Correlation in the tolerance to ozone between sporophytes and male gametophytes of several fruit and nut tree species (Rosaceae)

We analyzed relative sensitivities to ozone partial pressure for male gametophytes (pollen and pollen tubes) of five tree-crop species in the family Rosaceae (almond, apple, apricot, nectarine/peach, pear) and of four cultivars of almond. Relative sensitivities to ozone partial pressure were previously described using field-based, whole-plant, physiological measurements for the sporophytes of each of the species and cultivars used in this study. Our objective was to determine the extent of correlation between sporophyte and gametophyte responses to ozone among and within these tree species. If the relative sensitivities prove to be similar for the two generations, two research strategies become possible for breeders interested in developing new cultivars with improved tolerance to atmospheric ozone: First, because screening large numbers of sporophytes for their responses to ozone partial pressure is a formidable task, exploiting the much more easily manipulated male gametophyte generation for large-scale screening of individuals for ozone tolerance could greatly facilitate identification and selection of tolerant genotypes. Second, it opens the possibility of applying selection pressure to the gametophyte generation (as during pollen germination or pollen tube growth) to favor production of ozonetolerant progeny. Results indicate that, among and within species, relative responses of pollen tube growth to ozone partial pressure are highly correlated with that of the sporophytes. Pollen germination was inhibited by ozone treatments for all but one species (pear), but differences among and within species were neither significant nor (with the exception of pear) did they correlate with relative sporophyte sensitivities.