In developing countries, tree seedlings are often produced in polybags filled with mixtures of locally available materials. Seedling growth and quality can be affected by the type and amount of these substrates used in the mixture. Differences in seedling growth and quality can also be significantly affected when fertilization is employed during the nursery growing period. In this study, we assessed the effects of five different growing media and two fertilization regimes on nursery growth, seedling morphology and early post-planting response to drought of Eucalyptus benthamii (Maiden & Cambage) seedlings. First, we evaluated the effects of each media by fertilizer treatment combination on morphological attributes during a nursery growing period. Seedlings raised in fertilized media without rice hulls yielded higher growth, root dry mass, shoot dry mass, total dry mass, Dickson quality index (DQI) scores, and number of first order lateral roots (FOLRs). Root to shoot ratio (R:S ratio) was, however, greater in non-fertilized media that contained rice hulls. We then conducted a simulated outplanting and drought hardiness experiment, in which seedlings were planted in 13.2 L containers and irrigated for one month, followed by the imposition of drought stress. Seedlings in fertilized media composed of sand, topsoil and compost showed greater growth than those in rice hull-containing media, during the irrigation phase. With the discontinuation of irrigation and prevention of precipitation reaching the seedlings, seedlings grown in non-fertilized media containing rice hulls survived longer than those in other media. There were no large differences in survival among other media or between fertilized and other non-fertilized seedlings. Seedling total size and shoot height at the time of planting played a major role in survival. Smaller seedlings with smaller shoot sizes and greater R:S ratios survived longer. This study demonstrates that growing media and fertilization can be manipulated to affect seedling morphology in the nursery and, ultimately, seedling performance and survival under water stressed conditions.

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The correspondence between breeding values of 65 loblolly pine (Pinus taeda L.) genotypes from clonal genetic tests and half-sib seedling progeny tests was studied in the southern United States. The two experiments were established separately, 10 years apart. Additive genetic variance estimates from clonal tests were larger compared with the estimates from the half-sib progeny tests, regardless of the covariance structure used in the statistical models and the traits. However, clone-mean and half-sib family-mean heritability estimates were comparable for all traits, ranging between 0.88 and 0.99. Based on the independent analysis, the correlation between the breeding values of the same genotypes from two propagule types was moderate (0.59) for tree height and stem volume. The combined analysis resulted in a strong genetic correlation (>0.93) between the breeding values of two propagule types. Herein the large discrepancy is mainly the outcome of different data analytical approaches. Conclusively, selecting genotypes for deployment based on clonal testing may not be optimal, but forest tree breeders can use the results from clonal tests to make some informed decisions. Study Implications: Selection of next-generation parents in loblolly pine breeding could be enhanced by clonal testing for growth traits; however, the results indicated that the ranking of genotypes from clonal testing and seedling progeny testing is far from perfect (rank correlation, r = 0.60). This outcome could be partially an artifact of the data and the experimental design as two propagule types were not tested in the same environment. For fusiform rust, clonal testing would not be informative because of the low incidence observed in the clonal tests. Breeders may still benefit from using clonal data by culling the lower-ranking genotypes and deploying a larger number of higher-ranking clones in their seed orchards to account for uncertainty. Once more data become available for the genotypes, they can rogue the seed orchards to increase the genetic gain. In the near future, DNA markers will likely play an important role for within-family selection in forest trees. If proved successful, breeders may forgo cloned genetic tests for conifers. Genomic selection studies are underway at major breeding centers.

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