Primary root and lateral root development in guar seedlings

Abstract

Primary root and lateral root length of 7- and 10-day-old seedlings of three guar ( Cyamopsis tetragonoloba (L.) Taub.) seed sources were evaluated under several temperature and pre-germination seed treatment regimes to determine optimum conditions for root development. Seeds were germinated and seedlings grown in polyethylene growth pouches at constant temperatures in the dark. Primary root length, lateral root length and number of lateral roots were evaluated for 7 consecutive days after planting (DAP) in Experiment 1, and for 7 days with a final measurement at day 10 (DAP) in Experiment 2. In Experiment 1, seed sources differed significantly in primary root length, lateral root length, and number of lateral roots when grown at 30°C for 7 days. Mean primary root lengths were greatest (11.0 cm) for untreated seed grown in distilled water. Hot-water treated seed grown in distilled water produced the greatest number of lateral roots and total lateral root length. Hoagland's solution, in combination with either hot-water treated, sodium hypochlorite treated or no seed treatment, adversely affected primary root growth but increased branching intensity. Primary roots of all strains had four distinct xylem bundles. In Experiment 2 primary root length, number of laterals and lateral root length were greatest at 30–35°C. Branching intensity was greatest at 35°C. Primary root length was significantly correlated with number of laterals and lateral root length in all three seed sources and significantly correlated with branching intensity in the cultivar “Lewis”. The influence of the environment on mature seed during the pre-harvest period and its potential for masking genetic differences in primary root and lateral root development is discussed.