ARTIFICIAL SELECTION AND HERITABILITY OF OZONE RESISTANCE IN 2 POPULATIONS OF PLANTAGO-MAJOR

Geographically separated populations of Plantago major L. differ in oz one resistance, and this is correlated with the exposure to ozone at t he location of each population. In addition, two populations of P. maj or have been demonstrated to show an increase in ozone resistance afte r summers when ozone concentrations were high. However, if evolution o f ozone resistance has occurred in the field there must be appropriate heritable genetic variation and this must be demonstrated. In the pre sent study, artificial selection for ozone resistance and sensitivity was imposed on a resistant ('Lullington Heath') and sensitive ('Bush') population of P. major. Artificial selection is an efficient means of demonstrating additive genetic variance for a character. Selection wa s based on 2 wk growth in ozone (70 nl O-3 l(-1) for 7 h d(-1)), and s elected lines were tested for ozone resistance under both short and lo ng term ozone exposures. Changes in ozone resistance were demonstrated for each population. On the basis of a 2-wk screening test, selection from the initially sensitive Bush population led to a line that was s ignificantly more resistant to ozone, but it was not possible to selec t a line with greater sensitivity than the original population. Conver sely, selection from the initially resistant Lullington Heath populati on led to a line with increased sensitivity but not to a line with inc reased resistance. Differences in ozone resistance between the selecte d lines were maintained over the long term and were reflected in growt h and seed production at the final harvest. Net assimilation rate, sto matal conductance and leaf pigments were measured. In both populations the lines selected for sensitivity showed a greater effect of ozone o n net assimilation rate. Ozone had a minor effect on chlorophyll conte nt in the Lullington Heath sensitive line but tended to increase carot enoid concentrations. However, this effect on carotenoids was not rela ted to ozone resistance. The experiment demonstrated that ozone resist ance in P. major is heritable. The response to selection reported here supports previous evidence from field collections of a rapid evolutio n of ozone resistance.