Identification of a New Cotton Disease Caused by an Atypical Cotton Leafroll Dwarf Virus in Argentina

Abstract

An outbreak of a new disease occurred in cotton (Gossypium hirsutum) fields in northwest Argentina starting in the 2009-10 growing season and is still spreading steadily. The characteristic symptoms of the disease included slight leaf rolling and a bushy phenotype in the upper part of the plant. In this study, we determined the complete nucleotide sequences of two independent virus genomes isolated from cotton blue disease (CBD)-resistant and -susceptible cotton varieties. This virus genome comprised 5,866 nucleotides with an organization similar to that of the genus Polerovirus and was closely related to cotton leafroll dwarf virus, with protein identity ranging from 88 to 98%. The virus was subsequently transmitted to a CBD-resistant cotton variety using Aphis gossypii and symptoms were successfully reproduced. To study the persistence of the virus, we analyzed symptomatic plants from CBD-resistant varieties from different cotton-growing fields between 2013 and 2015 and showed the presence of the same virus strain. In addition, a constructed full-length infectious cDNA clone from the virus caused disease symptoms in systemic leaves of CBD-resistant cotton plants. Altogether, the new leafroll disease in CBD-resistant cotton plants is caused by an atypical cotton leafroll dwarf virus.

P0 protein of cotton leafroll dwarf virus‐atypical isolate is a weak RNA silencing suppressor and the avirulence determinant that breaks the cotton Cbd gene‐based resistance

“…Although the CBD resistance gene has not been cloned yet, it has been shown to be a single dominant resistance gene called Cbd that has been mapped to the chromosome 10 telomeric region (Fang et al ., ). Cbd confers absolute resistance to CLRDV and no systemic virus replication on leaves was observed (Agrofoglio et al ., ). Moreover, CBD‐resistant cotton varieties are also resistant to cotton bunchy top virus (CBTV), a recombinant virus between the 5′ region of CLRDV and the 3′ of an uncharacterized polerovirus.…”

“…The new disease, which is still spreading, is caused by a resistance‐breaking CLRDV isolate (atypical CLRDV, CLRDV‐at). The CLRDV‐at genome is positive‐sense, single‐stranded RNA and comprises 5866 bases (Agrofoglio et al ., ).…”

“…It has previously been demonstrated that P0 protein encoded by CLRDV‐ARG (P0 CL ) inhibits local but not systemic RNA silencing (Delfosse et al ., ). P0 CL‐at protein has an amino acid point mutation in the F‐box‐like motif, where the isoleucine (I) at position 72 is replaced by a valine (V) (Agrofoglio et al ., ). Interestingly, three resistance‐breaking CLRDV isolates from Brazil (Acr9, Ima2 and Ipa4) present the same amino acid point mutation in the F‐box‐like motif as P0 CL‐at and were characterized as weaker VSRs than Brazilian P0 CL (Cascardo et al ., ).…”

Chemical inhibition of Kir channels reduces salivary secretions and phloem feeding of the cotton aphid, Aphis gossypii (Glover)

“…Aphids are one of the most economically important plant‐sucking pests in agriculture, inducing physical injury and transmitting plant viruses that result in economic losses exceeding US$1 billion dollars annually . For example, the cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is a polyphagous pest species that is considered to be one of the most destructive sucking pests worldwide due to the direct feeding damage to plant tissue as well as the transmission of viruses that reduce fruit development or palatability . Synthetic insecticides targeting the nervous system remain the primary method for controlling aphid populations in agricultural settings, yet the rate of evolution for the development of insecticide resistance is increased in aphids when compared to other insect pest species due to aphid parthenogenesis, which allows for dozens of generations within a single growing period .…”

“…1,2 For example, the cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is a polyphagous pest species that is considered to be one of the most destructive sucking pests worldwide due to the direct feeding damage to plant tissue 3 as well as the transmission of viruses that reduce fruit development or palatability. [4][5][6] Synthetic insecticides targeting the nervous system remain the primary method for controlling aphid populations in agricultural settings, yet the rate of evolution for the development of insecticide resistance is increased in aphids when compared to other insect pest species due to aphid parthenogenesis, which allows for dozens of generations within a single growing period. 7 To this point, control failures are common with A. gossypii as they are highly resistant to the majority of approved chemical classes through increased metabolic detoxification [8][9][10] and target site mechanisms.…”