Maize morphology and shoot CO2 assimilation after root damage by western corn rootworm larvae

Knowledge of the physiological stress mechanisms triggered by corn rootworm larval feeding damage may suggest new ways of maintaining maize (Zea mays L.) productivity in plants damaged by this important insect pest. Western corn rootworm [Diabrotica virgifera virgifera (LeConte)] larval feeding damage to maize root systems causes complex changes in leaf CO2 assimilation. The objective of our study was to further explore the relationships between plant morphology and CO2 assimilation in rootworm-damaged maize. The effects of moderate or severe root damage caused by larval feeding or by mechanical damage on root system morphology, shoot dry weight, leaf area, stomatal conductance, and CO2 assimilation were investigated in greenhouse experiments. Rootworm larval feeding, which removed about 75% of the total root system volume, or mechanical cutting treatments imposed at the V12 leaf stage, which removed about 30% of the total root system volume, bad no effect upon leaf CO2 assimilation but significantly reduced stomatal conductance when measured at the tassel development stage. During the time when larvae were damaging root systems or when specific root node axes were mechanically cut, however, leaf CO2 assimilation was less in root-damaged plants than in undamaged plants. Larval-damaged root systems had accelerated adventitious root axis growth and development in the nodes located immediately above the damaged nodes. This compensatory root growth was more pronounced under the moderate root feeding damage treatments than in the severe root damage treatments. Total leaf area and shoot CO2 assimilation were less in plants with severe larval feeding damage than in plants with moderate damage or in control plants. Thus, the severity of root damage plus the level of root compensatory growth play important roles in mediating shoot growth and CO2 assimilation responses to stress imposed by rootworm larval feeding.