RESUMO
Ascochyta rabiei causes Ascochyta blight disease on C. arietinum as well as on annual C. reticulatum, C. pinnatifidum and C. judaicum and perennial C. montbretii, C. isauricum, C. ervoides species (Can et al. 2007; Frenkel et al. 2007; Ozkilinc et al. 2019; Peever et al. 2007; Tekin et al. 2018). During field survey studies carried out on annual Cicer spp. in June 2022, concentric ring-shaped lesions were observed on the stems and leaves of C. bijugum in Mardin province and C. turcicum in Elazig province. Cicer reticulatum and C. arietinum plants were also found in the location where C. bijugum was found. No disease symptoms were observed in other Cicer species, while C. bijugum had 32% disease incidence. The disease incidence among the C. turcicum population was 37.3 %, and no chickpea cultivation area was found near it. Diseased plant parts were surface sterilized, placed on ½ potato dextrose agar (PDA) and incubated at 24±2 oC in 12 hours light/dark photoperiod. Each symptomatic plant was considered as one isolate. Monosporic isolates were obtained and the same colony morphology developed from all plant parts of C. turcicum and C. bijugum. Spores were oblong and spore sizes were 10.73±0.62 µm (n=15) in length and 3.60±0.25 (n=15) µm in width, 10.64±0.98 (n=15) µm in length and 3.00±0.26 (n=15) µm in width for isolates obtained from C. turcicum and C. bijugum, respectively. Amplicons for all 40 isolates were generated with mating type (MAT) primers, and the ITS region was amplified and sequenced by using the ITS4 and ITS5 primers (Peever et al. 2007). For the MAT primers, a 700 bp amplicon was observed for all the 20 isolates obtained from C. bijugum conferring to MAT1.1 idiomorph. In contrast, for the isolates obtained from C. turcicum 14 isolates had a 700 bp amplicon for MAT1.1 and 6 isolates had a 500 bp amplicon for MAT1.2, thus representing both idiomorphs in a ~2:1 ratio. BLAST analysis of the ITS sequences showed 100% homology with the reference ITS sequences for A. rabiei except for 23 SVRC CT 09/22 and 23 SVRC CT 22/22 isolates showing 99.81 % similarity. All sequences were submitted to GenBank (OP967923, OP967924, OP967925, OP967926 and OP967927 for A. rabiei isolates from C. turcicum; OP981072, OP981073 and OP981074 for A. rabiei isolates from C. bijugum). A phylogenetic tree was constructed using MEGAX software and the Neighbor-Joining method, using the ITS sequences of A. rabiei, other Ascochyta spp. and Colletotrichum gloeosporioides. The A. rabiei isolates from C. turcicum and C. bijugum clustered together with A. rabiei sequences from the NCBI (Kumar et al. 2018). Twelve-day-old C. bijugum and C. turcicum seedlings were inoculated with 5 x 105 spore/mL concentration of spores from 5 C. turcicum and 3 C. bijugum isolates and put in plastic bags for 24 hours (Can et al. 2007). Pathogenicity tests were carried out in triplicate pots with four plants each for each isolate in a controlled climate chamber at 24±2 oC, 70% humidity under 12 hours light/dark conditions. The first symptoms were observed within 7 days after inoculation (dai) and severe Ascochyta blight symptoms developed on all plants by 21 dai. Cicer bijugum and C. turcicum are endemic Cicer species exhibiting narrow distribution in the Southeastern region of Republic of Türkiye. As a major biotic stress source, A. rabiei could be an important threat to Cicer spp (Abbo et al. 2003). To our knowledge, this is the first report of A. rabiei from C. bijugum and C. turcicum species.
RESUMO
Ascochyta blight (AB) is a major disease in chickpeas (Cicer arietinum L.) that can cause a yield loss of up to 100%. Chickpea germplasm collections at the center of origin offer great potential to discover novel sources of resistance to pests and diseases. Herein, 189 Cicer arietinum samples were genotyped via genotyping by sequencing. This chickpea collection was phenotyped for resistance to an aggressive Turkish Didymella rabiei Pathotype IV isolate. Genome-wide association studies based on different models revealed 19 single nucleotide polymorphism (SNP) associations on chromosomes 1, 2, 3, 4, 7, and 8. Although eight of these SNPs have been previously reported, to the best of our knowledge, the remaining ten were associated with AB resistance for the first time. The regions identified in this study can be addressed in future studies to reveal the genetic mechanism underlying AB resistance and can also be utilized in chickpea breeding programs to improve AB resistance in new chickpea varieties.
