Kin discrimination in allelopathy and consequences for agriculture.
Niels P. R. Anten1,* & Bin J. W. Chen2
1 Centre for Crop Systems Analysis, Wageningen University, Wageningen, the Netherlands
2 College of Biology and the Environment, Nanjing Forestry University, Nanjing, China
*Correspondence author: Centre for Crop Systems Analysis, Wageningen University, Droevendaalsesteeg 1, 6708PB Wageningen, the Netherlands
Recent research has shown that plants can distinguish genetically-related individuals from strangers (kin recognition) and exhibit more cooperative behaviours towards these more related individuals (kin discrimination). The first evidence for this was found when Cakile edentula plants growing with half-sibs allocated relatively less biomass to roots than plants growing with unrelated individuals, indicating that kin recognition can reduce the intensity of competition (Dudley & File, 2007). Since then, kin discrimination has been shown to result in reduced competition for soil resources (Semchenko, Saar, & Lepik, 2014), light (Crepy & Casal, 2015) and pollinators (Torices, Gómez, & Pannell, 2018). On the other hand, allelopathy, plants producing chemical compounds that negatively affect performance of neighbour plants, has also been widely documented (Inderjit & Duke, 2003) and shown to profoundly affect local species coexistence and plant community structure (Meiners, Kong, Ladwig, Pisula, & Lang, 2012). In crops allelopathy can also be beneficial in suppressing weeds (Macías, Mejías, & Molinillo, 2019). In the current issue, Xu, Cheng, Kong, and Meiners (2021) published the first study to show that kin discrimination can also affect the balance between direct competition for resources and allelopathy, and this together may lead to improved weed suppression in rice.
Xu et al. grew target plants of two rice cultivars known to be both allelopathic and capable of kin recognition, with four different neighbour-plant treatments in order of decreasing relatedness: neighbours being of the same cultivar, a genetically closely-related cultivar, a genetically more distant cultivar but of the same ecotype (‘indica’) or of a different type (‘japonica’). They explored: root allocation, allelopathy, weed suppression and biomass production of target plants in these treatments. They found that plants grown with neighbouring rice plants of the same cultivar or a closely-related cultivar allocated their roots less towards neighbouring rice plants but more towards weeds, with a consequence of greater suppression of the weeds. This showed that kin interaction could lead to reduced intraspecific and more effective interspecific competition, consistent with results from wild plants Semchenko et al. (2014). However, results for allelopathy were less clear. Rice plants produced less allelochemicals when growing with neighbours of a closely-related cultivar than when growing with less related ones, but produced the highest level when growing with neighbours of the same cultivar. This indicates that the pattern through which kin recognition may affect allopathy is still unclear. Moreover, despite of the differences in root allocation, allelochemical production and weed suppression among treatments, there was no clear pattern in grain production of rice plants across treatments. This could imply that weed suppression did not contribute to yields. It could also be that more related individuals being phenotypically more similar competed more intensively for e.g. light, a phenomenon known as kin competition (Platt & Bever, 2009), so that positive kin cooperative effects and negative kin competitive effects compensated each other in their effects on yield (Anten & Chen, 2021).