Phytoplasmas and disease symptoms of crops and weeds in the semi-arid tropics of the Northern Territory, Australia

This study used molecular techniques to investigate the little-known characteristics of phytoplasmas in the semi-arid tropics of northern Australia in sesame, mung bean and peanut crops, and in adjacent non-crop species. Five new records of plant species associated with phytoplasma diseases are reported. No phytoplasmas were associated with fasciation but four phytoplasma strains were linked with other symptoms. Sweet potato little leaf variant Vinca 4, the most prevalent phytoplasma, was associated with symptoms of little leaf, or little leaf and phyllody, in all hosts (crop and non-crop species) except sesame, where it was most often associated with floral dieback. Tomato big bud was found only in sesame showing phyllody. Pigeon pea little leaf occurred in one mung bean and one peanut plant with little leaf and phyllody, and one non-crop species with yellowing and rosette formation. Waltheria little leaf was found in a single non-crop individual with little leaf and bunching symptoms. The findings show that adjacent non-crop species have the potential to function as reservoirs of phytoplasma disease for crop species but symptoms alone are not sufficient to diagnose specific phytoplasma strains.