Weedy rice (Oryza spp.): what’s in a name?

Abstract

There are two species of cultivated rice in the world - Oryza sativa L. from Asia and O. glaberrima from Africa. The former was domesticated from the wild progenitor, O. rufipogon and the latter from the African wild rice species O. barthii. The first known center of rice cultivation in China generated the O. sativa subspecies japonica. The indica subspecies arose from the second center of domestication in the Ganges River plains of India. Variants of domesticated lines and the continuous hybridization between cultivated varieties and the wild progenitor(s) resulted in weedy rice types. Some weedy types resemble the wild ancestor, but the majority of weedy rices today bear close resemblance to cultivated rice. Weedy rice accompanies rice culture and has increased in occurrence with the global shift in rice establishment from transplanting to direct-seeded, or dry-drill-seeded rice. Weedy rice (Oryza spp.) is the most-difficult-weed to control in rice, causing as much as 90% yield loss or abandonment of severely infested fields. The gene flow continuum between cultivar and weedy rice or wild relative, crop dedomestication, and regionalized adaptation has resulted in a myriad of weedy rice types. The complex lineage of weedy rice has resulted in confusion of weedy rice nomenclature. Two names are generally used for weedy rice – O. sativa L. and O. sativa f. spontanea. Genomic data shows that Oryza sativa L. applies to weedy rice populations derived from cultivated O. sativa whereas spontanea applies only to weedy types that primarily descended from O. rufipogon. Neither of these names apply to African weedy rice, which are of African wild rice, or O. glaberrima lineage. Therefore, unless the lineage of the weedy population in question is known, the proper name to use is the generalized name Oryza spp.

Genetic Variability in Weedy Rice Biotypes Found in Direct-Seeded Rice Areas in the Philippines

“…Of the wild rice relatives, more WR biotypes are highly similar to O. rufipogon. The common wild rice (O. rufipogon) has been found to contribute to the evolution of sympatric weedy rice in South and Southeast Asia, however, studies do not show direct evolution of WR from O. rufipogon, indicating crop-wild hybridization (reviewed by Burgos et al, 2021). In Malaysia and Thailand, studies on WR using SSRs and SNPs revealed natural gene flow and hybridization between known wild rice and cultivated rice as the major causes of occurrence and spread of WR biotypes (Pusadee et al, 2013;Song et al, 2014;Neik et al, 2019;Vigueira et al, 2019;Wedger et al, 2019).…”

“…The seemingly recurrent genetic evolutions of WR have spurred several nonmutually exclusive hypotheses on the possible origins, according to Burgos et al (2021): a) de-domestication of cultivated rice (Kanapeckas et al, 2016;Li et al, 2017;Qiu et al, 2017), b) intervarietal hybridization among cultivated rice cultivars (Pusadee et al, 2013;Qiu et al, 2014;Ishikawa et al, 2005), c) crop-wild hybridization between domesticated and wild rice (Pusadee et al, 2013;Song et al, 2014); and d) wild-derived origin from wild ancestors adapted in rice areas (Huang et al, 2017).…”

Elevated CO2 concentration enhances Oryza sativa seed shattering and affects seed shattering gene expression

“…is recognised as the most competitive and significantly reduces rice yields even at small densities (Smith, 1988). Weedy rice control is very difficult due its similarities with rice associated with its origin and resilience to environmental factors (for review see Burgos et al, 2021). Weedy rice is of taller height and easy shattering, have high seed dormancy and often pigmented seeds (Burgos et al, 2014; Durand‐Morat et al, 2018; Engku et al, 2016; Fogliatto et al, 2011).…”

“…Weedy rice is of taller height and easy shattering, have high seed dormancy and often pigmented seeds (Burgos et al, 2014; Durand‐Morat et al, 2018; Engku et al, 2016; Fogliatto et al, 2011). These traits make weedy rice competitive and persistent and highly difficult to control, leading up to 90% in rice harvest losses, increases in soil seed reservoir and decreases in rice grain price due to contamination (reviewed by Burgos et al, 2021; Nadir et al, 2017).…”

Weedy rice update in Arkansas, USA, and adjacent locales

“…When present, weedy rice is the most difficult weed to control in rice because its biological traits are nearly identical to those of cultivated rice. When not controlled, weedy rice is one of the most economically damaging rice weeds globally, due to severe yield losses (reviewed in Roma- Burgos et al 2021) and reduction of grain quality (Ottis et al 2005). In Arkansas, weedy rice is deemed the third most problematic weed in rice, behind Echinochloa spp.…”