Murcha de Fusarium em Heliconia spp.: ocorrência, variabilidade e resistência genética em espécies ornamentais cultivadas em Pernambuco, Alagoas e Sergipe

Abstract

Heliconias are flowers most cultivated inside world floriculture tropical in Brazil northeast, but its yield has being affected by Fusarium wilt caused by Fusarium oxysporum f.sp. cubense. The present study had as objective to verify disease occurrence, to evaluate inoculation methods, characterize isolates considering morphology, aggressivety and genetical diversity, identify resistance sources, to verify efficiency of fungical filtrate in distinction of resistance and susceptibility and, at the end, involvement of structural mechanisms in pathogen-host interaction. The disease occurrence was evaluated in 28 farms at Pernambuco, Alagoas and Sergipe, Brazil. After isolates obtaintion, were tested inoculation methods by injection on bottom of pseudo stem, “meia lua” method, depositing inoculants around plant and “dipping”, where roots are wounded, immersed in suspension and replanted after. The plants were evaluated by external and internal symptoms, considering disease index with variation of 1 to 6. For morphological characters, isolates were incubated for five days in microculture, after observed with optical microscopy. Micro and macroconidia were measured by micrometric lents, with increase of 40X. The aggressivity of isolates was determined colony disks in stems of H. psittacorum cv. Alan carle detached and perfured. Stems were incubated in humid chamber during five days. The evaluation was according with vascular darking in stem diameter and was based in index disease with notes variation of 1 a 4. Genetical diversity was verified bymolecular analysis and vegetative compatibility agroupment technique. For molecular analysis, it was realized Polymerase Chain Reaction (PCR) using 37 oligonucleotides of Inter-simple Sequence Repeat (ISSR) and eletrophoretical run in agarosis gel (2%). Binary data were analyzed by GENES 2.0 program. VCG was determined by nit mutants obtaintion, by complete medium (CM), potato-dextrose-clorate (PDC) and minimum medium (MM) sequence. For groupment formation Mutants were pared for complementary test by observation of heterocarion. For identification of resistance sources, 12 species of heliconia were inoculated by injection with isolate considering higher aggressivity and, after 40 days were done evaluations based on disease index. Fungical extract was obtained after fungus incubation during 24 days in Czapek medium, being used concentrations of 25, 50, 75 and 100%. Aliquots of 1mL were deposited on detached leaves of resistant plants of Heliconia psittacorum cv. Golden Torch, and of susceptible H.psittacorum cv. Alan Carle. Leaves inoculated were in humid chamber condition for 24, 48 and 72 hours. Structural mechanisms involved in interaction were observed by histological cuts on roots of used species at resistance sources studies and treatments wereinoculated and no inoculated with F.oxysporum f.sp. cubense. It was observed Fusarium wiltoccurrence in 88% of farms of tropical flowers production, where were obtained 31 isolates of F. oxysporum f.sp. cubense. Injection method showed be more efficient, with characteristics disease symptoms in lower time interval, at 36 days. Macroconidia showed variation of 25,56 μm x 3,7 μm to 33,92 μm x 3,39 μm and microconidia variation of 6,23 μm x 2,01 μm to 10,3 μm x 3,35 μm, dimension obtained for conidia were with variation for specie. It was observed distinction of three groups for aggressivity, where 15 isolates were considered intermediary aggressivity, eight lower aggressivity isolates. Methods used for genetical diversity showed genetical variability. At molecular analysis was formed five groups considering a genetical distance of 70% and genetical similarity varying of 0,51 to 0,94. At VCG study was observed formation of three groups, but 71% of isolates did not belong none group. Both of techniques determined high genetical diversity and not geographical correlation among isolates of the same area. Species H. bihai, H. psittacorum cv. Golden Torch, H. psittacorum cv. Golden Torch Adrian, H. rostrata, H. stricta Capri, H. psittacorum cv. Sassy and H. caribea were considered resistant to Fusarium wilt. Species moderally resistant were H. latispatha and H. wagneriana. Heliconia. psittacorum cv.Alan Carle and H. chartacea cv. Sexy Pink were susceptible while H. stricta Fire Bird was highly susceptible. Fungical filtrate concentrate in 50 % was the mostefficient of resistance distinction and susceptibility on cultivars. In structural mechanisms it was observed that there is not relation between diameter and lignification of celular wall with pathogen resistance, because in some resistant species did not show increase of diameter or lignin accumulation.