Selection for Seedling Cold Tolerance in Safflower with Modified Controlled Environment Chambers¹

Abstract

The unpredictable occurrence of cold stress in the southwestern U. S. makes selection in the field for seedling cold tolerance in safflower (Carthamus sp.) a sporadic effort. Use of a conventional cold chamber has not been practical for us because temperatures within it differed by as much as 3 C among positions only 30 cm apart, and they changed among subsequent tests. Installation of a turntable made it possible to subject seedlings growing in pots placed within the same radius (circle) to a similar cold stress. We were then able to differentiate known genotypes for degree of seedling cold tolerance with as few as 10 plants of each. This degree of precision, along with controlled hardening temperatures for as little as 1 week before the cold stress, gave considerable flexibility in selection for seedling cold tolerance. In a fourway cross in which one parent was a cold tolerant selection out of the wild species, Carthamus flavescens Spreng, it was possible to program a cold stress (_16 C for hours) in which none of the most cold tolerant domestic parent, about 50% of the wild parent, and 0.5% of the seedlings in the segregating population survived. With controlled hardening temperatures and programmed cold stresses, time involved in breeding and genetic studies of seedling cold tolerance in safflower need be limited only to the time required for growing the filial generations.

Autumn growth and its relationship to winter survival in diverse safflower germplasm

“…Cultivars N-8 and Frio have been reported to have considerably more cold tolerance than other cultivars (Gilbert and Lorance 1966;Zimmerman and Buck 1977) but they had generally poor winter survival in the environments tested (Table 4). These cultivars are both traditionally spring-sown or planted in the milder winter conditions of the southwest USA and may indeed have superior cold tolerance under those conditions.…”

“…During the rosette stage, safflower is relatively resistant to cold temperatures (YazdiSamadi and Zali, 1979). The duration of this stage is not only dependent on environment but on heritable genetic traits (Zimmerman 1976;Zimmerman and Buck 1977). Ghanavati and Knowles (1977) found high cold tolerance in plants with a long rosette period collected from northwest Iran.…”

“…Early crop development of winter safflower would occur when temperatures are lower and moisture more plentiful than for spring sown safflower (Yazdi-Samadi and Zali 1979). Safflower, as a dicot, is potentially an excellent rotation crop with winter annual monocots such as wheat in semiarid regions (Zimmerman and Buck 1977).…”

Theoretical hybridization potential of transgenic safflower (Carthamus tinctorius L.) with weedy relatives in the New World

“…Seeds of C. persicus were able to withstand temperatures of -16°C for 4 h with about 50% of the seeds remaining viable. Crosses with C. tinctorius and C. persicus produced hybrid plants with cold tolerance similar to the latter species (Zimmerman and Buck 1977). Gupta and Murty (1986) reported seeds of C. oxyacanthus to be resistant to low and high humidity and both high and fluctuating temperatures.…”

“…Seeds of C. lanatus were unaffected by freezing at -16°C while other thistle species (not members of Carthamus) were injured. Experimental varieties of C. tinctorius have been able to withstand temperatures as low as -15°C following a hardening period (Zimmerman and Buck 1977;Knowles and Ashri 1995). Seeds of C. persicus were able to withstand temperatures of -16°C for 4 h with about 50% of the seeds remaining viable.…”