IMPROVEMENT OF GROWTH AND YIELD OF GYPSOPHILA-PANICULATA BY SOLARIZATION OR FUMIGATION OF SOIL OR CONTAINER MEDIUM IN CONTINUOUS CROPPING SYSTEMS

Disinfestation by solarization, fumigation with methyl bromide, and tr eatment with metam-sodium were studied in commercial greenhouses growi ng Gypsophila paniculata and experiencing yield decline under continuo us cropping. Disinfestation of soil or tuff container medium (volcanic ash), each at two sites, resulted in improved growth and increased fl ower yield, Flower weight was increased 17-65% by solarization, 26-97% by methyl bromide, and 51% by metam-sodium. Solarization combined wit h a half-dose of methyl bromide increased yield to the same level as a full dose of methyl bromide. A long-term effect on yield increase ove r two to five successive crop cycles was apparent with solarization an d methyl bromide fumigation, but not with metam-sodium. The quality of flowers also was improved by solarization of a tuff container medium. Disinfestation increased the percentage of early yield. Solarization or sterilization nullified growth reduction or mortality of gypsophila seedlings grown in pots containing soil or tuff container medium with a history of continuous gypsophila cropping or in noninfested soil in which roots of gypsophila plants had been incorporated. Pathogenic is olates of Pythium spp. and Rhizoctonia solani were isolated from plant s from the commercial greenhouses and from roots of diseased plants fr om controlled studies. Microscopic observation of roots of gypsophila grown in monoculture systems revealed infection by Olpidium brassicae and Polymyxa betae.