Has Chromatography Found the Key to Beating Citrus Fruit Greening?

Huánglóngbing — or HLB to his friends — is not a new 21^st century version of Hong Kong Phooey (ask your Dad). In fact, HLB is possibly one of the most destructive diseases that can affect citrus crops. Since its spread to Florida, millions of citrus trees have been killed and this has resulted in a decline in production of many citrus fruits in growing regions.

A recent study published in the journal Plant Physiology and Biochemistry looks at the issue of HLB disease and sets out to discover why a new mandarin hybrid seems to be tolerant of the disease. Let’s find out more about HLB and what the team from the Florida has found.

Beware the yellow dragon

Citrus greening disease or HLB is a disease that can decimate citrus plantations. The literal translation of huánglóngbing is yellow dragon disease — perhaps due to the yellowing of the veins and tissue of leaves, the initial symptoms of HLB. This if followed by a discoloration of the entire leaf, defoliation of the tree and the death of twigs. After the disease has spread to the roots, the entire plant dies. But one of the symptoms is the greening of citrus fruit after they have ripened on the tree.

The disease is caused by a bacterium that is spread by a jumping plant louse. In Florida, the effect of HLB is to potentially ruin the state’s multimillion dollar industry — but researchers are fighting back and the first step is Sugar Belle®.

Sugar Belle® or LB8-9 — take your pick

In their quest to beat HLB, researchers at the University of Florida are developing new citrus fruit hybrids. One hybrid that they have developed is a mandarin hybrid known as Sugar Belle®. This mandarin seems to fight off the greening better than other citrus fruits — but how?

In a paper titled Metabolically speaking: Possible reasons behind the tolerance of ‘Sugar Belle’ mandarin hybrid to huanglongbing, a team from the University of Florida Institute of Food and Agricultural Sciences report on the possible mechanism used by the hybrid mandarin to defeat the greening disease.

Using gas chromatography – mass spectrometry (GC-MS) the team found that the mandarin is high in several volatiles and compounds known as phenolics. GC-MS is a commonly used technique when analysing volatiles as discussed in the article, Rapid Screening of Volatile and Semi-Volatile Organic Components in Cocoa Beans and Chocolate Products Using a Portable GC/MS System.

The mandarin hybrid is a mix of sweet Clementine and a bell-shaped fruit known as Minneola and has a strong aroma and rich taste. Best described as a mandarin with a tangy punch. In a press release one of the paper’s authors states: ‘The results of this study gives more insights about the mechanism behind tolerance of some citrus cultivars to HLB. Understanding of the mechanisms behind tolerance to HLB could help in developing economically tolerant citrus cultivars’