GENETIC-VARIATION FOR RESISTANCE TO LOW-TEMPERATURE PHOTOINHIBITION OF PHOTOSYNTHESIS IN MAIZE (ZEA-MAYS L)

Sixty-seven inbred lines of maize were evaluated for resistance to low -temperature photoinhibition of photosynthesis, using a pulse-modulate d chlorophyll fluorescence technique. The evaluation procedure was bas ed on leaf discs, which were exposed to a high irradiance (1000 mu mol /m(2)/s) at 7 degrees C. The efficiency of open PSII reaction centres as a reflection of overall photosynthesis was measured before and afte r a photoinhibition-inducing treatment. Exposure of leaf discs to phot oinhibitory conditions for 2, 4, and 8 hours resulted in an efficiency reduction of 30, 53 and 83%, respectively. Testing of inbred lines sh owed large differences for photoinhibition susceptibility. The differe nce in photosynthetic efficiency between the most extreme lines after a treatment of eight hours was 39%. Resistance to photoinhibition was shown to be relevant under cool field conditions. It proved to be a tr ait strongly amenable to selection.