Foliar application of boron to almond trees affects pollen quality

The effect of boron (B) on in vivo and in vitro development of almond [Prun us dulcis (Mill.) D,A. Webb (syn, P.amygdalus Batsch)] pollen and pollen tu bes and the resultant effect on fruit set was studied in mature trees. The cultivars Mono (pistil donor) and Butte (pollinizer) in an orchard with low soil a in Fresno, California were sprayed with a at 0, 0.8, 1.7, or 2.5 kg .ha(-1) during Fall 1993. Pollen viability as indicated by the fluorescein diacetate method (FDA) was >85% and was not affected by field-applied B, ho wever, in vivo pollen germination and tube growth were enhanced by foliar-a pplied B, More effect of applied B on in vivo growth appeared as pollen tub es progressed toward the ovary. For in vitro germination, foliar-applied B reduced bursting of tubes, and addition of B to the culture media significa ntly increased pollen germination and pollen tube growth.