Selection Criteria for Genotypes and Identification of Plant Characteristics for Phosphorus-Efficient Wheat

Most genetic analyses of wheat crops concentrate on elucidating the mode of inheritance of plant characteristics. However, it is equally important to study the genetic relationship between different characteristics so that the consequences of selection for one characteristic on the performance of another can be predicted. Three field experiments with 15 wheat genotypes were conducted at two sites with similar soil types and agroecological conditions (two experiments at site 1 and one experiment at site 2) to evaluate wheat genotypes through correlation and path analyses for identification of plant characteristics responsible for high grain yield at low phosphorus (P) (7.86-8.23 mg P kg-1 soil; control, no application of P) and adequate P (52 kg P ha-1) in soil. On the average of the three experiments, the genotypic and phenotypic coefficients in correlation analysis agreed closely in each case. Relatively high values of genotypic coefficient showed a masking influence of genetic factors in the grain production. Grain yield correlated significantly with P-uptake parameters, such as P uptake in grain and straw. Integration of P in grain formation varied among wheat genotypes because of differences in their abilities to absorb, translocate, distribute, accumulate, and utilize P. The integrated effect of these physiological processes appeared in the form of end product (i.e., grain). The yield potential of a genotype to produce grain can be measured directly from absolute grain yield, but when selection was made through the involvement of plant factors such as harvest index, it proved to be a good predictor of grain yield. Positive relationship of harvest index with grain yield indicated an increase in grain yield. Because grain production is an outcome of the integrated effect of many P-related physiological processes, P efficiency was measured by P harvest index, P efficiency ratio, and P physiological efficiency index. The P physiological efficiency index was found to be an appropriate measure of P-use efficiency. When the selection was made through path analysis, it was observed that the genotypes that had high harvest index, absorbed more P, accumulated more P in grain, and produced more grain per unit of absorbed P were efficient in P use and produced high grain yield under low available soil P field conditions. Wheat genotypes 'Inqlab 91,' 'Pak 81,' '4072,' '4943,' and '5039' were capable of producing high grain yield under low soil P field conditions in this study.