The importance of light intensity for pollen tube growth and embryo survival in wheat x maize crosses

The success of Triticum aestivum x Zea mays crosses, used to produce wheal doubled haploids, is influenced by light intensity. To examine the basis for this response, pollen tube growth, embryo survival and indicators of photosynthetic rate were measured in two wheat cultivars ('Karamu' and 'Kotuku') crossed with maize at two irradiance levels (250 or 750 mu mol m(-2) s(-1), PAR). pollen tube growth was significantly affected by light intensity in 'Karamu' plants but not in 'Kotuku' plants, despite both cultivars being pollinated by the same maize source. The percentage of pollen tubes reaching the cavity between the ovarian wall and integuments, or in the micropyle of 'Karamu' plants at high light intensity (65%) was nearly three-times greater than that at low light intensity (22%). Thus. either low light intensity can affect the maternal wheat plant in a way that inhibits pollen tube growth and/or high light intensity may promote pollen tube growth in 'Karamu' plants. Significant differences in rates of electron transport in plants grown at the two light intensities indicated that the rate of photosynthesis may also have an effect on pollen tube growth. These results have importance for improving the efficiency of wheat x maize crosses and other wide cereal crosses. (C) 2001 Annals of Botany Company.