2.1 Plant materials, soil and chemicals
Seven rice (Oryza sativa ) cultivars, Huagan-3, Huagan-8, Huafeng,
Lingyou-6173, Lingyou-6365, Lingyou-3826 and Liaojing, were used for
this study. Among them, allelopathic Huagan-3 and Lingyou-6173 have the
ability for kin recognition (Yang, Li, Xu, & Kong, 2018), and other
cultivars are non-allelopathic. ‘Huagan-3’ and ‘Huagan-8’ or
‘Lingyou-6173’ and ‘Lingyou-6365’ were bred or hybridized from
reciprocal parents or identical male sterile, resulting in their
relatedness. ‘Huafeng’ or
‘Lingyou-3826’ was obtained from other parents or male sterile that do
not have consanguinity ties with the ‘Huagan-3’ and ‘Huagan-8’ or
‘Lingyou-6173’ and ‘Lingyou-6365’. These cultivars with different
relatedness were divided into two sets of genotypes, indica-inbred and
indica-hybrid. In the indica-inbred rice set, ‘Huagan-3’ was the focal
rice cultivar (same cultivar, self). ‘Huagan-8’ and ‘Huafeng’ were the
closely related (kin) and distantly related (non-kin) cultivars,
respectively. In indica-hybrid rice set,
‘Lingyou-6173’
was the focal rice cultivar (same cultivar, self). ‘Lingyou-6365’ and
‘Lingyou-3826’ were the closely and distantly related cultivars,
respectively. In addition, a japonica-inbred cultivar ‘Liaojing’ was
used for comparative evaluation as a more distant non-kin for both sets.
Finally, the relatedness of cultivars in both sets was determined
by genetic distances relative to
the focal cultivar (Yang, Li, Xu, & Kong, 2018). The genetic distance,
allelopathic potential and grain biomass of these cultivars were
presented in Supplementary Table
1.
Weeds seeds and soil were collected at Nanling experimental station of
rice research, Anhui Province, China (30°56′52′′ N, 118°23′15′′ E),
located in the low mountains on the southern side of the Yangtze River.
Soil was collected randomly from the surface (0-10 cm) of a paddy field.
The soil is typical fluvaquent, Etisol (US taxonomy) with pH 5.6,
organic matter of 24.5 g·kg-1 and a fertility for
total nitrogen of 1.4
g·kg-1,
available phosphourus of 29.3 mg·kg-1 and available
potassium of 56.8 mg·kg-1. Soil samples were
air-dried, sieved (2 mm mesh) to remove plant tissues, and used in the
series of greenhouse experiments described below.
The rice
allelochemicals
tricin and momilactone B were isolated from allelopathic rice PI312777
seedlings following
Kong
et al. (2004). Allantoin, related to kin recognition in rice lines
(Yang, Li, Xu, & Kong, 2018), and other chemicals were purchased from
China National Chemical Corporation (Beijing, China) and were of the
highest purity available.