the fungus F. pseudograminearum from the isolate named “Karbala-1”. The draft genome sequence has been deposited in the GenBank database under the accession number JBMUMR000000000.1. Several pathogenicity genes of this fungus were also sequenced, which may be the reason behind the high pathogenicity shown by this isolate in the pathogenicity test. The genes, such as: ABC transporter, cutinase, and endo-1,4-beta-xylanase, have been documented in the GenBank database under the accession numbers: PV505458, PV505457, and PV505459, respectively. The fungal species F. culmorum was identified using some genetic markers represented by the internal transcribed spacer gene, beta-tubulin gene, calmodulin gene, RNA polymerase II second gene, and translation elongation factor 1-alpha gene. The nitrogenous base sequences of these genes were documented in GenBank under special accession numbers and it was named Fusarium culmorum strain Karbala-1 and were PV640836, PV654533, PV654534, PV654535, and PV654536, respectively. The draft genome of the mitochondrial fungus F. culmorum was determined for the first time in Iraq, as it was obtained using whole genome sequencing data. Based on these results, the mitochondrial genome of the fungus was deposited in GenBank under the accession number PV453989. In this study, the first complete genome sequence of F. culmorum from the isolate named “Karbala-1” was documented. The draft genome sequence was deposited in GenBank under the accession number JBNBBB000000000.1. These data represent the first comprehensive genomic resource for this type of pathogen that infects wheat and causes one of the important and serious diseases, namely crown rot and head blight, in the region. Molecular characterization and identification of several genes and mitochondria, as well as the complete genome, enabled us, through bioinformatics analysis, to identify sequences of a number of pathogenicity genes that may be the reason behind the high pathogenicity shown by this isolate in the pathogenicity test. The genes were ABC transporter, cutinase, and xylanase. These genes were also documented in the GenBank database under the accession numbers: PV654537.1, PV654538.1, and PV654539.1, respectively.
The results of the response of a number of wheat varieties to root rot and head blight infection showed that Tammuz 3 and Ibaa 99 were the most responsive varieties with an infection rate of 100% for F. pseudograminearum and 90.0% for F. culmorum compared to the control treatment which reached 0.0%. The antagonistic ability test of the two pesticides Goldazim 50 SC (Carbindazim) Score 25 EC, (Difinoconazole) on PDA culture medium showed that the two pesticides achieved a high inhibition rate for the two fungi at all used concentrations. The two concentrations (0.50 and 0.75) of the pesticides were superior in achieving 100% inhibition rate for the two pathogenic fungi in the PDA culture medium. The results of estimating the residues of the pesticides Goldazim and Score on wheat grains showed that the half-life of the two pesticides was 5-7 days and 12.2 days, respectively. The integration coefficients between all biological and chemical factors (F.c + Car+ Dif + Blu+ Bio and F.p+ Car+ Dif + Blu+ Bio) used in the study were significantly (P>0.05) superior to the other treatments in reducing the percentage and severity of infection by the two pathogenic fungi in plastic pots under field conditions, as it reached 0.0%. The same treatment was superior in increasing the average number of branches, average plant length, average number of spikes, and average weight of 1000 grains, compared to treating the pathogenic fungus alone