Identification of pea genotypes with enhanced thermotolerance using temperature induction response technique (TIR)

Thermotolerance is one of the various acquired stress tolerance phenomenons observed in all living organisms, when the stress is imposed gradually. Based on this fact a very efficient technique termed as Temperature Induction Response (TIR) technique has been developed to identify and select the thermotolerant genotypes. It involves exposing seedlings and or plants to induction stress and subsequently challenging with severe temperature and selecting the surviving seedlings at the end of a recovery period. Pea seedlings exposed to induction temperature prior to challenge temperature, exhibited higher recovery growth compared to seedlings which were directly exposed to challenge temperature. Moreover, the induced seedlings accumulated higher levels of hsp18.1 and hsp70 transcripts as well as HSP104 and HSP90 proteins. A similar response was also seen when the experiment was done in mature plants as well. Using TIR technique 32 pea (Pisum sativum L. Hortense) genotypes were screened. Genetic variability for thermotolerance was seen only upon induction treatment. Further, by employing Z-analysis we have grouped genotypes into thermotolerant (Acc.623, Acc.765) and susceptible (Acc.476, Bonneville) genotypes. Amongst the tolerant lines one of the cultivars, Acc.623, showed a higher threshold temperature for thermotolerance compared to the other two. The tolerant genotype Acc.623 showed higher expression of a few HSP genes compared to the susceptible genotype Acc.476 upon temperature induction. Thus, it confirms that through TIR, thermotolerant genotypes can be identified from a large germplasm. The advantage of this technique in identifying tolerant lines from segregating populations and subsequently developing tolerant progenies has been discussed.