Host-Parasite Relationships in Root-Knot Disease Caused by Meloidogyne inornata in Common Bean (Phaseolus vulgaris)
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Bean crops have their productivity limited by biotic factors, as the phytonematodes. Several species have been reported causing damage to the crop, especially those from the Meloidogyne genus. Recently, a new species was reported parasitizing bean plants in Parana State, Brazil, Meloidogyne inornata. The present work was aimed in order to study the pathosystem bean and M. inornata, through the evaluation of host reaction of 32 bean cultivars to the nematode, the potential damage of this pathogen to the crop, and the biology and parasitism of M. inornata on bean, under different temperatures, comparing with M. incognita. The host reaction was accessed under greenhouse conditions, with an initial population density of 2000 eggs of each nematode species per plant. Fifty days after inoculation, it was found that all tested cultivars were susceptible to M. inornata, however with varying extent. Pathogenicity of M. inornata on bean cv. Tuiuiu was also evaluated under greenhouse conditions, with the following initial population densities: 0 (check); 0.0625; 0.125; 0.25; 0.5; 1; 2; 4; 16; 32; and 64 eggs per cm(3) of soil. Tolerance limit obtained to this cultivar was 9.9 nematodes per cm(3). In relation to the comparative biology between M. inornata and M. incognita, under growth chamber and three different temperatures, 18, 25 and 32 degrees C, results showed that under 18 degrees C, both species have their life cycles retarded, while under 32 degrees C, the cycle is accelerated.