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Screening sorghum seedlings for heat tolerance using a laboratory method

Setimela, P.S., Andrews, D.J., Partridge, J., Eskridge, K.M.
European journal of agronomy 2005 v.23 no.2 pp. 103–107
coleoptiles, crop losses, crop yield, cultivars, genetic improvement, genotype, heat, heat stress, heat tolerance, heat treatment, plant establishment, planting date, screening, seedlings, soil temperature, surface temperature, tropics
High soil temperatures at planting time can seriously reduce plant populations in the semi-arid tropics where surface temperatures can exceed 50 °C leading to loss of crop yield. Seedling heat tolerance is critical for adequate crop establishment. Because field screening for emerging seedling heat tolerance is tedious, inconsistent, and seasonally limited, it is essential for genetic improvement to have effective and validated techniques to identify sources of tolerance and for evaluating breeding material. The objective of this research was to define a simple laboratory procedure for evaluating sorghum seedlings for their capacity to survive a controlled heat shock and resume growth, and to determine if there were significant differences for heat tolerance among the cultivars tested. Seven genotypes were grown between vertical transparent plexiglass plates in a growth chamber at 30 °C, exposed to direct heat shock via a water bath at 50 °C for 0, 10, 20 and 30 min and then returned to the 30 °C growth chamber. Coleoptile growth was measured at 8, 20, 32, and 44 h after the heat treatment. Heat tolerance per se was expressed by a heat tolerance index (HTI) defined as a ratio of resumed coleoptile growth after the controlled heat shock, compared to normal growth. Ten minutes heat exposure-separated genotypes better across the time interval for coleoptile recovery compared to other exposures. Genotype × exposure interaction for HTI was significant at P < 0.001 and < 0.05 for 32 and 44 h intervals, respectively. The technique for heat screening at 50 °C, 10 min of exposure and measuring coleoptile length after 32 h of recovery was the best treatment combination. This method is relatively simple and inexpensive and can be used to screen a large number of genotypes.