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 fo r this response, pollen tube growth, embryo survival and indicators of phot osynthetic 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 i n 'Karamu' plants but not in 'Kotuku' plants, despite both cultivars being pollinated by the same maize source. The percentage of pollen tubes reachin g the cavity between the ovarian wall and integuments, or in the micropyle of 'Karamu' plants at high light intensity (65%) was nearly three-times gre ater than that at low light intensity (22%). Thus. either low light intensi ty can affect the maternal wheat plant in a way that inhibits pollen tube g rowth 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 photosynthesi s may also have an effect on pollen tube growth. These results have importa nce for improving the efficiency of wheat x maize crosses and other wide ce real crosses. (C) 2001 Annals of Botany Company.