Influence of plant volatiles on the Heterodera glycines hatching and effects of temperature on the duration of the life cycle of Meloidogyne enterolobii and Meloidogyne floridensis

Abstract

Plant-parasitic nematodes are important soil born pathogen causing losses in quantity and quality of the agricultural products. New management strategies are necessary to reduce the damage caused by these parasites. The identification of chemical molecules capable of stimulating the second-stage juveniles (J2) hatching or killing them can contribute to this purpose. In the present study we evaluated the effect of volatile organic compounds (VOCs) emitted by different plant species on the Heterodera glycines J2 hatching in in vitro experiments. VOCs of all tested plant species increased H. glycines J2 hatching. VOCs emitted by soybean and bean leaves and roots increased the hatching of the J2 up to 71.4%. Four compounds identified in plant emissions by gas chromatography analysis were individually tested as inductors or inhibitors hatching which were 3-octanol, 1-hexanol, hexanal and linalool. Under concentrations of 200, 600 e 1000 μg/mL, there was no hatching induction of H. glycines J2 by these compounds. On the other hand, in the three concentrations tested, the compounds 3-octanol and 1-hexanol reduced the hatching and, in subsequent tests, they showed mean lethal concentration values (LC50) to H. glycines J2 of 177 and 219 μg/mL, respectively. Therefore, molecules mixed in plant emissions induce hatching, but some of them alone cause toxicity to the nematode without causing hatching induction. In the second part of this thesis, the effects of temperature on the life cycle of Meloidogyne enterolobii, M. floridensis and M. incognita was studied. Invasion of the roots by the three species at 5 days after inoculation (DAI) was higher at 30°C than at 25°C and 30- 25°C. However, there was no difference in the percentage of penetrated J2 among species in each temperature regime. All three RKN species had shorter generation time at 30°C. Developmental time from infective J2 to reproductive stage was shorter at 30°C than at 25°C and 30-25°C with egg mass production observed at 17 DAI for all three species. During the timeframe of 29 days at 30°C, for all three species, a single generation from J2 to J2 was completed while at 30-25°C it occurred only for M. floridensis, and at 25°C no species managed to complete the life cycle. At 30°C, M. enterolobii completed the life cycle (from J2 to J2) at 23 DAI (506.9 DD) and M. floridensis and M. incognita at 25 days (552.3 DD). At 30°C, second-generation juveniles penetrated the roots after 12 days (266.6 DD) from the first observation of egg mass formation for M. floridensis and M. incognita and after 10 days (221.2 DD) for M. enterolobii. At 30-25°C, it occurred after 12 days (196.1 DD) only for M. floridensis. Exposure to the temperature of 25°C decreased root invasion and delayed the life cycle completion of M. enterolobii and M. floridensis on tomato plants.