Study of the peculiarities of the main phenological growth and development phases, as well as commercial qualities of fruits of rare citrus taxa under conditions of humid subtropics of Russia

Abstract

   The citrus collection of the FRC Subtropical Research Center of the RAS includes 144 genotypes and contains rare species and cultivars that are of great interest for use in production, breeding, and ornamental horticulture.   The research examined 13 rare taxa: Citrus aurantifolia, C. aurantifolia ‘Foro’, C.×latifolia, C.×bergamia, C. ichangensis, C. limon ‘Del Brasil’, C.×limonelloides, C.×limetta ‘Chontipico’, C. maxima ‘Sambokan’, C. medica, C. medica var. sarcodactylus, C.×meyeri, C.×myrtifolia.   The research established the times and differences in the passage of the main phenological phases, namely bud opening and flower-bud formation, flowering, second and third active growth, fruit ripening. The beginning of the growing season of the studied objects was registered in the second and third decades of March; the difference between the early onset for C. aurantifolia (16.03) and the late onset for C. ichangensis (01.04) is 14–20 days. Two active growth periods were established for C. ichangensis, C. limon ‘Del Brasil’, C. maxima ‘Sambokan’, and C. medica, while the other citrus taxa under study had three periods of active growth. According to their flowering dates, taxa with early (April 11–13), middle (April 18–19), and late (April 23–28) flowering time were identified. Long flowering (29–36 days) is typical for taxa with early flowering. Remontant taxa, i. e. C. aurantifolia, C. aurantifolia ‘Foro’, C.×latifolia, C.×bergamia, C.×limonelloides, C.×limetta ‘Chontipico’, C. limon ‘Del Brasil’, C.×meyeri were identified. From the beginning of the growing season to fruit ripening, the effective heat summation was determined to be 4710–5250 ℃. The study also identified taxa with late fruit ripening, namely C. medica and C.×myrtifolia (third decade of December – first decade of January). The taxa with the best commercial qualities and biochemical composition of fruits were C. maxima ‘Sambokan’, C.×meyeri, and C.×limetta ‘Chontipico’.