3.8.8
NEW DISEASE IN MOTHER PLANTS OF GYPSOPHILA PANICULATA REDUCES PRODUCTION OF CUTTINGS AND CONTROL OF THIS DISEASE

Y BEN-YEPHET1, M REUVEN1, I MOR2, A GERA3 and U GERZON4

1Plant Pathology and 3Virology, The Volcani Center, Bet-Dagan, Israel; 2Ministry of Agriculture, Israel; 4Entomology, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel

Background and objectives
Rooted cuttings of Gypsophila paniculata L. planted in fumigated Tuft (crushed volcanic stones) are used as mother plants to produce rooted cuttings from which to obtain new cuttings for flower production. Harvesting of cuttings begins 4-5 weeks after planting and continues for several months. An unknown disease, which affects growth, induces stunting and may, consequently, reduce the yield of cuttings by up to 50%, was found in the mother plants. There is no report available in the literature which describes such a disease in gypsophila mother plants or discusses how to reduce yield losses. The purpose of this study was to describe the disease and to evaluate treatments which reduce disease incidence.

Materials and methods
Rooted cuttings of G. paniculata were planted in 10 L containers filled with steamed or naturally infested Tuft. Each of the following biocides, in the indicated dose(s), was used to disinfest naturally infested substrates, the dose applied to each container being suspended in 1 L of water. The biocides were: metham-sodium (Vapam, Edigan), (5 ml) formalin (Fordor-37) (10, 5, and 2.5 ml), chlorothalonil (Bravo) (1, 0.5, 0.25, and 0.125 ml), mancozeb (Manzidan), (8, 4, and 2g) captan (Captan) (8, 4, and 2g), benomyl (Benlate) (10, 5, and 1g) chloramphenicol, (0.5 and 1g) streptomycin (0.5 and Ig) or propamocarb (Dynon) (30 ml). Ten days after Tuft disinfestation, four rooted cuttings were planted in each container and for each treatment five containers were used. Three weeks after planting, plants were cut to induce development of new cuttings and new cuttings were harvested every 7-10 days.

Results and conclusions
Diseased plants are recognizable by yellowing of leaves, slower growth of stems and, in severely affected plants, by "broom-like" growth caused by the loss of apical control. Disease incidence in mother plants appeared after several cycles of harvest of cuttings, and usually began 2-3 months after planting. Rooted cuttings planted as mother plants in a naturally infested Tuff substrate developed yellowing of the apical stem parts within 3 weeks, followed by severe deformations of the emerged cuttings. We suggest the name "deformation disease" for this affliction. Deformation of mother plants was induced by the addition of roots of diseased plants or by adding a water extract from naturally infested growth substrates. Incidence of disease was positively correlated with the intensity of solar radiation. Involvement of viruses, viroids, phytoplasma or mites as causal agents of the disease in mother plants was ruled out. Disease incidence in mother plants in steamed or naturally infested Tuff was 0 or 100%, respectively. All biocides used except Dynon and streptomycin reduced deformation disease incidence in mother plants. Disease incidence in the Vapam treatment was 20%. Of the other biocides tested, Fordor-37, Bravo, Manzidan and Captan, the minimal doses required to reduce disease incidence to about zero were 5 ml, 0.25 ml, 4 g and 8 g, respectively; Benlate partially reduced disease, to 40% at 10 g per container. The antibiotic, choloramphenicol was phytotoxic at 1g, while at 0.5 g it reduced disease incidence to 30%. Most of the biocides were effective in reducing disease incidence, but the most effective ones were Bravo, Manzidan and Fordor-37. Reduction of disease incidence both by chemicals known as fungicides or by those known as bactericides strongly suggests that deformation disease is associated with the presence of both fungi and bacteria.