RESPONSE OF WHEAT GENOTYPES TO SOWING DATE AND BORON FERTILIZATION AIMED AT CONTROLLING STERILITY IN A RICE-WHEAT ROTATION IN NEPAL

Spikelet sterility in wheat (Triticum aestivum L.) is emerging as a pr oduction threat in different parts of Nepal. This study was aimed at d etermining the effects of sowing date and boron application in control ling spikelet sterility in four different genotypes of spring wheat in a rice-wheat system in the western hills of Nepal. Four genotypes of known different responses to boron were planted on 21 November, 6 Dece mber and 21 December, 1994 with or without boron application at 1 kg B ha(-1) (i.e. 9 kg borax ha(-1)) on a soil that was known to be defici ent in boron. The effect of sowing: date was significant for the pheno logy, yield components, percentage sterility and grain yield. Sterilit y was significantly increased in the crop planted on 21 December, whic h had also the lowest 1000 seed weight and grain yield; there was an a lmost 50% grain yield reduction compared to the crop planted on 21 Nov ember. Terminal moisture stress (i.e, lack of moisture during the late r part of the development) was observed in the late sown crop which al so amplified the extent of sterility associated with boron deficiency. Genotypes differed in response to sowing dates and boron treatment fo r all of the phenological events measured, yield components, grain yie ld and percentage sterility. SW-41 and BL-1022 had significantly highe r sterility at all sowing dates. BL-1249 showed a consistently lower % sterility over all sowing dates and boron treatments. The addition of boron significantly increased the number of grains set per spike ther eby decreasing the total sterility in boron responsive genotypes SW-41 and BL-1022 while those not susceptible did not respond. The baron co ncentration in the flag leaf at anthesis was increased in treatments w ith added B in the soil but genotypes did not differ in boron concentr ation for any soil treatment.