Isolation and Diagnosis of the Bacterium Pectobacterium Caratovorium, the Causative Agent of Soft Rot Disease on Potatoes, Macroscopically and Biochemically

Abstract

This study aimed to isolate the bacterium Pectobacterium sp., the causal agent of soft rot disease on potato tubers, and to test its pathogenicity on potato tuber slices. It was also aimed to diagnose it macroscopically and biochemically to the species level. The isolation results showed that 40 bacterial isolates were obtained from potato stems, tubers, and soils collected from potato cultivation fields and storage facilities for the 2021 agricultural season from the areas of Yusufiyah, Radwaniyah, Abu Ghraib, Taji, Madaen, and Alwa Jamila. The results of the pathogenicity test for 40 isolates on potato slices showed that they had different pathogenicity in damaging potato slices, with three isolates (Pc1, Pc4, and Pc11) significantly outperforming the remaining isolates and the control treatment. The three isolates (Pc1, Pc4, and Pc11) were diagnosed to the species level based on morphological characteristics, ability to grow on some selective and differential media, and biochemical reactions as Pectobacterium carotovorum. The microscopic examination of samples from bacterial growth showed short rod-shaped cells, single or paired, negative for Gram staining, and motile. The biochemical reaction results showed that they had the ability to hydrolyze artificial pectin and reduce sucrose, were negative for oxidase test, methyl red test, Fox-Proskauer test, and phenylalanine deaminase test, and positive for free oxygen test, tolerance to salinity, production of ammonia from peptone, production of gas from glucose, hydrolysis of starch, ability to consume simple sugars, hydrolysis of gelatin, and ability to grow at 38°C.