“Witches’ broom” disease of lime suppressed by some resistance inducers

Abstract

“Witches’ broom” disease of lime (WBDL) has been considered as one of the most economically devastating diseases of Mexican lime in southern Iran with poor information on the management and almost no available cure. Resistance inducers are known as chemical compounds that enable plant defense system to suppress pathogens. In this study the effects of ascorbic acid (300 µM); ascorbic acid (600 µM), ascorbic acid (300 µM) plus MgCl2 (200 µM), salicylic acid (150 µM); salicylic acid (300 µM), salicylic acid (300 µM) plus MgCl2 (200 µM), Phosetyl aluminum (Aliette) (2/000), Nano silver (10 µM) and STARNER™ (3 g/L), 31% Phosetyl-Al plus 53% propamocarb (Privicure Energy™) (17.5 µM), Hymexazol 70% (Tachigaren™) (30 µM) and NORDOX(30 µM) spray on 2-years-old seedlings infected WBDL were investigated at greenhouse and field conditions simultaneously. Disease severity data were recorded during seven visual evaluations for greenhouse experiment and five evaluations time points for the field experiment. To determine disease severity, each tree was divided into three sections, and each zone was scored individually based on the visual symptoms from 0 to 5. Also, the fruit yield data were collected for the two harvest seasons in Minab, Hormozgan province of Iran. A significant suppression effect on WBDL was observed after spraying 31% of Phosetyl aluminum plus 53% propamocarb (Privicure Energy™) and 70% of Hymexazol separately two times per year. Ascorbic acid, salicylic acid, Aliette, NanoSilver and STARNER also showed transient effect against WBDL after three or four applications per year. The treatments of 31% Phosetyl-Al plus 53% propamocarb (Privicure Energy™) 4/000, Hymexazol 70% (2/000) and NORDOX (0.5/000) decreased WBDL severity by approximately 10 to 40% in the greenhouse and 25% in the field. The average number of fruit per tree was 2300.1 fruit/tree, while that of the negative control was only 1800.5 fruit/tree. Due to positive effect of these resistance inducer compounds on WBDL severity, fruit yield significantly increased in infected lime orchards. The results of this study indicate some promising signs of induced resistance for suppressing the severity of the disease in WBDL infected orchards.