August 2009. Dieback of papaya plants occurs in Tonga in a plot of 8-9 months old papaya (Solo sunise) that is fruiting for the first time. More than 50% of the papaya plot is infected with water-soaked lesions on the stem just below the inner crown leaves. The lesions spread rapidly and eventually the crown collapses. Bunchy inner crown leaves and rapid drying of the older leaves normally occurs before the visual appearance of the lesion on the stem as shown on the attached photos.
In some parts of the Caribbean, papaya is affected by Erwinia spp. The symptoms look similar. It was unlikely to be symptoms of Phytothphora, but the trees should be split down the middle to determine where the rots start. Phytothphora rots begin below ground. In some cases, the rot originates in the crown, initiated by insects and fungi.
Trujillo and Schroth described two Erwinia species on papaya in the Mariana Islands. Since then, reports of Erwinia have been published from America, including Venezuela and the French Antilles. Hawaiian varieties are very susceptible. Some Marianas varieties are resistant. One of the isolates was systemic (so cutting back the stem, would not solve the problem.
Later, Tonga reported the roots and stem, up to the crown where infection occurs, is healthy. In the last two 5-6 weeks, the plants have shown symptoms of phytoplasma infection, with the oily, water-soaked lesions on the stems starting to appear 2 weeks ago. It took only a few days to spread rapidly throughout the entire plot (13 acres). Therefore, it is not clear if the stem lesions (which are likely to be bacterial) are secondary infection, which lead to the rapid dieback of the plants.
Tonga intends to: 1) rogue the diseased plants by cutting off the infected parts of the plants leaving about one meter of the stem from the base to shoot back; 2) cover the cut ends of the plants with plastic to avoid infections and 3) spray with copper oxychloride (the only bactericide available).
Malaysia has reported Erwinia papayae as the cause of dieback. There are photos showing similar symptoms to those above. There is also a reference to the condition in the Caribbean.
It looks a very serious disease.
Later, The Queensland Primary Industries Department warned the country’s papaya growers that if Bacterial crown rot disease gets into Australia, it would cost millions of dollars and devastate the industry.