The Developmental Stage During Which Boron Limitation Causes Sterility in Wheat Genotypes and the Recovery of Fertility

Abstract

Sterility in wheat in parts of the subtropics has been linked primarily with low-boron soils and its variability between years and locations with variation in the weather. This paper shows, from reciprocal transfers of plants between adequate and zero boron root media at different developmental stages, that the period during which florets are sterilised by boron insufficiency can be very short. For any ear it extends from after its flag leaf tip has emerged until shortly after the flag leaf has become fully expanded. This critical period of up to 1 week in length has already passed when the ear begins to emerge. Because tillers are sequential, the critical stage for the whole plant is longer than 1 week. It was shown that ears could also be sterilised by enclosing the whole plant in a clear plastic bag during this critical period, even though the plants were growing with adequate boron provided in sub-irrigated gravel culture. It is suggested that one of the effects of enclosure is to prevent transpiration and possibly the associated uptake and movement of boron to the reproductive growth centres. The six genotypes tested did not differ in the developmental stage at which they were sensitive, and all were completely sterile when they were grown without boron up to and including that stage. However, it appeared that a prior period in adequate boron had a different effect on sterility amongst genotypes. One genotype (Fang 60) showed evidence of a boron reserve that could be utilised even after a period equivalent to 3 phyllochrons whereas others appeared to have no boron pool. Ears which were fully sterilised by inadequate boron could have their fertility raised marginally by a spray of boric acid even several days after they had emerged. The implications of these results to grain yield in the subtropics are discussed.