COLD TEMPERATURES AND BORON DEFICIENCY CAUSED GRAIN SET FAILURE IN SPRING WHEAT (TRITICUM-AESTIVUM L)

Boron (B) deficiency and cold temperatures during the reproductive dev elopment 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 re sponse to these stresses, if any stage during reproductive development was more sensitive than another, and whether the effects of B deficie ncy and cold temperature were reversible. The experiment comprised a f ull four-factor combination of two cultivars of spring wheat with diff erent field responses to B and cold temperature (Annapurna-3 and NL-68 3), three B treatments (no B added, 20 mu M B L-1 from sowing to matur ity and 20 mu M B L-1 from flag leaf first visible (GS 37) to maturity ), two temperature regimes (ambient UK temperatures and 8 degrees/2 de grees C day/night temperatures in growth cabinets), and three stages f or different temperature regimes to be applied [flag leaf ligule visib le (GS 39) to awn first visible (GS 49), from GS 49 to full ear emerge nce (GS 59) or from GS 59 to the completion of anthesis (GS 69)]. Cont rol plants remained outdoors throughout. An additional B treatment was also applied in which 20 mu M B L-1 was supplied only until GS 37 wit hout any cold treatments. NL-683 was more sensitive to cold temperatur e, producing > 80% sterility, than Annapurna-3 (40% sterility). In con trast, 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, shrivel led and rarely dehisced. More than 75% of pollen grains were dead in N L-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 39-4 9) was relatively more sensitive. The adverse effect of cold was irrev ersible even if ear emergence and anthesis of the stressed plants was in ambient temperatures. Cold temperature significantly reduced the re sponse of plants to B and when cold stressed the cold susceptible cult ivar (NL-683) accumulated less B. The effect of added B in terms of im proved fertility was smaller in the main shoot ear but the fertility o f tillers was greatly enhanced. Plants were more responsive to added B after the emergence of the penultimate leaf: the interruption of B su pply during this stage led to a similar degree of sterility, as in pla nts grown without B throughout. However, resupply of B at this stage i n the plants initially grown without B led to similar B concentrations and grain set as in plants grown with adequate B throughout. Boron co ncentrations in the flag leaf and ear also increased considerably from GS 39 to GS 60 indicating that these are the most sensitive stages fo r B nutrition and wheat plants can recover all of their B requirements if supply is not restricted from GS 37 onwards. (C) 1998 Elsevier Sci ence B.V. All rights reserved.