Dwarfing potential of indigenous mango varieties

Abstract

The Project on 'Dwarfing potential of indigenous mango varieties' was undertaken at the Department of Pornology and Floriculture, College of Horticulture, Kerala Agricultural University, Vellanikkara during the period 1999- 2000. Observations on the shoot extension growth of the parent rootstock trees for a period of one year, showed a rhythmic growth with periods of active growth and quiescence, except in the variety Moovandan. However no definite synchrony between the climatic parameters and flushing pattern of the varieties could be . noticed. Among the different morphological characters, a fair amount of variation could be noted with regard to number of shoots per half meter square, internodal length and number of leaves. But as such, no definite relationship could be noted between the growth potential of the tree and other characters. The varieties viz., Moovandan, Olour and Vellaikolumban exhibited distinct polyembryony, whereas only one sprout per stone could be noted in the case of other varieties including the variety Chandrakkaran. Mechanical manipulation through splitting of endocarp of the seed stone was advantageous by reducing the days taken for germination, enhancing the rate of germination and increasing the extent of polyembryony. Anatomy of the roots and leaves, made it possible to approximately place the varieties into groups of 'low growth potential' (LGP) and 'high growth potential' (HGP). Accordingly Vellaikolumban, Kalapady and Olour could be brought under the former and Moovandan, Chandrakkaran and Mundappa under the latter.

The varieties showed a clear variation with respect to the stomatal density of leaves. Stomatal density was highest in Moovandan and lowest 111 Vellaikolumban. Anatomy of the graft union indicated higher accumulation of calcium containing crystals in the conducting phloem of Bangalora/Vellaikolumban graft combination. The electrical resistance of the rootstock seedlings was found to be higher in Moovandan and Chandrakkaran and lower in Vellaikolumban, Olour and Kalapady. The apparent velocity of sap flow/transpiration stream in the grafted plants showed higher rates in the graft combinations involving Moovandan, Chandrakkaran and Mundappa and lower rates in Vellaikolumban, Kalapady and Olour as rootstocks. The rate of leaf respiration 111 one year old graft combination of Bangalora/Moovandan and Bangalora/ Vellaikolumban and their seedlings showed relatively higher rate of respiration in the grafted plants on Moovandan rootstocks than those on Vellaikolumban. Total phenol content in the dormant buds as well as in leaves of the mango rootstocks varieties showed higher values in Vellaikolumban and Kalapady and lower values in Moovandan and Chandrakkaran. Observations of the one year old graft plants in the nursery in terms of the maiden shoot growth did not reflect an immediate expected effect of the rootstock on the total growth and vigour of the combinations.