In this research we successfully analyzed 16
micosatellite markers as well as DNA sequence variation from the pVAT
gene region in order to understand the origins of US weedy red rice.
Using standard phylogeographic methods, it was clear that US weedy
rice is most similar to Oryza sativa indica rice, the type of
rice typically grown in the lowlands of Asia. Here in the United States,
Oryza sativa japonica is preferentially cultivated. |These
results suggested that US weedy red rice is of Asian origin but the DNA
sequence variation was insufficient to understand the dynamics of weedy
red rice in US cultivation systems. We were able to resolve some
of these dynamics by examining the variation in microsatellite markers
distributed across the genome using genetic distance and the population
assignment program STRUCTURE (Pritchard et al 2000). These results
demonstrated that US weedy red rice is composed of two major forms, or
ecotypes, Stawhull and Blackhull. Both of these weedy rice forms
likely arose from hybridization between cultivated rice in Asia and
sympatric Oryza rufipogon (wild rice). Additionally,
some forms of weedy rice showed evidence of hybridization with US
cultivated rice, suggesting that weedy red rice is capable of crossing
with O. sativa japonica. This may lead to the development
of new weedy rice ecotypes in US rice cultivation. In particular,
crop allele escape, including any transgenic crop alleles, could likely
enter the weedy rice populations and contribute to more aggressive weed
dynamics in the future.
Weedy Red Rice is an increasingly
problematic agricultural problem in the major rice producing areas of the
southern midwest and south. This form of rice is found mixed into
cultivated rice fields and shares traits common in both cultivated and wild
rice. These plants are high yield plants with seeds which shatter, fall
off before harvest, and often have awns, long hair-like structures common in
wild populations. Concerns exist for the introgression of these wild
traits into cultivated rice and forming super-weeds. Additionally,
the possibility for genetically modified crops to hybridize with these weedy
forms exists. Understanding where these weedy forms come from,
genetically and geographically, is important for proper control and containment
of weedy red rice in the United States. I plan to examine the DNA
sequences of cultivated, wild, and weedy rice and analyze mutational differences
in order to understand the history and spread of weedy rice. Applying
phylogenetic techniques, I hope to understand the number of introductions of
weedy rice to US rice fields as well as the geographic regions from which
they arose.
