Seedling vigour as a potential indicator for rapid screening of rice (Oryza sativa L.) genotypes for aluminium (Al) toxicity tolerance
Aluminium (Al) is solubilized into a phytotoxic form [Al(H2O)63+] in acid soil, which is known as Al3+. Al toxicity is the primary growth-limiting factor for plants in acid soils. Breeding of rice for enhanced Al tolerance considered to be an important approach for increasing grain yield in acid soils. In the present endeavour, we studied the effects of toxic levels of Al on vigour of rice seedlings under hydroponics and finally grouped the genotypes with varied degree of tolerance to Al toxicity based on vigour index. Good seed germination (%), high speed of germination and high vigour index indicate uniform crop stand. Germination ranged from 72-99.50%. It was significantly high for almost all genotypes (³80%) except three. The speed of germination ranged from 9.75 to 29.99 in control. Most of the genotypes showed high speed of germination (>15.00) except a few. Remarkable reduction in seedling vigour has been reported earlier under stressed environments. Low seedling vigour has been identified as the key factor responsible for poor germination and uneven seedling establishment. Based on the vigour index, nine genotypes were classified as tolerant, 19 as moderately tolerant and 12 as susceptible. Among the tolerant genotypes, UBKVR-3 showed maximum value for vigour index followed by UBKVR 19, UBKVR 9, UBKVR 8, Parijat, MTU 1075 and Radhunipagal. Most susceptible genotypes based on seedling vigour were found to be Pusa Basmati, Aiswarya and Pratikha. It is to be mentioned that till now there is no clear and distinct divisions of vigour index for classification into different levels of tolerance towards Al toxicity. In our study, we have identified distinct classes for grouping of genotypes endowed with different levels of tolerance. The values of the vigour index depend upon root length, shoot length or some other characters used for calculation of vigour index. The magnitude of the vigour index may not be useful for classification uniformly across the crops as well as genotypes within the crop. Hence, the procedure used in this work may overcome the above mentioned constraints.
Acid soil, Germination speed, Paddy, Soil acidity
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