FLORAL NECTAR SECRETION AND PLOIDY IN BRASSICA-RAPA AND BRASSICA-NAPUS (BRASSICACEAE) .1. NECTARY SIZE AND NECTAR CARBOHYDRATE PRODUCTION AND COMPOSITION

Haploid (n = 10), diploid (2n = 20) and tetraploid (4n = 40) lines of Brassica rapa (syn campestris), and a line of allotetraploid (4n = 38) B napus, were examined to determine whether ploidy can influence nect ar production. Flowers of all lines developed functional nectaries. Ov erall, nectar carbohydrates consisted almost exclusively of glucose an d fructose, present in quantities slightly in favour of the former. Su crose was detected in only 15% of samples, usually in trace amounts. F or all levels of ploidy, 95% of total nectar carbohydrate per flower w as expelled from the lateral (inner) pair of glands. These glands were directly supplied with phloem alone, whereas the median (outer) gland s, which were poor nectar yielders, usually did not receive any vascul ar supply. Haploids only produced 30% as much nectar carbohydrate as 2 n and 4n lines of B rapa, which in turn exuded only 44-50% of the aver age quantity of nectar carbohydrate released by B napus. A linear regr ession (r = 0.803) of mean lateral-nectary volume on average total nec tar-carbohydrate per flower was determined for all plants of B rapa, b ut this was modified (r = 0.445) when data for B napus were included. In all lines, opportunity exists for selection for high nectar-carbohy drate production. Plants yielding the most floral nectar carbohydrate had high frequencies (80-95%) of lateral glands that were symmetrical and of uniform size within a flower.