COLCHICINE-MEDIATED CHROMOSOME DOUBLING DURING ANTHER CULTURE OF MAIZE (ZEA-MAYS L)

Efficient methods of chromosome doubling are critical for the producti on of microspore-derived, doubled-haploid (= DH) plants, especially if , as in maize anther culture, spontaneous chromosome doubling occurs i nfrequently. In the present study, colchicine (5-1000 mg/l) was added to the induction medium and maize anthers were incubated in the colchi cine-containing medium for different durations (1-7 days). In order do ubling to improve overall anther culture response, the culture cytomet er temperature was adjusted to 14 degrees C during the first 7 days. C olchicine applied at low concentration, i.e. 5 mg/l (7 days), or for s hort duration, i.e. 1-3 days (250 mg/l), Introduction showed beneficia l effects on the formation of embryo-like structures (= ES) and thus l ed to increased plant production, but was comparatively ineffective re garding chromosome doubling. Optimal doubling effects were observed wh en anthers had been exposed to culture medium containing 250 and 1000 mg/l of colchicine (7 days); in these treatments the doubling index (= DI), defined as the quotient of the number of DH plants and the numbe r of totally regenerated plants in a specific treatment, rose to 0.56 and 0.53, respectively, compared to 0.20 in the untreated control. How ever, colchicine administered at concentrations higher than 250 mg/l s eemed to be detrimental to general plant production; thus, in spite of a high DI, the overall DH plant production was even lower than in the control treatment. Maximum DH plant production for three different ge notypes was accomplished with culture medium containing 250 mg/l of co lchicine (7 days). With the best-responding genotype (ETH-M 36) a DH p lant production of 9.9 DH plants/100 anthers was accomplished, i.e. a 7-fold increase compared to the non-treated anthers. This is the first report on efficient chromosome doubling in anther culture by subjecti ng anthers to colchicine-containing induction medium during a post-pla ting cold treatment. Chromosome doubling as described here becomes an integral part of the maize anther culture protocol and thus represents a rapid and economical way to produce DH plants.