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.
Wild parents of safflower (Carthamus palaestinus L.) had abundant pappus and small seed, whereas domestic parents had little or no pappus and large seed. Low variances of nonsegregating populations suggested that environmental effects on pappus and seed weight were not strong and that variability was largely genetic. Nonadditive gene action for seed weight and pappus was indicated by the Mather and Jinks model. Heritability estimates in the broad sense for pappus were high (above 93%); however, they ranged from 66 to 85% for seed weight. Heritability estimate in the narrow sense for pappus was 88%. Maternal effects were not observed for seed weight. At least two loci are involved in the inheritance of seed weight and pappus. Anthocyanin pigmentation and striped hull assorted independently. Correlation coefficients for seed weight with pappus were low.
By growing castorbeans, Ricinus communis L., in different environments, genotypes were obtained with both the N‐pistillate gene ƒ for female racemes and environmentally sensitive genes for interspersed‐staminate flowers. These genotypes were homozygous for the ƒ gene, but not always for the genes for interspersed‐staminate flowers. With penetrance of the genes for interspersed‐staminate flowers at a location having high summer te~nperatures, a July average of 91 F, plants were propagated by selfing or sibbing. With nonpenetrance at locations having lower summer temperatures, July averages of 75 to 83 F, F1 hybrid seed was produced without roguing. Previous methods using the ƒ gene required roguing monoecious plants from the female parent, often involving more than 50% of the plants.In test crosses, presence of interspersed‐staminate flowers was recessive to absence. There was wide variation among genotypes tested for frequency of interspersed‐staminate flowers, suggesting a polygenic system with considerable opportunity for selection.
Rosette habit is an important component in the length of the life cycle of safflower (Carthamus spp.). Rosette habit results from nonelongation of internodes. Segregating populations indicated that time of internode elongation, a measure of duration of rosette habit, was influenced by a major gene and modifier genes in C. tinctorius L. (cultivated safflower) and C. flavescens Spreng (an annual herbaceous weed, indigenous to the Middle East). All crosses showed that earliness of internode elongation had dominance, ranging from partial to over dominance. At threshold levels of expression, the frequency of rosette habit in some C. tinctorius genotypes changed with environments; however, the mean length of the first internode of these nonrosette plants was from 1/5 to 1/2 that of ‘Gila,’ which is noted for its nonrosette habit in a wide range of environments.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.