Phytoplasma disease outbreaks in multiple crops in eastern Australia

Abstract

Phytoplasma disease outbreaks were common and widespread in grain legume crops including mung bean (Vigna radiata), soybean (Glycine max) and peanut (Arachis hypogaea) in late 2016 and early 2017. Mung bean crops were affected in all major production areas spanning a distance of over 1,200 km from north to south with numerous crops having greater than 40% disease incidence near Dalby.

Several soybean crops from Cecil Plains were also affected by phytoplasma in late autumn 2016. Almost 100% of plants were affected in some paddocks and virtually no yield.

During the 2016/17 summer, some vegetable and pawpaw crops also had damaging outbreaks of disease. Several tomato crops in south-east Queensland had incidences of “big-bud” disease in excess of 50%. Capsicum and eggplant crops also had phytoplasma at higher than normal levels. In coastal Queensland, pawpaw (Carica papaya) crops had about 30% of plants affected by yellow crinkle disease but up to 80% in some younger plants.

The P1/P7 region of the 16S gene was amplified from several different crop types. Resulting sequences had close to 100% nucleotide identity to pigeon pea little leaf phytoplasma, Candidatus Phytoplasma aurantifolia (16Sr-II group), which has been previously reported in Australia from pigeon pea (Canjanus cajan) and stylosanthes.

A known leaf hopper vector of phytoplasma, Orosius orientalis, was collected from some affected mung bean crops but it is not certain it was associated with these disease outbreaks.

To our knowledge, this is the most significant, widespread outbreak of phytoplasma in broad acre crops to occur in this region of Australia. It is unclear what the underlying reasons are for this sudden increase in disease incidence. We are continuing further studies to determine: the diversity of phytoplasma across crop and weed hosts and geographical range, which insect species are vectors, and possible management options.