Variation in microbial feature perception in the Rutaceae family with immune receptor conservation in citrus.

Although much is known about the responses of model plants to microbial features, we still lack an understanding of the extent of variation in immune perception across members of a plant family. In this work, we analyzed immune responses in Citrus and wild relatives, surveying 86 Rutaceae genotypes with differing leaf morphologies and disease resistances. We found that responses to microbial features vary both within and between members. Species in 2 subtribes, the Balsamocitrinae and Clauseninae, can recognize flagellin (flg22), cold shock protein (csp22), and chitin, including 1 feature from Candidatus Liberibacter species (csp22CLas), the bacterium associated with Huanglongbing. We investigated differences at the receptor level for the flagellin receptor FLAGELLIN SENSING 2 (FLS2) and the chitin receptor LYSIN MOTIF RECEPTOR KINASE 5 (LYK5) in citrus genotypes. We characterized 2 genetically linked FLS2 homologs from "Frost Lisbon" lemon (Citrus ×limon, responsive) and "Washington navel" orange (Citrus ×aurantium, nonresponsive). Surprisingly, FLS2 homologs from responsive and nonresponsive genotypes were expressed in Citrus and functional when transferred to a heterologous system. "Washington navel" orange weakly responded to chitin, whereas "Tango" mandarin (C. ×aurantium) exhibited a robust response. LYK5 alleles were identical or nearly identical between the 2 genotypes and complemented the Arabidopsis (Arabidopsis thaliana) lyk4/lyk5-2 mutant with respect to chitin perception. Collectively, our data indicate that differences in chitin and flg22 perception in these citrus genotypes are not the results of sequence polymorphisms at the receptor level. These findings shed light on the diversity of perception of microbial features and highlight genotypes capable of recognizing polymorphic pathogen features.

Identification and management of tomato brown rugose fruit virus in greenhouses in Mexico.

Tomato brown rugose fruit virus (ToBRFV) has become a cause of great concern in the global tomato agro-industry since its first report in Israel in 2014. Global tomato production is affected by ToBRFV, and management practices are being evaluated. We tested seed lots from international producers as well as greenhouse substrates and water wells as possible sources of virus contamination. We identified a second introduction of ToBRFV in Mexico by a strain closely resembling isolates from the Netherlands and the Middle East. ToBRFV was detected by RT-PCR in seed coats and epicotyls (from commercial seeds and seedlings obtained from infected tomato plants), indicating a transmission rate of 9%. Virus-like particles (VLPs) were found in wells used for irrigation in greenhouses, but these exhibited low infectivity. These findings suggest that water sources could serve as ToBRFV reservoirs. We evaluated four chemical and six thermal methods for sanitizing substrates, plasticware, and other greenhouse utensils, using detached leaf bioassays in Nicotiana rugosa. The most effective chemical sanitization method was treatment with glutaraldehyde plus quaternary ammonium salts and pentapotassium salts. The most effective heat treatment was at 92°C for 30 minutes, which inactivated the virus. Tomato producers could implement these sanitization methods to control ToBRFV.