Khankahdani, Hamed Hasanzadeh

Abstract Witches’ broom disease of lime (WBDL) associated with ‘ Candidatus Phytoplasma aurantifolia’ is a destructive disease affecting Mexican lime in southern Iran. Typical symptoms of the disease including internode shortening, little leaf and witches'-broom. This study was conducted to investigate changes in the concentrations of nutrient elements in the symptomatic branches, asymptomatic branches, and roots of Mexican lime trees infected with ‘ Ca. P. aurantifolia’, compared to healthy trees in an orchard in Roudan, Hormozgan Province, Iran. Leaf samples were collected from symptomatic branches, asymptomatic branches of infected trees, and healthy trees. In addition, root samples were separately collected from symptomatic and healthy trees. The concentrations of twelve nutrient elements were determined in leaves and roots. The results showed that in symptomatic branches, phosphorus (P), potassium (K), copper (Cu), iron (Fe), chlorine (Cl) and sodium (Na) elements were significantly higher than asymptomatic ones. Conversely, magnesium (Mg), calcium (Ca), manganese (Mn), and boron (B) levels were significantly lower in symptomatic branches. No significant differences were observed in nitrogen (N) and zinc (Zn) levels between symptomatic and asymptomatic leaves. The Na and Cu concentrations showed the most significant increases in symptomatic versus asymptomatic leaves. In the roots, symptomatic lime trees exhibited significantly lower concentrations of N, P, K, Na, Cu, Mn, Fe, and Mg compared to healthy trees; however, no significant differences were found for Cl, B, Zn, and Ca. Overall, these findings suggest that nutritional management, particularly targeting symptomatic trees, could potentially play a role in the management of WBDL in infected orchards.

Abstract Citrus huanglongbing (HLB) associated with Candidatus Liberibacter spp. is the most destructive bacterial disease of citrus crops worldwide. In this study, the response of three-year-old seedlings of 14 commercial citrus cultivars and rootstocks to the Asian form of HLB disease ( Ca . L. asiaticus) was investigated through graft-inoculation. The seedlings' reactions to the HLB disease were evaluated based on the PCR detection of CLas after grafting, the disease incubation period (time between graft-inoculation and appearance of the first disease symptoms), and disease severity. Depending on the time of the positive PCR detection of CLas and appearance of disease symptoms, Mexican lime, Persian lime and Volkamer lemon were ranked at the highest level of tolerance (lowest susceptibility), and Rough lemon and Local orange were at the next level, i.e., semi-tolerance (intermediate susceptibility). Alemow, Bakraei, Rangpur lime, Cleopatra, Clementine mandarin, Local mandarin, Blood orange, and Washington navel orange were classified as susceptible to the disease, followed by Valencia orange, which was the most susceptible. In conclusion, all citrus genotypes studied, were affected by HLB. However, symptoms varied by cultivar, with the most severe observed on Valencia sweet orange and Local mandarin, while less severe symptoms were observed on Mexican lime, Persian lime and Volkamer lemon.