A Farmer’s Approach to Detecting Photoperiod Sensitivity in Rice (Oryza sativa ssp. indica) Landraces

Most indigenous rice landraces are sensitive to photoperiod during short day seasons, and this sensitivity is more pronounced in indica than in japonica landraces. Attempts to identify photoperiod sensitive (PPS) cultivars based on the life history stages of the rice plant, and several models and indices based on phenology and day length have not been precise, and in some cases yield counterfactual inferences. Following the empirical method of traditional Asian rice farmers, the author has developed a robust index, based on the sowing and flowering dates of a large number of landraces grown in different seasons from 2020 to 2023, to contradistinguish PPS from photoperiod insensitive cultivars. Unlike other indices and models of photoperiod sensitivity, the index does not require the presumed duration of different life history stages of the rice plant but relies only on the flowering dates and the number of days till flowering of a rice cultivar sown on different dates to consistently identify photoperiod sensitive cultivars.