Clonal Variation of Eucalypts in Susceptibility to Bacterial Wilt Detected by Using Different Inoculation Methods

Summary Four inoculation methods were investigated for assessing the clonal variation of eucalypts in susceptibility to bacterial wilt (Ralstonia solanacearum). The results showed that these inoculation methods obviously differed in the disease infection process, clonal variation and clonal mean repeatability in susceptibility of stock materials inoculated. For each inoculation method, the clonal effect was consistently significant over the assessment period. Root-collar suspension injection method (RSI) yielded the highest relative clonal variation (0.67±0.086) and clonal mean repeatability (0.92±0.038) in both disease infected incidence and severity at the end of assessment, attributable to the enhanced genetic variation or low environment effect. For a given inoculation method, an early assessment time might exist for maximizing relative clonal variation or repeatability. It is desirable in breeding to adopt an inoculation method and/or efficient assessment time with high clonal variance component, which would in turn improve the efficiency of clonal screening.

Phenotypic stability and genetic gains in six-year girth growth of Hevea clones

Rubber tree [Hevea brasiliensis (Willd. ex Adr. de Juss.) Müell. Arg.] budgrafts of seven clones were evaluated on five contrasting sites in the plateau region of the São Paulo State, Brazil. The objective of this work was to study the phenotypic stability for girth growth. The experimental design was a randomized block design with three replications and seven treatments. Analysis of variance of girth at six-year plant growth indicated a highly significant clone x site interaction. Only linear sites and clone x site components of clone x year interaction were significant, indicating that the performance of clones over sites for this trait could be predicted. The clones GT 1 and PB 235 showed the greatest stability in relation to girth growth, with foreseen responses to change, introduced in the sites. The clones PB 235 and IAN 873 showed significative difference in relation to regression coefficient, representing clones with specific adaptability on favorable and unfavorable sites respectively. The clone GT 1 became the most promissory one in the study of stability and adaptability even showing low girth growth. Expected genetic gains from planting sites, along with estimates of clonal variance and repeatability of clonal means are generally greatest or close to the greatest when selection is done at the same site.

Genetic improvement of sugar maple for high sap sugar content. I. Clone selection and seed orchard development

A grafted seed orchard of Acersaccharum Marsh, was established in Ohio in 1957 as part of a program of genetic improvement of sugar yield. During the 3rd decade, the orchard trees averaged 4.2% sap sugar. Although environmental sources of variance in sugar concentration were large, clonal differences were evident and generally consistent over the years; the clone × year interaction was negligible. Sap sugar concentration varied from year to year, but after an increase coinciding with early crown development in the 1st decade, there was no upward or downward trend with age. Inclusion of one seedling family in the orchard made it possible to obtain an approximation of within-family variance by comparison with within-clone variance. It was estimated to be about one-third of total family variance. The clone–family comparison also suggested that about 11% of total clonal variance was a rootstock effect. Sap tests over 3 years in a plantation of seed-orchard offspring showed that an initial thinning to an average 6.3 × 6.3 m spacing would leave trees with an average 4% sap sugar concentration. At final spacing the concentration would be higher. Only a few clones in the orchard produced medium or heavy crops of male or female flowers prior to age 27, but those from which seed was collected in early years averaged at least 4% sap sugar. All clones and the seedling family flowered by age 27.

Height and growth habit of Norway spruce rooted cuttings compared between two serial propagation cycles

Rooted cuttings from 10 Norway spruce (Piceaabies (L.) Karst.) clones, arising from both second and third serial propagation cycles, were established in a field trial. Total height was measured annually for 6 years, while growth habit was measured for the first 5 years. Results of analyses for height revealed (i) significant clonal variance at each age, (ii) no differences between propagation cycles at any age, and (iii) a significant clone × propagation cycle interaction at all ages. A similar variation pattern existed for growth habit: (i) significant clonal variance at each age; (ii) propagation cycle differences were significant only at age 2; and (iii) the clone × propagation cycle interaction was significant only at ages 1,3, and 4.

Genetic variances among clonally propagated populations of tamarack and the implications for clonal forestry

Genetic variances of three tamarack (Larixlaricina (Du Roi) K. Koch.) populations in central New Brunswick were examined using vegetatively propagated materials. The component of variance due to clones within families was large for both 5-year height and survival and was partitioned into additive and nonadditive genetic variances. About 85% of the clonal variance for height was additive for the AFES and CANAAN populations but was only 18% for the NORTON population. For survival, the proportion of nonadditive variance was larger than additive variance for the AFES and CANAAN populations, whereas for the Norton population it was negligible. The possibility of clonal propagation and selection is explored as a tree improvement –reforestation option and a strategy is discussed.