Characterization of multisporic and monosporic isolates of Lecanicillium (= Verticillium) lecanii for the management of Toxoptera aurantii in cocoa

Seven multisporic isolates, two from Cuba, four from the Southeastern State ofTabasco and two from Central Mexico, weremorphologically and physiologically comparedwith 28 monosporic isolates (four permultisporic isolate) of the fungus Lecanicillium (= Verticillium) lecanii.Mycelium type and colony appearance wereassociated with specific conidial length,conidial production and germination speed. Ingeneral, isolates with a cottony-likeappearance of the mycelium and without anystriations had small conidia and a highconidial production; the opposite was found forisolates with sparse mycelium and striatedcolonies. There was an inverse correlationbetween germination time of 50% of theconidia (GT₅₀) and their length (r =–0.72, P = 0.01). Three conidia length groupswere determined: small (2.9–3.9 µm),intermediate (4.6–5.8 µm), and large(6.5–8.8 µm). Based on shape, five groups of conidia were distinguished:cylindrical with half constriction and roundedends; crescent-shape, curved with both endsacute; conidia with one end somewhat moredistinctly narrowed; lanceolate form; andovoid to ellipsoidal shape. Differenceswere found between monosporic cultures andmultisporic isolates, particularly withGTM₅₀ and conidial production where severalmonosporic cultures exceeded their multisporicisolates. Results of analyses with singlecharacteristics were also confirmed withmultivariate analysis helping to identify thatthe four Tabasco groups were morphologicallyand physiologically more variable. Based onthese results it is possible to improve thecontrol potential of isolates of L. lecaniiby making monosporic cultures.