3.1 Kin recognition in allelopathic rice interference with paddy
weeds
When allelopathic rice cultivars
were each paired with itself or other rice cultivars, the growth of four
common paddy weeds
(Echinochloa
crusgalli, Leptochloa chinensis, Cyperus difformis andEclipta prostrata ) were
inhibited. However, inhibitory effects were dependent on the genetic
relatedness and proportions of rice cultivars. The mixtures with closely
related cultivars (kin) had stronger weed inhibition than the mixtures
with distantly related cultivars (non-kin) regardless of
proportions or weed species.
Significant inhibition occurred at the 2:2 proportion with an exception
of the broadleaf weed E. prostrata (Supplementary Table 2).
When each mixture of allelopathic rice cultivars with other cultivars at
different levels of genetic relatedness was grown in a paddy field at a
1:1 proportion, the emergence and growth of paddy weeds varied greatly
in mixed culture with kin and non-kin cultivars (all weeds pooled,
Figure 1). Allelopathic rice cultivars grown alone and with kin
cultivars showed stronger weed inhibition than when grown with non-kin
cultivars. Compared with allelopathic rice cultivars and their mixtures
with kin cultivars, a significant reduction in weed inhibition occurred
in the mixtures with non-kin cultivars. The results implied the role of
kin recognition in mediating allelopathic rice interference with paddy
weeds.
3.2 Kin recognition
meditated allelopathic rice against weeds at the root level
Greenhouse experiment 1 further confirmed that rice cultivars inhibited
the growth of
paddy
weeds and that the inhibition was dependent on the genetic relatedness
of the mixture (Figure 2). Allelopathic rice cultivars grown with kin
cultivars caused stronger weed inhibition than mixtures with non-kin
cultivars. Regardless of weed species and the genetic relatedness of
rice cultivars, there was always stronger inhibition in root growth than
in shoot growth of weeds (Figure 2). Further, rhizobox experiment 5
revealed that rice and weeds showed different
root
placement patterns measured by horizontal asymmetry in response to
interacting neighbors. (Supplementary Figure 3 & 4). Rice roots always
grew towards the roots of weeds
(intrusive pattern), while the roots
of all weeds trended to avoid growing towards roots of rice (avoidance
pattern). However, root placement patterns between rice cultivars
depended on genetic relatedness.
Focal
rice cultivars grown by themselves or with closely related cultivars had
a more root intrusion towards paddy weeds than when grown with distantly
related cultivars (Figure 3). Similarly, the largest avoidance by weed
roots occurred in allelopathic cultivars grown by themselves or in
mixture with closely related cultivars
(Figure
4). These results indicated that kin recognition in allelopathic rice
could regulate belowground interactions with weeds by optimizing root
placement and distribution.