Correlation of allelic content with tree characteristics in a hybrid alder stand | Hibridizācijas pakāpes ietekme uz hibrīdalkšņu taksācijas rādītājiem

English. The aim of this research was to determine the correlation between allelic content and tree characteristics in a hybrid alder stand. Common alder (Alnus glutinosa) and grey alder (Alnus incana) are found in natural stands throughout Latvia. Alnus species are not commercially grown; however there is interest in utilising these species for commercial plantations due to their rapid growth rate and ability to grow in, and to improve poor quality soils. Of particular interest are hybrids of these two species, as naturally occurring hybrids have been reported to be faster-growing and larger than the parent species. The use of molecular markers is becoming more common in applied forestry studies, due to the decrease of the cost of genotyping, and more widespread access to genotyping facilities. Molecular markers have not been widely applied or developed in Alnus species, however we developed species-specific markers from sequences available in the GenBank database (http://www.ncbi.nlm.nih.gov/), as well as utilising simple sequence repeat (SSR) markers developed for a related species – Betula pendula. In this study, we utilised 7 species-specific markers (1 SSR marker and 6 SNP markers) to genotype a hybrid alder stand, and to determine correlation of the allelic content with tree characteristics of individuals from this stand. The individuals used in this study were collected from a 43 year old alder stand, which according to available records was an established utilising seed from naturally occurring hybrids. Given the fact that the individuals in this stand have been subject to identical growing conditions, differences in tree characteristics could be attributed to differences in their allelic content. These species-specific markers were used to characterise 132 individuals from the stand. The use of multiple species-specific markers allowed us to quantify the allelic content in hybrids. From the total number of individuals characterised, 19 (14.4%) were designated as pure common alder, 5 (3.8%) as grey alder, and 108 (81.8%) as hybrids with differing proportions of species contributions (Table 1). However, the proportion of 1st generation hybrids, with all markers in a heterozygous state was low – only 3 individuals (2.3%). The other hybrid individuals had differing ratios of species contributions, and these were distributed equally between an excess of common alder alleles (51 individuals, 38.6%) and an excess of grey alder alleles (52 individuals, 39.4%), (Figure 1). Given the allelic distribution found with these species-specific markers, it is probable that the seed used to establish this stand was obtained from a naturally occurring hybrid or hybrids, which were pollinated with an equal mix of common and grey alder pollen. This research showed that there was a significant correlation between allelic content of these trees and both stem diameter and volume (Figures 2 and 3). Tree height was not correlated with allelic content, which could be due to the fact that alders are light-requiring species, and the tree crown height of within even-aged stands will be similar. The highest diameters and stem volumes were found in individuals that had a 1:1 ratio of common and grey alder alleles, which is consistent with the theoretical basis of heterosis. In conclusion, these results show that the use of hybrid alder material can increase the productivity of plantations.

Latvian. Pētījuma mērķis – noteikt hibridizācijas pakāpes ietekmi uz hibrīdalkšņa taksācijas rādītājiem. Hibridizācijas pakāpes noteikšanai izmantota LVMI „Silava” Ģenētisko resursa centrā izstrādātā metodika, kas paredz no stumbra aplievas koksnes izdalīt DNS un to genotipēt ar alkšņu sugu specifiskiem marķieriem. Pētījumu materiāls (132 koki) iegūts 43 gadu vecā alkšņu audzē, kas pēc pieejamās informācijas ierīkota, izmantojot stādus, kas izaudzēti no dabā sastopamo hibrīdalkšņu sēklām. Ņemot vērā, ka visu audzes koku augšanas apstākļi bijuši vienādi, augsta ticamība ir skaidrojumam, ka koku taksācijas rādītāju atšķirības noteikusi to hibridizācijas pakāpe. Audzē sastopamajiem kokiem raksturīgs dažāds baltalkšņa un melnalkšņa alēļu skaits, t.sk. 100% baltalkšņa un 100% melnalkšņa alēļu (1. attēls). Vienāds baltalkšņa un melnalkšņa alēļu skaits ir tikai 5 kokiem (3,8%), no kuriem 3 (2,3%) varētu būt pirmās paaudzes hibrīdi (1. tabula). Pētījumā konstatēts, ka hibridizācijas pakāpe būtiski ietekmē koku caurmēru un stumbra tilpumu (2. un 3. attēls). Alksnis ir gaismas prasīga suga, tomēr tā augstumu hibridizācijas pakāpe būtiski neiespaido. Lielākais heterozes efekts novērots kokiem ar baltalkšņa un melnalkšņa alēļu attiecību 1:1, kas atbilst hibridizācijas teorijai. Pētījuma rezultāti rāda, ka alkšņu hibrīdu audzēšana var nozīmīgi palielināt audžu ražību.