Fisiologi adaptasi Sorgum (Sorghum bicolor L. Moench) terhadap toksisitas aluminium dan defisiensi fosfor di tanah masam

Abstract

Sorghum (Sorghum bicolor (L) Moench) is an ideal crop to be developed as food diversification and source of bioethanol in Indonesia because this crop has high adaptability to be grown in dry lands. From a total of 148.2 millions ha dry land in Indonesia, an estimated are of 108 millions ha are acid soil (ultisols). Acid soils have low fertility and Al toxicity which are major constraints for crop production in acid soil. For sorghum production in acid dry lands, sorghum varieties having high adaptation to acid soil have to be developed. The objectives of this study was to obtain complete information about the physiological adaptation to aluminum toxicity and phosphorus deficiency which can be used as the character selection in breeding program to obtain the tolerant sorghum in acid soils. The genotypes used was Numbu (Tolerant), ZH-30-29-07 (Tolerant), B-69 (sensitive) and B-75 (sensitive) from selected on acid soils in Lampung. The study on physiological mechanism of sorghum adaptation to acid soils has resulted in information that the main limiting factor in soghum growth in acid soil was phosphorous deficiency. Under sufficient P, without liming, the sensitive genotype produced similar yield. The tolerant genotype, Numbu and ZH30-29-07 showed higher ability to maintain root growth under Al stress and P deficiency. The tolerant genotypes also showed higher ability to absorp nutient under low P condition compared to sensitive genotypes. The lowest concentration of 74 μM Al can reduce the growth in all genotypes tested. The longer the sorghum roots exposed to the stress, the higher the value of scoring and the accumulation of aluminum in the roots under Al toxicity. Sorghum genotypes had specific absorption rate was high, but it was not followed by increasing of roots length, roots dry weight and shoot dry weight. Specific absorption rate is more affected by Al stress rather than increasing level of P. Genotype ZH-30-29-07 were tolerant in identified in acid soils showed the moderate response to Al toxicity in nutrient solution. The higher aluminum concentration leading to greater plant growth inhibition. The tolerant genotypes had the internal mechanism (tolerance) in the face under low P condition by increasing the efficiency of internal phosphor (interrelated), otherwise the sensitive genotype had the external mechanism (avoidance) through increased P absorption or total P . There was no relationship between the use efficiency of P with total P content of plant both in testing using the acid soils in rhizotron and nutrient solution.