Journal of Advances in Biology & Biotechnology

Accumulated growing degree days (GDD) are important parameters for predicting the onset of phenological stages such as bud emergence, flowering, and maturity. Growing degree days are based on the idea that the real time needed to reach the phenological stage is a function of temperature in the range between the optimal and base temperatures. The GDD data can help farmers estimate the timing of these critical growth stages, aiding in the planning and management of agricultural practices. The current study was carried out in 2021-22 and 2022-23 to study growing degree days and photo-thermal response of African marigold under year-round transplanting in Punjab, at Punjab Agricultural University, Ludhiana, Punjab, India. The established agroclimatic indices for temperature studies in the domain viz., growing degree days (GDD), helio-thermal units (HTU) and photothermal units (PTU) were computed for year-round transplanting of the crop. The present study, the crop transplanted from 15^th March to 15^th July recorded higher GDD (1930.35-2207), PTU (25037.26 ^-27965.65) and HTU (16176.19 -14951.97) due to extended day sunshine hours and thus, witnessed shorter duration of flowering period and lower flower yield. Whereas, earlier days to full opening of flower when plant was transplanting September and October month, respectively. Optimum flower yield/m² in African marigold (July to August), (1521 to 2465 g/plant) however, recorded lower GDD, HTU and PTU for attainment of bud appearance, color break stage and full opening of flower as compare to summer transplanting periods consequently had longer duration of flowering resulting in higher heat use efficiency and flower production.