Evidence of a Low Rate of Seed Transmission of Citrus tatter leaf virus in Citrus

Abstract

Citrus tatter leaf virus (CTLV) (Apple stem grooving virus) is mechanically-transmitted in citrus, causing bud-union crease in trees budded on trifoliate orange and its hybrids, but is symptomless in most scions. Seed transmission of a strain of CTLV has been reported in Lilium longiflora and Chenopodium quinoa. In order to test whether CTLV is seed transmitted in citrus, seed was collected from four adjacent CTLV-infected citrus trees of different species, namely Clementine mandarin, Meyer lemon, Eureka lemon and Meiwa kumquat. The resulting 355 seedlings and the four parent trees were tested for CTLV presence by RT-PCR using three primer sets. The four parents and two of the 136 Eureka lemon seedlings were found to be CTLV positive. This is the first report of CTLV seed transmission in citrus. Cloning and sequencing of the coat protein gene amplified using primer set TL1 showed that the sequence from the seedlings had an 89.7% homology with the parent tree, but 100% homology with the Meyer lemon and Meiwa kumquat trees, suggesting a filtering effect during transmission through the Eureka lemon parent as reported elsewhere.

Pest categorisation of Tatter leaf virus

“…Seed transmission of ASGV was reported for Eureka lemon ( Citrus limon cv. ‘Eureka’) at a rate of 1.4%, while seeds from ASGV‐infected plants of Clementine mandarin, Meiwa kumquat and Meyer lemons did not develop into infected seedlings (Tanner et al., ). Seed transmission may exist for other citrus cultivars, but this has not yet been investigated.…”

“…Considering citrus hosts, the most important pathway for entry of ASGV is the trade of plants for planting of Citrus, Fortunella and Poncirus species and their hybrids, which is closed by the existing Annex III legislation (see Section 3.3.2 and Table 4 above). ASGV is seed transmitted at a low rate in some of its citrus hosts (Tanner et al, 2011). Citrus seeds are regulated in Annex V of Directive 2000/29/EC, which specifies that they must be submitted to a general plant health inspection.…”

“…Similarly, the Panel was unable to identify evidence for natural spread of ASGV in citrus groves. Spread of ASGV may, however, occur in some citrus hosts at a low level, through seed transmission (Massart et al, 2011;Tanner et al, 2011).…”