Pepper mild mottle virus: a formidable foe of capsicum production—a review

Abstract

Viruses are one of the major restraining factors in pepper cultivation globally. Among different viruses, pepper mild mottle virus (PMMoV) is one of the most detrimental plant viruses infecting Capsicum spp. belonging to the genus Tobamovirus and Virgaviridae family. It has a monopartite positive-sense single-stranded RNA genome of 6.35 kb size. On an average, PMMoV results in 15%–40% losses in capsicum fruit yield. However, the incidence of PMMoV can reach as high as 95%, leading to substantial yield losses ranging from 75% to 95%. The virus is transmitted via contact, soil, and seeds rather than via insect vectors. PMMoV, because of its seed-borne nature, now occurs worldwide. PMMoV mainly infects Capsicum spp. under natural conditions; however, it can experimentally be transmitted to other plants species belonging to the families Solanaceae, Cucurbitaceae, Labiatae, Chenopodiaceae, and Plantaginaceae. The resistance to tobamoviruses in capsicum is conferred by L locus. Mutations in the coat protein of PMMoV are responsible for the emergence of L-mediated resistance-breaking pathotypes. The highly contagious nature of the virus, seed transmission behavior, and the emergence of virulence complicate its management through a single approach. Therefore, efforts are directed towards providing a more practical and efficient integrated management solution using the RNA interference approach; exploitation of the L gene for resistance breeding; and the inhibitory potential of natural products, systemic resistance-inducing antagonistic bacteria, and chemically synthesized silver nanoparticles. Markers linked to L alleles have been observed to accelerate capsicum breeding programs through marker-assisted selection. In this study, an attempt has been made to compile the recent developments in PMMoV biology, pathogenic variability, genomic organization, and management strategies.

Assessment of elite pepper breeding lines using molecular markers

“…Because thrips are found inside pepper flowers with closed petals, chemical control is very difficult. In addition, although there are many viral pathogens for which pepper is a host, TSWV (Karavina and Gubba 2017) and Pepper Mild Mottle Virus (PMMoV) (Kumari et al 2023) cause major problems, especially in greenhouse pepper production. Although cultural methods (Fajinmi and Odebode 2010;Karungi et al 2013) are often used to control viral diseases in pepper, the most effective way to control viral diseases is genetic control (Sreenivas et al 2020;Parisi et al 2020), i.e., the development of virus-resistant varieties.…”

Engineered Resistance to Tobamoviruses

“…The leucine-rich repeat domains of the L proteins encoded by different L alleles differ in recognition specificity creating a hierarchy of different tobamovirus pathotypes, which can be classified depending upon whether they are controlled by or overcome the major alleles L 1 through L 4 . Thus, TMV is controllable by L 1 but some variants of PMMoV, the most problematic of the Capsicuminfecting tobamoviruses [33,34], can break resistance conferred by L 4 , the allele that confers resistance against the widest spectrum of tobamoviruses [32,33,35,36]. Together with deployment of resistance genes, other much more basic measures such as improved phytosanitary measures to prevent mechanical transmission from workers' hands, tools and other equipment as well as cultivation under protected conditions, i.e., under glass or in tunnel houses, have also helped by excluding inoculum from susceptible crops susceptible.…”

Engineered Resistance to Tobamoviruses

“…These L resistance genes encode NB-LRR immune sensors for which the elicitors are amino acid sequences within the CP orthologs produced by pepper-infecting tobamoviruses [31][32][33]. Pepper lines lacking L genes can be susceptible to systemic infection by a broad range of tobamoviruses that include TMV, ToMV, tobacco mild green mosaic virus, paprika mild mottle virus, and PMMoV [5,33,34]. The leucine-rich repeat domains of the L proteins encoded by different L alleles differ in recognition specificity, creating a hierarchy of different tobamovirus pathotypes, which can be classified depending upon whether they are controlled by or overcome the major alleles L 1 through L 4 .…”

“…The leucine-rich repeat domains of the L proteins encoded by different L alleles differ in recognition specificity, creating a hierarchy of different tobamovirus pathotypes, which can be classified depending upon whether they are controlled by or overcome the major alleles L 1 through L 4 . Thus, TMV is controllable by L 1 but some variants of PMMoV, the most problematic of the Capsicum-infecting tobamoviruses [33,34], can break resistance conferred by L 4 , the allele that confers resistance against the widest spectrum of tobamoviruses [32,33,35,36]. Together with the deployment of resistance genes, other much more basic measures such as improved phytosanitary measures to prevent mechanical transmission from workers' hands, tools and other equipment, as well as cultivation under protected conditions, i.e., under glass or in tunnel houses, have also helped by excluding inoculum from susceptible crops.…”