The influence of citrus rootstocks on lime genotype tolerance to witches’ broom disease

Unfortunately, over the past two decades, Mexican lime orchards have faced a significant threat from witches' broom disease of lime (WBDL), associated with 'Candidatus Phytoplasma aurantifolia', leading to the ruin of many orchards in southern Iran. One effective strategy for controlling vector-borne diseases like WBDL is to find and use tolerance/resistance genotypes. Although a number of studies have shown that using tolerated cultivars, rootstocks or scion/rootstock combinations may affect phytoplasma disease severity, no studies have compared different Mexican lime genotypes/rootstock combinations against 'Ca. P. aurantifolia' infection. This study assessed the tolerance and response of four Mexican lime genotypes (G5, G8, G16 and G17) grafted on two commercial rootstocks (including Mexican lime and sour orange) against WBDL under controlled conditions. The results showed that foliar disease expression was observed in all limes grafted on Mexican lime. Disease symptoms were not recorded in lime genotypes × sour orange except G5. All lime genotypes grafted on the two commercial citrus rootstocks were infected with 'Ca. P. aurantifolia' at varying rates. However, in the three genotypes grafted on sour orange rootstock, the phytoplasma titer was significantly reduced. Furthermore, growth parameters, including leaf width and length, internode length, and greenness, showed fewer significant differences compared to control. The findings of this study enhance our understanding of the influence of rootstock on the performance of WBDL-infected citrus in controlled greenhouse conditions and acknowledge that WBDL management may require tolerance of both scions and rootstocks.