Retention of latex at harvest, enhanced mango (Mangifera indica L.) fruit resistance and reduced anthracnose and stem-end rot

Abstract

Unripe mangoes contain a network of minute latex canals in its exocarp, outer mesocarp and the pedicel. Latex, when retrieved, separates into an upper oily layer containing antifungal resorcinols and a lower aqueous layer with chitinase activity. Latex disappears in coincidence with ripening and decline of fruit resistance to fungal pathogens. The present study investigated if retention of latex at harvest enhances fruit resistance and reduces anthracnose and the stem-end rot (SER) development during ripening. Latex was retained by harvesting fruit with a portion (approximately 1 cm) of pedicel while in the controls, latex was drained off by removing the pedicel. Anthracnose and SER development from natural infections or following artificial inoculation was assessed at ripe stage. The results showed a significant reduction in the incidence and severity of anthracnose in the cultivar 'Willard' susceptible to anthracnose when latex was retained at harvest. There was delayed SER development when latex was retained in the susceptible cultivar 'Karutha Colomban'. A negative trend was observed between the pedicel length and anthracnose or SER level in cultivars susceptible to the two respective diseases. The fruit peel in which latex was retained had greater chitinase activity. The reduction of anthracnose and SER could be due to the greater resorcinols and chitinase activity respectively in latex-retained fruit. The results indicate a direct involvement of latex in fruit resistance and the possibility of its manipulation to protect ripe fruit from fungal rotting.

A qualitative analysis of mango (<em>Mangifera indica</em> L.) latex and anatomy of latex canals

“…The non-aqueous phase of latex is a rich source of 5-n-heptadecenylresorcinol and 5-n-pentadecylresorcinol [6]. The aqueous phase of mango latex also contributes towards fruit resistance, by having Chitinase enzyme [7]. Gallotannins, reported to be predominant antifungal compounds in mango peel [14,15] with antifungal inhibition zones at Rf 0.00 are absent in latex.…”

“…During harvest of mangoes, latex spurts out and is frequently deposited on the surface of the same or neighboring fruits causing sap injury, making the fruit skin brown and un-attractive [3].The non-aqueous phase of mango latex contains antimicrobial substance [5,6].Mango latex contains antifungal resorcinols in the nonaqueous phase and [6] chitinase enzyme in the aqueous phase [7] that play a defensive role against postharvest pathogens. Retention of latex in fruits was found to reduce postharvest disease development [7]. A high correlation exists between the concentration of resorcinols in mango latex and the (w/w) percentage of the non-aqueous phase of mango latex [6].…”

Harvesting Mango Fruit with a Short Stem-End Altered Endophytic Microbiome and Reduce Stem-End Rot

“…These findings suggested that the stem plays a crucial role in SER resistance, and even a short stem that retains on harvested fruit can protect the fruit from postharvest decays. [12] also reported that mango fruit that was harvested with stem reduces anthracnose and SER development during ripening when compared to fruit that the stems were removed. [11] also received similar results and showed a reduction in anthracnose and SER incidence and severity in fruit with a long stem attached.…”

“…Indeed, harvesting fruit with long stem was previously reported to reduce both anthracnose and SER development during ripening [11][12][13]. However, harvesting fruit with a long stem could be problematic for the packing-house application, as the stem can easily break and the latex can leak on the processing line.…”

“…Differing relationships were found between the resorcinol levels and relative susceptibilities of different mango cultivars to anthracnose [11,37]. Strong positive relationships occur between resorcinol concentration in the peel and latex and fruit resistance to artificially inoculated anthracnose [12].…”