Calcuim Nutrition of Taro (Colocasia esculenta (L.) Schott) and Its Possible Relationship to Guave Seed Disease

Miyasaka, Susan Chie
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Calcium deficiency symptoms on taro (Colocasia esculenta (L.) Schott cv. 'Lehua maoli') grown in nutrient solution culture for 7 weeks were leaf blade interveinal chlorosis and necrosis, failure of the leaf blades to unfurl, collapse of petioles, and die-back of roots. Death of the growing point occurred in severely Castressed plants. Sections of the leaf blades of taro grown in solutions varying in Ca concentration were sampled after 5 months to study the longterm effects of calcium deficiency on the ultrastructure of parenchyma cells. The disintegration of the plasmalemma, tonoplast, and all other membranous systems in the cytoplasm was observed in calcium deficient cells. Taro was grown for 3 months in nutrient solution culture with 1, 2, 4, and 20 ppm of Ca and 21 and 100 ppm of nitrogen. Leaf dry weight increased significantly with increasing solution Ca and decreased significantly with increased solution nitrogen. Leaf Ca concentration increased linearly with increasing solution Ca, however the increase in leaf Ca was significantly less at the higher N treatment compared to the lower N treatment. Calcium levels were increased to 2, 4, 8 and 40 ppm from month 4 through month six. The N treatments were both 42 ppm for the duration of the fourth month. For the fifth and six months, the 2 N levels were 42 and 84 ppm. Dry weight of the conn plus cormels, dry matter content of the corm, and starch content of the corm at 6 months all increased with increasing levels of solution calcium. A Mitscherlich type growth response to Ca was found at the lower N treatment but not at the higher N treatment. The best tissue to sample for plant Ca levels is the third blade at 3 to 6 months of growth. The critical Ca concentration range for the third blade during this growth period was estimated to be 0.7 to 1.0% Ca on a dry weight basis. Nutrient concentration in the solution was decreased for the final 2 months of the experiment. Starch content, dry matter and specific gravity of the corms as well as fresh weight of the corm plus cormels at 8 months all increased with increasing Ca in solution. The corms at the highest level of solution of Ca were mature as indicated by the specific gravity and dry matter percentage of the corms. Guava seed disease was not found to be associated with any of the treatments at 6 or 8 months harvest. The disease was not directly caused by Ca deficiency, NH4 toxicity, or N-induced Ca deficiency under the relatively sterile conditions of a solution culture experiment.
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