N-acetylcysteine in transmission studies of Xylella fastidiosa by sharpshooters

Author(s)

Karla Kudlawiec

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2021-02-08

Examining board members

Joao Roberto Spotti Lopes; Alberto Fereres Castiel; José Belasque Júnior; Alessandra Alves de Souza

• Advisor: Joao Roberto Spotti Lopes

Abstract

Citrus variegated chlorosis (CVC), caused by the Xylella fastidiosa bacterium, is an important disease which incidence has decreased in citrus orchards in the State of São Paulo. The incidence reduction is related to the preventive control tactics used, such as eradication of diseased plants, planting of certified healthy seedlings and the chemical control of the insect vector, which are leafhoppers belonging to the subfamily Cicadellinae (Hemiptera: Cicadellidae). Recent studies have shown that the mucolytic agent N-acetylcysteine (NAC), used to treat human respiratory bacterial infections, has the potential to control bacterial diseases in plants. When applied to Citrus sinensis(L) Osbeck plants with CVC, NAC reduced the X. fastidiosa bacterial population and the disease symptoms. Thus, it was postulated that this mucolytic could also affect the transmission efficiency of X. fastidiosa by the insect vectors. That said, the objectives of this research were: a) to evaluate the X. fastidiosa acquisition efficiency by leafhopper in CVC plants treated and nontreated with NAC, and the subsequent transmission to healthy test plants; b) to evaluate the NAC effect on bacteria transmission after acquired by the vector; c) to evaluate the X. fastidiosa transmission to healthy test plants, previously treated or nontreated with NAC and; d) to evaluate the insect vector feeding behavior in NAC treated and nontreated plants, using the electrical penetration graph (EPG) technique. The leafhopper Macugonalia leucomelas (Walker) was used in the transmission experiments (a-c), which involved NAC treated and nontreated (control) plants. To assess the effect on acquisition, NAC was applied via humic fertilizer (3N:10P2O5:10K2O), (proportion: 2 g for each 1 kg of fertilizer) in C. sinensis plants infected by X. fastidiosa (source plants). To evaluate the effect after acquisition, leafhoppers were fed in an artificial diet mixed with X. fastidiosa cells after fed for different periods (24, 72, 120 h) in C. sinensis healthy seedlings treated with NAC in a nutritive solution. In a third experiment, transmission to Catharanthus roseus (test plant) healthy plants, previously treated with humic fertilizer containing NAC was evaluated. The results showed that the efficiencies of X. fastidiosa acquisition and following transmission by the M. leucomelas were not affected by the NAC treatment in a source bacterium plants for 90 days. After X. fastidiosa acquisition, vector exposure for up to 120 h in a healthy citrus plants NAC treated does not influence the positive bacterium insect rates or transmission probability to test plants. The pretreatment with NAC in healthy C. roseus plants for 30 days did not prevent their infection by X. fastidiosa after inoculation by the insect vector. Finally, it was verified that the NAC application in Sonchus oleraceus plants does not alter the Philaenus spumarius (Hemiptera: Aphrophoridae) feeding behavior, does not influencing EPG variables related to the X. fastidiosa transmission. Thus NAC under conditions tested here, did not affect X. fastidiosa acquisition and transmission by M. leucomelas and did not change the P.spumarius feeding behavior. (AU)

• FAPESP's process: 18/19980-9 - N-acetylcysteine in acquisition and transmission studies of Xylella fastidiosa in citrus
• Grantee: Karla Kudlawiec
• Support Opportunities: Scholarships in Brazil - Master