Studies of mycoplasma-like organisms in plants
The disease clover phyllody (CP), caused by a mycoplasma-like organism (MLC), was studied from two wild clover populations. Disease organisms were transferred to Vinca rosea using the leafhopper Suscelis plebejus. V. rosea was a useful test plant and such infected plants were used for further MLO transmission experiments as well as for testing possible chemotherapeutants. Attempts to culture clover phyllody on artificial media were unsuccessful. Monstrose and cristaxe forms of seme cacti were examined and found to contain MLC. Infected cacti were used for comparison with CP and for use in transmission and chemotherapy experiments. Other MLO diseases including those of Rosa sp., Fragaria vesca and Helenium hybridium were used in conjunction with CP, to find a specific light-microscope stain for MLO diseases. Dienes' stain was tested and successfully developed as a specific stain for MLQs, requiring no specialised equipment. A new fluorescent staining technique was also developed using europium chaelate. The MLO found in the phloem of a range of different MLO diseases were compared by electron microscopy. MLO from cacti, although larger than those from herbaceous plants, were otherwise very similar. In the course of the EM examination it was possible to observe replicative stages in the life cycle of the MLO and their movement through sieve pores which allows the MLO to spread through the host plant. Subcellular content and structural changes of the host plants were also noticed. The major change was the reversion of coloured plastids to green chloroplasts. The phenomenon was followed in a series of petals from Vinca rosea showing progressive greening.