Symbiotic fixation of atmospheric nitrogen in legumes as a genetic and selection trait

Abstract

The results of long-term studies on the symbiogenetics and selection of leguminous cultures on the example of the Pisum sativum L. pea were summarized. Using the method of chemical and radiation mutagenesis, a collection of symbiotic mutants was created and genetically studied on different pea varieties. Two types of superand hypernodulating mutants were isolated from a large group of symbiotic mutants for selection purposes. Supernodulating mutants are recessive, while hypernodulating mutants are dominant. Hypernodulating mutants were isolated among the studied pea varieties (mainly among ancient varieties). However, the varieties differed sharply from each other by the degree of hypernodulation. The forms marked by recessive supernodulation genes (nod4) and dominant hypernodulation genes (Nod5) were selected for the development of the methods of selection for increasing nitrogen fixation. The recurrent method of using symbiotic mutants in the pea selection for increasing nitrogen fixation was developed. The best results were obtained when combining two sym-genes (the Nod5 dominant hypernodulation genes and the nod4 recessive supernodulation gene) in the same pea genotype. A series of recurrent lines simultaneously marked by these two genes were created. At present, these lines are used in selection as donors for increasing the nitrogen fixation at a good productivity. In addition, these are good precursors for subsequent cultures. A large number of root and bacterial biomass with increased nitrogen content is accumulated in the soil after harvesting such forms. This nitrogen is prolonged for several years, while mineral nitrogen is rapidly washed out by rain and snow. The endemic pea forms originating from different regions can be successfully used as the initial material in the selection for increasing the nitrogen fixation. The best results were obtained in the experiments with forms from Egypt and Syria. Estimation by nodulation and the activity of nitrogen fixation was carried out for seven varieties of three promising pea lines selected at the Siberian Research Institute of Plant Growing and Selection.