Identification of secreted proteins as detection markers for citrus disease

A method of detecting secreted protein in a citrus plant, the method comprising

• forming a mixture of a sample from a citrus plant with a first antibody specific for a protein identical or substantially identical to a protein as listed in Table 1 or Table 2;
• incubating the mixture with a polypeptide linked to solid support, wherein the polypeptide is the protein as listed in Table 1 or Table 2 or a protein comprising a fragment of at least 20 contiguous amino acids thereof;
• washing unbound components of the mixture from the polypeptide linked to solid surface;
• and
• detecting the presence or amount of first antibody bound the polypeptide linked to solid surface, thereby detecting secreted protein from Spiroplasma citri or Candidatus Liberibacter asiaticus.