Interference of allelopathic rice with paddy weeds at the root level

Abstract

Despite increasing knowledge of the involvement of allelopathy in negative interactions among plants, relatively little is known about its action at the root level. This study aims to enhance understanding of interactions of roots between a crop and associated weeds via allelopathy. Based on a series of experiments with window rhizoboxes and root segregation methods, we examined root placement patterns and root interactions between allelopathic rice and major paddy weeds Cyperus difformis, Echinochloa crus-galli, Eclipta prostrata, Leptochloa chinensis and Oryza sativa (weedy rice). Allelopathic rice inhibited growth of paddy weed roots more than shoots regardless of species. Furthermore, allelopathic rice significantly reduced total root length, total root area, maximum root width and maximum root depth of paddy weeds, while the weeds adjusted horizontal and vertical placement of their roots in response to the presence of allelopathic rice. With the exception of O. sativa (weedy rice), root growth of weeds avoided expanding towards allelopathic rice. Compared with root contact, root segregation significantly increased inhibition of E. crus-galli, E. prostrata and L. chinensis through an increase in rice allelochemicals. In particular, their root exudates induced production of rice allelochemicals. However, similar results were not observed in C. difformis and O. sativa (weedy rice) with either root segregation or root exudate application. The results demonstrate that allelopathic rice interferes with paddy weeds by altering root placement patterns and root interactions. This is the first case of a root behavioural strategy in crop-weed allelopathic interaction.

Kin recognition in rice (Oryza sativa) lines

“…These rhizobox‐ and segregation‐based approaches clearly demonstrated kin recognition in rice lines at the root level and identified belowground interactions as solely responsible for kin recognition responses. Window rhizobox techniques can be used to visualize interacting root systems (Belter & Cahill, ; Yang & Kong, ). With a series of window rhizobox experiments, root measures of focal cultivars developed differently in the presence of kin or nonkin.…”

“…To examine root production and placement patterns of each focal cultivar in the presence of the same cultivar and different cultivars, a series of window rhizoboxes were made of a 10 mm (width) × 200 mm (length) × 300 mm (height) poly(vinyl chloride) box with a clear poly(methyl methacrylate) front containing 500 g of soil (Yang & Kong, ). Each focal cultivar ‘Huagan‐3’ or ‘Lingyou‐6173’ was grown in monoculture or mixed culture with kin and nonkin in the rhizoboxes with three replicates.…”

“…A simple Pearson's correlation was used to test whether the allantoin level across cultivars and lines was associated with the root biomass of rice seedlings grown in root exudates. Horizontal asymmetry in root length or root biomass was calculated as response ratios Vn/Va (Yang & Kong, ), where Vn is the response value (total root length or root biomass) for the focal cultivar ‘Huagan‐3’ or ‘Lingyou‐6173’ in the presence of kin or nonkin, and Va is the response value when the focal cultivar was grown alone. If Vn/Va > 1, ‘Huagan‐3’ or ‘Lingyou‐6173’ root growth increased toward the roots of its neighbor, resulting in an intrusive pattern of root placement.…”

Barnyardgrass Root Recognition Behaviour for Rice Allelopathy

“…In addition, decline of barnyardgrass root growth is due to shift in microbial diversity and community structure shaped by the root exudates of the allelopathic rice [26]. In summary, these findings determine that the allelopathic rice varieties interfere with barnyardgrass performance by altering root traits [38], suggesting that root recognition could be one of important root behavioural strategies in crop-weed allelopathic interactions.…”

Intraspecific kin recognition contributes to interspecific allelopathy：A case study of allelopathic rice interference with paddy weeds

“…Elution was performed at a constant flow rate of 1.0 mL min -1 at 40 with acetonitrile and a mixture of 0.5% formic acid in a gradient: initial mobile phase of 10% acetonitrile for 4 min, increased to 35% for 4 min, then decreased to 10% for 4 min, for a total run time of 12 min. The allelochemicals tricin and momilactone B were quantified by interpolating the peak area on the HPLC chromatogram to a standard curve constructed from the peak area of authentic tricin and momilactone B (Yang & Kong, 2017).…”