[Study of morphological and symbiotic traits during the ontogeny of supernodular and hypernodular pea mutants].

Morphological (plant height and vegetative biomass amount) and symbiotic (number of nodules and nitrogenase activity) traits of six symbiotic pea mutants and the original cultivar Rondo were studied at different vegetation periods. Of the mutants studied, one (K10a) was supemodular and the remaining five (K1a, K2a, K5a, K7a, and K27a) were hypemodular. Essential distinctions in the absolute values and time course of the changes in individual morphological and symbiotic traits of different pea mutants were demonstrated. The supemodular type is inferior to the original cultivar in plant height and production of vegetative biomass, but exceeds it in nodulation and nitrogen fixation. The hypemodular mutants either surpass the original cultivar with respect to the production capacity or display similar results. The symbiotic traits-number of nodules and nitrogen fixation activity--of these mutants are higher compared with the Rondo cultivar. The mutants K1a, K2a, and K27a were demonstrated to be useful in breeding pea for an increase in nitrogen fixation.

[Expression of the symbiotic nod4 pea gene against various genotypic backgrounds].

Experiments on the effect of genotypic environment on the expression of the nod4 gene, responsible for supernodulation in pea, were performed. The genotypic background was found to affect the manifestation of both major symbiosis-related traits (number of nitrogen-fixing bacterial nodules and nitrogenase activity) and productivity-related traits (stem height, seed number, and seed weight), which form the pleiotropic complex of the mutant gene. Using recurrent selection, we developed supernodulating lines significantly exceeding the original mutant line and studied them up to generations F5-F6. Of special importance is the fact that these lines showed high levels of nodulation and nitrogen fixation. The results are discussed from the viewpoint of breeding.