Caracterização biológica e molecular de isolados e alternativas de controle de papaya lethal yellowing virus

Abstract

Papaya (Carica papaya) is an important tropical fruit crop which production is increasing in irrigated areas of Northeast of Brazil. Lethal yellowing is a papaya disease caused by Papaya lethal yellowing virus (PLYV) that occurs only in the Northeast of Brazil. The virus symptoms begin with a progressive leaf yellowing in the third superior part of the plant canopy, which wilt and finally die. Greenish circular spots also appear on the fruits which turn yellowish when the fruits are ripping. The PLYV has isometric particles with ac. 30 nm in diameter, genomic ssRNA of ac. 1.6 x 106 Da and a coat protein composed of a single component of ac. 35 Da. Although no biological vector has been confirmed for the virus, it is spreading every year in the Northeast of Brazil, probably by infected young plants and contaminated tools. The virus can be transmitted through the soil, irrigated water, agriculture tools and contaminated hands. The present research had the following objectives: evaluate the possibility of the virus to be transmitted by seeds and aphids; evaluate its possibility to infect other plant species from the family Caricaceae; evaluate the effects of soilarization in the virus infectivity and analyze the molecular and biological variability among the virus isolates. In the aphid transmission studies, the virus was not transmitted by Aphis craccivora neither by A. gossypii in persistent and non-persistent manners. In the seed transmission experiments, the virus was not detected by indirect ELISA in a total of 1,680 seedlings originated from PLYV infect fruits. The PLYV infected the plant species Jacaratia heterophila, J. spinosa, Vasconcella quercifolia and V. monoica, confirming that its host range is probably restricted to Caricaceae species. The virus was inactivated in leaves and roots eradicated from infected plants when they were submitted to a solarization for a period of 12 days, but maintained its infectivity when the leaves and the roots were maintained without solarization at natural conditions for a period of 32 days. The use of extract from fruits of Caesalpinia ferrea inactivated PLYV when it was mixed with extract from infected plants, although the C. ferrea extract did not interfered with the virus infection when it was sprayed on the plant leaves before or after the virus inoculation. The PLYV obtained from different regions from the State of Ceará: PLYVFC (Fortaleza-Centro), PLYVFQ (Fortaleza – Edson Queiroz), PLYVH (Horizonte), PLYVLN (Limoeiro do Norte), PLYVM (Marco), PLYVMD (Marco – DIBAU), PLYVP (Paraipaba), PLYVQ (Quixeré) and PLYVBE (Boa Esperança- Quixeré) showed low molecular variability when compared by its nucleotide sequences involving part of the genes RpRd/CP. When compared with members from the genera Sobemovirus and Tombusvirus, the PLYV showed more similarity with members from the genus Sobemovirus.