Suminar E, Budiarto R, Nuraini A, Mubarok S, Ezura H. 2022. Morpho-physiologicalresponsesof iaa9 tomato mutants to different levels of PEG simulated drought stress. Biodiversitas 23: 3115-3126. This study aimed to analyze the morphological and physiological responses of iaa9 mutants and its WT-MT to different levels of drought stress in in vitro growing medium. This study applied a completely randomized design with two factors, ie, tomato genotypes and polyethylene glycol (PEG)-induced drought stress levels. The factor of varieties consisted of three levels, ie, WT-MT as control (G1), iaa9-3 (G2), and iaa9-5 (G3). The factor of PEG-induced drought stress also consisted of four levels, ie, 0% PEG as control (PEG0), 5% PEG (PEG5), 10% PEG (PEG10), and 15% PEG (PEG15). The results observed 12 weeks after culture showed the variations of the morpho-physiological response of WT-MT and mutant genotypes to PEG-induced in vitro drought stress. The WT-MT showed a higher reduction in plantlet height, root number, and root length than mutants under severe drought conditions. The plantlet fresh and dry weight of iaa9-3and iaa9-5were higher than its WT-MT under no drought conditions. The total chlorophyll content of WT-MT was lower than iaa9-5due to the significant gain of chlorophyll-b on that mutant rather than its WT-MT. However, the analysis of principal components and correlation revealed the reduction of morphological size and leaf pigment content in response to drought stress, irrespective of genotype factor. These results suggest that in vitro selection techniques using PEG is useful for the initial screening of drought-tolerant tomato.