August 2001. An interesting request was received from the Central Research Laboratories, UK for information on Freckle disease (Guignardia musae (anamorph: Pyllosticta musarum) of banana: which cultivars (with genome make-up information if possible) are affected and which cultivars are not affected in the Pacific Island countries?
Guignardia musae affects both leaves and fruit of susceptible bananas. The disease is characterised by the dark-brown-black spots of pycnidial conidiomata of G. musae which protrude from banana surfaces and feel rough to the touch, like sandpaper.
Old reports in the scientific literature indicate that in Hawaii, Cavendish cultivars (AAA genome) and others are affected, but not cooking bananas in the ABB genome, such as 'Bluggoe'. This also holds true for Taiwan. In Papua New Guinea, and on Cape York Peninsula in Australia, the writer's surveys indicate that ABB cooking bananas, such as 'Bluggoe', and others are attacked by freckle, but not Cavendish. This also seems to hold true in New Caledonia and possibly other South Pacific countries. In Southeast Asia, it has been noticed that both Cavendish and ABB bananas are affected.
In the CABI publication Diseases of Banana, Abaca and Enset (1999), the writer hypothesised that there may be two forms of freckle that can be differentiated by their reactions on Cavendish cultivars and 'Bluggoe'. Both forms may exist in Southeast Asia, but only the 'Cavendish-attacking' one in the North Pacific and the 'Bluggoe-attacking' one in the South Pacific.
A response was provided by a SPC plant pathologist, who had taken part in plant disease surveys in far
north Queensland, mostly north of areas of intensive cultivation, as well as surveys in several parts of Irian Jaya, Indonesia, and nearby areas of Papua New Guinea. Bananas have always been one of the main food plants of interest. Samples of Phyllosticta musarum, freckle disease, were collected from banana plants growing through much of this survey region. On the Cape York Peninsula, this pathogen was found only in the Lockhart River area and the Northern Peninsula Area. By contrast, there are many records from the Torres Strait Islands. On the island of New Guinea, there are records from several locations in Irian Jaya and also in border regions of PNG.
Freckle-like disease symptoms or P. musarum were not found on Cavendish bananas. In most cases, P. musarum was found on various ABB cooking bananas (many named, some not). Bluggoe seems to be particularly susceptible. Of particular interest was that on several occasions in PNG (and also on some islands in the Torres Strait), cooking bananas were seen with relatively severe freckle symptoms growing adjacent to dwarf Cavendish bananas showing only symptoms of black Sigatoka. Similar comparisons were not made further south (NPA and Lockhart River area) as the Queensland Department of Primary Industries ensures no Cavendish bananas are grown in the rest of the Queensland survey area.
On a recent survey of parts of the coast of the Western Province of PNG, P. musarum was found causing freckle on what appeared to be cv. Mysore (AAB, Mysore sub group) in four villages. Again, in some of these locations, nearby Cavendish plants were unaffected.