Fusarium wilt disease is one of the most important diseases of melon, which causes damage between 20 and 80% in melon fields. In favorable conditions, the spread of the disease can reach 100%. In the improvement programs, achieving resistant cultivars is considered one of the most important methods of controlling this disease.

In this research, 46 melon landraces were collected from different parts of Razavi, Northern and Southern Khorasan provinces, along with two separate lines, Isabel and Charente T respectively as resistant and sensitive control cultivars to identify new sources of wilt disease resistance to Fusarium oxysporum f. sp. melonis. The experiments were carried out in a randomized complete block design with three replications in the greenhouse of the agricultural campus of Tarbiat Modares University. The seeds were grown in trays containing cocopeat and perlite in a ratio of 2:1; fourteen days after cultivation, the roots of the young seedlings were removed from the culture tray and inoculated for two minutes with the isolate Mt13-3a of F. oxysporum f. sp. melonis race 1.2 spore suspension solution, with a concentration of 106 conidium per milliliter. The symptom was evaluated nine days after inoculation. The spread of symptoms on the plants was recorded every day for 30 days until the complete death of the plant. Evaluation of resistance was calculated using the indices of the area under the disease progress curve (AUDPC), latent period (LP), disease severity index (DSI), and standardized area under the disease progress curve (SAUDPC) in landraces. Investigating the variation of the resistance of the studied landraces based on the mentioned indices was done using analysis of variance and cluster analysis.

The results of the analysis of variance of the data indicated the existence of a significant difference of 1% between the landraces for all four studied indices. Based on the heat map results, there is resistance to race 1.2 of F. oxysporum f. sp. melonis in the genotype Isabel and Tude Qaenat. Also, the cluster analysis of landraces based on Ward's method led to identifying six resistance groups from the 46 landraces studied, along with two differential control lines.

The results of the present research showed that for all four indices of LP, AUDPC, DSI and SAUDPC, there is resistance to race 1.2 of F. oxysporum f. sp. melonis in Isabel genotype as a resistant control and the landraces of Qaenat, Till Magasi, Till Zard, Till Torgh, Laki 1 and Till Keshideh compared to the sensitive control (Charente T).