Morphology of Malaysian Weedy Rice (Oryza sativa): Diversity, Origin and Implications for Weed Management

Abstract

Weedy rice is one of the most dominant and competitive weed species found throughout rice planting areas worldwide. In Malaysia, a combination of agricultural practices such as direct seeding and shared use of machinery has contributed to the rapid proliferation of weedy rice across paddy fields in recent decades. Here, we report on the morphological characterization of weedy rice populations and inferred origin(s) of different morphotypes present in Peninsular Malaysia. Eight weedy rice morphotypes were distinguished based on a combination of traits such as awn presence/absence and hull color, from 193 accessions collected in 17 locations. Results showed a high proportion of awnless accessions (strawhull-, intermediate strawhull-, and brownhull-colored morphotypes, together composing 65% of sampled accessions), with awned accessions represented by strawhull, brownhull, and blackhull forms. Clustering and PCA analyses revealed four major clusters: (1) O. rufipogon and the majority of awned, blackhull, and brownhull—suggestive of a type of weedy rice originating from wild Oryza populations; (2) elite indica cultivar rice and the majority of strawhull weeds—supporting a previous proposal that weedy rice from Malaysia mainly evolved from indirect selection on cultivars for easy-shattering feral forms; (3) the majority of brownhull; and (4) a mixture of other weedy morphotypes—potentially reflecting multiple origins and subsequent admixture. The combination of key morphological descriptors will be useful for advising farmers appropriately in strategies for controlling the spread of weedy rice, including periodic manual weeding to reduce buildup of the seed bank in the fields.

Ser-653-Asn substitution in the acetohydroxyacid synthase gene confers resistance in weedy rice to imidazolinone herbicides imazapic and imazapyr in Malaysia

“…Song et al [41] recommended that the modern elite rice cultivar is influential in the genetic evolution of Malaysian weedy rice. The recent morphological study of Malaysian weedy rice also supports the perception that the origin of Malaysian weedy rice was mainly contributed by the wild species of Oryza and the modern-bred elite cultivars [42]. The 99% identity of AHAS gene between the weedy rice S and MR219 in this study represented a close resemblance of Malaysia weedy rice to its local cultivated variety of rice.…”

Little White Lies: Pericarp Color Provides Insights into the Origins and Evolution of Southeast Asian Weedy Rice

“…Notably, more than three-quarters (77%) of weed accessions in our sample set carry functional Rc alleles, a marked contrast from allelic distributions at the domestication genes sh4 , Bh4 , and An-1 . In a recent morphology based study of a larger sampling of Malaysian weedy rice ( N = 193 accessions), Sudinato et al (2016) observed red or brown pericarp color in a comparable proportion of the samples (68%). This suggests that Rc allelic distribution observed here may be generally representative of Malaysian weed populations.…”

Cross-Resistance to Imazapic and Imazapyr in a Weedy Rice (Oryza sativa) Biotype Found in Malaysia

“…Moreover, Malaysian weedy rice is highly diverse in morphology and phenology. Molecular (Song et al, 2014) and morphological (Sudianto et al, 2016) studies collectively have claimed that the local conventional indica rice cultivars and wild rice (Oryza rufipogon) populations genetically contributed to the complexity of weedy rice in Malaysia. Therefore, synchronization in flowering period between the weedy and cultivated rice and genetic compatibility are expected to support intermittent gene flow across these Oryza groups.…”