A wheat and barley leaf blotch caused by Zymoseptoria tritici and Rhynchosporium graminicola, respectively, are the most important diseases. Thus, researchers have created resistant genotypes using percent disease severity and scales, as well as utilizing converted double-digit and scale data. Eyal and Brown used 0-5% (Very Resistant), 5-15% (Resistant), 15-30% (Moderately Resistant), 30-40% (Moderately Susceptible), and above 40% (Susceptible). Saari and Prescott used 0-3 scales (R), 3.1-4 scales (MR), 4.1-6 scales (MS), 6.1-8 scales (S), and 8.1-9 scales (HS). Medini and Hamza considered 0-2 scales (R) and 3-5 scales (S), and Ghaffary suggested least significant difference (LSD) for gene–gene postulation. Sharma and Duveiller, and Silvar developed the formulas percent severity index \((\text{PSI})=[(\frac{D1}{9})(\frac{D2}{9})]*100\) and \(\text{PSI}=\frac{Snr}{Npr*Msc}*100\) to convert double-digit and scales, respectively. Inoculations, or spores landing on leaves, is the first infection process. Spore germination is the production of germ tubes. The pathogen’s hyphae penetrate the crop’s apoplast through stomata opening, but Z. tritici doesn’t form haustoria. Z. tritici uses a mitogen-activated protein (MAP) kinase, ZtSlt2, to colonize a wheat mesophyll cell. The Zt3LysM effector protein triggers the infection latent phase in wheat. R. graminicola mycelium produces toxic metabolites that cause leaf symptoms during colonization. Cell wall structural change is one of the best resistance mechanisms in both crops. Wheat receptor proteins counter the pathogen’s Zt3LysM effector protein by hydrolytic enzymes. The Lb16q gene encodes a cysteine-rich receptor-like kinase (CRK) stand for identification of Z. tritici carbohydrate during activation of the resistant mechanism. Barley resists the pathogen by lengthening the latent and incubation periods. According to Sharma and Duveiller formula, 37 and 73 double-digits of the genotypes X and Y, respectively, are converted to a 25.9 value. This indicates both genotypes are the same in their reaction. But according to Eyal and Brown reaction classification, the genotypes are different. Silvar formula is appropriate to convert scale data into a percent severity index. MS, S, MR, and R reaction types are being derived from Eyal classes and Eyal and Brown reaction types in this review. At the seedling growth stage, a qualitative 0-5 scale has been used, but the LSD has become a common method to determine the reaction of both crops’ genotypes.
