Evaluation by PCR of Xylella fastidiosa subsp. pauca transmission through citrus seeds with special emphasis on lemons (Citrus limon (L.) Burm. f)

• Sweet orange seeds are considered to transmit Xylella fastidiosa subsp. pauca (Xfp), causal agent of citrus variegated chlorosis.
• There are no conclusive studies confirming lemon as a host of Xfp.
• In this study, Xfp was not found to be transmitted by lemon or sweet orange seeds.
• This study and field observations indicate that lemon is not a natural host of Xfp.

Citrus variegated chlorosis (CVC), caused by the xylem-limited bacterium Xylella fastidiosa subsp. pauca (Xfp), is a damaging disease of sweet oranges (Citrus sinensis (L.) Osbeck) in several citrus production areas of South America. CVC was first identified in sweet orange orchards in the Northwest region of São Paulo State, Brazil. Transmission of Xfp from seed of CVC infected sweet orange fruit to seedlings has been reported. However, Xfp has not been reported to infect or cause CVC in lemon (Citrus limon (L.) Burm. f). Therefore, the objectives of this study were 1) to further evaluate the potential for vertical transmission of the bacterium through sweet orange seeds originating from symptomatic fruits to sweet orange seedlings and 2) to examine lemon trees and seeds for PCR detection of Xfp. Based on our evaluations, Xfp was not detected by PCR in leaves and seeds of different lemon cultivars surrounded by sweet orange orchards with high incidence of CVC. Furthermore, we could not detect with PCR that Xfp is vertically transmitted through sweet orange seeds to seedlings of sweet orange even from fruits with typical CVC symptoms. Hence, in this study and with the cultivars tested, Xfp was not confirmed by PCR detection to be transmitted via infected seeds from fruits of Citrus spp. even in areas where CVC is endemic nor was lemon found to be a natural host of Xfp.