Possible association between grain protein content and yield as influenced by harvest index and biological yield in selected hard red winter wheat (Triticum aestivum L.) crosses

Graduation date: 1989Grain yield and grain protein are often negatively associated in\ud wheat. When yield increases and grain protein decreases, there can be\ud an adverse effect on the milling and baking quality if the desired end\ud product is bread flour. It has been suggested that this inverse\ud association is the result of selecting for a higher harvest index (ratio\ud of grain yield to total biomass), to enhance grain yield.\ud Parents, Fl, F2, and F3 generations of three crosses and\ud reciprocal backcrosses of one cross were space-planted to study the\ud association of grain protein content with grain and biological yields,\ud harvest index, and related traits. Selection P5221, a high protein\ud selection, was a common parent in crosses with three different\ud genotypes.\ud Differences were observed among generations within crosses for\ud biological yield, grain yield, harvest index, grain protein content,\ud grain hardness, and protein yield. The coefficients of variation for\ud the measured traits were low for the three crosses.\ud No associations between grain protein content and grain yield were\ud observed in the populations studied. The largest association detected\ud was between harvest index and grain protein. The r values ranged from\ud -0.39 to -0.46, and rho was not different from -0.50 in two of the\ud crosses. Path coefficient analyses revealed that this association was\ud mostly due to the direct effect of harvest index on grain protein\ud content, with little direct or indirect effect via other plant traits.\ud In the cross P5221/ORCR 8313, biological yield exhibited a moderately\ud large (0.64) direct effect on grain protein content; however this was\ud offset by the negative indirect effect of tiller number. The R2 of the\ud path analyses were relatively small for the three crosses, indicating\ud that most of the variation in grain protein content was not explained by\ud the variables included in the analyses.\ud A possible negative association between grain protein content and\ud harvest index, although moderate, suggests that selection for high yield\ud should not be based on further increases of harvest index because grain\ud protein could decrease