These results suggested that the genetic relationship between oil and protein content was complex and all of the 10 QTL were not useful for the simultaneous improvement of oil and protein content. Higher levels of correlation between oil and starch content than between protein and starch content were reflected by the higher reduction in variance (about 52%) for oil and starch content than that for protein and starch content (about 33%) when NU7441 purchase these traits

were conditioned on each other. When oil and protein content were conditioned on starch content, six of nine unconditional QTL for oil content and all of the five QTL for protein content disappeared. In contrast, all of eight and four of eight unconditional QTL for starch content failed to show significant effects in conditional QTL mapping for starch|oil and starch|protein content, respectively. These QTL are likely to represent substrate Proteases inhibitor level genes that affect starch content via indirect effects. For these unconditional traits, some new QTL also appeared in conditional QTL mapping, suggesting

that conditional QTL mapping could unravel additional QTL with minor effects for closely correlated traits. One noteworthy aspect in this study was that the effects of some major unconditional QTL for these quality traits were significantly reduced under conditional QTL mapping. When oil content was conditioned on starch content, two unconditional QTL showed reduced but still significant effects, and likewise, three QTL for Methocarbamol starch content. It indicates that these five QTL

for one trait were partly affected by another trait. In contrast, the effects of two unconditional QTL, oilc10 and stc6, showed slight reductions under conditional QTL mapping. It demonstrates that these two QTL each represent QTL that influence one trait independently of another trait. One of the great challenges to improve the relative proportions of oil, protein or starch in maize kernels for specific end-uses is the strong phenotypic and genetic correlations among them. For each trait, 55 to 100% of unconditional QTL were co-localized with QTL for the other two traits. Thus, the real genetic mechanism of the detected QTL regulating target traits remains unclear due to pleiotropic effects or tight linkages. However, the genetic interrelationships among oil, protein and starch content at the individual QTL level can be dissected by conditional QTL mapping. The information generated in the present investigation could be helpful in marker-assisted breeding of maize varieties with desirable kernel quality traits. For example, the genetic effect of QTL associated with oil content on chromosome 1 was sharply reduced but still remained significant when oil content was conditioned on protein or starch content. This indicated that this locus mainly affected variation in oil content, but still had weak effects on both protein and starch content.