Rapid burst of ethylene evolution by premature seed: A warning sign for the onset of spongy tissue disorder in Alphonso mango fruit?

Moisture stress induced in premature seeds due to the breakdown of funiculus in Alphonso mango led to the burst ofethylene evolution, which in turn caused a sudden increase of polyphenol oxidase activity in the pulp, resulting in thedevelopment of a black spot near the seed base. Reduced levels of very long chain fatty acids in 70% mature seeds withblack spots were associated with a sudden increase of cytokinins followed by a rapid rise of starch-metabolizing enzymesculminating in the onset of pre-germination events. Concurrently, an overproduction of p-OH benzoic acid inhibitedamylase and polygalacturonase enzymes and led to partial degradation of the stored starch and pectin in the pulp. A paralleldrop in climacteric ethylene production by the pulp led to incomplete ripening coupled with changes in composition, textureand aroma of the pulp, characteristic of spongy tissue. The results have provided strong experimental evidence to supportthe fact that increased competition for resources among developing fruits for the synthesis of seed fat plays a critical role inspongy tissue formation in Alphonso mango. The major highlight of the study is that rapid ethylene evolution by prematureseed is an early warning sign for the initiation of spongy tissue formation in Alphonso mango.

Do seed VLCFAs trigger spongy tissue formation in Alphonso mango by inducing germination.

Spongy tissue is a physiological disorder in Alphonso mango caused by the inception of germination-associated events during fruit maturation on the tree, rendering the fruit inedible. Inter-fruit competition during active fruit growth is a major contributing factor for the disorder which leads to reduced fat content in spongy tissue affected fruits. This study was, therefore, carried out to determine the possible association between seed fats and ST formation. The study of the fat content during fruit growth showed that it increased gradually from 40% fruit maturity. At 70% maturity, however, there was a sudden increase of fat content of whole fruit, leading to acute competition and resulting in differential allocation of resources among developing fruits. As a result, the seed in spongy-tissue-affected mature ripe fruit showed a marked drop in the levels of fats and the two very long chain fatty acids (VLCFAs), tetracosanoic acid and hexacosanoic acid together with an increase of linolenic acid and a fall in oleic acid contents, which are known to be key determinants for the initiation of pre-germination events in seed. Subsequently, a rise in the level of cytokinin and gibberellins in ST seed associated with a fall in abscisic acid level clearly signalled the onset of germination. Concurrently, a significant reduction in the ratio of linolenic acid/linoleic acid in pulp led to the loss of membrane integrity, cell death and the eventual formation of spongy tissue. Based on the above, it is concluded that a significant reduction in the biosynthesis of VLCFAs in seeds during fruit growth might trigger pre-germination events followed by a cascade of biochemical changes in the pulp, leading to lipid peroxidation and membrane injury in pulp culminating in ST development. Thus, this study presents crucial experimental evidence to highlight the critical role played by VLCFAs in inducing ST formation in Alphonso mango during the pre-harvest phase of fruit growth.