Thesis Abstract of AGS Students
Variation in responses to boron deficiency in wheat genotypes
Canhong Cheng (1992)
Variations in responses to B deficiency among genotypes in wheat (Triticum aestivum) were studied in a field and a pot experiment. The effect of sowing dates was also investigated in pot experiment.
In the field experiment, ten wheat genotypes were grown with 4 levels of soil B (0.09, 0.12, 0.16 and 0.24 mgB kg-1 soil). In SW 41 and BL 1022, grain yield was depressed by low soil through poor grain set caused by poor development of anther and pollen. In SW 23, Sonalika, Sonora 64, KUHR 12, CMU 28, NL 460 and CMU 285, there were no effects of B on grain set. In Kanchan, effects of B on grain set were slight.
In the pot experiment, one B deficient sensitive genotype (SW 41) and one tolerant genotype (Sonora 64) were sown in a sand culture on Oct. 24, 1991 and Jan. 15, 1992. The plants were watered twice daily with 1L of a complete nutrient solution with 4 levels of B supply (0, 0.001, 0.005 and 0.02 mg Bl-1). Pollen germination was examined in vitro on media containing 0.7% agar, 0.75 M raffinose and 300 mgl-1 CaCl2.2H2O with 5 B levels (0, 10, 15, 20 and 100 mgl-1 H3BO3) at 25 oC and 30 oC.
The effect of B supply in the sand culture on grain set was correlated with field responses. Pollen viability was depressed by B deficiency. Internal and external B supply was essential to pollen germination. The percentage of pollen germinated and length of pollen tube in vitro were markedly increased as medium B supply increased. Germination was poor at low medium B supply, regerdless of B supply to the plants. With high medium B supply, the percentage of germinated pollen and length of pollen tube responded strongly to B supply to the plants. Pollen germination was more severely affected by B deficiency at 30 oC than that at 25 oC. Grain set was depressed by low B supply in SW 41, but not in Sonora 64. However, no differences in pollen viability examined in vitro were found between both genotypes. These data suggested that the effect of B deficiency on in vitro fertilization may be more severe in SW 41.
Boron concentration at 4.5 mgB kg-1 dry weight or lower in developing ear during booting associated with poor grain set in SW 41, BL 1022 and Kanchan, but not in Sonora 64, KUHR 12, CMU 26 and CMU 285.
The results indicated that differences in response to B deficiency among wheat genotypes might be through: 1) internal B requirement; 2) capacity of B uptake; and 3) distribution of B, i.e. getting B into the developing spike and/or into pollen, stigma and style during booting. There is a possibility that higher internal B requirement in SW 41, BL 1022 and Kanchan, but with poor ability of uptake B (BL 1022) and with poor distribution of B into the reproductive tissue (SW 41 and Kanchan) may be the cause of sensitivity to B deficiency.