Elsevier

Field Crops Research

Volume 85, Issue 1, 8 January 2004, Pages 21-30
Field Crops Research

Analysis of cold tolerance in sorghum under controlled environment conditions

https://doi.org/10.1016/S0378-4290(03)00125-4Get rights and content

Abstract

Grain sorghum (Sorghum bicolor (L.) Moench) originated in the semi-arid tropics and is generally sensitive to low-temperature stress. Early planting and use of minimum tillage necessitate the development of sorghum hybrids with early season cold tolerance. Genetic variability for cold tolerance exists in sorghum and has been detected by early planting under field conditions and by analysis of seeds and plants under growth chamber conditions. There is limited information on the efficiency of evaluating cold tolerance under growth chamber conditions and the relationship with field performance. The objectives of this study were to quantify the variability of cold tolerance in commercial hybrid seed lots under growth chamber conditions, to exam different components of cold tolerance and their relationships, and to evaluate the consistency of lab test results with data from field tests. Thirty commercial hybrid seed lots were evaluated by growing the entries under 15/10, 13/10, 11/8, and 25/20 °C day/night temperature in a 13/11 h cycle in a growth chamber. Traits measured included emergence percentage, emergence index, shoot and root dry weight, seedling height, and vigor score. Significant genotypic differences were detected for all traits. Correlations among the traits were significant and favorable, which confirmed that simultaneous improvement of these traits should be possible. The same seed lots were also evaluated in a soil-free plate-based assay, in which percent germination, and shoot and root elongation of the seed lots grown in dark at 15 °C were measured. Results from both laboratory tests, soil-based and plate-based, were correlated with data collected in a field study, which was conducted to evaluate cold tolerance of commercial sorghum hybrids at Manhattan, Hesston, Bellville, and Garden City, KS in 1998 and 1999. Single-trait correlations between lab and field studies were significant. Differentiation based on rank-summation index of common traits, rank-summation index correlations and the overlap of best entries, further provided strong support of the efficiency of predicting and identifying elite hybrids using growth chamber assays.

Introduction

Sorghum originated in the semi-arid tropics and generally is sensitive to low-temperature stress in the range of 20 °C to about 0 °C (Peacock, 1982). Sorghum suffers chilling injury when subjected to nonfreezing temperatures below 10–15 °C (Peacock, 1982). Low-temperature stress at planting time usually results in poor seedling establishment of sorghum because of slow emergence rate, reduced emergence percentage, and reduced growth rate after emergence (Pinthus and Rosenblum, 1961, Singh, 1985).

Early planting, use of minimum tillage, and attempts to expand sorghum into higher elevations and more temperate latitudes necessitate the identification of genotypes that are tolerant to low temperatures during seed germination, seedling emergence, and early plant growth (Singh, 1985, Bacon et al., 1986). In maize (Zea mays L.), much effort has been devoted to improving seedling cold tolerance and numerous studies have been reported (Mock and Eberhart, 1972, Mock and Bakri, 1976, McConnell and Gardner, 1979a, Menkir and Larter, 1985). Progress made in cold tolerance research partially explained a broader range of adaptation for maize. Such parallel improvement of cold tolerance in sorghum is needed (Bacon et al., 1986).

Although large numbers of cultivars or advanced breeding lines can be evaluated for cold tolerance under field conditions by early spring planting, unpredictable climate conditions from year to year make field selection unreliable (McConnell and Gardner, 1979a, Haskell and Singleton, 1949). The presence of genotype×environment interactions also complicates field evaluation for cold tolerance, and proper characterization requires multi-environment testing (Mock and Eberhart, 1972, Mock and McNeill, 1979, McConnell and Gardner, 1979a). A growth chamber assay could substitute for early field sowings as a controlled selection method or at least as a preliminary test to discriminate weak from vigorous lines before spring planting (Pinnell, 1949). Few studies, however, have been done to evaluate the usefulness of growth chamber assays for quantifying cold tolerance in sorghum.

Genetic variability for cold tolerance exists in sorghum and has been detected both by early planting in the field and under controlled temperature conditions (Pinthus and Rosenblum, 1961, Stickler et al., 1962, Thomas and Miller, 1979, Miller, 1982, Brar and Stewart, 1994). Empirically, cold tolerance in sorghum was measured by different components such as germination, emergence, and seedling growth under low-temperature stress (Soujeole and Miller, 1984). Mesocotyl elongation was also suggested as an indicator of cold tolerance in sorghum (Maiti, 1996). Little research in sorghum, however, has been reported in simultaneous evaluation of cold tolerance during germination, emergence, and early seedling growth under low-temperature stress.

The objectives of this study were to quantify the variability of cold tolerance in commercial hybrid seed lots under growth chamber conditions, to examine different components of cold tolerance and their relationships, and to evaluate the consistency of laboratory results with data from field tests.

Section snippets

Soil-based assay

Thirty commercial grain sorghum hybrids with uniform seed quality (>90% germination potential at 25 °C) were evaluated for cold tolerance in growth chamber assays at four temperature regimes, 15/10, 13/10, 11/8, and 25/20 °C, using a 13/11 h day/night cycle. Low-temperature regimes were chosen for this study based on preliminary testing. Seed lots for this assay were the same as those used in field studies. Relative humidity and irradiance were controlled as 90–95% and 350 μmol m−2 s−1, respectively.

Results

Combined analysis of the three low-temperature soil-based experiments indicated that the temperature effect was significant for emergence index, seedling height, and shoot dry weight (Table 1). The lack of significant effect of temperature on emergence and root dry weight were partly caused by the relatively large effects of replication within run by temperature as denoted by term Error (a) in Table 1. The relative narrow range of temperature regimes (15/10, 13/10, 11/8 °C) used in this study

Discussion

The absence of entry by temperature interactions indicated that the seed lots evaluated in the soil-based assay performed similarly under the three cold-temperature stress conditions. These results are consistent with reports in maize. Eagles (1982) tested emergence of four maize inbreds and their 12 F1 hybrids under 11/11, 15/10, and 15/5 °C and concluded that genotype×temperature interactions were not significant. Pesev (1970) also described a similar reaction: the tolerance rankings of maize

Conclusions

Significant variation of cold tolerance existed in commercial sorghum hybrid seed lots studied under controlled low temperature. Cold-tolerance traits measured under controlled low-temperature conditions were correlated significantly, indicating that simultaneous improvement of these components could be captured in new hybrid cultivars. Significant correlations among traits measured in laboratory and field assays for cold tolerance indicated that a soil-based laboratory assay could be used as

Acknowledgements

Thanks to the Director of the Kansas Agricultural Experiment Station, Kansas State University, Manhattan, for approving the publication of this paper.

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