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 of Tabasco and two from Central Mexico, were morphologically and physiologically compared with 28 monosporic isolates (four per multisporic isolate) of the fungus Lecanicillium (= Verticillium) lecanii. Mycelium type and colony appearance were associated with specific conidial length, conidial production and germination speed. In general, isolates with a cottony-like appearance of the mycelium and without any striations had small conidia and a high conidial production; the opposite was found for isolates with sparse mycelium and striated colonies. There was an inverse correlation between germination time of 50% of the conidia (GT₅₀) and their length (r = -0.72, P = 0.01). Three conidia length groups were 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 rounded ends; crescent-shape, curved with both ends acute; conidia with one end somewhat more distinctly narrowed; lanceolate form; and ovoid to ellipsoidal shape. Differences were found between monosporic cultures and multisporic isolates, particularly with GT₅₀ and conidial production where several monosporic cultures exceeded their multisporic isolates. Results of analyses with single characteristics were also confirmed with multivariate analysis helping to identify that the four Tabasco groups were morphologically and physiologically more variable. Based on these results it is possible to improve the control potential of isolates of L. lecanii by making monosporic cultures.