Coconut Lethal Yellowing Diseases: A Phytoplasma Threat to Palms of Global Economic and Social Significance

Abstract

The recent discovery of Bogia coconut syndrome in Papua New Guinea (PNG) is the first report of a lethal yellowing disease (LYD) in Oceania. Numerous outbreaks of LYDs of coconut have been recorded in the Caribbean and Africa since the late Nineteenth century and have caused the death of millions of palms across several continents during the Twentieth century. Despite the severity of economic losses, it was only in the 1970s that the causes of LYDs were identified as phytoplasmas, a group of insect-transmitted bacteria associated with diseases in many other economically important crop species. Since the development of polymerase chain reaction (PCR) technology, knowledge of LYDs epidemiology, ecology and vectors has grown rapidly. There is no economically viable treatment for LYDs and vector-based management is hampered by the fact that vectors have been positively identified in very few cases despite many attempted transmission trials. Some varieties and hybrids of coconut palm are known to be less susceptible to LYD but none are completely resistant. Optimal and current management of LYD is through strict quarantine, prompt detection and destruction of symptomatic palms, and replanting with less susceptible varieties or crop species. Advances in technology such as loop mediated isothermal amplification (LAMP) for detection and tracking of phytoplasma DNA in plants and insects, remote sensing for identifying symptomatic palms, and the advent of clustered regularly interspaced short palindromic repeats (CRISPR)-based tools for gene editing and plant breeding are likely to allow rapid progress in taxonomy as well as understanding and managing LYD phytoplasma pathosystems.

Expanding and exploring the diversity of phytoplasmas from lucerne (Medicago sativa)

“…This indicates that the collection of Hemiptera species (even those present in large numbers) from host plants that are proven to be infected by phytoplasmas (two diverse strains) is not evidence for vector status. Clearly sampling over a larger spatio-temporal scale will be necessary to establish which insect species may test PCR positive though transmission tests are necessary to provide definitive evidence of vector capacity32.…”

Relative contribution of rainfall and coconut hybrids to the abundance and composition of the Auchenorrhyncha community as potential vectors of phytoplasmas in the state of Sergipe, Brazil

“…Lethal palm declines also occur in some countries of North and Central America, Africa, Caribbean and Oceania (Dollet et al ., ; Harrison et al ., ; Gurr et al ., ). They are quarantine diseases that still remain undetected in Brazil.…”

Sandalwood spike disease: a brief synthesis

“…Mycoplasmas are now referred as phytoplasmas, i.e., prokaryotes lacking cell walls, infecting a wide range of plant taxa (Marcone 2015). Plant diseases caused by, or associated with, phytoplasmas occur in many agricultural and horticultural plants species of importance (Bertaccini et al 2014;Arunkumar et al 2016;Gurr et al 2016). There are several reviews on various aspects of phytoplasma research (Marcone 2011;Kube et al 2012;Marcone 2012;Bertaccini et al 2014;Bertaccini 2015;Marcone 2015;Gurr et al 2016;Trivedi et al 2016).…”

“…PCR-based methods revealed that Ca. Phytoplasma cynodontis belongs to 16SrI, which is one of the major groups of phytoplasmas associated with different plant species reported to be infected with phytoplasmas worldwide (Lee et al 1998;Hogenhout et al 2008;Bertaccini, Duduk 2009;Laimer et al 2009;Marcone 2011;Rao et al 2011;Delić 2012;Kube et al 2012;Gurr et al 2016). An understanding of phytoplasma ecology and epidemiology has increased as a result of the use of these PCR-based methods (Martin et al 2000).…”

“…Thus, the most effective methods to eliminate SSD from sandalwood tissue are likely to be the use of tissue culture to create disease-free superior genotypes (Balasundaran, Muralidharan 2004), or to employ genetic transformation to introduce sequences that, once overexpressed, will reduce the phytoplasma titre, or the development of insect-resistant plants. Phytoplasma-induced disease can be controlled by proper management of insect vectors (Weintraub, Beanland 2006;Gurr et al 2016), removal of infected plants from the field (Gurr et al 2016), and of the application of plant growth-promoting microbes that not only enhance nutrient levels but also provide protection against microbial and insect vectors (Trivedi et al 2016). …”