Grain set failure in wheat, caused by boron (B) deficiency, is associated with poorly developed pollen and anthers. This paper presents results of a study of the effect of B on pollen viability when it was supplied "internally" through the roots and externally in an agar medium for in vitro germination.

There was no major effect of B supply to wheat plants on the number of pollen anther^-1 or the percentage of pollen with positive reaction to iodine. Pollen germination in the medium was, however, responsive to both internal and external B supply. When B was not added to the medium, germination was poor, regardless of the level of B supplied to the plant, in both a B deficiency sensitive (SW41) and a B deficiency tolerant (Sonora 64) genotypes. The percentage of germinated pollen and length of the pollen tube increased with increasing medium B. With 20–100 mg H₃BO₃ L^-1 in the medium, the percentage of germinated pollen and length of the pollen tube responded positively to increasing B supply to the plant.

No difference was found between sensitive and tolerant genotypes in the effect of B on their pollen viability. On the other hand, without added B in the nutrient solution applied to the plant, grain set was depressed in the B deficiency sensitive SW41 and not in the B deficiency tolerant Sonora 64. A difference in B supply to the germinating pollen in the stigma and style is one possible explanation for this variation in the response to B among wheat genotypes.