Analysis of Factors Determining Yield in Crop Plants. I. Varietal Differences in Yield of Grain and Straw of Wheat As Influenced by Photoperiodic Treatments.

Abstract

Seeds of 3 varieties of wheat (Triticum vulgare vars. N.P. 165; N.P. 52 and P.C. 591) were germinated and subjected to 5 seedling treatments: 0, 6, 12, 18 and 24 hour illumination for 12-14 days. These were then transplanted and exposed to 3 post seedling treatments: short day (SD), normal day (ND) and long day (LD). The grain and straw yields are markedly reduced both under short and long post seedling treatments. The seedling treatment effects are not as pronounced as post seedling treatments. The interactions between seedling treatment and variety, and post seedling treatment and variety are also significant. Thus for instance, seedling treatment 5 which, causes a reduction in the yields of N.P. 165 and N.P. 52, increases the yield of P.C. 591, which is a late flowering variety. The reasons for the lowering of yields under the 2 light treatments - SD and LD- are quite different. In SD treatment the reduction is directly due to the low rate of assimilation, as is evident from the highly significant positive correlation that is found between yields of grain and straw and net assimilation rates of SD-ND plants. In the case of LD treatment, on the other hand, the reduction in yield is due to neither deficiency of carbohydrates nor any other nutritional factors but is mediated through some regulatory mechanism of its developmental process. The increase in the yield of P.C. 591 under the seedling treatment 5 is considered to be partly due to shifting of the ripening period of the variety in a range of temperature which is more favorable for the grain filling processes, and is caused by earliness in flowering. The reduction in the grain yield of SD plants, similarly, may not be due entirely to a lower assimilatory activity but may also be partly due to shifting of the ripening period in a higher range of temperature caused by delayed flowering. This is also indicated by lower grain/straw ratios under SD and LD treatments.