In the 1980s, it was discovered that many of the second generation trees in cultivation suffered from inbreeding depression (extremely low genetic variability) which could lead to increased susceptibility to disease and reproductive failure.
A finais da década de 1980, descubriuse que moitas das árbores da segunda xeración que se cultivaban sufriron depresión por endogamia (variabilidade xenética extremadamente baixa) a cal podería conducir a un incremento crecente de doenzaes e á falla reprodutiva.