Responses of Asparagus officinalis pollen to the culture filtrate of Fusarium oxysporum f. sp. asparagi

Abstract

Fusarium crown and root rot in asparagus is the main cause of crop decline in the world. Because chemical treatments are not effective, disease control efforts should focus on the development of genetically resistant cultivars. This is a long process when traditional methods are used, because of the complexity of this pathosystem. In several species, the application of selective agents to gametophytes has been found to increase the efficiency of selection; however, there is no information on either pollen response to selective agents or gametophytic selection in asparagus. Therefore, and as a preliminary study, the effect of a toxic culture filtrate of Fusarium oxysporum f. sp. asparagi on in vitro and in vivo pollen germination was evaluated on two susceptible pistillate genotypes and one tolerant and one susceptible staminate genotypes. In vitro, the toxic culture filtrate did not affect either pollen germination or tube growth of the tolerant genotype, but diminished the percentage of pollen germination and increased the percentage of germinated grains with long tubes of the susceptible genotype with respect to the control. Although no useful selection for resistance was achieved, these results suggest that the percentage of pollen germination in a toxic medium might be correlated with the plant response to the pathogen. In vivo, the toxic culture filtrate negatively affected pollen germination and tube growth in all combinations; furthermore, it induced several abnormalities in pollen tube growth, that varied with the genotypic combination. The correlation between pollen reaction in vivo and the plant response was not studied, but it was observed that pollen was not insensitive to the culture filtrate of the fungus in vivo. These results suggest that the feasibility of application of gametophytic selection in asparagus merits further investigation.