Seleção de isolados de Pochonia chlamydosporia para o controle de Meloidogyne javanica

Abstract

The aim of this paper was to isolate, characterize and select isolates of Pochonia chlamydosporia, aiming the control of Meloidogyne javanica. In order to obtain isolates, soil samples, naturally infested by Meloidogyne spp. were plated in a semiselective culture medium, according to the serial dilutions technique. The plates were incubated at 24 ºC, for 21 days in darkness. Then, the fungal colonies were repicated to Petri dishes containing culture medium potato-dextrose-agar (PDA) and incubated at 24 ºC, for 15 days, in darkness. As a result, were obtained 12 isolates, identified as P. chlamydosporia. They were stored in sílica-gel for later studies. The species of isolates were determined through visualization of the reproductive structures of the fungus and the isolates were repicated to PDA medium for the determination of their color and diameter. All the isolates were specie chlamydosporia, with colony diameter ranging between 6.97 e 7.78 cm and yellow coloration or beige. To quantify the chlamydospores production, 3 fungal mycelium discs of 8 mm diameter were deposited in plastic bag, which contained 150 g of rice and 70 mL of water, previously autoclaved for 30 minutes at 120 ºC and 1 atm. The plastic bags were sealed and incubated at 24 ºC, for 21 days in darkness. The isolates that produced the higher amount of chlamydospores were PC-8 e PC-2. Another experiment was done under greenhouse conditions, to evaluate the efficiency of the isolates in controlling of Meloidogyne javanica. For this, a mixture of soil:sand, in the ratio 2:1 (v:v), was sterilized in autoclave for 1 hour at 120 ºC and 1 atm. That substrate was transferred to plastic bags and infested with 8,000 eggs of M. javanica Kg-1 of soil. Rice grains colonized by P. chlamydosporia isolates, were separately added in to bags containing the substrate, which were the treatments. The control treatment was just the substrate infested with nematodes. The humidity of the treamentes was adjusted by the field capacity, and the substrates were homogenized and incubated in growing chambers at 24 ºC for 15 days in darkness. Then, the substrate was homogenized one more time and 500 g of it was deposited in vases, which capacity was 700 mL. A tomato seedling, at age of 21 days, was transplanted in each vase. After 41 days, the evaluation of fresh root mass, height and mass of fresh aerial part, number of galls and eggs in the root system was done. The isolates PC-2, PC-4, PC-5, PC-6 and PC-13 reduced the number of galls in 65%, 61%, 57%, 64% e 48%, when compared to the control treatment. Already the isolates PC-2, PC-4 e PC-5 reduced the number of eggs in 77%, 75% e 80%, in relation to control. All isolates multiplied in the soil. As conclusion, PC-2 has potential to be studied in a biological control program, once it has good characteristics for mass production and nematode control.