Production of yellow strapleaf of chrysanthemum & similar disorders by amino acid treatment.

An apparent physiological disease, Yellow Strapleaf (YSL) of Chrysanthemum morifolium Ram., was described by Jackson and Woltz (1) in 1959. The disease has been observed in Florida plantings during the last 6 years and has been noted in Massachusetts 3. Symptoms include chlorosis of new growth, green netting of leaves, and narrow strapshaped leaves that hook at the distal ends (fig 1A). The condition may persist for 2 to 8 weeks causing mild to severe stunting of plants and has been found in 20 commercial chrysanthemum varieties. YSL has not been corrected by the application of inorganic nutrient elements or linked directly with any fungal, bacterial, or viral pathogen. Chemical analyses of plant and soil have not indicated any significant differences in content of inorganic nutrients. Higher soil pH was usually associated with the disorder. Woltz and Jackson (6) presented results of experiments that linked frenching of tobacco (Nicotiana tabacumii L.) and YSI, of chrysanthemum as being apparently caused by similar soil conditions and resulting in similar syndromes. Both disorders are favored by relatively high soil pH, periods of high soil moisture levels, and high soil temperatures. The symptoms displayed with the diseases (1, 5) have three common features: A: green netting or reticular chlorosis of leaves, B: narrow, strap-shaped leaves, and C: growth retardation. Tobacco and chrysanthemum plants growing together in containers of soil that had produced YSL in the field developed symptoms of the respective diseases of frenching and YSL. Following the information set forth by Steinberg (5) that isoleucine and certain other amino acids were effective in producing frenching, DL-isoleucine with DL-alloisoleucine was applied to the root zone of chrysanthemum plants. This amino acid treatment uniformly and quickly produced YSL symptoms with plants growing in solution culture, steamed soil, methyl bromide-treated soil, untreated soil, quartz sand and expanded volcanic glass (perlite). Six chrysanthemum varieties of varying degrees of susceptibility to YSL were treated with isoleucine in this experiment. YSL symptoms developed in all varie-