Chlorophyll Stability Index (CSI)
Chlorophyll Stability Index (CSI) is an indicator of the stress tolerance capacity of plants and is a measure of integrity of membrane [129]. Mohan et al. (2000) reported that high CSI value means that the stress did not have much effect on chlorophyll content of plants. A higher CSI helps the plants to withstand stress through better availability of chlorophyll, leading to increased photosynthetic rate, more dry matter production and higher productivity this indicates how well the chlorophyll can perform under stress. CSI has been used as an indicator of stress tolerance in rice as reported by [73] and [192]. Drought tolerant verieties had higher Chlorophyll Stability [158; 10; 132]. The CSI was positively and significantly correlated with root thickness and proline under stress (190). Contradictory results were also reported that the Chlorophyll Stability Index was found to be correlated to drought tolerance in rice by Thangaraj and Sivasubramanian [1990]. Meenakumari et al. [2004] reported that chlorophyll content as well as Chlorophyll stability index decreased during drought environments. Konwar [2009] stated that the Chlorophyll stability index decreased with increasing water stress in rice. The genotypes showed higher Chlorophyll stability index under water stress possessed higher glutathione reductase and peroxidase activity.