Friday, 14 July 2006

Screening of Sorghum (Sorghum bicolor) Genotypes.

Ramasamy Krishnasamy, D. Jegadeeswari, U. Surendran, and Chinnappan Sudhalakshmi. Tamil Nadu Agricultural University, Lawley Road, Coimbatore, India

The role of plant factors on micronutrient uptake and utilization has been a highly neglected field. Iron is an essential micronutrient for almost all living organisms because of its critical role in processes such as DNA synthesis, respiration and photosynthesis and iron itself is a prosthetic group constituent of many enzymes. Discrepancies between the solubility of iron in the soil and the demand for iron by the plant are the primary causes of iron chlorosis. Iron deficiency chlorosis is a common disorder for plants grown on many soils in India. Iron fertilization is not helpful as soil applied iron is fixed in soil due to various chemical reactions. Irrigation water is another contributing factor for carbonates, bicarbonates and sometimes for calcium to the rhizosphere, which immobilize iron in soil. Since it is very difficult to bring about drastic alterations in pH values and calcium levels of soils, one has to look into other factors, which can be considered to alleviate iron deficiency in plants. The root-soil interface (rhizosphere) plays an important role in iron acquisition. Plants adapted to iron stress condition have evolved various iron deficiency induced adaptation mechanisms that are genetically controlled. The inherent ability of crop varieties to produce such compounds differs widely. Some crop varieties respond remarkably to iron application while the response is poor in others. The present investigation was framed with the objective of screening sorghum genotypes for their tolerance to iron stress. A suitable methodology was developed for the initial screening with modified Hoagland's solution. Varieties like K 1, K 8, K10, K11, Co 26 and CSV15 exhibited no or less severe symptoms of iron chlorosis and are highly tolerant to iron deficiency hence classified as resistant. Genotypes / cultures like VMS 98001, Co 21, Co 25 and DMS 652 exhibited chlorosis within few days in all the treatments till the end of the study and rated as susceptible. Varieties like APK 1, TNS 340, TNS 587, Co 18, and TNS 334 exhibited chlorosis in control and lower iron levels and they reclaimed green when Fe was applied and hence they were classified under moderately tolerant group. Secondary screening of the same genotypes was done through sand culture experiment with pure quartz. Varieties identified as susceptible, moderately tolerant and tolerant to Fe stress under solution culture showed similar results under sand culture studies also. The physiological parameters like chlorophyll a, chlorophyll b, total chlorophyll and enzymes like peroxidase and catalase were found to be less in the Fe susceptible cultivars than in the resistant cultivars. The Fe efficiency of tolerant genotypes portrays the functioning of an unidentified mechanism in them allowing them to more effectively utilize low levels of cytoplasmic Fe for biochemical processes and physiological mechanisms. These Fe resistant genotypes can be grown in Fe deficient soils without incurring any additional cost on Fe containing fertilizers. Key words: Genotypes, iron stress, resistant, susceptible.

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