Factors affecting calving date and its relationship with production traits of Hereford dams

Calving date (CD) records of 68896 polled Hereford dams of 120 682 calves were coded within herd-year-season with date 1 being the date the first calf was born. Factors affecting CD and its relationship with production traits were investigated. Early calving was found to be associated with high performance, conceivably because dams calving early were able to utilize the season-dependent range pastures to their advantage thus providing adequate milk supply to their calves. Weight and age of dam, weight of calf, initial CD, index of milk production potential, and previous CD were found to have significant influence on current CD. Extremely small cows at previous weaning had a tendency to calve late. Cows calving in the spring produced calves with higher overall weight per day of age than did cows calving in other seasons. Initial CD was found to affect CD in subsequent parties. Repeatability of CD was estimated at 0.23. Heritability was estimated at 0.16 (s.e.0.05) and indicated that additive genetic variance constitutes a moderate proportion of the variation in CD. Genetic correlation of CD with birth weight (-0.30), s.e. 0.10), post-weaning rate of gain (-0.64, s.e. 0.19) and yearling weight (-0.60), s.e. 0.11) indicated that `plus' additive genes for CD influenced these traits favourably. However, the corresponding correlations with pre-weaning rate of gain (-0.03, s.e. 0.08) and weaning weight (-0.05, s.e. 0.03) were not significant

QTL mapping of pomological traits in peach and related species breeding germplasm

Peach is an economically important fruit tree crop that exhibits high phenotypic variability yet suffers from diversity-limited gene pool. Genetic introgression of novel alleles from related species is being pursued to expand genetic diversity. This process is, however, challenging and requires the incorporation of innovative genomic and statistical tools to facilitate efficient transfer of these exotic alleles across the multiple generations required for introgression. In this study, pedigree-based analysis (PBA) in a Bayesian QTL mapping framework was applied to a diverse peach pedigree introgressed with almond and other related Prunus species. The aim was to investigate the genetic control of eight commercially important fruit productivity and fruit quality traits over two subsequent years. Fifty-two QTLs with at least positive evidence explaining up to 98 % of the phenotypic variance across all trait/year combinations were mapped separately per trait and year. Several QTLs exhibited variable association with traits between years. By using the peach genome sequence as a reference, the intrachromosomal positions for several QTLs were shown to differ from those previously reported in peach. The inclusion of introgressed germplasm and the explicit declaration of the genetic structure of the pedigree as covariate in PBA enhanced the mapping and interpretation of QTLs. This study serves as a model study for PBA in a diverse peach breeding program, and the results highlight the ability of this strategy to identify genomic resources for direct utilization in marker-assisted breeding