Citrus greening woes - Tackling the disease calls for integrated approach
Christopher Serju, Gleaner Writer
With no known cure for citrus greening or resistant citrus varieties, controlling the disease in Jamaica will require a national effort. Consultants hired by the Food and Agriculture Organisation of the United Nations (FAO) working with the Ministry of Agriculture and Fisheries have determined that it will take an Area Wide Integrated Management System dubbed AIMS to adequately raise awareness in the first place and then implement the necessary strategies to adequately cope with the disease which is here to stay.
In addition to citrus, the insect (Asian Citrus Psyllid) which spreads the bacterium (Candidatus Liberibacter) has also been observed on the ornamental known locally as Orange Jasmine (Murraya paniculata), so widespread and invasive is it. So unlike other plant diseases which usually are restricted to commercial plots, tackling citrus greening will require the cooperation of even householders who have only one orange tree at home.
By the time symptoms of the disease are manifested by way of mottling in leaves or notching on leaves caused by psyllid feeding it has in all likelihood already compromised the quality of fruits on the tree. The extent, however, will depend on the period of infection which results in deterioration of the fruit quality and size with some so lopsided they appear to have been beaten.
Consultant Paul Mears explains: "The fruit itself, the sugar content is not evenly distributed and the ripening process is compromised so the fruit is not fully ripe. You'll find a part of the fruit is green and when you actually taste that fruit it's actually terrible tasting and you'll get a poor quality fruit. So the sugar is not gonna be inside, it's all gonna be acidic."
Infected fruits ripen from the top where they are attached to tree, resulting in colour inversion or the top of the fruits showing the yellowing signs of ripening while the lowest quarter remain green, a testament to the fact that it is still underdeveloped. Invariably the fruits fall from the tree before reaching maturation resulting in serious economic loss.
Planting out new trees is not practical since the psyllid reproduces only on the new soft flushes and with their devastating nutrient-leaching impact young plants are not likely to survive to the stage where they start bearing.
It is in a bid to save the local industry that the FAO has stepped in to provide the technical competence to firstly arrest the decline in citrus production, with the aim of ultimately ratcheting this to a level where it can become profitable despite the prevalence of citrus greening. The organisation is aware that if nothing is done now, in five years time there will be no citrus industry in Jamaica.
FAO representative in Jamaica Jerome Thomas offered this update on its involvement: "We have identified two persons from Florida because they have had some success in managing the disease, and the effort to revive the industry is also going to mean not only addressing the disease situation but propagation is critical. There is need to change the method of propagation to something more advanced, something minuscule, something called shoot tip culture and that expertise exists in Cuba."
For Paul Mears, an FAO consultant out of Florida with considerable experience in treating with citrus greening, the information gap about the disease is a major hurdle. "The Jamaican society is aware, not on a large scale, of the impact of the disease. On a technical level most people are aware this disease is possibly the most devastating disease for citrus in the world and Jamaica is taking advanced steps to protect the industry and cooperation at every level is paramount to achieve success."
He was part of a team which visited Jamaica recently to spearhead training in shoot tip grafting a process for producing pathogen-free cultivars. Dr Olga Mas Camacho, a graduate of the University of Havana with considerable expertise in the technique, explained that the training of scientists in this area is a long-term investment.
"It is important to know that we will need at least two years to obtain pathogen-free plants in Jamaica. If we consider that the first shoot tip plants are just growing, they have been grafted during this week and the team will continue performing shoot tip grafting in coming weeks and months. It is indispensable to complete the value indexing and molecular indexing in order to know if this material is pathogen-free and this will need time.
Continuing, she said: "There are some tests that need a time period of six months, while there are others that need one year. So you will take into consideration the period needed for the shoot-tip grafted plants then the grafting on to developed rootstock to speed up the procedure and then it is possible to start indexing. After that is when the Jamaican growers could be happy because then they will receive pathogen-free bud wood."
For Barrett, one of the foremost local experts on citrus greening and who identified it here in 2009, Jamaica's hilly terrain will mitigate against the use of mechanised equipment to facilitate boom sprayers and aerial spraying which would be two very cost-effective options. However, he is pleased with the level of help from the FAO, especially with respect to the establishment of facilities to provide clean, pathogen-free planting stock.
"They have helped us with setting up a model nursery which is going to produce about 10-20,000 plants a year based on the capacity and they are also providing us with a bud wood facility at Bodles Research Station and this will then generate all the bud wood, clean material that we can then distribute to these nurseries." With the cost of setting up a covered nursery running anywhere between J$2 and J$10 million proving prohibitive most private citrus nurseries have gone out of business.
Still, even with the welcomed intervention, the Jamaica Citrus Protection Agency executive believes that things will get worse for the local industry before they pick up, citing the impact of multiple infection points which is a feature of the manifestation locally.
"Based on the fact that you can find it in almost all the groves and one of the symptoms of citrus greening is that the fruit falls, so you are losing production on the infected branch. What we are finding is that our trees do not only have single-point infection, which is just one branch, instead they have multiple-point infection.
"When you have multiple-point infection it means your fruit drop is going to be heavy and I would go further to say that one of the more susceptible varieties is the ortanique which is an indigenous cultivar This year they are very small and most of them have dropped off, so it really has put a squeeze on the industry because most farmer have not been doing what they need to do in terms of managing the disease."