citrus packing machine

Diseases caused by CTV and symptoms

There are three principal diseases caused by CTV citrus packing machine in citrus trees: tristeza, stem pitting, and seedling yellows (Figure 12) (Table 5). The severity of these diseases is dependent on the strain of CTV present and on the sus­ceptibility of the host. Tristeza is a decline of different scion cultivars grafted onto sour orange rootstocks. This decline can occur over a period of several years, or in only a few months (this rapid form of the disease is also known as “quick decline”). Trees with tristeza initially appear water stressed; this stage is followed by defolia­tion and death. In Hawai‘i, tristeza is rarely encountered because sour  citrus packing machine orange rootstocks are no longer used.

Stem pitting is a disease most commonly seen in grapefruits, sweet oranges, and some lime cultivars. Trees with severe stem pitting appear stunted, with chlo­rotic leaves that often display “vein-clearing” symptoms (Figure 13). Twigs and small branches on these trees are brittle and can be snapped with little effort. When the bark is removed from twigs or branches, the wood will have small pinhole-like pits, or long grooves that give it a rope-like texture. In Hawai‘i, stem pitting is the most prevalent and important disease of citrus caused by CTV.

Seedling yellows is a disease of sour orange,  citrus packing machine lemon, and grapefruit seedlings. Susceptible seedlings infected with these CTV strains become stunted and have small, chlorotic leaves. Seedling yellows is most devastating in nursery operations, and therefore not an important

disease for growers in Hawai‘i who have citrus packing machine established trees and who import all their planting stocks.

Insect vectors and transmission of CTV

CTV is transmitted by several aphid species in a semi-persistent manner (Table 6). The brown citrus aphid (Toxoptera citricida) (Figures 8, 9) is by far the most efficient vector of CTV, followed by the melon aphid (Aphis gossypii) (Figure 10). The black citrus aphid (T. aurantii) and spirea (or citrus) aphid (A. spiraecola=A. citricola) are inefficient vectors of CTV, or are only able to transmit certain strains of the virus. These aphids, however,  citrus packing machine can build up large populations in citrus groves and therefore may contribute to the spread of CTV in some circumstances (Table 6). All of these aphid species are present in Hawai‘i.

Although CTV is not seed-transmissible, it is readily transmitted through grafting. Since most citrus species are vegetatively propagated, dissemination of infected budwood has greatly increased the distribution of CTV worldwide. CTV can also be transmitted by parasitic plants called dodder (Cuscuta sp.), but this means of transmission is not thought to be important in the spread of the virus.

Disease diagnosis and CTV detection

Accurate diagnosis of citrus diseases caused by citrus packing machine CTV and characterization of the virus in infected plants is critical for any successful implementation of management strate­gies. For example, tristeza occurs only when sour orange rootstocks are used. In Hawai‘i, this roostock is rarely used, and therefore this disease is rare. Yet many citrus trees displaying wilt and decline symptoms on rootstocks other than sour orange are often misdiagnosed as hav­ing tristeza when in fact they are in decline due to other causes citrus packing machine such as citrus blight or foot rot. The cause of citrus blight is currently not known, but it can be distinguished from tristeza in the field and laboratory. Foot rot, caused by Phytophthora spp., can also be easily distinguished from tristeza (Table 8). In addition, foliar symptoms of the milder forms of CTV-induced diseases may resemble nutrient deficiencies in citrus plants. Stem pitting can be diagnosed positively in citrus packing machine the field by the grooves or pinholes in the wood of young branches when the bark is removed (Figures 3, 4).

There are many methods used for laboratory de­tection of CTV strains within plants and even within insect vectors when disease symptoms are absent. These methods vary in terms of sensitivity, cost, reliability, and equipment needed or citrus packing machine other technical aspects (Table 7). For example, CTV can be indexed on Mexican lime, where symptoms of vein-clearing develop 3–6 weeks after inoculation (Figure 13).

CTV disease management

Effective management of CTV is essential for success­ful commercial cultivation of citrus in Hawai‘i. For the industry to expand in the Islands, additional manage­ment strategies must be adopted for CTV. Yet, with high disease incidence, geographically widespread pathogen distribution, and high diversity of CTV populations in Hawai‘i, the development of such management strategies is a daunting task. Currently there is no single manage­ment strategy citrus packing machine used to control CTV-caused diseases; rather, various strategies are integrated. The choice of which strategies to implement depends upon the inci­dence and strains of CTV in any particular region.

In regions where CTV incidence is low,  citrus packing machine management efforts should focus on quarantine of incoming materi­als, budwood certification programs, and suppression or eradication programs (29). In these low-incidence regions, the biggest threat to citrus growers is the introduction of infected materials as planting stocks.