Regression analysis of growth pattern in different Citrus species and their cultivars in relation to heat units under semi-arid conditions of Hisar

The experiment was conducted by using well maintained 12 year old trees each of sweet orange (Citrus sinensis (L.) Osbeck) cv. Jaffa and Pineapple, mandarin hybrids Pearl Tangelo (Citrus reticulate Blanco x Citrus paradisi Macf.) and kinnow (Citrus nobilis Lour. x Citrus deliciosa Tenore) and grapefruit (Citrus paradisi Macf.) cv. Duncan and Ruby Red was carried out at CCS HAU, Hisar during 2014 and 2015. Spring flush was taken for the investigation, where all Citrus species and cultivars behaved differently from each other. Under North-Indian conditions flowering occurs only once in the year during February-March. Shoot length and specific leaf area were observed maximum in grapefruits, shoot diameter in Jaffa, shoot inter-nodal length in mandarin Kinnow and the leaf area and specific leaf weight in Pearl Tangelo. On the basis of these regression findings of present studies, it may be concluded that Citrus species sense the low temperature growth and phenology based on accumulation of required heat units.