Characterisation of Bacterial Blight Disease in Walnut Caused by (Xanthomonas arboricola pv. juglandis)

ABSTRACT: Bacterial walnut blight is a plant disease caused by the bacterium Xanthomonas arboricola pv.

juglandis (Xaj) which significantly impacts the health and productivity of walnut trees, leading to reduced

yields and economic losses for walnut growers. In this study, characterisation of Xanthomonas arboricola pv.

juglandis (Xaj), the causative agent of walnut blight disease, was investigated. Bacterial isolates were collected

from diseased walnut leaves and fruits, and tests were conducted to determine their pathogenicity. Five

bacterial isolates tested positive in HR tests and displayed bright mucoid yellow-colored colonies. In these

results, all isolates tested positive in tomato plants, whereas only the Xaj-2 isolate tested positive in tobacco

plants, and the other isolates gave negative results in the HR test. Additionally, all isolates yielded positive

results in the KOH test and showed growth in YDCA medium as bright mucoid yellow colonies. In the starch

hydrolysis test, Xaj-2 and Xaj-3 isolates tested positive, while the remaining isolates yielded negative results.

All isolates grew in 2% and 5% NaCl medium, but Xaj-1, Xaj-2, and Xaj-3 exhibited weak growth in 5%. None

of the isolates grew in 8% NaCl medium. Lastly, all isolates tested negative on SNA medium. Among the

isolates, three showed positive results in the pathogenicity test, but the Xaj-2 isolate was more effective than

the others. After 7 days, the isolates caused brown-black spots on the leaves, and these spots grew and merged

after 14 days, leading to the formation of necrotic tissue. After 28 days, these necrotic formations expanded

further, causing drying at the leaf edges and wilting throughout the leaf.