UV tolerance in weedy rice (Oryza rufipogon) is inferred from dihybrid cross with Oryza sativa cv. Meghadambaru: a roadmap in rice domestication

Genotype is an important factor for calibrating plant response to UV-B stress, but little is known about how it reduces yield. Oryza rufipogon (weedy rice) is sensitive to UV stress. It was crossed with Oryza sativa cv. Meghadambaru (a UV-tolerant genotype), and the impact on stress tolerance was assessed in the progeny and progenitors in F1 and F2 populations. UV stress affected photosynthetic activity in leaf, lemma + palea, and awns, showing inhibitory effects on SPAD, maximal photochemical efficiency of PSII (Fv/Fm), electron transport rate (ETR), photochemical quenching (qP), maximal fluorescence (Fm), and O-J-I-P curve in all genotypes. The weedy traits of O. rufipogon and UV-tolerance traits of cv. Meghadambaru were inherited by the integrated hybrid genotypes from the parental cross in F1 and F2 generations. O. rufipogon exhibited rapid evolution to gain UV stress tolerance in the natural cross, while cv. Meghadambaru exhibited a resurgence of weedy attributes, such as obtaining long awns. Flavonoid development genes of cv. Meghadambaru and long awn genes of O. rufipogon were found to be dominant alleles. Thus, weedy genes did not weaken the expression of flavonoid genes and vice-versa. Our results provided genomic evidence for the rice domestication process. Cultivated rice can be feralised into weedy rice, and weedy rice could be de-domesticated into cultivated rice.