Saturday, 15 July 2006

Chlorosis in Sugarcane.

R. B. Somawanshi, Mahatma Phule Agricultural Univ, Rahuri, 12-A , Siddhivinayak Society, Savedi, Ahmednagar, 414003, India

Greenhouse and field experiments were conducted using different chlorosis susceptible and tolerant cultivars to relate chlorosis to soil properties and root growth of sugarcane. Chlorosis prone soils had chlorotic and nonchlorotic plants growing side by side in the same field. Another group of soils had no chlorotic plants even in a highly susceptible sugarcane cultivar CO 7219. Chlorosis prone soils had higher Mg supplying capacity than chlorosis-resistant soils. Both the groups of soils were highly calcareous (5-17 CaCO3 equivalent %). As such, the term lime induced chlorosis needs to be used cautiously. Soils from chlorisis-prone fields had average DTPA-Fe 5.57 mg/kg, Mn 7.44 mg/kg and CaCO3 13.2% and the respective values for chlorosis resistant soils were 7.46, 7.31 and 9.7. For comparison of green plant with chlorotic plant an arbitrary limit of 1 mg chlorophyll/g fresh leaf was fixed below which sugarcane plant looked chlorotic. The chlorosis prone soils had DTPA Fe/Mn ratio of 0.74, which was significantly lower than chlorosis resistant soils (1.02). The K content of saturated paste extract of chlorosis prone soils was exceptionally high (2.7 meq/L) compared to K content of chlorosis resistant soils (0.59 meq/L). Chlorosis-prone soils had colour notations ranging from 10 YR 2/2 to 10 YR 5/2 whereas chlorosis-resistant soils had a range of 10 YR 1/1 to 10 YR 2/2 with vertic properties. Vertisols rarely induced chlorosis in sugarcane even in most susceptible cultivars like CO 7219. Restricted root growth and very few white tender roots (1.7 g/plant) were the characteristic features of chlorotic plant as compared to 3.33-g/green plant. The plants in which initiation of new roots stopped first turned chlorotic first whereas plant in which new roots formation started first turned green first thus chlorosis is a dynamic phenomenon related to root growth. Wider shoot - root ratio (7.81) was another typical feature of chlorotic plants from chlorosis-prone foils, while plants from chlorosis-resistant soil had narrow ratio of 2.3. Leaf chlorophyll concentration was significantly correlated with dry matter of white tender roots. Average dry matter of roots of 17 cultivars was 39.8 g/plant during summer season, which was higher than same cultivars grown in winter season (12.3 g/plant). Study suggested that screening of sugarcane for their tolerance to chlorosis may be done during winter season. The cultivar CO 419 was observed to be tolerant to chlorosis under chlorosis-prone soil conditions. Chlorosis resulted in significant reduction, (38.2%) in millable cane yield, (33.2%) in juice and (7.5%) in sugar yield compared to green plants. Foliar application of 0.5% of ferrous ammonium sulphate corrected chlorotic condition of young plants but its effect could last for a few days suggesting periodical spraying of chemical. Key words: Chlorosis, DTPA-Fe, lime, root growth, and chlorophyll.

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