Variability in multiple embryo formation and seedling development of mandarin orange (Citrus reticulata Blanco) of the north-eastern Himalayan region of India

摘要

Occurrence of multiple embryos in a seed is a common phenomenon in citrus. Among the multiple embryos, nucellar embryos are taken as an advantage in propagation of citrus as plantlets originating from them are considered to be true to the parental type. In a natural cross-pollinated population, the extent of multiple embryo formation in the plants developed from zygotic and nucellar origins has a direct effect on the genetic variability observed in the offspring population. In a study with mandarin orange plants, collected from different locations of the north-eastern Himalayan region of India, the number of different multiple embryos per seed was found to be a variable trait. In spite of the existence of nucellar embryos, a good proportion of identical zygotic twin and triplet seedlings were also observed in most of the plants. Twins from nucellar embryos were also found in some cases. Some twin seedlings were developed having a common primary root. Also in a few cases, anastomosis-like development of the primary roots of the two closely developing twin seedlings was observed. Of 15 RAPD markers tested, three could differentiate zygotic, nucellar and twin seedlings initially identified on the basis of their morphological origins. The number of zygotic twin seedlings recorded in different plants indicated that this character might substantially contribute to creating genetic heterogeneity in the seed-propagated population of mandarin orange in this region.