Cold temperatures and boron deficiency caused grain set failure in spring wheat ( Triticum aestivum L.)

Abstract

Boron (B) deficiency and cold temperatures during the reproductive development of wheat ( Triticum aestivum L.) cause failure of grain to set. A pot experiment at the Plant Environment Laboratory, The University of Reading, UK, in 1996 examined whether wheat cultivars differ in response to these stresses, if any stage during reproductive development was more sensitive than another, and whether the effects of B deficiency and cold temperature were reversible. The experiment comprised a full four-factor combination of two cultivars of spring wheat with different field responses to B and cold temperature (Annapurna-3 and NL-683), three B treatments (no B added, 20 μM B L −1 from sowing to maturity and 20 μM B L −1 from flag leaf first visible (GS 37) to maturity), two temperature regimes (ambient UK temperatures and 8°/2°C day/night temperatures in growth cabinets), and three stages for different temperature regimes to be applied [flag leaf ligule visible (GS 39) to awn first visible (GS 49), from GS 49 to full ear emergence (GS 59) or from GS 59 to the completion of anthesis (GS 69)]. Control plants remained outdoors throughout. An additional B treatment was also applied in which 20 μM B L −1 was supplied only until GS 37 without any cold treatments. NL-683 was more sensitive to cold temperature, producing >80% sterility, than Annapurna-3 (40% sterility). In contrast, Annapurna-3 was more susceptible to B deficiency (22% sterility compared to only 14% in NL-683). The principal effect of cold was to impair pollen viability: anthers were poorly developed, small, shrivelled and rarely dehisced. More than 75% of pollen grains were dead in NL-683 compared to about 25% in Annapurna-3. All periods from GS 39 to GS 69 were vulnerable to cold damage although the first stage (GS 39–49) was relatively more sensitive. The adverse effect of cold was irreversible even if ear emergence and anthesis of the stressed plants was in ambient temperatures. Cold temperature significantly reduced the response of plants to B and when cold stressed the cold susceptible cultivar (NL-683) accumulated less B. The effect of added B in terms of improved fertility was smaller in the main shoot ear but the fertility of tillers was greatly enhanced. Plants were more responsive to added B after the emergence of the penultimate leaf: the interruption of B supply during this stage led to a similar degree of sterility, as in plants grown without B throughout. However, resupply of B at this stage in the plants initially grown without B led to similar B concentrations and grain set as in plants grown with adequate B throughout. Boron concentrations in the flag leaf and ear also increased considerably from GS 39 to GS 60 indicating that these are the most sensitive stages for B nutrition and wheat plants can recover all of their B requirements if supply is not restricted from GS 37 onwards.