Recent changes in thermal indices in Mango cv Dashehari under subtropical climate

Systematic recording of changes in thermal indices at tree phenological stages is prerequisite to understand the impact of environmental factors on mango. Keeping this in view, latest information on growing degree day units, heliothermal and photothermal units were cumulated at flowering, fruit set, fruit development and maturity stages in mango cv Dashehari during growing season of 2021 and 2022. Recent data showed variability in environmental indicators during critical reproductive stages. Highest weekly mean maximum temperature of 39.50 and 44.21°C were recorded in 2021 and 2022 fruiting cycles while minimum temperature showed 1.29°C during 2022 and 3.79°C in 2021. During 2022, bright sunshine hours had maximum value of 15.59h whereas in 2021, 10.7 h. During reproductive stage, weekly mean pan evaporation of 4.46 to 10.01 mm/day was recorded in 2021 fruiting cycle; in contrast, in the next season, 4.77 to 10.06 h was observed. Weekly average growing degree day from January to June varied between 860.51 to 2347.91°Cd and 917.16 to 2597.30°Cd respectively in 2021 and 2022 growth cycles. The heliothermal units had 3094.05 to 17727.54 and 3534.42 to 23219.79°Cdh with photothermal of 8932.92 to 32084.15 and 9517.23 to 35498.52 °Cdh respectively in 2021 and 2022 fruiting seasons. The flowering stages experienced lower heat accumulation in 2021 as compared to 2022 fruiting seasons. It was observed that peanut and marble phase had around 884.48 to 1606.44°Cd GDD across fruiting season. Maturity period had 1655.41 to 2597.3°Cd GDD across seasons. Histographic distribution of these thermal indices at vegetative, flowering, fruit setting to maturity had indicated widespread distribution pattern of GDD, HTU and PTU across seasons. It was found that a 1500 to 1600°Cd GDD at frequency level of <5 per cent in 2021 marble stage while the same GDD at 6 per cent frequency level with higher 1600 to 1700°Cd class intervals at <2 per cent was noted in the next season fruiting. Such widespread distribution indicated the affect of climatic factors at each stage and season. Lower fruit production of 6 to 8 t ha-1 was accorded due to severe atmospheric aberration during the 2022 cropping cycle. Results suggested the impact of environmental factors on tree performances and thus resource conservation practices needs to be followed rigorously to attain optimum yield of mango at subtropics.