Resistance of wild emmer wheat to stem rust: Ecological,pathological and allozyme associations

Summary Seedling resistance to wheat stem rust was determined in populations of wild emmer wheat, Triticum dicoccoides, and characterized by means of ecological factors and allozyme genotypes. Reactions to wheat stem rust were studied in 102 single plant accessions of T. dicoccoides from ten populations by inoculation with Puccinia graminis tritici race 14, isolate GSR-739. Six populations displayed different degrees of response polymorphism with reactions ranging from high resistance to complete susceptibility, whereas four populations contained only susceptible plants. In some of the accession, unexplained intrasib variation in resistance and intraplant variation of infection-types were found. Resistance to stem rust was negatively correlated with two ecological factors, altitude and number of Sharav (hot-dry) days which are unfavorable to disease development. Variation in stem rust response was shown to exist in ecogeographic regions where climatic variables enhanced the development of the fungus, conceivably maintained by natural selection. Likewise, allozyme genotypes, single or in multiple loci combinations, appeared to be associated with resistance or susceptibility to rust. Such association need to be verified by genetic studies in order to become established as useful markers.     

Genetic variation in seine escapability of the common carp

During the years 1970, 1971 and 1972, 26 genetically diverse groups of common carp were tested in communal ponds, i.e., all the tested groups were co-stocked into the same ponds. These groups included inbred and crossbred domesticated European carp, one representative of the Chinese Big-Belly race, and several hybrids between the two races. The results led to the following conclusions concerning the genetics of seine escapability. (1) The Chinese race is much more adept at escaping seines than the European race. (2) The hybrids between the two races are intermediate with incomplete dominance of the higher escapability of the Chinese race. (3) Genetic variation was found within the European race with a strong dominance, or heterosis, of higher escapability. (4) Body weight as well as growth capacity were not associated with seine escapability. The absence of correlation between growth capacity and seine escapability contradicts earlier results that suggested a strong genetic correlation between the two characters.     

Failure to respond to endogenous or exogenous melatonin may cause nonphotoresponsiveness in Harlan Sprague Dawley rats

Background  

Responsiveness to changing photoperiods from summer to winter seasons is an important but variable physiological trait in most temperate-zone mammals. Variation may be due to disorders of melatonin secretion or excretion, or to differences in physiological responses to similar patterns of melatonin secretion and excretion. One potential cause of nonphotoresponsiveness is a failure to secrete or metabolize melatonin in a pattern that reflects photoperiod length.