Influence of greenbug on root growth of resistant and susceptible barley genotypes

Abstract

The aim of this work was to compare the root system growth in greenbug ( Schizaphis graminum, Rond.) susceptible and resistant barley cultivars under infested conditions with uninfested controls. Seedlings of identical physiological age were sand-cultured and irrigated with a complete nutrient supply (Hoagland's solution) under controlled conditions. Seminal root lengths, number and length of nodal root axes, fresh and dry weights, and root volumes were measured every 2 days from the day of infestation. Aerial growth was studied by analyzing vegetative production on the main and secondary shoot apices. On the second day after infestation, growth in the infested susceptible seedlings was already inhibited in lateral branches and existing nodal axes; no further production of new nodal roots was registered; volume remained at significantly low levels compared with the controls. At the same time apical shoot inhibition occurred. Resistant seedlings showed slight delays in root and aerial growths only. Damage in the susceptible cultivar reached 18% of the total leaf area after 6 days of infestation. Greenbug inhibition may be caused by aphids that remove metabolites (including plant hormones) rather than by chlorotic damage on leaf feeding sites. However, inhibitory substances could have been increased by the aphids' presence.