Cross-resistance against diseases and insects in a breeding
population of Pinus pinaster
Alejandro Solla, María Vivas and Elena Cubera, Universidad de Extremadura, Virgen
del Puerto 2, 10600 Plasencia, Spain; Luis Sampedro and Xoaquín Moreira, Centro de
Investigación Forestal de Lourizán, Apdo 127, 36080 Pontevedra, Spain; Esther Merlo,
CIS Madeira, Ourense; Raúl de la Mata and Rafael Zas Misión Biológica de Galicia,
CSIC, Carballeira 8, 36143 Pontevedra, Spain; rzas@cesga.es
The different plant defences existing within a given taxon have been commonly assumed to tradeoff among each other because of both evolutionary and physiological reasons. On one hand, the
highest the efficiency of a single defensive trait, the lowest the selective pressure for other
redundant defences. Besides, production of multiple defences might be constrained by the
resources required for maintaining, at a time, high grow and reproductive rates. However,
different defensive traits do not need to be always redundant, and plants may require the
combination of multiple defences to contest all possible enemies. This is particularly the case in
forest trees, which due to their large size and long-life span, are apparent targets for a wide range
of enemies. Theory predicts that these apparent species will tend to evolve generalized defences
that are effective against a wide array of herbivores, and that will function by means of
quantitatively reducing the edibility or nutritional quality of the plant, and thus the herbivore
performance. Empirical evidences for this expected crossresistance in forest trees are, however,
lacking.
Here, we have put together data from several independent experiments on the same genetic
material to explore whether resistance to different pests and diseases are genetically correlated in
Pinus pinaster, an emblematic forest species of SW Europe. We also aimed to determine at what
extent resistance is based on quantitative defensive traits, and may be genetically related to other
fitness correlates such as growth and cone production. We compile data of several field and
greenhouse experiments designed for screening resistant genotypes to insects and diseases and for
exploring the role of different phenotypic traits in tree resistance. Plant material consisted of
open-pollinated families of 39 maternal plus trees selected for superior growth and form in
mature plantations of P. pinaster in NW Spain. The selected trees have been established in
several clonal seed orchards that provide genetically superior seeds for reforestation in the region.
The pathogens tested included Fusarium circinatum, F. oxysporum and Armillaria ostoyae, and
the insects tested included Thaumetopoea pithyocampa, Hylobious abietis and Dioryctria
sylvestrella, all of them causing important damage to P. pinaster forests in the area. Quantitative
resistance traits examined were the constitutive levels and inducibility potential of diterpene
content in the stem, leaf total phenolics and leaf condensed tannins. Seed weight, early growth,
cone production, and root morphology were also considered as fitness related traits. The
relationships between parameters were examined by Pearson’s correlation between parental
breeding values estimated independently from each experiment. Principal Component Analysis
was also applied in order to reduce the dimensionality of the data, and to enable clustering and
identification of putative defence syndromes.
Results do not support the initial hypothesis, and lack of cross-resistance appears to be
the norm in this pine species. Although some significant correlations revealed a relevant
role of some defensive traits protecting the plant against specific pests or pathogens, the
quantitative defences studied can not be classified as generalized defences against all
enemies. Rather, pines appear to be jacks of-all-trades, masters of all and may need to
combine multiple defensive traits to fight against the wide range of potential enemies.