Implications for ecological weed control in agricultural crops
Farmers generally aim to maximize performance (e.g. yields or
resource-use efficiency) at the crop stand (hence, plant population)
level. This may be in conflict with the fact that in dense vegetation
natural selection favours the most competitive plants rather than those
maximizing group performance (see Anten & Vermeulen 2016; Denison,
2011). As kin selection can lead to more cooperative traits in plants
and greater group performance, its potential use in crop breeding could
be considered (Anten & Chen, 2021; Murphy, Van Acker, Rajcan, &
Swanton, 2017). The results of Xu et al. are particularly interesting in
this regard. Among all biotic stress types (i.e. pathogens, pests and
weeds), weeds have the largest potential for yield reduction (larger
than the other two stress types combined) (Oerke, 2006). Chemical
control of weeds is coming under increasing pressure due to concerns
about their health- and environmental impacts and increasing herbicide
resistance of weeds. This in turn, has led to an increased interest in
ecological weed control, of which development of weed-suppressive crops
can be an important part (Bastiaans, Paolini, & Baumann, 2008). Thus,
if kin discrimination can reduce intraspecific competition among crop
plants in favour of interspecific competition with weeds as shown by Xu
et al., this could be part of a strategy for ecological weed control.
The question however is whether kin selection is the most effective
means of obtaining cooperative crop types. Conceptually, kin
discriminating plants can be considered as facultative co-operators,
that is, they exhibit cooperative behaviours only in the presence of kin
and not in the presence of non-kin. In a crop variety mixture such a
facultative co-operator may do worse than an obligate co-operator, i.e.,
a crop type that expresses cooperative behaviours irrespective of
whether it interacts with kin or non-kin (Anten & Chen, 2021). Thus,
the question arises whether preferential root placement towards the
roots of weeds rather than towards con-specific crop plants could also
be selected as a constitutive trait.