York river destratification: an estuary-subestuary interaction

Destratification in the York River during high spring tides is the result of the interruption of normal two-layer estuarine flow by the advection of relatively fresh water into the river mouth from the Chesapeake Bay. This advection is due to the presence of a longitudinal salinity gradient in the bay and a difference in the tidal current phase between the river and the bay. Similar behavior is seen in other subestuaries of the Chesapeake Bay and may be common in subestuary-estuary interactions.     

The application of the diallel cross to outbreeding crop species

Summary The use of the diallel cross as an aid in the breeding of outbreeding crop species is considered from two aspects. Firstly, for the strategic survey of populations as the initial material of a breeding programme and secondly for the tactical assessment of the genetic relationships of elite selected genotypes. Comparisons with alternative procedures indicate that the diallel crossing scheme is generally only applicable where dominance and gene interaction are likely to be of importance.Text of a paper presented to the Study Circle for Plant Breeding, Wageningen 1977.     

Genetic Analysis of Production Characters in Lolium

A Triple Test Cross and basic generations (i.e. inbred parents, F1′s, F2′s and backcrosses) have been used to investigate the genetics of dry matter yield in a population of Lolium perenne. Two trial designs, short, individual plant drills and larger sown plots were used at each of two sites in the U.K., at Aberystwyth and Birmingham. The families studied correspond to those raised as spaced plants and reported in the first paper in this series. In contrast to the spaced plants trial, the drill trial resulted in considerable epistasis as well as additivity and dominance variation whilst the plot trial failed to identify any significant genetic variation. There was considerable G × E interaction over sites and harvests, particularly in the amount of dominance. The latter showed a clear linear relationship with mean performance at both sites, the dominance ratio being higher in the poorest environments. This is largely due to the additive variance decreasing in the poor environments rather than the dominance being higher. The implications of these results to grass breeding are discussed.     

Histidine nutrition and genotype affect cataract development in Atlantic salmon, Salmo salar L

The aim of this study was to investigate effects of dietary levels of histidine (His) and iron (Fe) on cataract development in two strains of Atlantic salmon monitored through parr-smolt transformation. Three experimental diets were fed: (i) a control diet (CD) with 110 mg kg(-1) Fe and 11.7 g kg(-1) His; (ii) CD supplemented with crystalline His to a level of 18 g kg(-1) (HD); and (iii) HD with added iron up to 220 mg kg(-1) (HID). A cross-over design, with two feeding periods was used. A 6-week freshwater (FW) period was followed by a 20-week period, of which the first three were in FW and the following 17 weeks in sea water (SW). Fish were sampled for weighing, cataract assessment and tissue analysis at five time points. Cataracts developed in all groups in SW, but scores were lower in those fed high His diets (P < 0.05). This effect was most pronounced when HD or HID was given in SW, but was also observed when these diets were given in FW only. Histidine supplementation had a positive effect on growth performance and feed conversion ratio (P < 0.05), whereas this did not occur when iron was added. Groups fed HD or HID had higher lens levels of His and N-acetyl histidine (NAH), the latter showing a marked increase post-smoltification (P < 0.05). The HD or HID groups also showed higher muscle concentrations of the His dipeptide anserine (P < 0.05). There was a strong genetic influence on cataract development in the CD groups (P < 0.001), not associated with tissue levels of His or NAH. The role of His and His-related compounds in cataractogenesis is discussed in relation to tissue buffering, osmoregulation and antioxidation.