Weeds as Alternative Hosts of the Citrus, Coffee, and Plum Strains of Xylella fastidiosa in Brazil

Abstract

In Brazil, Xylella fastidiosa is present in citrus (Citrus sinensis), coffee (Coffea arabica), and plum (Prunus sp.) crops, causing the citrus variegated chlorosis (CVC), coffee leaf scorch (CLS), and plum leaf scald (PLS). Also present in these crops and infesting weeds, which ultimately could serve as sources of inoculum for the cultivated trees, are diverse populations of xylem-feeding leafhopper vectors. In order to assess host range of X. fastidiosa among weeds and to better understand their role in epidemics, field surveys, mechanical inoculations, and insect transmission tests were conducted. Polymerase chain reaction (PCR) and culture plating were used to detect the pathogen from plant tissues. X. fastidiosa was detected in 10 out of 23 species of the weed plants sampled in two citrus groves affected by CVC. None of the weed plants showed external symptoms. In the greenhouse, the average percentages of infection on plants mechanically inoculated with the CVC, CLS, and PLS strains of X. fastidiosa were, respectively, 25, 10, 0 in Medicago sativa; 70, 45, 20 in Echinochloa crus-galli; 45, 30, 0 in Brachiaria decumbens; 72, 70, 40 in Brachiaria plantaginea; 13, 10, 0 in Digitaria horizontalis; 31, 30, 0 in Solanum americanum; and 17, 0, 0 in Bidens pilosa. Symptoms were observed only in S. americanum and citrus and only when inoculated with the CVC strain. In insect transmission tests, the grass leafhopper Ferrariana trivittata was first caged on citrus plants showing CVC symptoms and then on healthy citrus and on the four most common weeds. No plants tested positive by PCR or culture, or showed symptoms for at least 4 months after inoculation. The amount of X. fastidiosa cells that may accumulate in weeds inoculated by leafhoppers is probably under insect acquisition thresholds, a factor that would limit their importance to the CVC epidemics, as studies on spatial distribution of diseased citrus trees over time indicate.

Levantamento populacional de cigarrinhas (Hemiptera: Cicadellidae) associadas à transmissão de Xylella fastidiosa em pomares cítricos do Litoral Norte da Bahia

“…No estado de São Paulo, F. trivittata é abundante em gramíneas da vegetação rasteira (Paiva et al 1996), enquanto que B. xanthophis é o cicadelíneo mais frequente em viveiros cítricos abertos (Roberto et al 2000) ou pomares em formação (Yamamoto et al 2001). Algumas plantas invasoras presentes em pomares cítricos podem hospedar X. fastidiosa; no entanto, não há evidências de que as mesmas sejam importantes como fontes de inóculo do patógeno para aquisição pelas cigarrinhas e posterior transmissão para plantas cítricas (Lopes et al 2003). Além disso, as cigarrinhas predominantes nesse tipo de vegetação raramente são observadas nas plantas cítricas ou vice-versa (Paiva et al 1996).…”

Genomic Insights into Xylella fastidiosa Interactions with Plant and Insect Hosts

“…This bacterium is capable of multiplying in almost all tested plant species under greenhouse conditions when mechanically inoculated (Purcell and Saunders 1999). It can also be recovered from a wide range of plants in the field (Lopes et al 2003), although X. fastidiosa does not cause disease in most of these species (Purcell and Saunders 1999). Thus, X. fastidiosa colonization of plants does not necessarily equal disease development.…”

Effects of weed species competition on the growth of young coffee plants

“…Different crop yield losses due to weed competition have been observed, such as 77% (Blanco et al, 1982), 55% (Oliveira et al, 1979), 65% (Eshetu, 2001), 52% (Pereira & Jones, 1954), 28% (Merino et al, 1996) and 24% (Moraima, et al, 2000). In addition to yield losses, several other harmful effects of weed competition on this crop are discussed elsewhere (Friessleben et al, 1991;Toledo et al, 1996;Njoroge, 1994;Ronchi et al, 2001;, including weeds as an alternative host to the coffee strain Xilella fastidiosa, which causes coffee leaf scorch (Leite Júnior & Nunes, 2003;Lopes et al, 2003) and possesses a greater nutrient competitive potential than the coffee plants (Gallo et al, 1958;Ronchi et al, 2003).…”