Cold tolerance of sorghum [Sorghum bicolor (L.) Moench] during germination and early seedling growth

Abstract

Both laboratory and field experiments were conducted to investigate the level of cold tolerance in early seedling stages of 5 sorghum lines originating from China (kaoliang), 5 temperately (TE) and 5 tropically (TA) adapted sorghums. A randomized complete block design with 3 planting dates was used in the field during the spring of 1984 and variables related to emergence, seedling vigor and seedling growth rate were measured. Laboratory experiments involved determining base temperature for germination (G50) and seedling emergence in growth chambers set at 14, 17 and 26 C. Kaoliang lines grown in the field under sub-optimal temperatures displayed good emergence and seedling vigor but lower percent survival than TE lines. In the laboratory TA and kaoliang lines showed low G50 values; however, subsequent growth at low temperature of the TA group was poor. Rapid and superior increase in shoot length of most kaoliangs at low temperature conferred to them an advantage for both field and laboratory emergence. Considering the field conditions in the spring of 1984, the 17 C emergence test in potting medium would be effective for screening germplasm that would emerge well in cold field soils. Selection should be done for seedlings that exhibit high seedling height, emergence index and percent emergence. Studies pointed out that germination, emergence and seedling growth were independent in their sensitivity to sub-optimal temperature (17 C) and parameters such as G50, emergence index, maximum emergence, seedling weight and height were valuable to quantify cold tolerance at each of these stages. Cold tolerance evaluation using plantings done in the fall were not successful and there was no correlation between the parameters measured in the fall and in the spring. Low temperature laboratory tests F1 and F2 progenies of crosses between kaoliang and either TA or TE sorghum lines indicated that maternal effects were present for all characters related to emergence. Little heterosis was noticed for percent emergence and emergence index of F1 hybrids while seedling dry weight, height and leaf area exhibited high heterosis percentage. Data from a combining ability study demonstrated the consistency of 376 and 391 in transmitting positive combining ability effects. It was concluded that 376 and 391 kaoliang lines possessed a high degree of tolerance to low temperature during germination and emergence and that this characteristic could be used effectively in a breeding program to develop cold tolerant female lines to use in hybrid production...