CONTAMINATION OF WHITE CLOVER SEED CROPS BY BURIED SEEDS

Abstract

Thirty five certified seed lines of 'Grasslands Pitau' white clover produced under OECD rules showed marked variations in growth and morphological characteristics according to their region of origin. Of lines grown in Oamaru district, South Canterbury, 90% were significantly different from a Pitau breeders (pre-basic) line in winter growth scores, leaf size and picric acid scores. 90% of lines grown in Marlborough were similar to a Pitau breeders line. Buried white clover seed counts were 260/m' (2 kg/ha) in Marlborough and 1060/m (7.5 kg/ha) in Oamaru. Plants grown from buried seed collected in Canterbury generally had smaller leaves, less winter growth and lower picric acid scores than Pitau. The additional possibility that natural selection of genotypes occurred because some crops of Pitau have been grown under climates and/or managements to which it is not adapted, is also discussed. Preliminary studies of 43 commercial lines of 15 cultivars from 4 countries grown outside New Zealand indicated that 3540% showed significant differences in winter growth and leaf size between lines of the same cultivar. New Zealand grown commercial lines of Huia obtained overseas showed good uniformity. It appears that there is a world-wide problem of genetic contamination in white clover cultivars. High buried seed loads are a potential long term source of contamination which is being exaggerated by the increasing numbers of cultivars. New Zealand has already moved to implement tighter certification standards than those recommended by OECD. Keywords: Trifolium repens, 'Grasslands Pitau', buried seed, seed certification, OECD, genetic contamination.