Caracterização e diversidade de Lasiodiplodia spp. associadas à queima das folhas e podridão peduncular de frutos em coqueiros no Nordeste brasileiro

Abstract

Coconut (Cocos nucifera) cultivation is distributed throughout most of Brazil. However, the Northeast region stands out as the main coconut-producing region in the country, with the States of Ceará, Bahia and Pernambuco being the largest producers. Among the diseases that affect the crop, leaf blight and stem-end rot caused by Lasiodiplodia spp. are responsible for crop losses in the field and in post-harvest, respectively. The objective of this study was to identify the etiological agents of leaf blight and stem-end rot in coconut, and to characterize the genetic diversity of Lasiodiplodia theobromae sensu stricto in coconut in the Brazilian Northeast. For this purpose, 188 isolates of Lasiodiplodia spp. associated with coconut trees in the Brazilian Northeast were obtained and preserved. Then, 50 representative isolates from the sampled regions were selected to identify the Lasiodiplodia species associated with coconut palms through phylogenetic analyses based on the internal transcribed spacer (ITS) region of rDNA, and the genes elongation factor 1-α (TEF1), β- tubulin (TUB2) and the second largest subunit of RNA polymerase II (RPB2), as well as the analysis of existing haplotypes. Morphological and cultural characterizations and pathogenicity trials were performed for the representatives of the species found. Inter Simple Sequence Repeat (ISSR) molecular markers were used to study the genetic diversity of L. theobromae sensu stricto, the predominant species among the isolates obtained from coconut palms. Among the 50 isolates selected from different organs of coconut trees in the States of Bahia, Ceará, Maranhão, Pernambuco and Rio Grande do Norte, four species and 20 haplotypes of Lasiodiplodia were identified, namely L. brasiliensis, L. hormozganensis, L. pseudotheobromae and L. theobromae sensu stricto. Lasiodiplodia theobromae sensu stricto was the most frequent species (84%), followed by L. brasiliensis (12%), L. pseudotheobromae (2%) and L. hormozganensis (2%). The isolates were all pathogenic and varied in aggressiveness, with L. pseudotheobromae being the most aggressive among the species. This study represents the first report of L. hormozganensis as a causal agent of stem-end rot in coconut fruits. Three ISSR primers used in this research (UBC 884, UBC 811 and UBC 825) showed a moderate level of polymorphism and the primers UBC 810, UBC 818, UBC 840, UBC 880, UBC 885, UBC 888, UBC 890, (GA)9T were uninformative. The populations of L. theobromae sensu stricto in coconut trees in Northeastern Brazil evaluated in this study, presented low genetic diversity and did not show population structure.