GROWTH AND DEVELOPMENT OF YOUNG ROOTS OF BARLEY (HORDEUM-VULGARE L) GENOTYPES

Barley (Hordeum vulgare L.) genotypes from countries with a Mediterran ean climate were grown in temperature-controlled glasshouses in nutrie nt solution to determine whether the co-ordination of root branching a nd growth found by other workers applied to a wider range of up to 14 genotypes. There was substantial variation in the number of seminal ax es produced by the genotypes, ranging from about seven for Hoshimasari and Swanneck to about four for Gerbel 'B'. The number of nodal axes w as linearly related to the number of leaves and typically between one and two mainstem leaves were required before nodal axes appeared. Ther e were small genotypic differences in the number of axes produced per leaf with values ranging from 1.5 to 2.3. The production and growth of lateral roots were coordinated so that the mean length of laterals ge nerally increased with time. Landraces (Arabic abiad and Arabic aswad) produced more lateral roots with a faster rate of extension compared with other genotypes. The length and number of primary and secondary l ateral roots were related linearly, but no genotypic differences in th is relation were evident. Length of primary lateral roots increased mo re rapidly than that of secondary lateral roots throughout the three t o five leaf stage. The ratio of root weight to total plant weight decr eased with time but there were only small differences within this rang e of genotypes.