Cytological and physiological basis for tomato varietal resistance againstAlternaria alternata

Abstract

Since tomato is an important food component, it is imperative to enhance its yield against the activities of many devastating fungal pathogens such as Alternaria alternata. The exploitation of plant innate resistance by cultivation of resistant varieties is an effective measure in this regard. In the present study, 28 tomato varieties were tested against 32 A. alternata isolates, and representative varieties were further evaluated to determine the extent and basis of their antifungal resistance. A significant increase (104.7%) in polyphenols was recorded in the resistant variety Dinaar compared with the susceptible variety Red Tara. Dinaar also exhibited 100% enhancement of alkaloids and terpenoids along with a 30.7% increase in cell wall hemicellulose content. Significant differences were found in physical barriers (cellulose, lignin and pectin) of the representative varieties when stained tissue sections were subjected to colorimetric analysis. Similarly, polyphenol oxidase, peroxidase and phenylalanine ammonia lyase showed increases of 78.37, 114.67 and 125.11% respectively in the resistant variety. Higher expression of glucanase genes was evident from native gel analysis, in which not only the number of isozymes but also the quantity of individual isozymes was significantly increased. The resistant variety Dinaar had strong antifungal resistance and can therefore be recommended as suitable for cultivation in the agricultural system of Pakistan.