physical resistance components of onion genotypes, resistant and susceptible to root and basal plate rot disease caused by fusarium oxysporum f. sp. cepae

one of the growth limiting factors of onion plants is root and basal plate rot disease, caused by fusarium oxysporum f. sp. cepae. in this research, eight iranian onion genotypes, azarshahr red, ghom white, herssin, isfahan dorcheh, kashan white, nishabour ishaghabad, yazd abarkoh, zanjan gholigheseh and two commercial genotypes, texas erly grano and yellow sweet spanish were investigated. genotypes were first divided in to resistant, tolerant and susceptible groups depends on disease factors. the root anatomical components including epidermis size, derma parenchyma (size and layer numbers), endodermis size, pericycle size, different xylem sizes, phloem size, central cylinder size, and sizes of sclerenchyma layer of root cortex were also assessed in genotypes. the results indicated that some of these anatomical components were different among onion genotypes. there was a direct and high correlation between some of these anatomical components and resistance of onion genotypes to root and basal plate rot disease. layer numbers of derma parenchyma had the most important and significant role in the resistance level of onion genotypes. resistant genotypes such as kashan white and ghom white had the maximum layer number of derma parenchyma but susceptible genotypes such as hersssin and zanjan gholighese had the minimum layer number.