Preliminary evidence of seed transmission of Xylella fastidiosa in pecan (Carya illinoinensis)
Pecan bacterial leaf scorch is caused by Xylella fastidiosa subsp. multiplex (EPPO A2 List) and occurs across the southern part of the pecan-growing region of the USA. It is generally accepted that X. fastidiosa is not seed-transmitted. The fact that the bacterium might be transmitted from seed to seedling has been studied for citrus variegated chlorosis, as X. fastidiosa subsp. pauca had been detected in fruit, seed coats and embryos of three sweet orange cultivars. However, all attempts to detect or isolate the bacterium in the seedling progeny have failed. In pecan (Carya illinoinensis), an earlier study had also detected the presence of X. fastidiosa in the endosperm of pecan seeds and this triggered further research on the possible seed-transmission of X. fastidiosa.
Molecular studies (qPCR and sequencing) confirmed the detection of X. fastidiosa in mature pecan seeds collected from 7 infected trees in New Mexico and Texas (US), and also confirmed the transmission of the bacterium from infected seed to seedlings with a transmission rate of 80%. The highest concentrations of X. fastidiosa DNA were found in the seed hilum and outer teguments, as well in the seedling petioles. However, further research is needed to understand the movement of X. fastidiosa within the seed, and from the seed to the seedling during the germination process. It is also noted that during these seed-transmission studies it has not been possible to determine the subspecies of X. fastidiosa present in the seed and seedling progeny. The authors concluded that their study provides preliminary evidence that seed-to-seedling transmission of X. fastidiosa can occur in pecan.
Sources
Cervantes K, Hilton AE, Stamler RA, Heerema RJ, Bock C, Wang X, Jo YK, Grauke LJ, Randall JJ (2022) Evidence for seed transmission of Xylella fastidiosa in pecan (Carya illinoinensis). Frontiers in Plant Science 13, 780335. https://doi.org/10.3389/fpls.2022.780335