No abstract

No abstract

The occurrence of vesicular–arbuscular mycorrhizae (VAM) root colonization and spore number in soil was assessed for 18 fields under intensive lettuce (Lactuca sativa L.) production in California during July and August of 1995. Data on management practices and soil characteristics were compiled for each field, and included a wide range of conditions. The relationship between these factors and the occurrence of VAM in these fields was explored with multivariate statistical analysis. VAM colonization of lettuce tended to decrease with the use of chemical inputs, such as pesticides and high amounts of P and N fertilizers. Addition of soil organic matter amendments, the occurrence of other host crops in the rotation, and soil carbon[ratio ]phosphorus and carbon[ratio ]nitrogen ratios, were positively associated with VAM colonization of lettuce roots. The number of VAM spores in soil was strongly correlated with the number of other host crops in the rotation, the occurrence of weed hosts and sampling date, but was more affected by general soil conditions than by management inputs. Higher total soil N, C and P, as well as CEC, were inversely related to soil spore number. A glasshouse study of the two primary lettuce types sampled in the field showed no significant differences in the extent of root colonization under similar growing conditions. The results of this study are compared with other studies on the effects of management and soil conditions on mycorrhizal occurrence in agriculture.

Seven cycles of high‐intensity within half‐sib family selection for percent oil in the ‘Reid Yellow Dent’ corn (Zea mays L.) cultivar resulted in an increase in oil from 4.0 to 9.1%, while kernel weight and ear height were reduced slightly and grain moisture at harvest increased. No significant changes in yield, silking date, or plant height were found. Realized heritability for percent oil was 43%.Estimates of genetic variance for percent oil and 100‐kernel‐weight were obtained in 1977 and 1978, for Cycles 0 and 5. All estimates of additive genetic variance (ó2A) were greater than zero; however, change in ó2A occurred between cycles. Estimates of dominance genetic variance did not differ from zero.A comparison of the predicted gains from within half‐sib family selection, mass selection, and combined selection among and within half‐sib families revealed that maximum gain is expected when a higher selection intensity is used within half‐sib families than among half‐sib families.

No abstract