GENOME SIZE AND NUMERICAL POLYMORPHISM FOR THE B-CHROMOSOME IN RACES OF MAIZE (ZEA-MAYS SSP. MAYS, POACEAE)

Twenty-one native populations (1120 individuals) of maize from Norther n Argentina were studied. These populations, which belong to 13 native races, were cultivated at different altitudes (80-3620 m). Nineteen o f the populations analyzed showed B chromosome (Bs) numerical polymorp hism. The frequency of individuals with Bs varied from 0 to 94%. The n umber of Bs per plant varied from 0 to 8 Bs. with the predominant dose s being 0, 1, 2 and 3. Those populations with varying number of Bs sho wed a positive and statistically significant correlation of mean numbe r of Bs with altitude. The DNA content, in plants without Bs (A-DNA)(2 n = 20), of 17 populations of the 21 studied was determined. A 36% var iation (5.0-6.8 pg) in A-DNA content was found. A, significant negativ e correlation between A-DNA content and altitude of cultivation and be tween A-DNA content and mean number of Bs was found. This indicates th at there is a close interrelationship between the DNA content of A chr omosomes and doses of Bs. These results suggest that there is a maximu m limit to the mass of nuclear DNA so that Bs are tolerated as long as this maximum limit is not exceeded.