GENOME SIZE AND ENVIRONMENTAL-FACTORS IN THE GENUS PINUS

Nuclear 1C DNA content in haploid megagametophyte tissue of 18 North A merican and one exotic Pinus species was determined using scanning mic rospectrophotometry. The nuclear DNA content in root meristematic cell s of Zea mays L. ssp. mays, inbred line Va35 (4C = 10.31 pg) was used as a standard. DNA content measured by microspectrophotometry was veri fied using laser flow cytometry with two additional standards, Hordeum vulgare cv. Sultan (2C = 11. 12 pg) and P. eldarica (2C = 47.30 pg). DNA values obtained by both methods were significantly correlated (r = 0.987). The 1C nuclear DNA content ranged from 21 pg to 31 pg. The ra tio of DNA content in embryo tissue of P. eldarica to that in megagame tophyte tissue was 1.72 by scanning microspectrophotometry and 1.74 by laser flow cytometry. To date, this is the most comprehensive data se t available for North American Pinus species. Relationships between ge nome size of 18 North American Pinus species and climatic factors and indices of growth were investigated using regression and correlation a nalyses. Positive correlations were observed between nuclear DNA conte nt and growth indices, minimum seed-bearing age, and seed dimensions. Strong negative correlations were observed between nuclear DNA content and two climatic factors, the lowest mean annual and monthly precipit ation (excluding January) and the highest mean monthly spring air temp erature. These correlations suggest that the large genome size and its variation in Pinus are adapted responses to the habitats of these spe cies.