Jackfruit - Postharvest Fruit Rot

One of the most common problems in the jackfruit trade is post-harvest fruit rot. Although the condition rarely occurs before maturity, it often develops at the onset of ripening and can cause significant losses at the wholesaler and retailer level.

The Problem
The problem can first be detected when a slightly discoloured soft area appears. Typically these soft spots are somewhat circular or elliptical in shape, and a few inches in diameter. In some cases depressions are visible in the skin. Sometime later, fungal mycelia become visible, and from there the disease progresses outward until the entire jackfruit is destroyed. At the early stages of the infection, the affected portion can be cut out allowing salvage of part of the fruit. Normally, jackfruit is shipped as a mature but unripe fruit, and the final ripening occurs either in transit or at the destination. Although low temperatures during transit and storage do help to reduce fruit rot, they also tend to induce dormancy in the ripening process of the jackfruit, which in many cases, is difficult or impossible to break. Chilling can also lead to water condensation inside the fruit cavity, which in some cases makes the fruit arils wet and less appealing. The inability to use low temperatures to manage fruit rot is one of the important limitations in the development of jackfruit exports. The portion of fruit affected by rot increases naturally with the storage time. If managed well, only a small percentage of the fruit are affected during the first two weeks after harvest; however, progressively more are affected in the third and fourth weeks, and this occurs principally while the fruit are at the warehouses of the destination wholesaler or retailer.

The Cause
To aid in ripening, jackfruit are often either wrapped or placed into a box in order to contain and concentrate the ethylene gas released by the fruit. The ripening process results in a considerable elevation of the sugar levels in the fruit tissues, and considerable amounts of heat and water vapour are given off. The combination of the warmth and the high humidity, combined with the creation of nutrient-rich tissues results in an excellent environment for the development of saprophytic fungi. The reported causal agents of fruit rot in jackfruit are Rhizopus artocarpi, Colletotrichum lagenarium, and Sclerotinia rolfsii. We have also encountered periodic problems with premature post-harvest fermentation apparently caused by opportunistic yeast infections. In all cases, the problem is made more severe if there are abrasions on the skin of the fruit. The practice of some producers to use ripening aids such as calcium carbide or ethephon seems to worsen the fruit-rot problem.

Possible Solutions
Ideally, management of jackfruit rot needs to start in the orchard. Most jackfruit are bagged in order to reduce attack from insects, but ideally these bags should be porous and should not allow moisture to build up next to the fruit as such conditions encourage the development of the fungal inoculums. Paper, cloth, or plastic- woven bags seem preferable over impermeable plain-plastic materials.

At harvest time, the fruit must not be allowed to make contact with the soil. After cutting they should be placed on a clean bag or tarp, or put directly into the truck for transport to the packing house. The fruit should be subsequently washed in order to remove any adhering fungal spores, and then carefully dried before packing. Some workers have recommended post-harvest dipping in fungicide solutions such as benomyl, and others have suggested simply washing in plain or chlorinated water.

Shipping boxes should also be designed to absorb and minimize the moisture and heat build-up. We normally use cardboard boxes with a lot of paper to absorb the moisture given off by the fruit. I have also seen shippers use a plastic-mesh basket in order to maximize airflow around the fruit, and I have heard of other people who remove the outer rind entirely in order to minimize the inoculum.

In airfreight shipments, it seems impractical to ship jackfruit that are in the peak of ripening as the temperature and humidity in the shipping container would become very high, and fruit rot would develop rapidly. In the summer, we ship jackfruit while they are still very hard with no detectable smell, and in the winter we send them at the stage where they have a slight smell but are still fairly hard. In both cases additional ripening may need to be done at the destination, especially in winter.

We find that even with good management and careful selection of ripening stages before shipping, post-harvest rot losses from farm to consumer affect between 5 to 10% of our jackfruit. Clearly, additional research would be worthwhile. In particular, better recommendations for post-harvest handling are needed, including better ways use dips and hot water washes, as is often done with mangoes.

Ref:  forum of http://www.itfnet.org 2007

Authored by: 
Bruce Milligan
Sourced from: 
STFC Newsletter April-May 2007