HEXAPLOID ALFALFA, MEDICAGO SATIVA L.: ORIGIN, FERTILITY AND CYTOLOGY

Abstract

Two spontaneously occurring hexaploids, 6-1 and 6-2, 2n = 6x = 48, were discovered among tetraploid plants of the variety 'Saranac'. They were selfed, crossed with each other and with diploid (2x), triploid (3x), and tetraploid (4x) alfalfa. Self and cross progeny of 6-1 and 6-2 were all hexaploid; 2x-6x crosses produced a plant with 32 chromosomes; 3x-6x crosses produced hexaploids probably due to unreduced triploid gametes; and 4x-6x crosses produced plants with 32, 34, 35, 36, 37, 38, 40, and 56 chromosomes. Thus many additional hexaploids, two pentaploids, 2n = 40, and a septaploid, 2n = 56, were obtained.Chromosome associations were mostly bivalents, with a low frequency of univalents and quadrivalents in hexaploids with six sativa genomes or five sativa and one falcata genome. Pollen stainability was in excess of 95%, ovule number averaged 12 per carpel, and several grams of hexaploid seed were produced from hand crosses. Five different hexaploid synthetics with narrow and wide genetic bases were produced for future seed increase and field testing. The value of hexaploids in breeding and cytogenetic research was discussed.