A BBCH-scale code for the phenology of sand rice (Agriophyllum squarrosum (L.) Moq.)

Sand rice (Agriophyllum squarrosum (L.) Moq.), an annual psammophyte, is a promising wild plant for de novo domestication. Although many related studies have been documented recently, a basic phenological scale describing its growth stages is lacking. To address this gap, we have defined nine principal growth stages, each subdivided into several secondary stages according the international BBCH coding system. The growth stages mainly include seedling emergence, leaf development, formation of the primary branches, main stem elongation, inflorescence emergence, flowering, fruit development, ripening and senescence. Importantly, the growth sequence of sand rice reveals a distinctive stage, coded as BBCH21, characterized by the elongation of the first pair of primary branches, which occurs prior to main stem visible (BBCH30). This branch priority phenotype in sand rice strongly challenges the generally recognized growth pattern of ‘apical dominance’ in dicotyledons. The sequential and chronological progression of principal growth stages of sand rice was further determined in an experimental field with a representative genotype from the Tengger desert of Northwest China in 2023. The establishment of BBCH scale of sand rice lays a methodological foundation for morphological assessment among different germplasms and between wild-type and mutant plants. This will accelerate the de novo domestication process of sand rice using natural selection and artificial mutagenesis.