CARBON (13C) AND NITROGEN (15N) TRANSLOCATION IN A MAIZE-STRIGA HERMONTHICA ASSOCIATION

The translocation of C and N in a maize-Striga hermonthica association was investigated at three rates of nitrogen application in a glasshouse experiment. The objectives were to measure the transfer of C and N from maize to S. hermonthica and to determine whether the amount of N in the growing medium affected the proportions of C and N transferred. Young plants of maize were labelled in a 13CO2 atmosphere and leaf tips were immersed in (15NH4)2SO4 solution. The Striga×N interaction was not significant for any of the responses measured. Total dry matter for infected maize was significantly smaller than for uninfected maize from 43 to 99 days after planting, but N application increased total dry matter at all sampling times. Infected maize plants partitioned 39–45% of their total dry matter to the roots compared with 28–31% for uninfected maize. Dry matter of S. hermonthica was not affected by the rate of N applied. S. hermonthica derived 100% of its carbon from maize before emergence, decreasing to 22–59% thereafter; the corresponding values for nitrogen were up to 59% pre-emergence and up to 100% after emergence. The relative proportions of nitrogen depleted from the host (up to 10%) were greater than those of carbon (maximum 1.2%) at all times of sampling after emergence of the parasite. The results show that the parasite was more dependent on the host for nitrogen than for carbon.