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 charac teristics 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 repo rted. No phytoplasmas were associated with fasciation but four phytoplasma strains were linked with other symptoms. Sweet potato little leaf variant V inca 4, the most prevalent phytoplasma, was associated with symptoms of lit tle leaf, or little leaf and phyllody, in all hosts (crop and non-crop spec ies) except sesame, where it was most often associated with floral dieback. Tomato big bud was found only in sesame showing phyllody. Pigeon pea littl e 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. Wa ltheria little leaf was found in a single non-crop individual with little l eaf and bunching symptoms. The findings show that adjacent non-crop species have the potential to function as reservoirs of phytoplasma disease for cr op species but symptoms alone are not sufficient to diagnose specific phyto plasma strains.