Maintenance of genetic diversity in Eucalyptus urophylla S. T. Blake populations with restriction of the number of trees per family

Abstract

Our aim was to verify the effect on gain and genetic diversity through the restriction of the number of trees per family in selection, in order to compose an elite population of Eucalyptus urophylla in two trials under distinct management levels.We studied 166 open-pollinated families of E. urophylla in Anhembi, Sao Paulo State, Brazil under commercial practices, and the same families in Selvíria, Mato Grosso do Sul State, Brazil under lower management level (mainly no mineral fertilization). Mortality, height and diameter at breast height (DBH) were measured. DBH was analyzed by the REML/BLUP to select the best 25 trees, with four levels of tree restriction per family (no restriction; 1; 2 and 3 per family). We evaluated heritability; genetic gain and effective size of number of total and private alleles; observed and expected heterozygosity; coancestry and fixation index. A large difference in survival (48 and 83 %) and productivity (MAI of 26 and 44 m 3 ha -1 y -1 ) was observed between trials due to the different levels of management applied. The highest restriction in number of individuals per family caused a small decrease in gain, corresponding to 7 % in the more productive trial and 3 % in the less productive one. Observed and expected heterozygosity, coancestry and fixation index were not significantly (lower than 5 %) affected by the restriction in both sites. The restriction of one tree per family allowed different alleles to be kept in the selected population and higher effective population size in order to insure variation for the next generations. Maintenance of genetic diversity in Eucalyptus urophylla S. T. Blake populations with restriction of the number of trees per family

Genetic Diversity and Genomic Selection in Eucalyptus Benthamii

“…urophylla (Silva et al 2018) showed higher expected heterozygosity. This occurs because the genetic diversity is associated with the environmental variability.…”

Impact of fertility variation on genetic diversity and phenotypic traits in second generation seed production areas and clonal seed orchards of Eucalyptus camaldulensis

“…Restriction in number of trees per family enables retention of alleles and high effective population size to sustain diversity in seed crop (Silva et al, 2018). When effective population size is low, relatedness increases giving little option for selection between families.…”

“…Johnson et al (2001) suggested that 200 outstanding selections would be enough to maintain gain in breeding programs, but to conserve diversity higher number of parent trees (400-1000) is desirable, as observed in SPA 1&2. Diversity in terms of number of families represented would be a prerequisite for advanced generation breeding; and restriction in selection from each family is often practiced to ensure that alleles are conserved in each generation (Silva et al, 2018). Constant seed collection is also a similar strategy as evidenced by only 1 % reduction in number of alleles in CSO 2 compared to CSO 1 (despite big difference in fecundity) whereas there was 9 % difference in alleles per locus between SPA 2 and SPA 3.…”

“…Optimizing these traits is a key factor in determining the genetic quality of seed crop (Funda and El-Kassaby, 2012). Silva et al (2018) emphasised the need to maintain adequate effective population size in breeding populations, to minimise productivity loss due to inbreeding, when high selection intensity is used for enhancing gain. They suggested using quantitative analysis and genetic marker based estimation of genetic variation in orchards, for balancing gain and diversity in breeding programs.…”

“…Estimation of genetic diversity loss from native base population to breeding and production populations, in relation to gain obtained (Silva et al, 2018), would be vital for scientific domestication of a species. Mating system may vary in different populations which can have a significant impact on allelic frequency and performance of the crop (Rao and Hodgkin, 2002).…”