Grape

"Candidatus Phytoplasma solani" is vectored by numerous planthoppers in the Cixiid and Cicadellid families (See CPHST Pest Datasheet for a complete listing). There is a wide range of preferred hosts among these vectors, therefore, transmission between plant hosts varies greatly depending on the vector. The most important vector is Hyalesthes obsoletus, which transmits "Ca. P. solani" to grape. Another important vector is Reptalus panzeri, which is now known to transmit "Ca. P. solani" to both grape and corn.

Follow instructions in Phytoplasma Sample Screening and Confirmation

If you have taken the hands-on phytoplasma specific training at S&T Beltsville lab, you can screen your own phytoplasma samples. Note: You will still have to follow the protocol in the linked document for confirmations.

No specific signs are present.

Symptoms vary by host. See CPHST pest datasheet for a complete list of hosts and the associated symptoms.

In grape: Typical symptoms comprise discoloration of leaves including the veins, often associated with downcurling of the leaf blade, lack of or incomplete lignification of shoots that later turn black, abortion of fruit clusters or shriveling of the ripening fruit. In most cultivars, the symptoms of bois noir remain restricted to parts of the infected vines for several years. Bois noir usually does not kill the infected vines, although their vigor can be significantly reduced. In red grape cultivars, leaf reddening occurs. In white cultivars, yellow, necrotic veins occur. Shriveled grape clusters occur in both red and white grape cultivars.

In corn: Symptoms include midrib, leaf, and stalk reddening, followed by desiccation of the entire plant, abnormal ear development, and incomplete kernel set. Maize redness (MR) may cause economic losses. Environmental factors play a role in both the intensity and incidence of MR, with more severe disease being associated with early-planted fields and hot, dry summers.

In potato: Symptoms in potato include reddening and upward rolling of leaflets, reduced size of leaves, shortened internodes, and aerial tuber formation. Plants grown from infected tubers give rise to normal or spindly sprouts (hair-sprouting). Where normal sprouts arise, symptoms are first apparent about 60 to 80 days after sowing, as a yellowing and rolling of the leaves. This is followed by production of aerial stolons and tubers in different parts of the stems close to the axils.

In tomato: Leaves that develop before infection become greenish-yellow, especially at the margins, which may roll upward. Newly formed leaves become more yellow and are smaller. Stems become thin at the apex as growth ceases, but stems enlarge at infection sites as a result of abnormal phloem formation. This abnormal phloem appears as a greenish, water-soaked band 1 to 2mm wide, which extends towards the xylem. Lateral shoots develop, giving the plant a bushy aspect. Flower buds assume an abnormally erect position; the sepals, whose veins develop a violet color, remain completely joined and the calyx is enlarged and cyst-like ("big bud").

Flowers, if already formed when infection occurs, become similarly erect and may be sterile, and petals are greenish instead of yellow. Flower distortion is common, and petals of young flowers become totally dwarfed and green (virescent). Peduncles are thicker than normal. Fruit development is arrested following infection. Green fruits already formed become solid, dry and ripen very slowly. Necrosis occurs at the embryonic center in younger fruits. Pedicels of fruits are thicker than in healthy plants, in spite of the relatively small fruit size.

Follow instructions in Phytoplasma Sample Screening and Confirmation

If you have taken the hands-on phytoplasma specific training at S&T Beltsville lab, you can screen your own phytoplasma samples. Note: You will still have to follow the protocol in the linked document for confirmations.

Bois noir (BN) may be confused with other yellowing diseases caused by different phytoplasmas or other pathogens. BN resembles Australian grapevine yellows ( "Candidatus Phytoplasma australiense"), Flavescence doree (FD, "Candidatus Phytoplasma vitis"), leaf curl, berry shrivel, and other grapevine diseases (e.g., North American grapevine yellows), tomato big bud, and an uncharacterized grapevine disease also believed to be caused by a phytoplasma. There is no way to visually distinguish BN from FD and other grapevine yellows diseases. Molecular methods for identifying the associated phytoplasma are used to distinguish the various grapevine yellows diseases.

The routine detection of bois noir and other grapevine yellows diseases depends on DNA based techniques (Maixner, 2011). Nested PCRs targeting the 16S rDNA, carried out using the primer pairs P1/P7 followed by R16F2n/R16R2, have been used to detect "Ca. P. solani" in grape and other hosts (Quaglino et al., 2014). The Stol11 nested PCR protocol with primers F2/R1 and F3/R2 (Clair et al., 2003) can be used to detect "Ca. P. solani" in plant and insect material (Jovic et al., 2009; Cvrkovic et al., 2014). Methods for DNA based identification of this phytoplasma are reviewed and described in numerous additional publications, including: Maixner et al. (2011); Lotos et al. (2013); Aryan et al. (2014); Mori et al. (2014).