New hosts of 16SrI phytoplasma group associated with edible Opuntia ficus-indica crop and its pests in Mexico

Abstract

In Mexico in the region of Nopaltepec in Mexico State, the edible Cactus crop, Opuntia ficus-indica is mainly cultivated for prickly pear fruit production. This crop has problems with common pests (insects, mollusks and weeds) which may serve as reservoirs and together with the named Cactus with phytoplasma-like symptoms which through the time inhibit the fruit production, and for this reason, the farmers called these Opuntia plants as Planta Macho (male plant). For molecular identification of the probably involved phytoplasma during 2005 and 2006, 38 samples of Opuntia plant tissues, fruit and some pests were collected for DNA extraction. By direct and nested PCR, 16S rRNA gene was amplified and sequenced. PCR products were analyzed by RFLP with restriction enzymes and in the sequences restriction sites were mapped. Phylogenetic analysis showed that the same phytoplasma was associated with Opuntia crop and its pests (the weeds Argemone mexicana, a grass and Lupinus sp.; a chinch bugs, Chelinidea sp. and the brown garden snail, Helix aspersa). Thus the edible Cactus crop and pests represented novel hosts of Cactus male plant Phytoplasma, and was classified as 16SrI Aster yellows group, of the species Candidatus phytoplasma asteris. This is the first report of this phytoplasma in Mexico and elsewhere.

Potential causal factors of “heart-shaped cladode” malformations in cactus pear (Opuntia ficus-indica (L.) Miller)

“…This could have implications for propagating diseases using as seed cladodes that could contain phytoplasmas but have no visible symptoms. Fucikovsky et al (2011) also identified phytoplasmas in healthy and diseased cladodes with the symptom of inhibition of fruit production, characteristic of cactus pear "macho plants", which also exhibit thickening and heart-shaped cladodes; these symptoms have been associated with phytoplasmas of the species Candidatus Phytoplasma asteris in the 16Srl group. These phytoplasmas have been also found in other plants (Argemone mexicana and Lupinus sp.…”

“…), as well as in bugs (Chelinidae sp. ), which can function as reservoirs and vectors of phytoplasmas, respectively (Fucikovsky et al 2011). Therefore, it is important to control weeds and insects in areas surrounding cactus pear plantations to reduce the risk of damage by phytoplasmas, among other pathogens.…”

“…The malformations in plants have been commonly attributed to infections by viruses, viroids and phytoplasmas (Spallino et al, 2017;Singh et al, 2018). However, heart-shaped cladode malformations are not entirely in accord with symptoms associated with phytoplasmas in other studies (Granata et al, 2006;Fucikovsky et al, 2011;Omar & Foissac, 2012;Suaste-Dzul et al, 2012;Martínez-Salgado et al, 2020). A group of pathogens that have recently received attention for their possible sanitary impact are geminiviruses that consist of circular single-chain DNA molecules.…”