Efeito do estádio fenológico da soja e da profundidade de coleta do solo e raiz na quantificação da população de Heterodera glycine

Abstract

Soybeans are the most widely cultivated oilseed grain in the world. Brazil is currently the largest producer and exporter of the grain, but production is largely limited by phytosanitary problems, among which are those caused by phytonematoids. The soybean cyst nematode (SNC), Heterodera glycines, is one of the most problematic for soybean cultivation. For the effective control of NCS it is essential to accurately identify where they are located in the area, thus the correct sampling is essential in the process. Several authors present divergent recommendations regarding the sampling process for nematological analysis. The divergences occur both in relation to vertical dispersion of nematodes in the soil, and in relation to temporal dispersion. Thus, the objective of this study was to increase the efficiency of nematode collection through the evaluation and characterization of the best time and depth for the determination of H. glycines populations. To conduct the study, samples were collected in areas naturally infested with NCS. Three points were selected in areas of 3 plots and samples were taken in a stratified manner every 10 cm in the first 30 cm soil. At each 10 cm section soil samples of approximately 700 grams and all root portion present were taken. The samples were collected from the beginning of the reproductive stage and were taken at R1, R3, R5.1 and R6. For nematode extraction in soil the method of Jenkins (1964) was used, for nematodes in roots the method of Coolen & D'Herde (1972) was used and for cyst extraction the method of Shepherd (1970) was used. The variables evaluated were: mass of roots, population of H. glycines in the roots, population of H. glycines in the soil, number of eggs in the roots and number of live cysts in the soil. The depth at which the samples were collected had an influence on all the variables analyzed, regardless of the time of collection. And the phenological stage of soybean influenced the root mass, the population of H. glycines and the number of eggs in the roots regardless of the collection depth. Thus, we conclude that the collection of soil and root of soybean aiming the maximum population of H. glycines should be done at a depth of 0 to 10 cm and from the R5.1 stage.