Regulasi Etilen dalam Respon Tanaman Sorgum [Sorghum bicolor (L.) Moench.] terhadap Cekaman Defisiensi P dan Toksisitas Al

Abstract

Understanding the tolerance mechanism of sorghum [Sorghum bicolor (L.) Moench] to aluminium (Al) toxicity and phosphorus (P) deficiency is of high importance to assists breeding program of acid soil-tolerant sorghum. The objective of this research was to study the role of ethylene in the response of sorghum to Al toxicity and P deficiency. This research was conducted in Cikabayan Experimental Field from March to June 2013. This research consisted of two experiments. The first experiment was aimed to determine etephon concentration that could distinguished Al accumulation in the root of Numbu (toleran) and B69 (sensitive) genotypes by haematoxylin staining. The Numbu and B69 seedlings were grown hydroponically for two days in the nutrient solutions containing 0 and 74 μM AlCl3, and different levels of etephon concentrations (i.e. 0, 12.5, 25 and 50 ppm). The first experiment result showed that under 74 μM AlCl3, 12.5 ppm etephon could distinguished the Al accumulation in Numbu and B69 root tip. The second experiment was arranged in randomized completely block design with two factors and three replications. The first factor was P availability and Al toxicity, consisted of four levels i.e. low-P (0.001 mM KH2PO4), sufficient-P (0.1 mM KH2PO4), low-P + 74 μM AlCl3, and sufficient-P +74 μM AlCl3. The second factor was the exogenous application of ethylene regulator, consisted of three levels i.e. control (without ethylene regulator), ethylene precursor (12.5 ppm ethepon), and ethylene action inhibitor (0.6 μM AgNO3). Two sorghum genotypes (Numbu and B69) were grown hydroponically for 14 days. The results showed that Numbu, the acid soil tolerant genotype, was less affected by the P-availability and Al toxicity. In contrast, low-P and Al toxicity significantly decreased root- and shoot length, and shoot- and root-fresh weight of B69, the acid soil sensitive genotype. Application of exogenous ethylene significantly decreased root length, while application of ethylene action inhibitor significantly increase root length in Numbu genotype but not in B69 genotype, indicating that Numbu was more responsive to ethylene. Inhibition of ethylene action under low-P and Al toxicity caused growth inhibition in B69 genotype. Taken together our results imply that the different tolerance to acid soil of Numbu and B69 genotype might be caused by the different responsiveness to ethylene.