Spongy tissue in Alphonso mango - significance of in situ seed germination events.
Ravindra V., Shivashankar S.
Author Affiliation: Division of Plant Physiology and Biochemistry, Indian Institute of Horticultural Research, Hessaraghatta, Bangalore 560 089, India.
87 : 1045-1049
Abstract : Mature green fruits of mango cv. Alphonso were harvested from trees grown in Bangalore, Karnataka, India, and ripened at an ambient temperature of 25±2°C and relative humidity of 70±5% for 1-10 days. The ripe fruits were cut open and classified as healthy or spongy-tissue-affected, based on visual scoring. Observations on various physiological and biochemical parameters were recorded during 1998-2003. To elucidate the causative role of seed in spongy tissue formation, pre- and postharvest treatment of fruits with plant growth regulators (GA3 and paclobutrazol) was conducted during the 2004 fruiting season. Moisture content was significantly higher in seeds from spongy-tissue-affected fruits (STS) than seeds from healthy fruits (HS), while there was a corresponding decrease in the spongy tissue. Analysis of other seed components revealed that STS had significantly lower starch content (33.5%) and higher levels of soluble sugars (27.7%) than HS. A significant rise in the content of both DNA (76.7%) and RNA (65.5%) in STS indicated the rapid progress of germination. A substantial increase in the content of soluble protein (43.1%) in STS indicated de novo synthesis of various enzymes associated with germination. The phenols also increased substantially (51.6%) due to high metabolic activity. There was a significant increase in spongy tissue incidence in preharvest treatment of fruits with GA3 (70.2%), while there was a considerable reduction in incidence with paclobutrazol (16.4%) compared to 51.5% incidence in the control. GA3 treatment also resulted in higher intensity of spongy tissue, where >70% of the fruit mesocarp was affected. Postharvest treatment of fruits with plant growth regulators did not have any effect on spongy tissue formation. More than 70% of the fruits with spongy tissue were observed at late mature-ripe harvest stage, irrespective of the year, age of tree, orchard spacing, fruit position and size. The seeds from HS and STS fruits were distinctly different in their physiological status and biochemical composition. The incidence of spongy tissue varied with seed respiration rate and amylase activity.