Zygotic embryogenesis and empty seed formation in European larch (Larix decidua Mill.)

Abstract

-Zygotic embryo development and its influence on empty seed formation of the European larch (Larix decidua Mill.) was studied within a seed orchard in the Slovak Republic. Histological study revealed a fertilization date early June. Although embryogenesis was most intensive in June, fully morphologically differentiated embryos were observed no earlier than in the second half of July. Multiple fertilization and simple polyembryony were relatively rare but their frequencies correlated with the efficiency of pollination. Only a small percentage of developing embryos reached full maturity. Degeneration included suppressed embryos from polyembryony as well as normal embryos occupying the optimal position within the corrosion cavity of the female gametophyte. The mean proportion of fertilized ovules without a viable embryo was 61% after open pollination and as high as 88% after controlled selfing. In total, embryo degeneration reduced the potential full seed percentage by almost 40% and is therefore considered the most important cause of unsound seed development in European larch.larch / embryo / embryogenesis / empty seed Résumé -Embryogenèse zygotique et formation des graines vides chez le mélèze d'Europe (Larix decidua Mill.). Le développement des embryons zygotiques et son influence sur la formation des graines vides du mélèze d'Europe (Larix decidua Mill.) ont été observés en condition de verger à graines en République Slovaque. L'étude histologique révèle que la période de fécondation la plus fréquente est le début du mois de juin. Bien que l'embryogenèse soit la plus intensive en juin, les embryons morphologiquement les plus différenciés sont observés dans la deuxième moitié du mois de juillet. Même si la fécondation multiple et la polyembryonie simple sont relativement rares, elles sont corrélées avec une pollinisation abondante. Le pourcentage d'embryons développés est très faible. La dégénérescence a affecté les embryons opprimés de polyembryonie ainsi que les embryons ayant la position optimale dans le gamétophyte femelle. La moyenne des ovules fécondés ne présentant pas d'embryon vivant a atteint 61 % après pollinisation libre et près de 88 % d'ovules après autopollinisation contrôlée. En moyenne, la dégénérescence des embryons a réduit le pourcentage potentiel de graines pleines de presque 40 % et c'est pourquoi elle est considérée comme la cause principale de la formation des graines vides chez le mélèze d'Europe. mélèze / embryon / embryogenèse / graine vide

Composition of hybrid larch (Larix × eurolepis Henry) forest reproductive materials: How much does hybrid percentage affect stand performance?

“…Considering the poor full seed yields resulting from controlled self-pollinations (Kosinski 1986;Slobodnik and Guttenberger 2005), it seemed unlikely at first sight that the high percentages of non-hybrid trees found in several orchard progenies (S, FP, M and FH) derived from selfing. However, Bergmann and Ruetz (1987) mentioned a very low percentage of hybrid seeds (19 %) in the first crop of a young bi-clonal orchard.…”

“…Considering the genetic and physiological mechanisms against selfpollination that result in embryo abortion and finally in empty or unviable seeds (Dieckert 1964;Kosinski 1986;Slobodnik and Guttenberger 2005;Philippe et al 2006), we expected hybrid percentage to be high in the progenies from orchards composed of a single mother clone, and lower in the progenies from orchards with several maternal clones. The limited data available in the literature generally concurs (Bergmann and Ruetz 1987;Häcker and Bergmann 1991;Ennos and Qian 1994).…”

“…The risk of obtaining non-hybrid seeds is a priori limited in orchards including a single maternal clone where intraspecific crossings are limited to selfing if the orchard is well-isolated from incoming pollen. As self-pollinated ovules often produce empty seeds due to embryo abortion (Kosinski 1986;Owens 1995;Slobodnik and Guttenberger 2005;Williams 2007) or seedlings with a low vigor (Dieckert 1964, Nanson 2004, this design is considered optimal for the production of high percentages of hybrid seeds.…”

Hybrid breakdown and inbreeding depression for seed yield and early growth in 2nd-generation interspecific hybrids of larch (Larix x eurolepis x L.x eurolepis)

“…For example Kosinski (1987) reported percentages of empty seeds as high as 62-89% in European larch. For the same species, Sloobodnik and Guttenberger (2005) estimated that 61% of fertilized ovules did not have a viable embryo after open pollination. Owens (2008) observed average proportions of empty seeds around 60 and 56% from lots of western larch, respectively, collected in natural stands and in one seed orchard.…”

Activity and localization of lipoxygenase in the ovule of Larix kaempferi (Lamb.) Carr. during megasporogenesis

“…Production of large quantity of empty seeds has been reported for several species such as Larix decidua, L. kaempferi and L. occidentalis (Hall and Brown 1977;Kosiński 1987;Owens et al 1994;Slobodník and Guttenberger 2005). The main biological constraints for seed production in Larix species are abnormal development of the female gamethopyte, degeneration of the ovule or early embryo, premature abortion of female strobili, insufficient female flowering, and perturbation in the pollination mechanism (Philipson 1996;Guttenberger 2000, 2005;Slobodník 2002). Isolation and preparation of the generative organs of gymnosperms is quite difficult because of occurrence of resins and some polyphenolic compounds.…”