SOME OBSERVATIONS ON THE INFLUENCE OF TEMPERATURE ON THE GERMINATION OF POLLEN ON EXCISED NASHI (PYRUS-SEROTINA REHDER VAR CULTA REHDER) FLOWERS

Pollen germination on excised nashi (Pyrus serotina Rehder var. culta Rehder) styles was compared at six constant temperatures (4, 17, 12,16, 20, and 25 degrees C). After 24 h pollen germination was highest at 12 degrees C for the cultivar 'Shinsui'. For the cultivars 'Hosui','Kosui', 'Nijisseiki', and 'Shinseiki', the optimum temperature for pollen germination was between 16 and 20 degrees C. The (green-skinned) cultivars 'Nijisseiki' and 'Shinseiki' showed higher levels of pollen germination and a higher optimum temperature than the (russeted) cultivars-'Hosui', 'Kosui', and 'Shinsui'. Field temperatures over the flowering period were lower than these in vitro optima, and so may have contributed to the varying levels of seed set observed.