Rickettsia-like and mycoplasma-like organisms associated with two yellows-type diseases of strawberries in Queensland

Abstract

Two yellows-type diseases occur in Queensland strawberries. Affected plants show purple or bronze pigmentation of older leaves, followed by the production of small chlorotic leaves. Flower production is inhibited, and some affected plants die. Thin-section electron microscopy showed that there were two diseases, one associated with rickettsia-like organisms (RLO) and the other with mycoplasma-like organisms (MLO), both of which were found only in sieve tubes. The MLO disease caused flower abortion but not green petals, and was not transmitted by Orosius argentatus (Evans), the tomato big bud vector. The RLO disease produced more bronze pigmentation and the young leaf chlorosis was interveinal rather than marginal. This organism was sensitive to penicillin, and soil drenches of 1 mg/ml every 5 days for 7 weeks caused complete remission of symptoms. No organisms were seen in thin sections of leaves after treatment. Although these RLO morphologically resembled those associated with rugose leaf curl (RLC) disease of legumes, experiments with the RLC vector Austroagallia torrida Evans indicated that they were probably distinct.

Plant hosts of the phytoplasmas and rickettsia-like-organisms associated with strawberry lethal yellows and green petal diseases

“…A rickettsia-like-organism (RLO) is also associated with SLY disease (Greber and Gowanlock 1979). Little is known about this RLO, as until recently there was no diagnostic test.…”

Rickettsia-like-organisms and phytoplasmas associated with diseases in Australian strawberries

“…Bronze discoloration of older leaves, stunted petioles and interveinal chlorosis on younger leaves are symptoms associated with a rickettsialike-organism (RLO) (Greber and Gowanlock 1979). Purple discoloration of older leaves, and stunted younger leaves with shortened petioles and marginal chlorosis are associated with Candidatus Phytoplasma australiense (Padovan et al 2000;Greber and Gowanlock 1979).…”

“…The relationship between these different organisms and SLY disease is poorly understood because it is difficult to differentiate the symptoms associated with an RLO from those associated with a phytoplasma (Greber and Gowanlock 1979). Although SLY diseased samples could be tested using PCR primers specific for the phytoplasma 16S rRNA gene or the Tu elongation factor (tuf ) gene (Padovan et al 2000), a diagnostic test for the SLY RLO has not been available.…”

“…To prevent this, plants exhibiting symptoms are rogued from runner beds during frequent disease inspections. However, it can take up to 8 weeks for the plants to exhibit SLY or SGP symptoms (Greber and Gowanlock 1979) making it possible for affected runners to be unintentionally sent to fruit production farms.…”

“…Of these diseases, SLY and SGP are caused by intracellular bacteria-like pathogens that can have a significant impact on productivity because flowering and fruit set are inhibited, and infected plants frequently die (Greber and Gowanlock 1979). These diseases can be transmitted from mother plants to runners and so can be passed in planting material from runner production farms to fruit production areas (Greber 1987).…”