INTRODUCTION
Rice (Oryza sativa L.) is one of most important food crops in
China, with an annual cultivated area of 30 million hectares and a yield
of 206 million tons (Deng et al., 2019). Due to the popularization and
application of direct-seeding cultivation technology, the harm of rice
root-knot nematode was becoming more and more serious (Jabbar et al.,
2020). Among all the root-knot nematodes (RKNs) that harm rice,Meloidogyne graminicola is considered to be one of the most
harmful plant parasitic nematodes in rice cultivation system (Jabbar et
al., 2020; Onkendi et al., 2013; Pokharel et al., 2007; Mantelin et al.,
2017). M. graminicola can infiltrate the roots, cause root
galling, inhibit plant defense systems, manipulate the plant’s metabolic
system, and establish giant cells for its nutrition(Jabbar et al., 2020;
Luo et al., 2020). Therefore, over time, the plant loses its vitality,
which eventually leads to a significant yield loss (Bridge et al., 2005;
Jabbar et al., 2020). M. graminicola is widely distributed in the
tropical and subtropical regions of China, India, Bangladesh, Thailand,
the United States, and other countries (Singh 2010). In China, it was
recorded for the first time on Alliumtistulosum in Hainan
province (Zhao et al., 2001). In recent years, the distribution of this
nematode has expanded from Hainan Province to Guangdong, Guangxi,
Fujian, Yunnan, Hunan, Hubei, Anhui, Sichuan, Jiangxi, Henan and other
provinces. A total of about 1 million hectares of rice were found to be
infected, with a high incidence(Du 2003; Liu et al., 2011; Luo et al.,
2020).Several studies have shown that M. graminicola infections
usually result in a 10-20% reduction in rice yield, and in severe
cases, a 50-72% reduction in rice yield (Khan and Ahamad 2009; Jabbar
et al., 2020; Luo et al., 2020).Thus, M. graminicola has becomea
major threat to rice production(Huang et al., 2018; Khan 2019; Jabbar et
al., 2020).
Mitochondrial DNA (mtDNA) has become an important genetic marker for the
study of nematode molecular phylogeography due to its matrilineal
inheritance, fast evolutionary rate, and lack of recombination (Derycke
et al., 2005; Saccone et al., 2000).Recent studies in nematology have
employed mitochondrial cytochrome oxidase subunit I (COI) as a molecular
marker to analyze the intra specific genetic structure of closely
related Xiphinema species (Gutierrez-Gutierrez et al., 2011).Sun
et al. (2005) and Deng et al. (2016) used barcoding techniques of
mitochondrial COII-LrRNA gene fragments to analyze the differences
between Meloidogyne spp. and Rotylenchulusreniformispopulations,and found that M. incongnita , M. javanica ,M. arenaria and R. reniformis could be identified by
mtDNA-PCR. Rashidifard (2019) studied the molecular characteristics of
37 Meloidogyne populations from four provinces in South Africa
and showed that COII-16S could accurately identify differentM . enterolobii populations. Additionally, the
characterization of COII and 16S rRNA has been proved to
be useful for the identification of different Meloidogyne species
from different geographical regions of the world (OnkendiandMoleleki
2013). Janssen et al. (2016) proved that analysis based on mitochondrial
haplotypes can reveal the evolution and genetic variation of root
nematodes, and pointed out that the barcode region Nad5 can reliably
identify the major lineages of tropical root-knot
nematodes.Based on the mtCOI gene,
four main plant-parasitic Aphelenchoides species were
successfully diagnosed, and the multiple origins of the parasitic genus
were proved (Sánchez-Monge et al. 2017).Ye et al. (2007) constructed 19Bursaphelenchus spp. phylogenetic trees using sequences including
COI genes and analysed the phylogenetic relationships among species in
this genus.Genetic diversity of the root-knot nematode M.
enterolobii in mulberry has been analyzed by Shao et al. (2020) and
observed that the high level of gene flow, a high genetic variation and
a small genetic distance among M. enterolobii populations. A
comprehensive phylogenetic analysis of several hundred COI and ITS rRNA
gene sequences from the Heterodera avenae group showed that COI
haplotypes corresponded to certain pathotypes of cereal cyst nematodes.
Therefore, compared to other molecular markers,mitochondrial DNA
markers emerged as a valuable tool in the study of genetic diversity,
population differentiation, and evolutionary relationship between
closely related nematode species.
To date, there are many studies focused on the genetic diversity of RKN
populations on different crops, but no work has been done on the genetic
diversity of M. graminicola in China. Therefore, the genetic
diversity, genetic differentiation and origin of M. graminicolacollected from10provinces of China based on the COI gene were
analysed. It will provide a theoretical basis to reveal the historical
dynamics of M. graminicola populations and develop efficient
management strategies in China.