Abstract
Crown gall is a globally distributed and economically important disease of grapevine and other important crop plants. The causal agent of grapevine crown gall is tumorigenic Allorhizobium vitis (Ti) strains that harbor a tumor-inducing plasmid (pTi). The epidemic of grapevine crown gall has not been widely elucidated. In this study, we investigated the genetic diversity of 89 strains of Ti and nonpathogenic A. vitis to clarify their molecular epidemiology. Multi-locus sequence analysis (MLSA) of the partial nucleotide sequences of pyrG, recA, and rpoD was performed for molecular typing of A. vitis strains isolated from grapevines with crown gall symptoms grown in 30 different vineyards, five different countries, mainly in Japan, and seven genomic groups A to F were obtained. The results of MLSA and logistic regression indicated that the population of genetic group A was significantly related to a range of prefectures and that the epidemic of group A strains originated mainly in Hokkaido in Japan through soil infection. Moreover, group E strains could have been transported by infected nursery stocks. In conclusion, this study indicates that both soil infection and transporting of infected nursery stocks are working as infection source in Hokkaido.
Highlights
Grapevine (Vitis vinifera L.) crown gall is caused mainly by tumorigenic Allorhizobium vitis
In the phylogenetic tree constructed by the ML method using the combined sequence data of three housekeeping genes, the 89 A. vitis strains separated into six clades (A to F) (Figure 1, Table 1)
The 79 tumorigenic Allorhizobium vitis (Ti) strains used in this study comprised four genetic groups, and 35, 5, 18, and 16 strains belonged to genetic groups A, D, E, and F, Life 2021, 11, 1265
Summary
Grapevine (Vitis vinifera L.) crown gall is caused mainly by tumorigenic Allorhizobium vitis We follow the nomenclature for Allorhizobium species adopted by Mousavi et al [1] to avoid confusion. This pathogen enters the grapevine through wounds due to a variety of causes, such as cold injury, mechanical damage, and grafting [2]. A. vitis (Ti) causes crown gall by transferring the T-DNA region of the tumor-inducing bacterial plasmid (Ti-plasmid) to the host cell, which subsequently integrates into the plant host genome [3,4,5]. Subsequent expression of T-DNA genes results in the overproduction of auxins and cytokinins, which eventually leads to abnormal gall formation in the host plant. Invasion of vascular tissue by galls can result in vine death [8,9]
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